Pin the assigner to mesh-sdk's head that reads a composer request from a file (issue 1622)

Reviewed-on: #32

merge-check.sh

@@ -1,74 +0,0 @@
-#!/bin/sh
-# mesh-check-toolchain: go
-#
-# This repository's own check, mesh/repo-check (novox/hq ADR 0238 §4), written with its first commit (ADR 0428 §4):
-# every Go module in the tree is vetted, its unit tests run, and then its integration tests (-tags integration).
-# A tree with no Go module has nothing to test, and the check says so and passes.
-#
-# No module commits its dependencies (no vendor directory: .gitignore). A module's dependencies are fetched, or a
-# requirement of the mesh's own forge (the pinned mesh-sdk commit) is taken from its repository's clone beside the check
-# (MESH_CHECK_BESIDE), through a go.mod of its own (-modfile), by mesh-catalog's helper checks/deps, built from the
-# clone of mesh-catalog beside this check and not copied here: the build seat forgets the forge credential before the
-# check runs, so a commit the seat's module cache does not hold cannot be fetched from the forge (novox/hq issue 385). A
-# module whose dependencies cannot be had **fails the check**, by name and why: its tests could not run, and a test that
-# could not run is a failure, never a note. Run by hand, without MESH_CHECK_BESIDE, the dependencies are fetched.
-set -eu
-cd "$(dirname "$0")"
-
-# The toolchain the check runs in sets -mod=vendor; there is no vendor directory, so the modules are used as they are.
-GOFLAGS="$(printf '%s' "${GOFLAGS:-}" | sed 's/-mod=[a-z]*//g') -mod=mod"
-export GOFLAGS
-export GOPRIVATE=git.novox.be
-
-modules=$(find . -name go.mod -not -path '*/vendor/*' -not -path './.git/*' | sort)
-if [ -z "$modules" ]; then
-  echo "This tree holds no Go module, so there are no tests to run; the check passes."
-  exit 0
-fi
-
-work=$(mktemp -d)
-trap 'rm -rf "$work"' EXIT
-deps=""
-helper="${MESH_CHECK_BESIDE:-}/mesh-catalog/checks/deps"
-if [ -n "${MESH_CHECK_BESIDE:-}" ] && [ -f "$helper/main.go" ]; then
-  if ! (cd "$helper" && go build -o "$work/deps" .); then
-    echo "FAILED: the dependency helper of mesh-catalog beside this check could not be built"
-    exit 1
-  fi
-  deps="$work/deps"
-elif [ -n "${MESH_CHECK_BESIDE:-}" ]; then
-  echo "NOT TAKEN FROM BESIDE: no mesh-catalog/checks/deps beside this check ($MESH_CHECK_BESIDE); the dependencies are fetched"
-fi
-
-untestable=""
-for mod in $modules; do
-  dir=$(dirname "$mod")
-  modfile=""
-  if [ -n "$deps" ]; then
-    if ! modfile=$("$deps" -beside "$MESH_CHECK_BESIDE" -work "$work" "$dir"); then
-      echo "FAILED: $dir could not be tested: $modfile"
-      untestable="$untestable $dir"
-      continue
-    fi
-    [ -n "$modfile" ] && echo "$dir takes its forge dependencies from the clones beside the check"
-  elif ! fetched=$(cd "$dir" && go mod download 2>&1); then
-    echo "FAILED: $dir could not be tested: its dependencies cannot be fetched: $(printf '%s\n' "$fetched" | tail -n 1)"
-    untestable="$untestable $dir"
-    continue
-  fi
-  mf=""
-  [ -n "$modfile" ] && mf="-modfile=$modfile"
-  unformatted=$(cd "$dir" && gofmt -l .)
-  if [ -n "$unformatted" ]; then
-    echo "$dir is not gofmt'd: $unformatted"
-    exit 1
-  fi
-  echo "== $dir: go vet and the unit tests"
-  (cd "$dir" && go vet $mf ./... && go test $mf ./...)
-  echo "== $dir: the integration tests (-tags integration)"
-  (cd "$dir" && go vet $mf -tags integration ./... && go test $mf -tags integration ./...)
-done
-if [ -n "$untestable" ]; then
-  echo "the check fails: the tests of$untestable could not run (novox/hq issue 385)"
-  exit 1
-fi

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/asks.go

@@ -0,0 +1,161 @@
+package main
+
+import (
+	"context"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+
+	"mesh-delivery-assigner/internal/assign"
+)
+
+// AssignerModule is the asker the assigner's compose asks name.
+const AssignerModule = "mesh-delivery-assigner"
+
+// composeAsks are the compose asks the assigner put on the Go build seat's check stream (novox/hq ADR 0482 clause 4,
+// issues 1622 and 1623), by what each composes: one ask per key, put once and followed by a watch of its step key until
+// it ends, which wakes a pass. No timer: an ask that waits in the stream waits (its backlog is the view's and the
+// watchman's to show). A restart forgets them and asks again; the build module keeps a composer built for a commit, so a
+// second ask builds nothing.
+type composeAsks struct {
+	ctx   context.Context
+	asker buildrun.Asker
+	wake  func()
+	logf  func(string, ...any)
+	now   func() time.Time
+
+	mu   sync.Mutex
+	asks map[string]*composeAsk
+}
+
+type composeAsk struct {
+	id     string
+	cancel context.CancelFunc
+	ran    *assign.Ran
+}
+
+func newComposeAsks(ctx context.Context, asker buildrun.Asker, wake func(), logf func(string, ...any)) *composeAsks {
+	return &composeAsks{ctx: ctx, asker: asker, wake: wake, logf: logf, now: time.Now, asks: map[string]*composeAsk{}}
+}
+
+// get is the end of the ask that composes key, or nil and its id while it runs. The first get of a key puts the ask.
+// A job its layout refuses ends at once, failed with why: never silent.
+func (a *composeAsks) get(key string, job delivery.ComposeJob) (*assign.Ran, string) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+	if k, ok := a.asks[key]; ok {
+		return k.ran, k.id
+	}
+	ask := delivery.StepAsk{ID: buildstep.NewID(), Kind: delivery.AskCheck, Language: delivery.AskGo, Asker: AssignerModule,
+		At: a.now(), Compose: &job}
+	ctx, cancel := context.WithCancel(a.ctx)
+	k := &composeAsk{id: ask.ID, cancel: cancel}
+	a.asks[key] = k
+	if err := a.asker.Put(ctx, ask); err != nil {
+		a.logf("the compose ask %s for %s could not be put: %v", ask.ID, key, err)
+		k.ran = &assign.Ran{State: delivery.StepFailed, Reason: "the compose ask could not be put on the Go build seat: " + err.Error()}
+		cancel()
+		return k.ran, k.id
+	}
+	go func() {
+		step, err := a.asker.Wait(ctx, ask)
+		if ctx.Err() != nil {
+			return
+		}
+		ran := assign.RanOf(step)
+		if err != nil {
+			ran = assign.Ran{State: delivery.StepFailed, Reason: "the compose ask's step could not be followed: " + err.Error()}
+		}
+		a.mu.Lock()
+		k.ran = &ran
+		a.mu.Unlock()
+		a.wake()
+	}()
+	return nil, k.id
+}
+
+// sweep forgets, and stops following, every ask whose key no pass asked for this time: a candidate gone or moved on.
+func (a *composeAsks) sweep(seen map[string]bool) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+	for key, k := range a.asks {
+		if !seen[key] {
+			k.cancel()
+			delete(a.asks, key)
+		}
+	}
+}
+
+// composeAtHead is the composition of a group with a mesh-sdk member: the composer at its head and at each reader's
+// mesh-sdk, asked of the Go build seat, and the verdict once every ask ended; until then the verdict waits, naming the
+// asks. The keys it used are marked in seen.
+func (p *passer) composeAtHead(ctx context.Context, m assign.Mesh, ch assign.Change, seen map[string]bool, began time.Time) delivery.CompositionVerdict {
+	waiting := func(words string) delivery.CompositionVerdict {
+		return delivery.CompositionVerdict{Group: ch.Group, Heads: ch.Heads, State: delivery.CompositionWaits, Words: words}
+	}
+	head, err := assign.HeadJob(m, ch)
+	if err != nil {
+		return delivery.CompositionVerdict{Group: ch.Group, Heads: ch.Heads, State: delivery.CompositionFail, SDK: "mesh-sdk " + ch.SDKHead,
+			Words: "the compose ask at the group's mesh-sdk head cannot be made: " + err.Error()}
+	}
+	var pending []string
+	key := "head." + ch.Group + "." + ch.Heads + "." + ch.SDKHead
+	seen[key] = true
+	headRan, id := p.asks.get(key, head)
+	if headRan == nil {
+		pending = append(pending, "mesh-sdk "+ch.SDKHead+" (ask "+id+")")
+	}
+	var readers []assign.Reader
+	var notJudged []string
+	for _, module := range sortedNames(assign.ReaderModules) {
+		repository := assign.ReaderModules[module]
+		var commits []string
+		member := false
+		if h := ch.Members[repository]; h != "" {
+			commits, member = []string{h}, true
+		} else {
+			commits = p.w.runningCommits(ctx, kvGetter(p.kvs[delivery.BuildsBucket]), module)
+		}
+		if len(commits) == 0 {
+			notJudged = append(notJudged, "not judged whether "+module+" reads the group's manifests: no build of it is assigned with a "+
+				"commit on record, and the group holds no member of "+repository)
+			continue
+		}
+		for _, commit := range commits {
+			job, err := assign.ReaderJob(ch, module, repository, commit)
+			if err != nil {
+				readers = append(readers, assign.Reader{Module: module, Commit: commit, Member: member,
+					Ran: assign.Ran{State: delivery.StepFailed, Reason: err.Error()}})
+				continue
+			}
+			rkey := "reader." + ch.Group + "." + ch.Heads + "." + module + "." + commit
+			seen[rkey] = true
+			ran, rid := p.asks.get(rkey, job)
+			if ran == nil {
+				pending = append(pending, module+" at "+commit+" (ask "+rid+")")
+				continue
+			}
+			readers = append(readers, assign.Reader{Module: module, Commit: commit, Member: member, Ran: *ran})
+		}
+	}
+	if len(pending) > 0 {
+		return waiting("composing on the Go build seat with the mesh-sdk of " + strings.Join(pending, ", "))
+	}
+	v := assign.FromComposer(m, ch, *headRan, readers, time.Since(began))
+	v.Warnings = append(v.Warnings, notJudged...)
+	return v
+}
+
+func sortedNames(m map[string]string) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/compose_integration_test.go

@@ -0,0 +1,180 @@
+//go:build integration
+
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/composer"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/provider"
+)
+
+// holder is a test holder of the Go build seat: it takes every ask from the seat's check worker, as mesh-build-go does,
+// and answers a compose ask by running mesh-sdk's composer over the request filled from the indexer's manifests (the
+// linked composer standing for the one the build module builds at the asked commit), writing its step on its node's key.
+type holder struct {
+	mu   sync.Mutex
+	asks []delivery.StepAsk
+}
+
+func (h *holder) taken() []delivery.StepAsk {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	return append([]delivery.StepAsk(nil), h.asks...)
+}
+
+func (b *bed) hold(t *testing.T) *holder {
+	t.Helper()
+	seat, _ := delivery.AskStream(delivery.AskGo)
+	worker, _ := delivery.AskWorker(delivery.AskGo, delivery.AskCheck)
+	subject, _ := delivery.AskSubject(delivery.AskGo, delivery.AskCheck)
+	cons, err := b.js.CreateOrUpdateConsumer(b.ctx, seat, jetstream.ConsumerConfig{Durable: worker, FilterSubject: subject, AckPolicy: jetstream.AckExplicitPolicy})
+	if err != nil {
+		t.Fatal(err)
+	}
+	steps := b.buckets[delivery.StepsBucket(goBuildModule)]
+	h := &holder{}
+	cc, err := cons.Consume(func(m jetstream.Msg) {
+		a, err := delivery.DecodeStepAsk(m.Data())
+		if err != nil || a.Compose == nil {
+			t.Errorf("the seat was put an ask that is not a compose: %v %s", err, m.Data())
+			m.Ack()
+			return
+		}
+		h.mu.Lock()
+		h.asks = append(h.asks, a)
+		h.mu.Unlock()
+		req, err := composer.Decode(a.Compose.Request)
+		if err == nil {
+			err = composer.Fill(&req, func(digest string) ([]byte, error) {
+				key, _ := delivery.ManifestsKey(digest)
+				e, err := b.buckets[delivery.ManifestsBucket].Get(b.ctx, key)
+				if err != nil {
+					return nil, err
+				}
+				man, err := delivery.DecodeManifest(e.Value())
+				return []byte(man.JSON), err
+			})
+		}
+		step := delivery.Step{ID: a.ID, Tool: "compose", Node: "ace", State: delivery.StepPassed, Started: time.Now().UTC(), Ended: time.Now().UTC()}
+		if err != nil {
+			step.State, step.Reason = delivery.StepFailed, err.Error()
+		} else if v, err := composer.Run(req); err != nil {
+			step.State, step.Reason = delivery.StepFailed, err.Error()
+		} else {
+			vr, _ := json.Marshal(v)
+			step.Result, _ = json.Marshal(delivery.ComposeAnswer{Built: true, Key: "composer-0123456789abcdef", Verdict: vr})
+		}
+		raw, err := delivery.EncodeStep(step)
+		if err != nil {
+			t.Errorf("the step cannot be written: %v", err)
+		}
+		key, _ := delivery.AskStepKey("ace", a.ID)
+		if _, err := steps.Put(b.ctx, key, raw); err != nil {
+			t.Errorf("the step %s: %v", key, err)
+		}
+		m.Ack()
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(cc.Stop)
+	return h
+}
+
+// 1622/AC1-AC3 and 1623 on the bus: started whole, the assigner composes a group holding a mesh-sdk pull request by
+// asking the Go build seat for the composer at the member's head, and for the composer at the mesh-sdk the running
+// controller pins; it waits naming the asks while they run, writes the verdict from their answers naming the mesh-sdk the
+// head's composer was built with, and asks nothing more on a later pass of the same heads.
+func TestAGroupWithAnSDKMemberIsComposedByTheComposerAtItsHead(t *testing.T) {
+	b := startBed(t, "")
+	trunk := b.manifest(t, "web", `{"module":"web","version":"1"}`)
+	changed := b.manifest(t, "web", `{"module":"web","version":"2"}`)
+	mod, err := delivery.EncodeModule(delivery.Module{FP2: delivery.SourcePrefix2 + strings.Repeat("a", 64), Manifest: trunk, Repository: "novox/web", Commit: strings.Repeat("1", 40), Path: delivery.RootPath})
+	if err != nil {
+		t.Fatal(err)
+	}
+	b.putJSON(t, delivery.ModulesBucket, "web", mod)
+	b.putJSON(t, provider.AssignmentsBucket, "g14.web", []byte(`{"node":"g14","module":"web","build":"build-1"}`))
+	running := strings.Repeat("3", 40)
+	b.putJSON(t, provider.AssignmentsBucket, "novox.mesh-controller", []byte(`{"node":"novox","module":"mesh-controller","build":"c-1"}`))
+	b.putJSON(t, delivery.BuildsBucket, delivery.BuildKey("mesh-controller", "c-1"), []byte(`{"id":"c-1","repository":"novox/mesh-controller","commit":"`+running+`"}`))
+	sdkHead := strings.Repeat("4", 40)
+	heads := []delivery.Head{{Repository: "novox/mesh-sdk", Number: 80, Head: sdkHead}, {Repository: "novox/web", Number: 7, Head: strings.Repeat("2", 40)}}
+	hash, _ := delivery.HeadsHash(heads)
+	pulls := []delivery.CandidatePull{{Head: heads[0]}, {Head: heads[1],
+		Modules: []string{"web"}, Fps: map[string]delivery.CandidateModule{"web": {FP2: delivery.SourcePrefix2 + strings.Repeat("b", 64), Manifest: changed}}}}
+	cand, err := delivery.EncodeCandidate(delivery.Candidate{Group: "feat/x", HeadsHash: hash, Pulls: pulls, FPSet: delivery.FingerprintSet(pulls)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	ckey, _ := delivery.CandidatesKey("feat/x")
+	b.putJSON(t, delivery.CandidatesBucket, ckey, cand)
+	b.start(t)
+	key, _ := delivery.CompositionKey("feat/x", hash)
+	// No holder takes the asks yet: the composition waits, naming them.
+	waits := b.verdict(t, key, func(v delivery.CompositionVerdict) bool { return v.State == delivery.CompositionWaits })
+	if !strings.Contains(waits.Words, "mesh-sdk "+sdkHead) || !strings.Contains(waits.Words, "mesh-controller at "+running) {
+		t.Fatalf("the waiting composition says %q, want the head's and the running controller's asks", waits.Words)
+	}
+	h := b.hold(t)
+	v := b.verdict(t, key, func(v delivery.CompositionVerdict) bool { return v.State != delivery.CompositionWaits })
+	if v.State != delivery.CompositionPass || len(v.Machines) != 1 || v.Machines[0] != "g14" || v.SDK == "" {
+		t.Fatalf("composition = %+v, want a pass on g14", v)
+	}
+	asks := h.taken()
+	if len(asks) != 2 {
+		t.Fatalf("the seat was asked %d composes, want two (the head, the running controller)", len(asks))
+	}
+	byRepo := map[string]delivery.StepAsk{}
+	for _, a := range asks {
+		byRepo[a.Compose.Fetch["repository"].(string)] = a
+		if a.Asker != AssignerModule || a.Kind != delivery.AskCheck || a.Language != delivery.AskGo {
+			t.Errorf("ask = %+v", a)
+		}
+	}
+	if a := byRepo["novox/mesh-sdk"]; a.Compose == nil || a.Compose.Fetch["commit"] != sdkHead || a.Compose.Dir != "go" {
+		t.Errorf("the head's ask = %+v", a.Compose)
+	}
+	if a := byRepo["novox/mesh-controller"]; a.Compose == nil || a.Compose.Fetch["commit"] != running || a.Compose.Dir != delivery.RootPath {
+		t.Errorf("the running controller's ask = %+v", a.Compose)
+	}
+	// A later pass of the same heads (woken by any change) asks nothing more.
+	on, _ := delivery.EncodePresence(delivery.Presence{Online: true})
+	b.putJSON(t, delivery.PresenceBucket, "ace", on)
+	time.Sleep(500 * time.Millisecond)
+	if n := len(h.taken()); n != 2 {
+		t.Errorf("a later pass of the same heads asked again: %d asks", n)
+	}
+}
+
+// verdict waits for the composition under key to satisfy ok, and answers it.
+func (b *bed) verdict(t *testing.T, key string, ok func(delivery.CompositionVerdict) bool) delivery.CompositionVerdict {
+	t.Helper()
+	var last delivery.CompositionVerdict
+	for deadline := time.Now().Add(10 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+		e, err := b.buckets[delivery.AssignerCompositionsBucket].Get(b.ctx, key)
+		if errors.Is(err, jetstream.ErrKeyNotFound) {
+			continue
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+		if last, err = delivery.DecodeCompositionVerdict(e.Value()); err != nil {
+			t.Fatal(err)
+		}
+		if ok(last) {
+			return last
+		}
+	}
+	t.Fatalf("no composition under %s as wanted after 10 s; last %+v", key, last)
+	return last
+}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/integration_test.go

@@ -0,0 +1,317 @@
+//go:build integration
+
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats-server/v2/server"
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/announce"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/process"
+	"git.novox.be/novox/mesh-sdk/go/provider"
+)
+
+// bed is an embedded bus with JetStream, every bucket the assigner reads and keeps, and the stream the mesh's events
+// are kept in, as the controller's broker raises them.
+type bed struct {
+	srv     *server.Server
+	js      jetstream.JetStream
+	ctx     context.Context
+	dir     string
+	buckets map[string]jetstream.KeyValue
+}
+
+func startBed(t *testing.T, leaveOut string) *bed {
+	t.Helper()
+	dir, err := os.MkdirTemp(os.Getenv("TMPDIR"), "assigner")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { os.RemoveAll(dir) })
+	srv, err := server.NewServer(&server.Options{Host: "127.0.0.1", Port: -1, JetStream: true, StoreDir: filepath.Join(dir, "js"), NoLog: true, NoSigs: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	go srv.Start()
+	if !srv.ReadyForConnections(10 * time.Second) {
+		t.Fatal("the bus did not come up")
+	}
+	t.Cleanup(srv.Shutdown)
+	nc, err := nats.Connect(srv.ClientURL())
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(nc.Close)
+	js, err := jetstream.New(nc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
+	t.Cleanup(cancel)
+	b := &bed{srv: srv, js: js, ctx: ctx, dir: dir, buckets: map[string]jetstream.KeyValue{}}
+	for _, name := range append(append([]string{}, readBuckets...), ownBuckets...) {
+		if name == leaveOut {
+			continue
+		}
+		kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: name, History: 5})
+		if err != nil {
+			t.Fatal(err)
+		}
+		b.buckets[name] = kv
+	}
+	if _, err := js.CreateStream(ctx, jetstream.StreamConfig{Name: "EVENTS", Subjects: []string{"mesh.mod.*.event.>"}}); err != nil {
+		t.Fatal(err)
+	}
+	// The Go build seat's work queue, as the broker derives it from the seat's accepted kinds (delivery.AskStream).
+	seat, _ := delivery.AskStream(delivery.AskGo)
+	if _, err := js.CreateStream(ctx, jetstream.StreamConfig{Name: seat, Subjects: []string{"mesh.seat.node-build-go.accept.>"},
+		Retention: jetstream.WorkQueuePolicy}); err != nil {
+		t.Fatal(err)
+	}
+	return b
+}
+
+// start runs the program as the node does, through run with its environment and a broker file; it answers the
+// channel run's error arrives on.
+func (b *bed) start(t *testing.T) <-chan error {
+	t.Helper()
+	broker := filepath.Join(b.dir, "broker")
+	cred, _ := json.Marshal(process.Account{URL: b.srv.ClientURL(), Node: "n1", Module: "mesh-delivery-assigner", User: "n1.mesh-delivery-assigner", Password: "pw"})
+	if err := os.WriteFile(broker, cred, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	env := map[string]string{"MESH_BROKER_FILE": broker}
+	ctx, stop := context.WithCancel(b.ctx)
+	done := make(chan error, 1)
+	go func() { done <- run(ctx, func(k string) string { return env[k] }, io.Discard) }()
+	t.Cleanup(func() {
+		stop()
+		select {
+		case <-done:
+		case <-time.After(10 * time.Second):
+		}
+	})
+	return done
+}
+
+// 1297/B2b: started whole on its credential, the assigner says on the bus the four states it keeps, each readable,
+// having opened every bucket it names.
+func TestTheAssignerStartsAndSaysWhatItKeeps(t *testing.T) {
+	b := startBed(t, "")
+	done := b.start(t)
+	events, err := b.js.Stream(b.ctx, "EVENTS")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var said announce.States
+	for deadline := time.Now().Add(10 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+		select {
+		case err := <-done:
+			t.Fatalf("the assigner stopped: %v", err)
+		default:
+		}
+		m, err := events.GetLastMsgForSubject(b.ctx, announce.Subject("mesh-delivery-assigner"))
+		if err != nil {
+			continue
+		}
+		if err := json.Unmarshal(m.Data, &said); err != nil {
+			t.Fatal(err)
+		}
+		break
+	}
+	if said.Module != "mesh-delivery-assigner" || said.Node != "n1" || len(said.States) != 4 || !said.Readable("asks") ||
+		!said.Readable("wants") || !said.Readable("differences") || !said.Readable("compositions") {
+		t.Fatalf("the assigner said %+v, want its four states, each readable", said)
+	}
+}
+
+// 1297/B2b: a bucket it reads that the bus does not hold stops the start, naming the bucket.
+func TestTheAssignerDoesNotStartWithoutABucketItReads(t *testing.T) {
+	for _, missing := range readBuckets {
+		b := startBed(t, missing)
+		select {
+		case err := <-b.start(t):
+			if err == nil || !strings.Contains(err.Error(), missing) {
+				t.Errorf("without %s the assigner stopped with %v, want the bucket named", missing, err)
+			}
+		case <-time.After(15 * time.Second):
+			t.Errorf("without %s the assigner started", missing)
+		}
+	}
+}
+
+// putJSON writes a value into one of the bed's buckets.
+func (b *bed) putJSON(t *testing.T, bucket, key string, value []byte) {
+	t.Helper()
+	if _, err := b.buckets[bucket].Put(b.ctx, key, value); err != nil {
+		t.Fatalf("%s %s: %v", bucket, key, err)
+	}
+}
+
+// manifest keeps a manifest in the indexer's bucket by its digest and answers the digest.
+func (b *bed) manifest(t *testing.T, module, body string) string {
+	t.Helper()
+	digest := delivery.ManifestDigest([]byte(body))
+	key, _ := delivery.ManifestsKey(digest)
+	value, err := delivery.EncodeManifest(delivery.Manifest{Module: module, JSON: body})
+	if err != nil {
+		t.Fatal(err)
+	}
+	b.putJSON(t, delivery.ManifestsBucket, key, value)
+	return digest
+}
+
+// 1297/AC1: against the real bus, a fixture change touching one module on one machine is composed and answered within
+// seconds under the checker's key of the check, naming the machine composed and the mesh-sdk it composed with.
+func TestAChangeIsComposedOnTheBus(t *testing.T) {
+	b := startBed(t, "")
+	trunk := b.manifest(t, "web", `{"module":"web","version":"1"}`)
+	changed := b.manifest(t, "web", `{"module":"web","version":"2"}`)
+	mod, err := delivery.EncodeModule(delivery.Module{FP2: delivery.SourcePrefix2 + strings.Repeat("a", 64), Manifest: trunk, Repository: "novox/web", Commit: strings.Repeat("1", 40), Path: delivery.RootPath})
+	if err != nil {
+		t.Fatal(err)
+	}
+	b.putJSON(t, delivery.ModulesBucket, "web", mod)
+	b.putJSON(t, provider.AssignmentsBucket, "g14.web", []byte(`{"node":"g14","module":"web","build":"build-1"}`))
+	b.putJSON(t, provider.AssignmentsBucket, "ace.other", []byte(`{"node":"ace","module":"other","build":"build-2"}`))
+	heads := []delivery.Head{{Repository: "novox/web", Number: 7, Head: strings.Repeat("2", 40)}}
+	hash, _ := delivery.HeadsHash(heads)
+	// 1927/AC1: the candidate carries the fingerprint set the SDK computes, as the indexer writes it.
+	pulls := []delivery.CandidatePull{{Head: heads[0],
+		Modules: []string{"web"}, Fps: map[string]delivery.CandidateModule{"web": {FP2: delivery.SourcePrefix2 + strings.Repeat("b", 64), Manifest: changed}}}}
+	cand, err := delivery.EncodeCandidate(delivery.Candidate{Group: "feat/x", HeadsHash: hash, Pulls: pulls, FPSet: delivery.FingerprintSet(pulls)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	ckey, _ := delivery.CandidatesKey("feat/x")
+	b.putJSON(t, delivery.CandidatesBucket, ckey, cand)
+	began := time.Now()
+	b.start(t)
+	key, _ := delivery.CompositionKey("feat/x", hash)
+	var v delivery.CompositionVerdict
+	for deadline := time.Now().Add(10 * time.Second); ; time.Sleep(50 * time.Millisecond) {
+		if time.Now().After(deadline) {
+			t.Fatalf("no composition under %s after 10 s", key)
+		}
+		e, err := b.buckets[delivery.AssignerCompositionsBucket].Get(b.ctx, key)
+		if err != nil {
+			continue
+		}
+		if v, err = delivery.DecodeCompositionVerdict(e.Value()); err != nil {
+			t.Fatal(err)
+		}
+		break
+	}
+	if v.State != delivery.CompositionPass || len(v.Machines) != 1 || v.Machines[0] != "g14" || v.SDK == "" {
+		t.Fatalf("composition = %+v, want a pass on g14 alone naming its mesh-sdk", v)
+	}
+	if took := time.Since(began); took > 5*time.Second {
+		t.Errorf("the composition took %s", took)
+	}
+	// 1622/AC3: a group without a mesh-sdk member builds no composer: no ask is put on the Go build seat.
+	seat, _ := delivery.AskStream(delivery.AskGo)
+	if st, err := b.js.Stream(b.ctx, seat); err != nil {
+		t.Fatal(err)
+	} else if info, err := st.Info(b.ctx); err != nil || info.State.Msgs != 0 {
+		t.Errorf("a group without a mesh-sdk member put %d asks on the Go build seat (%v)", info.State.Msgs, err)
+	}
+}
+
+// get waits for a key of one of the bed's buckets and answers its value.
+func (b *bed) get(t *testing.T, bucket, key string) []byte {
+	t.Helper()
+	for deadline := time.Now().Add(10 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+		if e, err := b.buckets[bucket].Get(b.ctx, key); err == nil {
+			return e.Value()
+		}
+	}
+	t.Fatalf("no %s %s after 10 s", bucket, key)
+	return nil
+}
+
+// 1297/B4, B5 on the bus: the controller sent F to g14 while the canary ace does not run F healthy yet. Started whole,
+// the assigner wants F on the canary, writes the difference on g14 explained by rule 3, and on ace one unexplained (the
+// controller sends ace the older fingerprint while ace wants F).
+func TestWantsAndTheirDifferencesOnTheBus(t *testing.T) {
+	b := startBed(t, "")
+	fNew, fOld := delivery.SourcePrefix2+strings.Repeat("b", 64), delivery.SourcePrefix2+strings.Repeat("a", 64)
+	digest := b.manifest(t, "web", `{"module":"web","version":"1"}`)
+	mod, _ := delivery.EncodeModule(delivery.Module{FP2: fNew, Manifest: digest, Repository: "novox/web", Commit: strings.Repeat("1", 40), Path: delivery.RootPath})
+	b.putJSON(t, delivery.ModulesBucket, "web", mod)
+	built, err := delivery.EncodeBuilderBuild(delivery.BuilderBuild{State: delivery.BuildDone, By: "builder.novox.1", Step: "pushed", Manifest: digest})
+	if err != nil {
+		t.Fatal(err)
+	}
+	bkey, _ := delivery.BuilderBuildKey("web", fNew)
+	b.putJSON(t, delivery.BuilderBuildsBucket, bkey, built)
+	gkey, _ := delivery.ControllerGrantKey("web", fNew)
+	grant, _ := delivery.EncodeControllerGrant(delivery.ControllerGrant{})
+	b.putJSON(t, delivery.ControllerGrantsBucket, gkey, grant)
+	for _, node := range []string{"ace", "g14"} {
+		on, _ := delivery.EncodePresence(delivery.Presence{Online: true})
+		b.putJSON(t, delivery.PresenceBucket, node, on)
+		have, _ := delivery.EncodeHave(delivery.Have{FP: fOld, Phase: delivery.PhaseRunning, Health: delivery.HealthOK})
+		b.putJSON(t, delivery.HaveBucket, node+".web", have)
+	}
+	b.putJSON(t, provider.AssignmentsBucket, "ace.web", []byte(`{"node":"ace","module":"web","build":"b-8"}`))
+	b.putJSON(t, provider.AssignmentsBucket, "g14.web", []byte(`{"node":"g14","module":"web","build":"b-9"}`))
+	b.putJSON(t, delivery.BuildsBucket, delivery.BuildKey("web", "b-8"), []byte(`{"id":"b-8","repository":"novox/web","source-fingerprint":"`+fOld+`"}`))
+	b.putJSON(t, delivery.BuildsBucket, delivery.BuildKey("web", "b-9"), []byte(`{"id":"b-9","repository":"novox/web","source-fingerprint":"`+fNew+`"}`))
+	b.start(t)
+
+	wkey, _ := delivery.WantKey("ace", "web")
+	want, err := delivery.DecodeWant(b.get(t, delivery.AssignerWantsBucket, wkey))
+	if err != nil || want.FP != fNew {
+		t.Fatalf("the canary ace's want = %+v, %v", want, err)
+	}
+	dkey, _ := delivery.DifferenceKey("g14", "web")
+	d, err := delivery.DecodeDifference(b.get(t, delivery.AssignerDifferencesBucket, dkey))
+	if err != nil || d.Rule != delivery.RuleCanary || d.Sent != fNew {
+		t.Fatalf("g14's difference = %+v, %v; want rule 3", d, err)
+	}
+	akey, _ := delivery.DifferenceKey("ace", "web")
+	a, err := delivery.DecodeDifference(b.get(t, delivery.AssignerDifferencesBucket, akey))
+	if err != nil || !a.Unexplained || a.Want != fNew || a.Sent != fOld {
+		t.Fatalf("ace's difference = %+v, %v; want it unexplained", a, err)
+	}
+	if e, err := b.buckets[delivery.AssignerWantsBucket].Get(b.ctx, "want.g14.web"); err == nil {
+		t.Errorf("g14, held back by the canary with no want before, was given one: %s", e.Value())
+	}
+}
+
+// 1297/B9 (the assigner's half, ADR 0528 clause 6): started whole, the assigner holds a fingerprint whose health check
+// failed on a node and writes the ask about it in its own asks, which the view and the teller read; its asks bucket is
+// the one its manifest declares (ownBuckets, held equal to the manifest by TestOpensWhatItsManifestNames).
+func TestAHeldFingerprintIsAskedAbout(t *testing.T) {
+	b := startBed(t, "")
+	fNew := delivery.SourcePrefix2 + strings.Repeat("c", 64)
+	digest := b.manifest(t, "web", `{"module":"web","version":"1"}`)
+	mod, _ := delivery.EncodeModule(delivery.Module{FP2: fNew, Manifest: digest, Repository: "novox/web", Commit: strings.Repeat("1", 40), Path: delivery.RootPath})
+	b.putJSON(t, delivery.ModulesBucket, "web", mod)
+	on, _ := delivery.EncodePresence(delivery.Presence{Online: true})
+	b.putJSON(t, delivery.PresenceBucket, "ace", on)
+	failed, _ := delivery.EncodeHave(delivery.Have{FP: fNew, Phase: delivery.PhaseRunning, Health: delivery.HealthFailed, Detail: "connection refused"})
+	b.putJSON(t, delivery.HaveBucket, "ace.web", failed)
+	b.putJSON(t, provider.AssignmentsBucket, "ace.web", []byte(`{"node":"ace","module":"web","build":"b-1"}`))
+	b.start(t)
+	hkey, _ := delivery.HeldKey("web", fNew)
+	if h, err := delivery.DecodeHeld(b.get(t, delivery.AssignerWantsBucket, hkey)); err != nil || h.Node != "ace" {
+		t.Fatalf("held = %+v, %v", h, err)
+	}
+	akey, _ := delivery.HoldAskKey("web", fNew)
+	a, err := delivery.DecodeAssignerAsk(akey, b.get(t, delivery.AssignerAsksBucket, akey))
+	if err != nil || a.Ask.ID != delivery.AskingID(akey, 0) || len(a.Ask.Options) != 2 {
+		t.Fatalf("the ask = %+v, %v", a, err)
+	}
+}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/main.go

@@ -0,0 +1,232 @@
+// Command mesh-delivery-assigner is delivery's assigner (novox/hq ADR 0429 §1 and §6, ADR 0446, ADR 0528, issue 1297): a
+// process on its own bus credential that watches what the indexer, the builder, the controller, the node-engines and
+// the watchman write, and writes what each node should run (`want.<node>.<module>`, by the six rules), the
+// fingerprints it holds, every difference between a want and what the controller sends, and the composition check's
+// verdict of each group the checker judges. In release 5 the wants are only compared: the controller still sends what
+// each node runs (ADR 0429 §7). It holds no timer: every pass is started by a change it watched.
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/announce"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+	"git.novox.be/novox/mesh-sdk/go/process"
+	"git.novox.be/novox/mesh-sdk/go/provider"
+)
+
+func main() {
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	if err := run(ctx, os.Getenv, os.Stderr); err != nil {
+		fmt.Fprintln(os.Stderr, "mesh-delivery-assigner:", err)
+		os.Exit(1)
+	}
+}
+
+// readBuckets are the buckets of other parts the assigner reads, each named in its manifest's reads (the manifest test
+// holds the two lists equal), so the controller's broker grants exactly these.
+var readBuckets = []string{
+	provider.AssignmentsBucket,
+	delivery.BuildsBucket,
+	delivery.ControllerGrantsBucket,
+	delivery.BuilderBuildsBucket,
+	delivery.CandidatesBucket,
+	delivery.ManifestsBucket,
+	delivery.ModulesBucket,
+	delivery.PresenceBucket,
+	delivery.HaveBucket,
+	delivery.StepsBucket(goBuildModule),
+}
+
+// goBuildModule is the Go build module, which takes the assigner's compose asks on its seat's check stream and writes
+// their steps in its steps state (novox/hq ADR 0482 clause 4).
+const goBuildModule = "mesh-build-go"
+
+// ownBuckets are the assigner's own states, as its manifest declares them.
+var ownBuckets = []string{delivery.AssignerAsksBucket, delivery.AssignerCompositionsBucket, delivery.AssignerDifferencesBucket, delivery.AssignerWantsBucket}
+
+// keptStates is what the assigner keeps and who may read it (ADR 0495 §2-§3): its wants by the watchman and the view
+// (and the node agent from release 6), its differences by the view, its compositions by the checker, its asks by the view
+// and the teller.
+var keptStates = []announce.State{
+	{Name: "asks", Readable: true},
+	{Name: "compositions", Readable: true},
+	{Name: "differences", Readable: true},
+	{Name: "wants", Readable: true},
+}
+
+// buckets is every bucket the assigner opened, by name.
+type buckets map[string]jetstream.KeyValue
+
+// open opens every bucket the assigner reads and writes; a bucket it cannot open stops the start, named, since a pass
+// without it would write wants from half the mesh.
+func open(ctx context.Context, js jetstream.JetStream) (buckets, error) {
+	out := buckets{}
+	for _, name := range append(append([]string{}, readBuckets...), ownBuckets...) {
+		kv, err := js.KeyValue(ctx, name)
+		if err != nil {
+			return nil, fmt.Errorf("the bucket %s cannot be opened: %w", name, err)
+		}
+		out[name] = kv
+	}
+	return out, nil
+}
+
+// run is the program: it returns when ctx ends or the bus cannot be used.
+func run(ctx context.Context, getenv func(string) string, logOut io.Writer) error {
+	logger := log.New(logOut, "mesh-delivery-assigner: ", log.LstdFlags)
+	path := strings.TrimSpace(getenv("MESH_BROKER_FILE"))
+	if path == "" {
+		return errors.New("MESH_BROKER_FILE is not set, so there is no credential to read the bus with")
+	}
+	account, err := process.ReadAccount(path)
+	if err != nil {
+		return err
+	}
+	opts := []nats.Option{
+		nats.Name(account.Node + "." + account.Module),
+		nats.UserInfo(account.User, account.Password),
+		nats.CustomInboxPrefix(account.InboxPrefix()),
+		nats.MaxReconnects(-1),
+		nats.RetryOnFailedConnect(true),
+	}
+	if strings.TrimSpace(account.Fingerprint) != "" {
+		opts = append(opts, nats.Secure(process.PinnedToFingerprint(account.Fingerprint)))
+	}
+	conn, err := nats.Connect(account.URL, opts...)
+	if err != nil {
+		return fmt.Errorf("connecting to the bus: %w", err)
+	}
+	defer conn.Close()
+	js, err := jetstream.New(conn)
+	if err != nil {
+		return err
+	}
+	kvs, err := open(ctx, js)
+	if err != nil {
+		return err
+	}
+	// What the assigner keeps, said on the bus (ADR 0495 §2-§3): a reader is granted from it. Not fatal when it cannot
+	// be said now: process.Conn says it again at every reconnect.
+	said, err := process.Connect(account, nats.Name(account.Node+"."+account.Module+".keeps"), nats.RetryOnFailedConnect(true))
+	if err != nil {
+		return err
+	}
+	defer said.Close()
+	if err := said.Keeps(keptStates...); err != nil {
+		logger.Printf("what the assigner keeps could not be said on the bus, so its readers are not granted until it is: %v", err)
+	}
+	logger.Printf("started on the account %s, reading %d buckets", account.User, len(kvs))
+	return follow(ctx, js, kvs, logger)
+}
+
+// watched are the buckets whose every value a pass reads; the manifests are read by digest when a pass needs one, and
+// watched only for keys, so a manifest that arrives wakes a composition that waits for it.
+var watched = []string{
+	provider.AssignmentsBucket,
+	delivery.ControllerGrantsBucket,
+	delivery.BuilderBuildsBucket,
+	delivery.CandidatesBucket,
+	delivery.ModulesBucket,
+	delivery.PresenceBucket,
+	delivery.HaveBucket,
+	delivery.AssignerAsksBucket,
+	delivery.AssignerCompositionsBucket,
+	delivery.AssignerDifferencesBucket,
+	delivery.AssignerWantsBucket,
+}
+
+// follow watches every bucket a pass reads and makes a pass at start, once every watch handed what stands, and after
+// each change; changes that come during a pass make one more. It returns when ctx ends or a watch ends.
+func follow(ctx context.Context, js jetstream.JetStream, kvs buckets, logger *log.Logger) error {
+	w := newWorld()
+	dirty := make(chan struct{}, 1)
+	wake := func() {
+		select {
+		case dirty <- struct{}{}:
+		default:
+		}
+	}
+	errs := make(chan error, len(watched)+1)
+	settled := make(chan struct{}, len(watched)+1)
+	watch := func(name string, opts ...jetstream.WatchOpt) error {
+		kw, err := kvs[name].WatchAll(ctx, opts...)
+		if err != nil {
+			return fmt.Errorf("the bucket %s cannot be watched: %w", name, err)
+		}
+		go func() {
+			defer kw.Stop()
+			for {
+				select {
+				case <-ctx.Done():
+					errs <- nil
+					return
+				case e, ok := <-kw.Updates():
+					if !ok {
+						errs <- fmt.Errorf("the watch of %s ended", name)
+						return
+					}
+					if e == nil {
+						settled <- struct{}{}
+						continue
+					}
+					var value []byte
+					if e.Operation() == jetstream.KeyValuePut {
+						value = e.Value()
+					}
+					w.put(name, e.Key(), value)
+					wake()
+				}
+			}
+		}()
+		return nil
+	}
+	for _, name := range watched {
+		var opts []jetstream.WatchOpt
+		if name == delivery.HaveBucket {
+			opts = append(opts, jetstream.IncludeHistory()) // what each node ran healthy before, for a set-back
+		}
+		if err := watch(name, opts...); err != nil {
+			return err
+		}
+	}
+	if err := watch(delivery.ManifestsBucket, jetstream.MetaOnly()); err != nil {
+		return err
+	}
+	for range len(watched) + 1 {
+		select {
+		case <-ctx.Done():
+			return nil
+		case err := <-errs:
+			return err
+		case <-settled:
+		}
+	}
+	p := &passer{kvs: kvs, w: w, logf: logger.Printf}
+	p.asks = newComposeAsks(ctx, buildrun.Asker{Publisher: buildrun.JetStreamAsks{JS: js}, Waiter: buildrun.JetStreamAsks{JS: js}}, wake, logger.Printf)
+	wake()
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case err := <-errs:
+			return err
+		case <-settled:
+		case <-dirty:
+			p.pass(ctx)
+		}
+	}
+}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/main_test.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"context"
+	"io"
+	"os"
+	"path/filepath"
+	"reflect"
+	"slices"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+)
+
+// 1297/B2a: the buckets the program opens are exactly the manifest's reads and states, as the broker names them
+// (`<module>.<state>` read as the bucket `<module>_<state>`), so it is granted what it reads and reads nothing else.
+func TestOpensWhatItsManifestNames(t *testing.T) {
+	raw, err := os.ReadFile(filepath.Join("..", "..", "module.json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	m, err := catalogue.ParseManifest(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var reads []string
+	for _, r := range m.Reads {
+		reads = append(reads, strings.Replace(r, ".", "_", 1))
+	}
+	var states []string
+	for _, s := range m.State {
+		states = append(states, m.Module+"_"+s.Name)
+	}
+	for _, pair := range []struct {
+		what       string
+		code, want []string
+	}{{"reads", readBuckets, reads}, {"states", ownBuckets, states}} {
+		got, want := slices.Sorted(slices.Values(pair.code)), slices.Sorted(slices.Values(pair.want))
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("the program's %s are %v, the manifest's %v", pair.what, got, want)
+		}
+	}
+	var kept []string
+	for _, s := range keptStates {
+		kept = append(kept, m.Module+"_"+s.Name)
+	}
+	if got, want := slices.Sorted(slices.Values(kept)), slices.Sorted(slices.Values(ownBuckets)); !reflect.DeepEqual(got, want) {
+		t.Errorf("the program announces %v, keeps %v", got, want)
+	}
+}
+
+// 1297/B2a: without a credential the program does not start, and says why.
+func TestNoCredential(t *testing.T) {
+	err := run(context.Background(), func(string) string { return "" }, io.Discard)
+	if err == nil || !strings.Contains(err.Error(), "MESH_BROKER_FILE") {
+		t.Errorf("run without a credential = %v", err)
+	}
+}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/pass.go

@@ -0,0 +1,232 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/sdkversion"
+
+	"mesh-delivery-assigner/internal/assign"
+)
+
+// passer makes the assigner's passes: from what the world holds now, it writes each key whose value differs from the
+// one written, and only those (the Same functions).
+type passer struct {
+	kvs  buckets
+	w    *world
+	logf func(string, ...any)
+	sdk  string
+	asks *composeAsks
+}
+
+func (p *passer) pass(ctx context.Context) {
+	p.compositions(ctx)
+	rules := p.wants(ctx)
+	p.differences(ctx, rules)
+}
+
+// differences writes, for each node and module the assigner wants or the controller sends, the difference between the
+// two with the rule that explains it or unexplained (ADR 0528 clause 4), and deletes the key of a difference that
+// ended; its history keeps what it was.
+func (p *passer) differences(ctx context.Context, rules map[string]map[string]assign.Holding) {
+	_, assignments := p.w.assigned()
+	wanted := p.w.wantsOf()
+	trunk := p.w.trunk()
+	pairs := map[[2]string]bool{}
+	for _, a := range assignments {
+		pairs[[2]string{a.Node, a.Module}] = true
+	}
+	for module, byNode := range wanted {
+		for node := range byNode {
+			pairs[[2]string{node, module}] = true
+		}
+	}
+	written := p.w.read(delivery.AssignerDifferencesBucket)
+	keep := map[string]bool{}
+	for pair := range pairs {
+		node, module := pair[0], pair[1]
+		key, err := delivery.DifferenceKey(node, module)
+		if err != nil {
+			continue
+		}
+		var want *delivery.Want
+		if w, ok := wanted[module][node]; ok {
+			want = &w
+		}
+		var sent assign.Sent
+		if a, ok := assignments[node+"."+module]; ok {
+			sent = assign.Sent{Sends: true, Build: a.Build, FP: p.w.sentFP(ctx, kvGetter(p.kvs[delivery.BuildsBucket]), module, a.Build)}
+		}
+		d, ok := assign.Compare(want, sent, trunk[module].FP2, rules[module][node])
+		if !ok {
+			continue
+		}
+		keep[key] = true
+		if before, err := delivery.DecodeDifference(written[key]); err == nil {
+			before.V = 0
+			if delivery.SameDifference(before, d) {
+				continue
+			}
+		}
+		p.put(ctx, delivery.AssignerDifferencesBucket, key, func() ([]byte, error) { return delivery.EncodeDifference(d) })
+	}
+	for key := range written {
+		if keep[key] {
+			continue
+		}
+		if err := p.kvs[delivery.AssignerDifferencesBucket].Delete(ctx, key); err != nil {
+			p.logf("the difference %s that ended could not be deleted: %v", key, err)
+			continue
+		}
+		p.w.put(delivery.AssignerDifferencesBucket, key, nil)
+	}
+}
+
+// wants writes, for every module the trunk holds a fingerprint of, each node's want by the six rules (ADR 0429 §6), and
+// the hold of a fingerprint whose health check failed. It returns, by module then node, the rule that holds a node
+// back, for the comparison.
+func (p *passer) wants(ctx context.Context) map[string]map[string]assign.Holding {
+	get := kvGetter(p.kvs[delivery.ManifestsBucket])
+	assigned, _ := p.w.assigned()
+	trunk := p.w.trunk()
+	manifests := map[string]catalogue.Manifest{}
+	for name, mod := range trunk {
+		if mod.Manifest == "" {
+			continue
+		}
+		if got := p.w.manifest(ctx, get, mod.Manifest); got.err == "" {
+			manifests[name] = got.manifest
+		}
+	}
+	nodes := p.w.nodes(manifests, assigned)
+	nodesOf := map[string][]string{}
+	for node, modules := range assigned {
+		for _, m := range modules {
+			nodesOf[m] = append(nodesOf[m], node)
+		}
+	}
+	wanted := p.w.wantsOf()
+	rules := map[string]map[string]assign.Holding{}
+	names := map[string]bool{}
+	for name := range trunk {
+		names[name] = true
+	}
+	for name := range wanted {
+		names[name] = true
+	}
+	for name := range names {
+		fp := trunk[name].FP2
+		m := assign.Module{Name: name, FP: fp, Manifest: manifests[name], Nodes: nodesOf[name]}
+		if fp != "" {
+			held, _ := delivery.HeldKey(name, fp)
+			grant, _ := delivery.ControllerGrantKey(name, fp)
+			m.Built, m.Held, m.Granted = p.w.built(name, fp), p.w.has(delivery.AssignerWantsBucket, held), p.w.has(delivery.ControllerGrantsBucket, grant)
+		}
+		last := map[string]string{}
+		for _, node := range m.Nodes {
+			last[node] = p.w.lastHealthy(node, name, fp)
+		}
+		out := assign.Wants(m, nodes, wanted[name], last)
+		rules[name] = out.Rules
+		if out.Held != nil {
+			key, err := delivery.HeldKey(name, fp)
+			if err == nil {
+				held := *out.Held
+				p.put(ctx, delivery.AssignerWantsBucket, key, func() ([]byte, error) { return delivery.EncodeHeld(held) })
+			}
+		}
+		if out.Held != nil || m.Held {
+			p.holdAsk(ctx, name, fp)
+		}
+		for node, want := range out.Wants {
+			key, err := delivery.WantKey(node, name)
+			if err != nil {
+				p.logf("no want of %s on %s is written: %v", name, node, err)
+				continue
+			}
+			want := want
+			p.put(ctx, delivery.AssignerWantsBucket, key, func() ([]byte, error) { return delivery.EncodeWant(want) })
+		}
+	}
+	return rules
+}
+
+// compositions writes the composition check's verdict of every group the indexer holds a candidate for, under the
+// checker's key of that check: waits, with why, while the indexer holds what it composes from only in part.
+func (p *passer) compositions(ctx context.Context) {
+	if p.sdk == "" {
+		p.sdk = sdkversion.Version()
+	}
+	written := p.w.read(delivery.AssignerCompositionsBucket)
+	trunk := p.w.trunk()
+	var mesh *assign.Mesh
+	seen := map[string]bool{}
+	if p.asks != nil {
+		defer p.asks.sweep(seen)
+	}
+	for key, value := range p.w.read(delivery.CandidatesBucket) {
+		c, err := delivery.DecodeCandidate(value)
+		if err != nil {
+			p.logf("the candidate %s cannot be read, so it is not composed: %v", key, err)
+			continue
+		}
+		out, err := delivery.CompositionKey(c.Group, c.HeadsHash)
+		if err != nil {
+			p.logf("the candidate %s names no composition key: %v", key, err)
+			continue
+		}
+		began := time.Now()
+		ch, waits := p.w.change(ctx, kvGetter(p.kvs[delivery.ManifestsBucket]), c, trunk)
+		var v delivery.CompositionVerdict
+		if waits != "" {
+			v = delivery.CompositionVerdict{Group: c.Group, Heads: c.HeadsHash, State: delivery.CompositionWaits, Words: waits}
+		} else {
+			if mesh == nil {
+				m := p.w.mesh(ctx, kvGetter(p.kvs[delivery.ManifestsBucket]))
+				mesh = &m
+			}
+			if ch.SDKHead != "" && p.asks != nil {
+				// A group with a mesh-sdk member is composed by the composer built at its head (ADR 0482 clauses 3 to 5).
+				v = p.composeAtHead(ctx, *mesh, ch, seen, began)
+			} else {
+				v = assign.Compose(*mesh, ch, p.sdk, time.Since(began))
+			}
+		}
+		if before, err := delivery.DecodeCompositionVerdict(written[out]); err == nil {
+			before.Took, before.V = v.Took, 0
+			if delivery.SameCompositionVerdict(before, v) {
+				continue
+			}
+		}
+		p.put(ctx, delivery.AssignerCompositionsBucket, out, func() ([]byte, error) { return delivery.EncodeCompositionVerdict(v) })
+	}
+}
+
+// put writes one key of the assigner's own bucket; a write that fails is said and made again at the next pass.
+func (p *passer) put(ctx context.Context, bucket, key string, encode func() ([]byte, error)) {
+	value, err := encode()
+	if err != nil {
+		p.logf("%s %s is not written: %v", bucket, key, err)
+		return
+	}
+	if _, err := p.kvs[bucket].Put(ctx, key, value); err != nil && !errors.Is(err, context.Canceled) {
+		p.logf("%s %s could not be written: %v", bucket, key, err)
+		return
+	}
+	p.w.put(bucket, key, value)
+}
+
+// holdAsk writes, once, the ask about a held fingerprint (ADR 0528 clause 6, ADR 0437 clause 10): the first ask that needs
+// no proof of who answered, which the view may answer and the teller fills. In release 5 an answer changes nothing on a
+// node (wants are only compared, ADR 0429 §7), and the options say so.
+func (p *passer) holdAsk(ctx context.Context, module, fp string) {
+	key, err := delivery.HoldAskKey(module, fp)
+	if err != nil || p.w.has(delivery.AssignerAsksBucket, key) {
+		return
+	}
+	a := assign.HoldAsk(key, module, fp, time.Now())
+	p.put(ctx, delivery.AssignerAsksBucket, key, func() ([]byte, error) { return delivery.EncodeAssignerAsk(key, a) })
+}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/world.go

@@ -0,0 +1,402 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"slices"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/provider"
+
+	"mesh-delivery-assigner/internal/assign"
+)
+
+// noModuleWords is the indexer's reason for a module of a candidate whose directory the merge preview holds no manifest
+// for (mesh-sdk delivery.CandidateNoneNoModule, which the indexer writes): the change removes the module.
+const noModuleWords = delivery.CandidateNoneNoModule
+
+// assignment holds only the fields of the controller's Assignment the assigner reads (the view's own, mesh-delivery-view
+// internal/view/view.go): an assignment stands while it has not ended and has no state.
+type assignment struct {
+	Node   string    `json:"node"`
+	Module string    `json:"module"`
+	Build  string    `json:"build"`
+	Ended  time.Time `json:"ended"`
+	State  string    `json:"state"`
+}
+
+func (a assignment) open() bool { return a.Ended.IsZero() && a.State == "" }
+
+// world is what the assigner watched, as it stands now: every value by bucket and key, and the manifests read by
+// digest. The watches write it; a pass reads it.
+type world struct {
+	mu        sync.Mutex
+	values    map[string]map[string][]byte
+	manifests map[string]parsed
+	// healthy is, by have key, every fingerprint the node ran healthy, oldest first, each once: what a set-back goes to.
+	healthy map[string][]string
+	// sent is, by build id, the fingerprint of the new form the controller's build record names, once it names one.
+	sent map[string]string
+}
+
+// parsed is a manifest read by digest: its module and its manifest, or why it cannot be read.
+type parsed struct {
+	module   string
+	manifest catalogue.Manifest
+	err      string
+}
+
+func newWorld() *world {
+	return &world{values: map[string]map[string][]byte{}, manifests: map[string]parsed{}, healthy: map[string][]string{}, sent: map[string]string{}}
+}
+
+// put takes a change of a watched bucket in: a value, or nil for a key deleted or purged.
+func (w *world) put(bucket, key string, value []byte) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if w.values[bucket] == nil {
+		w.values[bucket] = map[string][]byte{}
+	}
+	if value == nil {
+		delete(w.values[bucket], key)
+		return
+	}
+	w.values[bucket][key] = value
+	if bucket == delivery.HaveBucket {
+		if h, err := delivery.DecodeHave(value); err == nil && h.FP != "" && h.Phase == delivery.PhaseRunning && h.Health == delivery.HealthOK {
+			list := slices.DeleteFunc(w.healthy[key], func(fp string) bool { return fp == h.FP })
+			w.healthy[key] = append(list, h.FP)
+		}
+	}
+}
+
+// lastHealthy is the newest fingerprint other than fp the node ran the module healthy at, or empty.
+func (w *world) lastHealthy(node, module, fp string) string {
+	key, err := delivery.HaveKey(node, module)
+	if err != nil {
+		return ""
+	}
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	list := w.healthy[key]
+	for i := len(list) - 1; i >= 0; i-- {
+		if list[i] != fp {
+			return list[i]
+		}
+	}
+	return ""
+}
+
+// read is a copy of what a bucket holds now.
+func (w *world) read(bucket string) map[string][]byte {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	out := make(map[string][]byte, len(w.values[bucket]))
+	for k, v := range w.values[bucket] {
+		out[k] = v
+	}
+	return out
+}
+
+// getter reads one key's value; errNotThere when the key does not exist.
+type getter func(ctx context.Context, key string) ([]byte, error)
+
+var errNotThere = errors.New("no such key")
+
+// kvGetter reads keys of a bucket.
+func kvGetter(kv jetstream.KeyValue) getter {
+	return func(ctx context.Context, key string) ([]byte, error) {
+		e, err := kv.Get(ctx, key)
+		if errors.Is(err, jetstream.ErrKeyNotFound) {
+			return nil, errNotThere
+		}
+		if err != nil {
+			return nil, err
+		}
+		return e.Value(), nil
+	}
+}
+
+// manifest reads the manifest of a digest from the indexer's bucket once and keeps it: a digest's manifest never changes.
+func (w *world) manifest(ctx context.Context, get getter, digest string) parsed {
+	w.mu.Lock()
+	p, ok := w.manifests[digest]
+	w.mu.Unlock()
+	if ok {
+		return p
+	}
+	key, err := delivery.ManifestsKey(digest)
+	if err != nil {
+		return parsed{err: err.Error()}
+	}
+	value, err := get(ctx, key)
+	if errors.Is(err, errNotThere) {
+		return parsed{err: "the indexer holds no manifest of digest " + digest + " yet"}
+	}
+	if err != nil {
+		return parsed{err: err.Error()}
+	}
+	m, err := delivery.DecodeManifest(value)
+	if err != nil {
+		p = parsed{err: err.Error()}
+	} else if man, err := catalogue.ParseManifest([]byte(m.JSON)); err != nil {
+		p = parsed{module: m.Module, err: err.Error()}
+	} else {
+		p = parsed{module: m.Module, manifest: man}
+	}
+	w.mu.Lock()
+	w.manifests[digest] = p
+	w.mu.Unlock()
+	return p
+}
+
+// assigned is each node's modules with an open assignment, read from the controller's assignments, in name order.
+func (w *world) assigned() (map[string][]string, map[string]assignment) {
+	out, all := map[string][]string{}, map[string]assignment{}
+	for _, value := range w.read(provider.AssignmentsBucket) {
+		var a assignment
+		if json.Unmarshal(value, &a) != nil || a.Node == "" || a.Module == "" || !a.open() {
+			continue
+		}
+		out[a.Node] = append(out[a.Node], a.Module)
+		all[a.Node+"."+a.Module] = a
+	}
+	for _, mods := range out {
+		sort.Strings(mods)
+	}
+	return out, all
+}
+
+// trunk is every module the indexer holds at the trunk, with its value.
+func (w *world) trunk() map[string]delivery.Module {
+	out := map[string]delivery.Module{}
+	for key, value := range w.read(delivery.ModulesBucket) {
+		name, err := delivery.ParseModulesKey(key)
+		if err != nil {
+			continue
+		}
+		if m, err := delivery.DecodeModule(value); err == nil {
+			out[name] = m
+		}
+	}
+	return out
+}
+
+// mesh is the mesh as the trunk holds it, for the composition check.
+func (w *world) mesh(ctx context.Context, manifests getter) assign.Mesh {
+	m := assign.Mesh{Manifests: map[string]catalogue.Manifest{}, Unreadable: map[string]string{}, Digests: map[string]string{}}
+	m.Assigned, _ = w.assigned()
+	for name, mod := range w.trunk() {
+		if mod.Manifest == "" {
+			continue
+		}
+		m.Digests[name] = mod.Manifest
+		p := w.manifest(ctx, manifests, mod.Manifest)
+		if p.err != "" {
+			m.Unreadable[name] = p.err
+			continue
+		}
+		m.Manifests[name] = p.manifest
+	}
+	return m
+}
+
+// change is a candidate's change for the composition check, or why the composition waits for it.
+func (w *world) change(ctx context.Context, manifests getter, c delivery.Candidate, trunk map[string]delivery.Module) (assign.Change, string) {
+	ch := assign.Change{Group: c.Group, Heads: c.HeadsHash, Manifests: map[string]catalogue.Manifest{}, Unreadable: map[string]string{},
+		Twice: map[string][]string{}, Digests: map[string]string{}, Members: map[string]string{}}
+	definedIn := map[string]map[string]bool{}
+	for _, p := range c.Pulls {
+		if p.Repository == assign.SDKRepository {
+			ch.SDKHead = p.Head.Head
+		}
+		ch.Members[p.Repository] = p.Head.Head
+		for _, name := range p.Modules {
+			fp, ok := p.Fps[name]
+			if !ok || fp.Manifest == "" {
+				if ok && fp.None2 == noModuleWords {
+					ch.Removed = append(ch.Removed, name)
+					continue
+				}
+				return ch, fmt.Sprintf("the indexer holds no manifest of %s for %s#%d yet", name, p.Repository, p.Number)
+			}
+			if fp.FP2 != "" && fp.FP2 != trunk[name].FP2 {
+				ch.Rebuilt++
+			}
+			got := w.manifest(ctx, manifests, fp.Manifest)
+			if strings.HasPrefix(got.err, "the indexer holds no manifest") {
+				return ch, got.err
+			}
+			ch.Digests[name] = fp.Manifest
+			if got.err != "" {
+				ch.Unreadable[name] = got.err
+				continue
+			}
+			ch.Manifests[got.module] = got.manifest
+			if definedIn[got.module] == nil {
+				definedIn[got.module] = map[string]bool{}
+			}
+			definedIn[got.module][p.Repository] = true
+			if t, ok := trunk[got.module]; ok && t.Repository != "" && t.Repository != p.Repository {
+				definedIn[got.module][t.Repository] = true
+			}
+		}
+	}
+	for name, repos := range definedIn {
+		if len(repos) > 1 {
+			for r := range repos {
+				ch.Twice[name] = append(ch.Twice[name], r)
+			}
+			sort.Strings(ch.Twice[name])
+		}
+	}
+	return ch, ""
+}
+
+// wantsOf is the wants the assigner wrote, by module then node.
+func (w *world) wantsOf() map[string]map[string]delivery.Want {
+	out := map[string]map[string]delivery.Want{}
+	for key, value := range w.read(delivery.AssignerWantsBucket) {
+		node, module, err := delivery.ParseWantKey(key)
+		if err != nil {
+			continue
+		}
+		want, err := delivery.DecodeWant(value)
+		if err != nil {
+			continue
+		}
+		if out[module] == nil {
+			out[module] = map[string]delivery.Want{}
+		}
+		out[module][node] = want
+	}
+	return out
+}
+
+// nodes is what the six rules read of the nodes: presence, haves, and every provision's providers with their nodes.
+func (w *world) nodes(manifests map[string]catalogue.Manifest, assigned map[string][]string) assign.Nodes {
+	n := assign.Nodes{Online: map[string]bool{}, Haves: map[string]map[string]delivery.Have{}, Providers: map[string]map[string][]string{}}
+	for key, value := range w.read(delivery.PresenceBucket) {
+		node, _, _, err := delivery.ParsePresenceKey(key)
+		if err != nil || node == "" {
+			continue
+		}
+		if p, err := delivery.DecodePresence(value); err == nil {
+			n.Online[node] = p.Online
+		}
+	}
+	for key, value := range w.read(delivery.HaveBucket) {
+		node, module, isNode, err := delivery.ParseHaveKey(key)
+		if err != nil || isNode {
+			continue
+		}
+		if h, err := delivery.DecodeHave(value); err == nil {
+			if n.Haves[node] == nil {
+				n.Haves[node] = map[string]delivery.Have{}
+			}
+			n.Haves[node][module] = h
+		}
+	}
+	nodesOf := map[string][]string{}
+	for node, modules := range assigned {
+		for _, m := range modules {
+			nodesOf[m] = append(nodesOf[m], node)
+		}
+	}
+	for name, man := range manifests {
+		for _, o := range man.Provides {
+			if n.Providers[o.Name] == nil {
+				n.Providers[o.Name] = map[string][]string{}
+			}
+			n.Providers[o.Name][name] = nodesOf[name]
+		}
+	}
+	return n
+}
+
+// has says whether a bucket holds a key now.
+func (w *world) has(bucket, key string) bool {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	_, ok := w.values[bucket][key]
+	return ok
+}
+
+// built says whether the builder's build of a module at a fingerprint is done.
+func (w *world) built(module, fp string) bool {
+	key, err := delivery.BuilderBuildKey(module, fp)
+	if err != nil {
+		return false
+	}
+	w.mu.Lock()
+	value, ok := w.values[delivery.BuilderBuildsBucket][key]
+	w.mu.Unlock()
+	if !ok {
+		return false
+	}
+	b, err := delivery.DecodeBuilderBuild(value)
+	return err == nil && b.State == delivery.BuildDone
+}
+
+// sentFP is the fingerprint of the new form of the build the controller's assignment names, read from its build record
+// (mesh-controller_builds `<module>.build.<id>`) once and kept; empty when the record names none.
+func (w *world) sentFP(ctx context.Context, get getter, module, build string) string {
+	if build == "" {
+		return ""
+	}
+	w.mu.Lock()
+	fp, ok := w.sent[build]
+	w.mu.Unlock()
+	if ok {
+		return fp
+	}
+	value, err := get(ctx, delivery.BuildKey(module, build))
+	if err != nil {
+		return ""
+	}
+	var rec delivery.BuildRecord
+	if json.Unmarshal(value, &rec) != nil || !strings.HasPrefix(rec.SourceFingerprint, delivery.SourcePrefix2) {
+		return ""
+	}
+	w.mu.Lock()
+	w.sent[build] = rec.SourceFingerprint
+	w.mu.Unlock()
+	return rec.SourceFingerprint
+}
+
+// runningCommits is, of every open assignment of module, the commit of the build it names, read from the controller's
+// build record (`mesh-controller_builds` `<module>.build.<id>`), distinct and sorted: the commits a reader of the
+// manifests runs at (novox/hq ADR 0482 clause 5, issue 1623). A build whose record names no full commit is left out.
+func (w *world) runningCommits(ctx context.Context, get getter, module string) []string {
+	_, all := w.assigned()
+	seen := map[string]bool{}
+	for _, a := range all {
+		if a.Module != module || a.Build == "" {
+			continue
+		}
+		value, err := get(ctx, delivery.BuildKey(module, a.Build))
+		if err != nil {
+			continue
+		}
+		var rec delivery.BuildRecord
+		if json.Unmarshal(value, &rec) != nil || len(rec.Commit) != 40 {
+			continue
+		}
+		seen[rec.Commit] = true
+	}
+	out := make([]string, 0, len(seen))
+	for c := range seen {
+		out = append(out, c)
+	}
+	sort.Strings(out)
+	return out
+}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/world_test.go

@@ -0,0 +1,90 @@
+package main
+
+import (
+	"context"
+	"slices"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-assigner/internal/assign"
+)
+
+// fakeManifests is the indexer's manifests bucket in memory.
+type fakeManifests map[string][]byte
+
+func (f fakeManifests) add(t *testing.T, module, body string) string {
+	t.Helper()
+	digest := delivery.ManifestDigest([]byte(body))
+	value, err := delivery.EncodeManifest(delivery.Manifest{Module: module, JSON: body})
+	if err != nil {
+		t.Fatal(err)
+	}
+	f[digest] = value
+	return digest
+}
+
+func (f fakeManifests) get(_ context.Context, key string) ([]byte, error) {
+	if v, ok := f[key]; ok {
+		return v, nil
+	}
+	return nil, errNotThere
+}
+
+func fp(c byte) string { return delivery.SourcePrefix2 + strings.Repeat(string(c), 64) }
+
+func pull(repo string, number int, modules map[string]delivery.CandidateModule) delivery.CandidatePull {
+	p := delivery.CandidatePull{Head: delivery.Head{Repository: repo, Number: number, Head: strings.Repeat("3", 40)}, Fps: modules}
+	for m := range modules {
+		p.Modules = append(p.Modules, m)
+	}
+	slices.Sort(p.Modules)
+	return p
+}
+
+// 1297/B3b: a candidate's change reads each module's manifest by its digest, counts the modules rebuilt, takes a
+// module with no manifest in the preview as removed, a mesh-sdk member's head, and a module the trunk holds from
+// another repository as defined twice.
+func TestTheChangeOfACandidate(t *testing.T) {
+	f := fakeManifests{}
+	web := f.add(t, "web", `{"module":"web","version":"2"}`)
+	mail := f.add(t, "mail", `{"module":"mail","version":"1"}`)
+	trunk := map[string]delivery.Module{"web": {FP2: fp('a'), Repository: "novox/web"}, "mail": {FP2: fp('c'), Repository: "novox/mail"}}
+	c := delivery.Candidate{Group: "g", HeadsHash: "0123456789ab", Pulls: []delivery.CandidatePull{
+		pull("novox/web", 1, map[string]delivery.CandidateModule{"web": {FP2: fp('b'), Manifest: web}, "old": {None2: noModuleWords}}),
+		pull("novox/other", 2, map[string]delivery.CandidateModule{"mail": {FP2: fp('c'), Manifest: mail}}),
+		pull(assign.SDKRepository, 3, nil),
+	}}
+	ch, waits := newWorld().change(context.Background(), f.get, c, trunk)
+	if waits != "" {
+		t.Fatalf("the change waits: %s", waits)
+	}
+	if ch.Manifests["web"].Version != "2" || ch.Rebuilt != 1 || !slices.Equal(ch.Removed, []string{"old"}) || ch.SDKHead != strings.Repeat("3", 40) {
+		t.Errorf("change = %+v", ch)
+	}
+	if !slices.Equal(ch.Twice["mail"], []string{"novox/mail", "novox/other"}) || len(ch.Twice) != 1 {
+		t.Errorf("twice = %v, want mail in novox/mail and novox/other", ch.Twice)
+	}
+}
+
+// 1297/B3b: a candidate whose module has no manifest digest yet, or whose manifest the indexer does not hold yet, waits,
+// saying for what; an unreadable manifest is the change's, not a wait.
+func TestAChangeWaitsForItsManifests(t *testing.T) {
+	f := fakeManifests{}
+	bad := f.add(t, "web", `{"module":"web","version":"2","scope":"x"}`)
+	for _, c := range []delivery.CandidatePull{
+		pull("novox/web", 1, map[string]delivery.CandidateModule{"web": {None2: "no preview yet"}}),
+		pull("novox/web", 1, map[string]delivery.CandidateModule{"web": {FP2: fp('b'), Manifest: strings.Repeat("9", 64)}}),
+	} {
+		_, waits := newWorld().change(context.Background(), f.get, delivery.Candidate{Group: "g", HeadsHash: "0123456789ab", Pulls: []delivery.CandidatePull{c}}, nil)
+		if waits == "" {
+			t.Errorf("a change without its manifest %+v does not wait", c.Fps)
+		}
+	}
+	ch, waits := newWorld().change(context.Background(), f.get, delivery.Candidate{Group: "g", HeadsHash: "0123456789ab",
+		Pulls: []delivery.CandidatePull{pull("novox/web", 1, map[string]delivery.CandidateModule{"web": {FP2: fp('b'), Manifest: bad}})}}, nil)
+	if waits != "" || ch.Unreadable["web"] == "" {
+		t.Errorf("an unreadable manifest: waits %q, change %+v", waits, ch)
+	}
+}

modules/mesh-delivery-assigner/go.mod

@@ -0,0 +1,22 @@
+module mesh-delivery-assigner
+
+go 1.26.0
+
+require (
+	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024021031-66bf26c0d721
+	github.com/nats-io/nats-server/v2 v2.11.17
+	github.com/nats-io/nats.go v1.54.0
+)
+
+require (
+	github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op // indirect
+	github.com/google/go-tpm v0.9.8 // indirect
+	github.com/klauspost/compress v1.20.0 // indirect
+	github.com/minio/highwayhash v1.0.4 // indirect
+	github.com/nats-io/jwt/v2 v2.8.1 // indirect
+	github.com/nats-io/nkeys v0.4.16 // indirect
+	github.com/nats-io/nuid v1.0.1 // indirect
+	golang.org/x/crypto v0.57.0 // indirect
+	golang.org/x/sys v0.48.0 // indirect
+	golang.org/x/time v0.15.0 // indirect
+)

modules/mesh-delivery-assigner/go.sum

@@ -0,0 +1,31 @@
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261023150321-a2c813a6b468 h1:UcMee+IV2ii5E4dRZdQUaSaeh9IedTFYumuQbBiB0k0=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261023150321-a2c813a6b468/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024015135-4784762a70ce h1:9pNnygyhuYIpVs0HPzgheGLNjPXigGGQpnFTp8lw+X4=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024015135-4784762a70ce/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024021031-66bf26c0d721 h1:N//dDGmry1F3HKeBTWd+z/SfK+wb8bUUMJF0OlgR0/g=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261024021031-66bf26c0d721/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op h1:Z/MZK75wC/NSrkgqeNIa7jexam9uWzhLmFTSCPI/kn0=
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op/go.mod h1:FQyySiasQQM8735Ddel3MRojmy4dA1IqCeyJ5jmPMbI=
+github.com/google/go-tpm v0.9.8 h1:slArAR9Ft+1ybZu0lBwpSmpwhRXaa85hWtMinMyRAWo=
+github.com/google/go-tpm v0.9.8/go.mod h1:h9jEsEECg7gtLis0upRBQU+GhYVH6jMjrFxI8u6bVUY=
+github.com/klauspost/compress v1.20.0 h1:a3C1ke2ohxFymNlb2HWAHjDeKCI90scRskErZkR0ezA=
+github.com/klauspost/compress v1.20.0/go.mod h1:LUdAzn7YLVvxLpc7y3V1m40wESHTgc1422pwwBSKYuI=
+github.com/minio/highwayhash v1.0.4 h1:asJizugGgchQod2ja9NJlGOWq4s7KsAWr5XUc9Clgl4=
+github.com/minio/highwayhash v1.0.4/go.mod h1:GGYsuwP/fPD6Y9hMiXuapVvlIUEhFhMTh0rxU3ik1LQ=
+github.com/nats-io/jwt/v2 v2.8.1 h1:V0xpGuD/N8Mi+fQNDynXohVvp7ZztevW5io8CUWlPmU=
+github.com/nats-io/jwt/v2 v2.8.1/go.mod h1:nWnOEEiVMiKHQpnAy4eXlizVEtSfzacZ1Q43LIRavZg=
+github.com/nats-io/nats-server/v2 v2.11.17 h1:GKEghcFK6A+aFx11Yf1LjgLC3txAwvyhnYzhBIQZA8I=
+github.com/nats-io/nats-server/v2 v2.11.17/go.mod h1:B1sFVz4StNosQ903ak4N1G01Fl/9f8e06mXpFIE2K24=
+github.com/nats-io/nats.go v1.54.0 h1:vsXoOxjHp/GmPUN+EcI7uOf/uB+iAP+kEsAFNQN0yzA=
+github.com/nats-io/nats.go v1.54.0/go.mod h1:y+DZoD1oBOYfZTU681eTUiUjI0vbqYGixNVFHcjHJ0k=
+github.com/nats-io/nkeys v0.4.16 h1:rd5oAuLOb8mnAycB0xleuEBNS1pVVnN0fv/FF34Eypg=
+github.com/nats-io/nkeys v0.4.16/go.mod h1:llLgWoI0o4z/Q57q2R1kHfmocyhGV6VG/U18Glg1Afs=
+github.com/nats-io/nuid v1.0.1 h1:5iA8DT8V7q8WK2EScv2padNa/rTESc1KdnPw4TC2paw=
+github.com/nats-io/nuid v1.0.1/go.mod h1:19wcPz3Ph3q0Jbyiqsd0kePYG7A95tJPxeL+1OSON2c=
+golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
+golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
+golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
+golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
+golang.org/x/time v0.15.0 h1:bbrp8t3bGUeFOx08pvsMYRTCVSMk89u4tKbNOZbp88U=
+golang.org/x/time v0.15.0/go.mod h1:Y4YMaQmXwGQZoFaVFk4YpCt4FLQMYKZe9oeV/f4MSno=

modules/mesh-delivery-assigner/internal/assign/asks.go

@@ -0,0 +1,29 @@
+package assign
+
+import (
+	"fmt"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/asks"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// HoldAsk is the ask about a module's fingerprint the assigner holds, at its key (delivery.HoldAskKey), first asking: keep
+// it held or release it. Both options acknowledge and bind nothing: in release 5 the wants are only compared, so no answer
+// changes what a node runs (ADR 0429 §7); the node agent acts on the hold from release 6.
+func HoldAsk(key, module, fp string, now time.Time) delivery.AssignerAsk {
+	return delivery.AssignerAsk{Ask: asks.Ask{
+		ID:       delivery.AskingID(key, 0),
+		Headline: fmt.Sprintf("%s is held at %s", module, short(fp)),
+		Explanation: fmt.Sprintf("A node's health check of %s failed at %s, so the assigner holds that version and wants "+
+			"no node to move to it. Until release 6 this changes nothing a node runs: the controller still sends.", module, short(fp)),
+		Options: []asks.Option{
+			{ID: "keep", Label: "Keep it held", Does: "the version stays held", Level: asks.Acknowledge},
+			{ID: "release", Label: "Release it", Does: "the version is released when wants are applied, from release 6", Level: asks.Acknowledge},
+		},
+		Who:      asks.Operator,
+		Expires:  now.Add(7 * 24 * time.Hour),
+		OnExpiry: "the version stays held",
+		About:    key,
+	}}
+}

modules/mesh-delivery-assigner/internal/assign/asks_test.go

@@ -0,0 +1,28 @@
+package assign
+
+import (
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// 1297/B9 (the assigner's half): the ask about a held fingerprint is a valid ask of the router and of mesh-sdk's layout at
+// its key, of a kind the view may answer.
+func TestTheHoldAskIsValid(t *testing.T) {
+	key, err := delivery.HoldAskKey("mail", fNew)
+	if err != nil {
+		t.Fatal(err)
+	}
+	now := time.Now()
+	a := HoldAsk(key, "mail", fNew, now)
+	if err := a.Ask.Check(now); err != nil {
+		t.Errorf("the router refuses the ask: %v", err)
+	}
+	if _, err := delivery.EncodeAssignerAsk(key, a); err != nil {
+		t.Errorf("the ask cannot be written: %v", err)
+	}
+	if _, err := delivery.ViewAnswerKey(key); err != nil {
+		t.Errorf("the view may not answer it: %v", err)
+	}
+}

modules/mesh-delivery-assigner/internal/assign/compare.go

@@ -0,0 +1,52 @@
+package assign
+
+import (
+	"fmt"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// Sent is what the controller sends a node of a module: whether it sends it at all (an open assignment), the build its
+// assignment names, and that build's fingerprint of the new form (empty when its record names none).
+type Sent struct {
+	Sends bool
+	Build string
+	FP    string
+}
+
+// Compare is the difference between a node's want for a module and what the controller sends it (ADR 0528 clause 4),
+// and whether there is one. want is nil when the assigner wrote none; newest is the module's newest fingerprint and
+// hold the rule that holds the node back from it (Rule 0 when none does). A difference is explained by a rule when the
+// controller sent the newest fingerprint while that rule holds the node's want back; every other is unexplained, said
+// in words, for acceptance test 17 of design 47 to read.
+func Compare(want *delivery.Want, sent Sent, newest string, hold Holding) (delivery.Difference, bool) {
+	var d delivery.Difference
+	removed := want != nil && want.Removed
+	if want != nil && !removed {
+		d.Want = want.FP
+	}
+	d.WantRemoved = removed
+	if !sent.Sends {
+		if want == nil || removed {
+			return delivery.Difference{}, false
+		}
+		d.Unexplained, d.Words = true, "the node wants "+short(want.FP)+" and the controller sends it nothing"
+		return d, true
+	}
+	d.Sent, d.SentBuild = sent.FP, sent.Build
+	switch {
+	case sent.FP == "":
+		d.Unexplained, d.Words = true, fmt.Sprintf("the build %s the controller sends names no fingerprint of the new form", sent.Build)
+	case removed:
+		d.Unexplained, d.Words = true, fmt.Sprintf("the want is removed and the controller still sends %s", short(sent.FP))
+	case sent.FP == d.Want:
+		return delivery.Difference{}, false
+	case hold.Rule != 0 && sent.FP == newest:
+		d.Rule, d.Words = hold.Rule, fmt.Sprintf("the controller sent %s while %s", short(sent.FP), hold.Words)
+	case d.Want == "":
+		d.Unexplained, d.Words = true, fmt.Sprintf("the controller sends %s and the node has no want", short(sent.FP))
+	default:
+		d.Unexplained, d.Words = true, fmt.Sprintf("the controller sends %s and the node wants %s", short(sent.FP), short(d.Want))
+	}
+	return d, true
+}

modules/mesh-delivery-assigner/internal/assign/compare_test.go

@@ -0,0 +1,59 @@
+package assign
+
+import (
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// 1297/B5: given the controller sent F to a node while the canary is not yet healthy on F, the difference names rule 3.
+func TestADifferenceExplainedByTheCanary(t *testing.T) {
+	m, n := ready()
+	n.Haves["ace"]["mail"] = delivery.Have{FP: fOld, Phase: delivery.PhaseRunning, Health: delivery.HealthOK}
+	out := Wants(m, n, wantedOld(), nil)
+	want := delivery.Want{FP: fOld, Newest: fNew, Rule: delivery.RuleCanary}
+	d, ok := Compare(&want, Sent{Sends: true, Build: "b-9", FP: fNew}, fNew, out.Rules["g14"])
+	if !ok || d.Rule != delivery.RuleCanary || d.Unexplained || d.Want != fOld || d.Sent != fNew {
+		t.Fatalf("difference = %+v, %v; want rule 3", d, ok)
+	}
+	if _, err := delivery.EncodeDifference(d); err != nil {
+		t.Errorf("the difference cannot be written: %v", err)
+	}
+}
+
+// 1297/B5: a want equal to what is sent is no difference; nothing sent and no want is none; every other is written
+// unexplained, with words, and is writable.
+func TestCompare(t *testing.T) {
+	w := delivery.Want{FP: fNew}
+	if _, ok := Compare(&w, Sent{Sends: true, Build: "b", FP: fNew}, fNew, Holding{}); ok {
+		t.Errorf("an equal want and send is a difference")
+	}
+	if _, ok := Compare(nil, Sent{}, fNew, Holding{}); ok {
+		t.Errorf("no want and nothing sent is a difference")
+	}
+	removed := delivery.Want{Removed: true}
+	if _, ok := Compare(&removed, Sent{}, fNew, Holding{}); ok {
+		t.Errorf("a removed want and nothing sent is a difference")
+	}
+	old := delivery.Want{FP: fOld}
+	for name, c := range map[string]struct {
+		want *delivery.Want
+		sent Sent
+	}{
+		"sends an older one":     {&w, Sent{Sends: true, Build: "b", FP: fOld}},
+		"names no fingerprint":   {&w, Sent{Sends: true, Build: "b"}},
+		"sends a removed module": {&removed, Sent{Sends: true, Build: "b", FP: fNew}},
+		"sends nothing":          {&w, Sent{}},
+		"no want":                {nil, Sent{Sends: true, Build: "b", FP: fNew}},
+		"no rule holds it back":  {&old, Sent{Sends: true, Build: "b", FP: fNew}},
+	} {
+		d, ok := Compare(c.want, c.sent, fNew, Holding{})
+		if !ok || !d.Unexplained || d.Words == "" {
+			t.Errorf("%s: difference = %+v, %v; want it unexplained, with words", name, d, ok)
+			continue
+		}
+		if _, err := delivery.EncodeDifference(d); err != nil {
+			t.Errorf("%s: the difference cannot be written: %v", name, err)
+		}
+	}
+}

modules/mesh-delivery-assigner/internal/assign/compose.go

@@ -0,0 +1,282 @@
+// Package assign is the assigner's judgement, as functions over what it read from the bus: the composition check of a
+// change (novox/hq ADR 0446 clauses 1 to 5, ADR 0528 clause 5, issue 1297), the six rules of what each node should
+// run (ADR 0429 §6, ADR 0528 clause 3) and the comparison with what the controller sends (ADR 0528 clause 4). It reads
+// and writes nothing itself: the program hands it what it watched and writes what it answers.
+package assign
+
+import (
+	"fmt"
+	"slices"
+	"sort"
+	"strings"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/compose"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// SDKRepository is the repository of mesh-sdk: a group with a member there changes the composition itself.
+const SDKRepository = "novox/mesh-sdk"
+
+// NotJudged names, in a composition's warnings, the failures of ADR 0446 clause 1 the assigner cannot judge from the
+// bus, because what they need is only in the controller's facts snapshot, which is not on the bus yet (issue 1461;
+// the design limit of R4g, issue 1297): said on every verdict, never passed silently.
+const NotJudged = "not judged until the facts snapshot is on the bus (issue 1461): a consumer left out of a grant, a " +
+	"credential left bound elsewhere, a stored setting the changed definition cannot keep, and a new module the " +
+	"node-engine's validator would refuse"
+
+// Mesh is the mesh as the trunk holds it: every module's manifest by name, the manifests that cannot be read with
+// why, and each node's open assignments.
+type Mesh struct {
+	Manifests  map[string]catalogue.Manifest
+	Unreadable map[string]string
+	Assigned   map[string][]string
+	// Digests is every trunk module's manifest digest in the indexer's manifests bucket, readable or not: what a
+	// composer at another mesh-sdk reads (issue 1622).
+	Digests map[string]string
+}
+
+// Change is a group's change as the indexer's candidate holds it: the manifest of every module it moves or adds, those
+// it cannot read and why, the modules it removes, every module defined twice with where, the heads of a mesh-sdk
+// member (empty when none), and how many modules it rebuilds.
+type Change struct {
+	Group, Heads string
+	Manifests    map[string]catalogue.Manifest
+	Unreadable   map[string]string
+	Removed      []string
+	Twice        map[string][]string
+	SDKHead      string
+	Rebuilt      int
+	// Digests is the manifest digest of every module the change moves or adds, readable by the assigner or not, and
+	// Members the head of each member by repository: what a composer at the group's mesh-sdk reads (issues 1622, 1623).
+	Digests map[string]string
+	Members map[string]string
+}
+
+// Touched is the machines a change touches (ADR 0446 clause 3): those running a module the change moves, adds or
+// removes, those running a consumer of a provision such a module provides (before or after), and those running a
+// provider of a provision such a module requires after the change. A module the change adds that is assigned nowhere
+// touches no machine.
+func Touched(m Mesh, c Change) []string {
+	moved := map[string]bool{}
+	for name := range c.Manifests {
+		moved[name] = true
+	}
+	for name := range c.Unreadable {
+		moved[name] = true
+	}
+	for _, name := range c.Removed {
+		moved[name] = true
+	}
+	provided, required := map[string]bool{}, map[string]bool{}
+	for name := range moved {
+		for _, man := range []catalogue.Manifest{m.Manifests[name], c.Manifests[name]} {
+			for _, o := range man.Provides {
+				provided[o.Name] = true
+			}
+		}
+		for _, r := range c.Manifests[name].Requires {
+			required[r] = true
+		}
+	}
+	var out []string
+	for node, modules := range m.Assigned {
+		for _, mod := range modules {
+			man := m.Manifests[mod]
+			if moved[mod] || slices.ContainsFunc(man.Requires, func(r string) bool { return provided[r] }) ||
+				slices.ContainsFunc(man.Provides, func(o catalogue.Offer) bool { return required[o.Name] }) {
+				out = append(out, node)
+				break
+			}
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+// input is the composition's input for the mesh's catalogue and assignments: the nodes by name with what is assigned
+// to them, and every seat the assigned modules claim as held there. What the bus does not carry (places on the
+// private network, settings, credentials, licences) is left empty, so a trunk composition and a change's are made
+// with the same gaps and compared (ADR 0446 clause 1: what was already broken is said and fails nothing).
+func input(catalog map[string]catalogue.Manifest, assigned map[string][]string) compose.Input {
+	in := compose.Input{Catalogue: catalog}
+	nodes := make([]string, 0, len(assigned))
+	for n := range assigned {
+		nodes = append(nodes, n)
+	}
+	sort.Strings(nodes)
+	for _, n := range nodes {
+		in.Nodes = append(in.Nodes, compose.Node{Name: n, Assigned: slices.Clone(assigned[n])})
+		for _, mod := range assigned[n] {
+			for _, cl := range catalog[mod].Claims {
+				scope := cl.Scope
+				if seat, ok := catalogue.SeatNamed(cl.Name); ok && scope == "" {
+					scope = seat.Scope
+				}
+				in.Holdings = append(in.Holdings, catalogue.Held{Claim: cl.Name, Scope: scope, Node: n, Module: mod})
+			}
+		}
+	}
+	return in
+}
+
+// Compose is the composition check of change c over the mesh m, composed with the mesh-sdk version sdk: every touched
+// machine resolved as the trunk holds it and as the change leaves it. It fails on a manifest of the change that cannot
+// be read, a module a machine runs that the change removes, a module defined twice, and a machine that resolves on the
+// trunk and not with the change; a machine that does not resolve on either is said and fails nothing. It warns past
+// CompositionRebuildWarning modules rebuilt, says what it does not judge (NotJudged), and for a group with a mesh-sdk
+// member says it composed with its own mesh-sdk, not the member's head (issue 1621). took is how long it took.
+func Compose(m Mesh, c Change, sdk string, took time.Duration) delivery.CompositionVerdict {
+	v := delivery.CompositionVerdict{Group: c.Group, Heads: c.Heads, SDK: sdk, Took: took.Milliseconds()}
+	var fails []string
+	failAt := func(machine, words string) {
+		if v.Machine == "" && machine != "" {
+			v.Machine = machine
+		}
+		fails = append(fails, words)
+	}
+	for _, name := range sortedKeys(c.Unreadable) {
+		failAt("", fmt.Sprintf("the manifest of %s cannot be read: %s", name, c.Unreadable[name]))
+	}
+	for _, name := range sortedKeys(c.Twice) {
+		failAt("", fmt.Sprintf("%s is defined twice, in %s", name, strings.Join(c.Twice[name], " and ")))
+	}
+	machines := Touched(m, c)
+	v.Machines = machines
+	for _, node := range machines {
+		for _, name := range c.Removed {
+			if slices.Contains(m.Assigned[node], name) {
+				failAt(node, fmt.Sprintf("%s runs %s, which the change removes from its source", node, name))
+			}
+		}
+	}
+	trunk := input(m.Manifests, m.Assigned)
+	changed := map[string]catalogue.Manifest{}
+	for name, man := range m.Manifests {
+		changed[name] = man
+	}
+	for name, man := range c.Manifests {
+		changed[name] = man
+	}
+	for _, name := range c.Removed {
+		delete(changed, name)
+	}
+	after := input(changed, m.Assigned)
+	for _, node := range machines {
+		_, before := compose.Resolve(trunk, node)
+		_, now := compose.Resolve(after, node)
+		switch {
+		case now == nil:
+		case before != nil:
+			v.Warnings = append(v.Warnings, fmt.Sprintf("%s does not compose on the trunk either, so the change is not blamed: %v", node, before))
+		default:
+			failAt(node, fmt.Sprintf("%s composes on the trunk and not with the change: %v", node, now))
+		}
+	}
+	if c.SDKHead != "" {
+		v.Warnings = append(v.Warnings, fmt.Sprintf("composed with the assigner's own mesh-sdk %s, not the group's mesh-sdk head %s, "+
+			"and a field the running controller cannot read is not judged (issues 1621, 1622, 1623)", sdk, c.SDKHead))
+	}
+	return finish(v, m, c, machines, fails)
+}
+
+// finish adds what every composition says beside its own judgement (more modules rebuilt than CompositionRebuildWarning,
+// what is not judged, the machines not composed, a change that touches none) and its state from fails.
+func finish(v delivery.CompositionVerdict, m Mesh, c Change, machines []string, fails []string) delivery.CompositionVerdict {
+	if c.Rebuilt > delivery.CompositionRebuildWarning {
+		v.Warnings = append(v.Warnings, fmt.Sprintf("the merge rebuilds %d modules, more than %d", c.Rebuilt, delivery.CompositionRebuildWarning))
+	}
+	v.Warnings = append(v.Warnings, NotJudged)
+	if could := CouldRun(m, c, machines); len(could) > 0 {
+		v.Warnings = append(v.Warnings, "not judged until the facts snapshot is on the bus (issue 1461, ADR 0537 clause 1): "+
+			"the machines that could run a moved or added module and are not assigned it: "+strings.Join(could, ", "))
+	}
+	if grants := GrantsAlone(m, c, machines); len(grants) > 0 {
+		v.Warnings = append(v.Warnings, "not judged until the facts snapshot is on the bus (issue 1461, ADR 0537 clause 1): "+
+			"the machines whose grants alone the change alters: "+strings.Join(grants, ", "))
+	}
+	if len(machines) == 0 {
+		v.Warnings = append(v.Warnings, "the change touches no machine: no module it moves is assigned anywhere")
+	}
+	if len(fails) > 0 {
+		v.State, v.Words = delivery.CompositionFail, strings.Join(fails, "; ")
+		return v
+	}
+	v.State = delivery.CompositionPass
+	return v
+}
+
+// CouldRun is, by name, every machine of the mesh not composed that is not assigned a module the change moves or adds
+// (ADR 0537 clause 1): which of them could run it, the bus does not say (capabilities, settings and places are only in
+// the facts snapshot), so each is named as not judged.
+func CouldRun(m Mesh, c Change, composed []string) []string {
+	var out []string
+	for node, modules := range m.Assigned {
+		if slices.Contains(composed, node) {
+			continue
+		}
+		for name := range c.Manifests {
+			if !slices.Contains(modules, name) {
+				out = append(out, node)
+				break
+			}
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+// grantsOf is what of a manifest makes grants: its bus declarations and the provisions it requires and offers.
+func grantsOf(man catalogue.Manifest) string {
+	var offers []string
+	for _, o := range man.Provides {
+		offers = append(offers, o.Name)
+	}
+	return fmt.Sprint(man.Requires, offers, man.Reads, man.State, man.Emits, man.Consumes, man.Invokes, man.Claims, man.Grants)
+}
+
+// GrantsAlone is, by name, every machine not composed whose grants alone the change alters (ADR 0537 clause 1): for a
+// moved module whose grants differ from the trunk's, the machines assigned the bus's holder (whose user list carries
+// every module's bus grants) and those assigned a provider of a provision it requires, before or after.
+func GrantsAlone(m Mesh, c Change, composed []string) []string {
+	provisions := map[string]bool{}
+	altered := false
+	for name, man := range c.Manifests {
+		before, had := m.Manifests[name]
+		if had && grantsOf(before) == grantsOf(man) {
+			continue
+		}
+		altered = true
+		for _, r := range append(slices.Clone(man.Requires), before.Requires...) {
+			provisions[r] = true
+		}
+	}
+	if !altered {
+		return nil
+	}
+	var out []string
+	for node, modules := range m.Assigned {
+		if slices.Contains(composed, node) {
+			continue
+		}
+		for _, mod := range modules {
+			man := m.Manifests[mod]
+			if man.ClaimsSeat("mesh-broker") || slices.ContainsFunc(man.Provides, func(o catalogue.Offer) bool { return provisions[o.Name] }) {
+				out = append(out, node)
+				break
+			}
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+func sortedKeys[V any](m map[string]V) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}

modules/mesh-delivery-assigner/internal/assign/compose_test.go

@@ -0,0 +1,141 @@
+package assign
+
+import (
+	"slices"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+func meshOf() Mesh {
+	return Mesh{
+		Manifests: map[string]catalogue.Manifest{
+			"mail":  {Module: "mail", Version: "1", Requires: []string{"database"}},
+			"store": {Module: "store", Version: "1", Provides: []catalogue.Offer{{Name: "database"}}},
+			"web":   {Module: "web", Version: "1"},
+		},
+		Assigned: map[string][]string{"ace": {"mail", "store"}, "g14": {"web"}},
+	}
+}
+
+func hasWarning(v delivery.CompositionVerdict, part string) bool {
+	return slices.ContainsFunc(v.Warnings, func(w string) bool { return strings.Contains(w, part) })
+}
+
+// 1297/AC1 (its unit half): a change touching one module on one machine composes that machine alone, passes, names
+// the machine and the mesh-sdk it composed with, and says what it did not judge.
+func TestAChangeOfOneModuleComposesItsMachine(t *testing.T) {
+	c := Change{Group: "g", Heads: "0123456789ab", Manifests: map[string]catalogue.Manifest{"web": {Module: "web", Version: "2"}}}
+	v := Compose(meshOf(), c, "v0.1.14-x", 0)
+	if v.State != delivery.CompositionPass || !slices.Equal(v.Machines, []string{"g14"}) || v.SDK != "v0.1.14-x" {
+		t.Fatalf("composition = %+v, want a pass on g14 alone", v)
+	}
+	if !hasWarning(v, "issue 1461") {
+		t.Errorf("the verdict does not say what it did not judge: %v", v.Warnings)
+	}
+	if _, err := delivery.EncodeCompositionVerdict(v); err != nil {
+		t.Errorf("the verdict cannot be written: %v", err)
+	}
+}
+
+// 1297/AC2: a change that removes a module a machine runs fails, naming the machine and the module.
+func TestRemovingAModuleAMachineRunsFails(t *testing.T) {
+	c := Change{Group: "g", Heads: "0123456789ab", Removed: []string{"web"}}
+	v := Compose(meshOf(), c, "sdk", 0)
+	if v.State != delivery.CompositionFail || v.Machine != "g14" || !strings.Contains(v.Words, "g14 runs web") {
+		t.Fatalf("composition = %+v, want a fail naming g14 and web", v)
+	}
+}
+
+// 1297/B3c: a machine that composes on the trunk and not with the change fails it, naming the machine and why; the
+// consumer's machine is touched when its provider changes.
+func TestAMachineTheChangeBreaksFails(t *testing.T) {
+	c := Change{Group: "g", Heads: "0123456789ab", Manifests: map[string]catalogue.Manifest{"store": {Module: "store", Version: "2"}}}
+	v := Compose(meshOf(), c, "sdk", 0)
+	if v.State != delivery.CompositionFail || v.Machine != "ace" || !strings.Contains(v.Words, "database") {
+		t.Fatalf("composition = %+v, want a fail on ace naming the provision nothing provides", v)
+	}
+}
+
+// 1297/B3c: what was already broken on the trunk is said and fails nothing.
+func TestWhatWasBrokenBeforeFailsNothing(t *testing.T) {
+	m := meshOf()
+	m.Manifests["store"] = catalogue.Manifest{Module: "store", Version: "1"}
+	c := Change{Group: "g", Heads: "0123456789ab", Manifests: map[string]catalogue.Manifest{"mail": {Module: "mail", Version: "2", Requires: []string{"database"}}}}
+	v := Compose(m, c, "sdk", 0)
+	if v.State != delivery.CompositionPass || !hasWarning(v, "on the trunk either") {
+		t.Fatalf("composition = %+v, want a pass saying ace was already broken", v)
+	}
+}
+
+// 1297/B3c: an unreadable manifest and a module defined twice fail; more than twelve rebuilt modules warn.
+func TestUnreadableTwiceAndWide(t *testing.T) {
+	c := Change{Group: "g", Heads: "0123456789ab", Unreadable: map[string]string{"web": "unknown field \"scope\""}, Rebuilt: 13}
+	v := Compose(meshOf(), c, "sdk", 0)
+	if v.State != delivery.CompositionFail || !strings.Contains(v.Words, "web cannot be read") || !hasWarning(v, "rebuilds 13 modules") {
+		t.Fatalf("composition = %+v", v)
+	}
+	c = Change{Group: "g", Heads: "0123456789ab", Twice: map[string][]string{"web": {"novox/a", "novox/b"}}, Rebuilt: 12}
+	v = Compose(meshOf(), c, "sdk", 0)
+	if v.State != delivery.CompositionFail || !strings.Contains(v.Words, "web is defined twice") || hasWarning(v, "rebuilds") {
+		t.Fatalf("composition = %+v", v)
+	}
+}
+
+// 1622's criterion as R4g delivers it: a group with a mesh-sdk member is composed with the assigner's own mesh-sdk, and
+// the verdict says so, naming the member's head it did not use; a group without one says nothing of it.
+func TestAGroupWithAnSDKMemberSaysWhichSDKComposedIt(t *testing.T) {
+	c := Change{Group: "g", Heads: "0123456789ab", Manifests: map[string]catalogue.Manifest{"web": {Module: "web", Version: "2"}}, SDKHead: "f625d98713e4"}
+	v := Compose(meshOf(), c, "v0.1.14-own", 0)
+	if !hasWarning(v, "not the group's mesh-sdk head f625d98713e4") || !hasWarning(v, "v0.1.14-own") || !hasWarning(v, "1623") {
+		t.Errorf("the verdict does not say it composed with its own mesh-sdk: %v", v.Warnings)
+	}
+	c.SDKHead = ""
+	if v := Compose(meshOf(), c, "v0.1.14-own", 0); hasWarning(v, "mesh-sdk head") {
+		t.Errorf("a group without a mesh-sdk member says it has one: %v", v.Warnings)
+	}
+}
+
+// 1297/B3a: the machines touched are those running a moved module or a consumer of what it provides; an added module
+// assigned nowhere touches none, and the verdict says so.
+func TestTouched(t *testing.T) {
+	m := meshOf()
+	if got := Touched(m, Change{Manifests: map[string]catalogue.Manifest{"store": m.Manifests["store"]}}); !slices.Equal(got, []string{"ace"}) {
+		t.Errorf("touched by store = %v", got)
+	}
+	m.Assigned["g14"] = append(m.Assigned["g14"], "mail")
+	if got := Touched(m, Change{Manifests: map[string]catalogue.Manifest{"store": m.Manifests["store"]}}); !slices.Equal(got, []string{"ace", "g14"}) {
+		t.Errorf("touched by store with a consumer on g14 = %v", got)
+	}
+	c := Change{Group: "g", Heads: "0123456789ab", Manifests: map[string]catalogue.Manifest{"new": {Module: "new", Version: "1"}}}
+	if v := Compose(m, c, "sdk", 0); len(v.Machines) != 0 || !hasWarning(v, "touches no machine") || v.State != delivery.CompositionPass {
+		t.Errorf("an added module assigned nowhere: %+v", v)
+	}
+}
+
+// ADR 0537 clause 1: every verdict names, by machine, those that could run a moved or added module and are not assigned
+// it, and those whose grants alone the change alters (the bus's machine, a provider of what the module requires), as not
+// judged; shanks, providing what web now requires, is composed and so named in neither. A change that alters no grant
+// names none of the second.
+func TestTheMachinesNotJudgedAreNamed(t *testing.T) {
+	m := meshOf()
+	m.Manifests["bus"] = catalogue.Manifest{Module: "bus", Version: "1", Claims: []catalogue.Claim{{Name: "mesh-broker", Scope: "mesh"}}}
+	m.Manifests["db"] = catalogue.Manifest{Module: "db", Version: "1", Provides: []catalogue.Offer{{Name: "cache"}}}
+	m.Assigned["novox"] = []string{"bus"}
+	m.Assigned["shanks"] = []string{"db"}
+	c := Change{Group: "g", Heads: "0123456789ab", Manifests: map[string]catalogue.Manifest{
+		"web": {Module: "web", Version: "2", Reads: []string{"mesh-controller.assignments"}, Requires: []string{"cache"}}}}
+	v := Compose(m, c, "sdk", 0)
+	if !hasWarning(v, "could run a moved or added module and are not assigned it: ace, novox") || !slices.Contains(v.Machines, "shanks") {
+		t.Errorf("the machines that could run web are not named: %v", v.Warnings)
+	}
+	if !hasWarning(v, "whose grants alone the change alters: novox") {
+		t.Errorf("the machines whose grants alone change are not named: %v", v.Warnings)
+	}
+	c.Manifests["web"] = catalogue.Manifest{Module: "web", Version: "3"}
+	if v := Compose(meshOf(), c, "sdk", 0); hasWarning(v, "grants alone") {
+		t.Errorf("a change altering no grant names machines whose grants change: %v", v.Warnings)
+	}
+}

modules/mesh-delivery-assigner/internal/assign/composer.go

@@ -0,0 +1,241 @@
+package assign
+
+import (
+	"encoding/json"
+	"fmt"
+	"slices"
+	"sort"
+	"strings"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/compose"
+	"git.novox.be/novox/mesh-sdk/go/composer"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// The cases of a group's composition at its mesh-sdk head: the trunk as it is, and the trunk with the change.
+const (
+	CaseTrunk  = "trunk"
+	CaseChange = "change"
+)
+
+// SDKDir is the directory of mesh-sdk's Go module in its repository, where the composer is built at a head; a reader's
+// composer is built at its repository's root, at the mesh-sdk its go.mod pins.
+const SDKDir = "go"
+
+// The modules whose mesh-sdk reads the manifests a plan sends (ADR 0482 clause 5): the controller composes and sends
+// them, the node-engine applies them. Each is judged at its repository.
+var ReaderModules = map[string]string{"mesh-controller": "novox/mesh-controller", "mesh-host": "novox/mesh-host"}
+
+// HeadJob is the compose job of a group with a mesh-sdk member (ADR 0482 clauses 3 and 4, issue 1622): the composer
+// built at the member's head composes the machines the change touches, as the trunk holds them and as the change leaves
+// them, every manifest named by its digest in the indexer's bucket, the seats held from the claims (the assigner's input).
+func HeadJob(m Mesh, c Change) (delivery.ComposeJob, error) {
+	trunk, change := map[string]composer.Manifest{}, map[string]composer.Manifest{}
+	for name, digest := range m.Digests {
+		trunk[name] = composer.Manifest{Digest: digest}
+		change[name] = composer.Manifest{Digest: digest}
+	}
+	for name, digest := range c.Digests {
+		change[name] = composer.Manifest{Digest: digest}
+	}
+	for _, name := range c.Removed {
+		delete(change, name)
+	}
+	req := composer.Request{V: composer.Version, Input: plainInput(m.Assigned), Depth: composer.DepthResolve,
+		HoldingsFromClaims: true, Machines: Touched(m, c),
+		Cases: []composer.Case{{Name: CaseTrunk, Manifests: trunk}, {Name: CaseChange, Manifests: change}}}
+	return job(SDKRepository, c.SDKHead, SDKDir, req, "the mesh-sdk head of "+c.Group)
+}
+
+// ReaderJob is the compose job that reads the manifests a group changes with the mesh-sdk a reader module pins at
+// commit (ADR 0482 clause 5, issue 1623): no machine is composed, every changed manifest is only read.
+func ReaderJob(c Change, module, repository, commit string) (delivery.ComposeJob, error) {
+	changed := map[string]composer.Manifest{}
+	for name, digest := range c.Digests {
+		changed[name] = composer.Manifest{Digest: digest}
+	}
+	req := composer.Request{V: composer.Version, Cases: []composer.Case{{Name: CaseChange, Manifests: changed}}}
+	return job(repository, commit, delivery.RootPath, req, module+" at "+commit)
+}
+
+func job(repository, commit, dir string, req composer.Request, reader string) (delivery.ComposeJob, error) {
+	raw, err := json.Marshal(req)
+	if err != nil {
+		return delivery.ComposeJob{}, err
+	}
+	return delivery.ComposeJob{Fetch: map[string]any{"repository": repository, "commit": commit}, Dir: dir,
+		Package: composer.Package, Request: raw, Reader: reader}, nil
+}
+
+// plainInput is the composition's input without its catalogue: the nodes by name with what is assigned to them (the
+// composer derives the seats held from the claims, as input does).
+func plainInput(assigned map[string][]string) compose.Input {
+	var in compose.Input
+	nodes := make([]string, 0, len(assigned))
+	for n := range assigned {
+		nodes = append(nodes, n)
+	}
+	sort.Strings(nodes)
+	for _, n := range nodes {
+		in.Nodes = append(in.Nodes, compose.Node{Name: n, Assigned: slices.Clone(assigned[n])})
+	}
+	return in
+}
+
+// Ran is one compose ask's end: its step's state and reason, and the composer's verdict when the step passed.
+type Ran struct {
+	State   string
+	Reason  string
+	Verdict *composer.Verdict
+}
+
+// RanOf reads a compose ask's end from its step value; a step that passed with an answer that cannot be read is a
+// failure, named.
+func RanOf(step delivery.Step) Ran {
+	r := Ran{State: step.State, Reason: step.Reason}
+	if step.State != delivery.StepPassed {
+		return r
+	}
+	var a delivery.ComposeAnswer
+	var v composer.Verdict
+	if err := json.Unmarshal(step.Result, &a); err != nil {
+		return Ran{State: delivery.StepFailed, Reason: "the compose step's answer cannot be read: " + err.Error()}
+	}
+	if err := json.Unmarshal(a.Verdict, &v); err != nil || v.V != composer.Version {
+		return Ran{State: delivery.StepFailed, Reason: fmt.Sprintf("the composer's verdict cannot be read (version %d): %v", v.V, err)}
+	}
+	r.Verdict = &v
+	return r
+}
+
+func caseOf(v *composer.Verdict, name string) (composer.CaseVerdict, bool) {
+	if v == nil {
+		return composer.CaseVerdict{}, false
+	}
+	for _, c := range v.Cases {
+		if c.Name == name {
+			return c, true
+		}
+	}
+	return composer.CaseVerdict{}, false
+}
+
+// Reader is one module whose mesh-sdk reads the group's manifests, at the commit judged: the group's member head when
+// the group holds one in its repository, else a build its node runs.
+type Reader struct {
+	Module, Commit string
+	Member         bool
+	Ran            Ran
+}
+
+// FromComposer is the composition check of a group with a mesh-sdk member, judged from the composer built at its head
+// (ADR 0482 clauses 3 to 5, issues 1622 and 1623): the same failures as Compose, read from the composer's two cases, the
+// verdict naming the mesh-sdk the composer was built with; a trunk manifest the head's mesh-sdk refuses fails too (the
+// group would deliver a reader that refuses it); and each reader that refuses a changed manifest the head reads fails
+// it, naming the module and its words, unless the reader's mesh-sdk has no composer to ask (before issue 1621), which is
+// said and judged nothing.
+func FromComposer(m Mesh, c Change, head Ran, readers []Reader, took time.Duration) delivery.CompositionVerdict {
+	v := delivery.CompositionVerdict{Group: c.Group, Heads: c.Heads, SDK: "mesh-sdk " + c.SDKHead, Took: took.Milliseconds()}
+	machines := Touched(m, c)
+	v.Machines = machines
+	var fails []string
+	if head.State != delivery.StepPassed {
+		v.Words = fmt.Sprintf("the composer at mesh-sdk %s did not run: %s %s", c.SDKHead, head.State, head.Reason)
+		v.State = delivery.CompositionFail
+		return v
+	}
+	if head.Verdict.SDK != "" {
+		v.SDK = head.Verdict.SDK
+	}
+	trunk, okT := caseOf(head.Verdict, CaseTrunk)
+	change, okC := caseOf(head.Verdict, CaseChange)
+	if !okT || !okC {
+		v.State, v.Words = delivery.CompositionFail, "the composer's verdict holds no trunk or no change case"
+		return v
+	}
+	failAt := func(machine, words string) {
+		if v.Machine == "" && machine != "" {
+			v.Machine = machine
+		}
+		fails = append(fails, words)
+	}
+	for _, name := range sortedKeys(c.Digests) {
+		if r := change.Manifests[name]; !r.Accepted {
+			failAt("", fmt.Sprintf("the manifest of %s cannot be read by mesh-sdk %s: %s", name, c.SDKHead, r.Refused))
+		}
+	}
+	for _, name := range sortedKeys(trunk.Manifests) {
+		if _, changed := c.Digests[name]; changed || slices.Contains(c.Removed, name) || trunk.Manifests[name].Accepted {
+			continue
+		}
+		if _, before := m.Unreadable[name]; before {
+			continue // already unreadable on the trunk: not the group's doing
+		}
+		failAt("", fmt.Sprintf("mesh-sdk %s refuses the trunk's manifest of %s, which the group does not change: %s", c.SDKHead, name, trunk.Manifests[name].Refused))
+	}
+	for _, name := range sortedKeys(c.Twice) {
+		failAt("", fmt.Sprintf("%s is defined twice, in %s", name, strings.Join(c.Twice[name], " and ")))
+	}
+	for _, node := range machines {
+		for _, name := range c.Removed {
+			if slices.Contains(m.Assigned[node], name) {
+				failAt(node, fmt.Sprintf("%s runs %s, which the change removes from its source", node, name))
+			}
+		}
+		before, now := trunk.Machines[node], change.Machines[node]
+		switch {
+		case now.Composes:
+		case !before.Composes:
+			v.Warnings = append(v.Warnings, fmt.Sprintf("%s does not compose on the trunk either, so the change is not blamed: %s", node, before.Reason))
+		default:
+			failAt(node, fmt.Sprintf("%s composes on the trunk and not with the change: %s", node, now.Reason))
+		}
+	}
+	readerFails, readerWarnings := judgeReaders(c, change, readers)
+	fails = append(fails, readerFails...)
+	v.Warnings = append(v.Warnings, readerWarnings...)
+	return finish(v, m, c, machines, fails)
+}
+
+// NoComposer says whether a compose step failed because the mesh-sdk it was built at has no composer command (a mesh-sdk
+// from before issue 1621): Go's words for a package its module does not hold.
+func NoComposer(reason string) bool {
+	for _, words := range []string{"cannot find package", "no required module provides package", "is not in std", "cannot find module providing package", "does not contain package"} {
+		if strings.Contains(reason, words) {
+			return true
+		}
+	}
+	return false
+}
+
+func judgeReaders(c Change, head composer.CaseVerdict, readers []Reader) (fails, warnings []string) {
+	for _, r := range readers {
+		at := r.Module + " at " + r.Commit
+		if r.Member {
+			at = r.Module + "'s member head " + r.Commit
+		}
+		if r.Ran.State != delivery.StepPassed {
+			if NoComposer(r.Ran.Reason) {
+				warnings = append(warnings, fmt.Sprintf("not judged whether %s reads the group's manifests: the mesh-sdk it pins has no "+
+					"composer command (before issue 1621)", at))
+				continue
+			}
+			fails = append(fails, fmt.Sprintf("the composer of the mesh-sdk %s pins did not run: %s %s", at, r.Ran.State, r.Ran.Reason))
+			continue
+		}
+		read, ok := caseOf(r.Ran.Verdict, CaseChange)
+		if !ok {
+			fails = append(fails, fmt.Sprintf("the composer of the mesh-sdk %s pins answered no change case", at))
+			continue
+		}
+		for _, name := range sortedKeys(c.Digests) {
+			if !head.Manifests[name].Accepted || read.Manifests[name].Accepted {
+				continue
+			}
+			fails = append(fails, fmt.Sprintf("the manifest of %s uses what %s (mesh-sdk %s) cannot read: %s; the group must move %s onto "+
+				"mesh-sdk %s", name, at, r.Ran.Verdict.SDK, read.Manifests[name].Refused, r.Module, c.SDKHead))
+		}
+	}
+	return fails, warnings
+}

modules/mesh-delivery-assigner/internal/assign/composer_test.go

@@ -0,0 +1,184 @@
+package assign
+
+import (
+	"encoding/json"
+	"slices"
+	"strings"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/composer"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+var testTime = time.Date(2026, 10, 24, 3, 0, 0, 0, time.UTC)
+
+const sdkHead = "1111111111111111111111111111111111111111"
+
+// raws are the manifests of meshOf as their repositories hold them, by digest, as the indexer keeps them; `web2` is web
+// with a field `shares` that the assigner's own mesh-sdk does not read (the shape of issue 1593).
+var raws = map[string]string{
+	"d-mail":  `{"module": "mail", "version": "1", "requires": ["postgres-database"]}`,
+	"d-store": `{"module": "store", "version": "1", "provides": [{"name": "postgres-database"}]}`,
+	"d-web":   `{"module": "web", "version": "1"}`,
+	"d-web2":  `{"module": "web", "version": "2", "shares": ["photos"]}`,
+}
+
+// asTheHeadReads is how mesh-sdk at the group's head reads each manifest: as the assigner's own reads it, but for the
+// field it adds, which it accepts. The head's composer is built and run by the Go build module (ADR 0482 clause 4); here
+// its verdict is made by mesh-sdk's composer.Run over the same request, with `web2` read as the head reads it.
+var asTheHeadReads = map[string]string{"d-web2": `{"module": "web", "version": "2"}`}
+
+func digestedMesh() Mesh {
+	m := meshOf()
+	m.Digests = map[string]string{"mail": "d-mail", "store": "d-store", "web": "d-web"}
+	return m
+}
+
+// webShares is a group of mesh-sdk and mesh-catalog whose catalogue member gives web the field only the SDK head reads:
+// the assigner's own reader refuses it (Unreadable), as the indexer's manifest is read in world.change.
+func webShares(members map[string]string) Change {
+	_, err := catalogue.ParseManifest([]byte(raws["d-web2"]))
+	return Change{Group: "g", Heads: "0123456789ab", SDKHead: sdkHead, Manifests: map[string]catalogue.Manifest{},
+		Unreadable: map[string]string{"web": err.Error()}, Digests: map[string]string{"web": "d-web2"}, Members: members}
+}
+
+// run is the composer's step for a job, as the build module answers it: the request filled from the indexer's digests
+// (with read standing in for how that mesh-sdk reads a digest), run, and its verdict put in a passed step.
+func run(t *testing.T, job delivery.ComposeJob, read map[string]string) Ran {
+	t.Helper()
+	req, err := composer.Decode(job.Request)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := composer.Fill(&req, func(d string) ([]byte, error) {
+		if r, ok := read[d]; ok {
+			return []byte(r), nil
+		}
+		return []byte(raws[d]), nil
+	}); err != nil {
+		t.Fatal(err)
+	}
+	v, err := composer.Run(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	v.SDK = "(devel) " + job.Fetch["commit"].(string)
+	vr, _ := json.Marshal(v)
+	ans, _ := json.Marshal(delivery.ComposeAnswer{Built: true, Key: "composer-0", Verdict: vr})
+	return RanOf(delivery.Step{State: delivery.StepPassed, Result: ans})
+}
+
+// 1622/AC1: a group holding a mesh-sdk pull request is composed by the composer built at the member's head: the job
+// fetches mesh-sdk at that head, builds mesh-sdk's composer command in its Go module, and hands it the trunk and the
+// change by digest, never the manifests' bytes, composing the machines the change touches.
+func TestAGroupWithAnSDKMemberAsksTheComposerAtItsHead(t *testing.T) {
+	c := webShares(nil)
+	job, err := HeadJob(digestedMesh(), c)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if job.Fetch["repository"] != SDKRepository || job.Fetch["commit"] != sdkHead || job.Dir != "go" || job.Package != composer.Package {
+		t.Fatalf("job = %+v", job)
+	}
+	ask := delivery.StepAsk{ID: "mh3k2x9qa1b2c5", Kind: delivery.AskCheck, Language: delivery.AskGo, Asker: "mesh-delivery-assigner",
+		At: testTime, Compose: &job}
+	if _, err := delivery.EncodeStepAsk(ask); err != nil {
+		t.Fatalf("the ask is refused by its layout: %v", err)
+	}
+	req, err := composer.Decode(job.Request)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(req.Cases) != 2 || req.Cases[0].Name != CaseTrunk || req.Cases[1].Name != CaseChange {
+		t.Fatalf("cases = %+v", req.Cases)
+	}
+	if req.Cases[0].Manifests["web"].Digest != "d-web" || req.Cases[1].Manifests["web"].Digest != "d-web2" || len(req.Cases[1].Manifests["web"].Raw) != 0 {
+		t.Errorf("the cases do not name web by its trunk and its change digest: %+v", req.Cases)
+	}
+	if !slices.Equal(req.Machines, []string{"g14"}) || req.Depth != composer.DepthResolve || !req.HoldingsFromClaims {
+		t.Errorf("request = machines %v, depth %q, holdings from claims %v", req.Machines, req.Depth, req.HoldingsFromClaims)
+	}
+}
+
+// 1622/AC2, AC3: a catalogue member using a field only the SDK head reads passes with the head's composer, and the
+// verdict names the mesh-sdk the composer was built with; with the assigner's own mesh-sdk it fails.
+func TestAFieldTheGroupAddsPassesWithTheHeadsComposer(t *testing.T) {
+	c := webShares(map[string]string{"novox/mesh-controller": "2222222222222222222222222222222222222222"})
+	job, _ := HeadJob(digestedMesh(), c)
+	head := run(t, job, asTheHeadReads)
+	v := FromComposer(digestedMesh(), c, head, nil, 0)
+	if v.State != delivery.CompositionPass || v.SDK != "(devel) "+sdkHead || !slices.Equal(v.Machines, []string{"g14"}) {
+		t.Fatalf("with the head's composer: %+v", v)
+	}
+	if _, err := delivery.EncodeCompositionVerdict(v); err != nil {
+		t.Errorf("the verdict cannot be written: %v", err)
+	}
+	own := Compose(digestedMesh(), c, "v0.1.14-own", 0)
+	if own.State != delivery.CompositionFail || !strings.Contains(own.Words, "shares") {
+		t.Fatalf("with the assigner's own mesh-sdk: %+v, want a fail naming the field", own)
+	}
+}
+
+// 1623/AC1, AC2: the group of mesh-sdk and mesh-catalog adding and using a field, without a controller member, fails
+// naming the field and mesh-controller, whose running build pins an older mesh-sdk; with a controller member pinned to
+// the SDK head (its composer reads what the head reads) it passes.
+func TestAFieldTheRunningControllerCannotReadFailsTheGroup(t *testing.T) {
+	c := webShares(nil)
+	job, _ := HeadJob(digestedMesh(), c)
+	head := run(t, job, asTheHeadReads)
+	running := "3333333333333333333333333333333333333333"
+	rjob, err := ReaderJob(c, "mesh-controller", "novox/mesh-controller", running)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if rjob.Fetch["commit"] != running || rjob.Dir != delivery.RootPath {
+		t.Fatalf("reader job = %+v", rjob)
+	}
+	old := run(t, rjob, nil) // the running controller's mesh-sdk reads web2 as the assigner's own does: refused
+	v := FromComposer(digestedMesh(), c, head, []Reader{{Module: "mesh-controller", Commit: running, Ran: old}}, 0)
+	if v.State != delivery.CompositionFail || !strings.Contains(v.Words, "shares") || !strings.Contains(v.Words, "move mesh-controller onto mesh-sdk "+sdkHead) {
+		t.Fatalf("without a controller member: %+v, want a fail naming the field and mesh-controller", v)
+	}
+	member := "2222222222222222222222222222222222222222"
+	pinned := run(t, rjob, asTheHeadReads)
+	v = FromComposer(digestedMesh(), c, head, []Reader{{Module: "mesh-controller", Commit: member, Member: true, Ran: pinned}}, 0)
+	if v.State != delivery.CompositionPass {
+		t.Fatalf("with a controller member pinned to the head: %+v, want a pass", v)
+	}
+}
+
+// 1623: a reader whose mesh-sdk has no composer command (before issue 1621) is said, not failed; a reader's composer that
+// failed for another cause fails the group, loud.
+func TestAReaderWithNoComposerIsSaidAndAnotherFailureFails(t *testing.T) {
+	c := webShares(nil)
+	job, _ := HeadJob(digestedMesh(), c)
+	head := run(t, job, asTheHeadReads)
+	none := Ran{State: delivery.StepFailed, Reason: "go build: no required module provides package git.novox.be/novox/mesh-sdk/go/cmd/mesh-compose"}
+	v := FromComposer(digestedMesh(), c, head, []Reader{{Module: "mesh-host", Commit: "abc", Ran: none}}, 0)
+	if v.State != delivery.CompositionPass || !hasWarning(v, "mesh-host at abc") || !hasWarning(v, "before issue 1621") {
+		t.Fatalf("a reader with no composer: %+v", v)
+	}
+	broke := Ran{State: delivery.StepFailed, Reason: "the fetch could not reach the forge"}
+	v = FromComposer(digestedMesh(), c, head, []Reader{{Module: "mesh-host", Commit: "abc", Ran: broke}}, 0)
+	if v.State != delivery.CompositionFail || !strings.Contains(v.Words, "could not reach the forge") {
+		t.Fatalf("a reader whose composer failed: %+v", v)
+	}
+}
+
+// 1622: the head's composer that did not run fails the composition naming why, never passes it; a trunk manifest the
+// head's mesh-sdk refuses fails it too, since the group would deliver a reader that refuses it.
+func TestTheHeadsComposerFailingOrRefusingTheTrunkFails(t *testing.T) {
+	c := webShares(nil)
+	v := FromComposer(digestedMesh(), c, Ran{State: delivery.StepRefused, Reason: "the guard refuses it"}, nil, 0)
+	if v.State != delivery.CompositionFail || !strings.Contains(v.Words, "the guard refuses it") || !strings.Contains(v.Words, sdkHead) {
+		t.Fatalf("a head composer that did not run: %+v", v)
+	}
+	job, _ := HeadJob(digestedMesh(), c)
+	strict := map[string]string{"d-web2": asTheHeadReads["d-web2"], "d-mail": `{"module": "mail", "version": "1", "gone": true}`}
+	v = FromComposer(digestedMesh(), c, run(t, job, strict), nil, 0)
+	if v.State != delivery.CompositionFail || !strings.Contains(v.Words, "refuses the trunk's manifest of mail") {
+		t.Fatalf("a head that refuses a trunk manifest: %+v", v)
+	}
+}

modules/mesh-delivery-assigner/internal/assign/wants.go

@@ -0,0 +1,205 @@
+package assign
+
+import (
+	"fmt"
+	"slices"
+	"sort"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// Module is what the six rules read of one module (ADR 0429 §6, ADR 0528 clause 3): its newest fingerprint F at the
+// trunk (the indexer's modules), whether the builder's build of F is done, whether F is held, whether the controller
+// issued its credential for F, its manifest at F, and the nodes it is assigned to.
+type Module struct {
+	Name     string
+	FP       string
+	Built    bool
+	Held     bool
+	Granted  bool
+	Manifest catalogue.Manifest
+	Nodes    []string
+}
+
+// Node is what the rules read of the nodes: whether each is online (the watchman's presence) and each module's have.
+type Nodes struct {
+	Online map[string]bool
+	Haves  map[string]map[string]delivery.Have
+	// Providers is, by provision, the modules that provide it, with the nodes each is assigned to.
+	Providers map[string]map[string][]string
+}
+
+// healthy says whether a have runs fp healthy.
+func healthy(h delivery.Have, fp string) bool {
+	return h.FP == fp && h.Phase == delivery.PhaseRunning && h.Health == delivery.HealthOK
+}
+
+// Canary is the module's canary: the first of its nodes, by name, that is online (ADR 0435 §3; one ring, ordered by
+// name, ADR 0528 clause 3). Empty when none is online.
+func Canary(nodes []string, online map[string]bool) string {
+	sorted := slices.Sorted(slices.Values(nodes))
+	for _, n := range sorted {
+		if online[n] {
+			return n
+		}
+	}
+	return ""
+}
+
+// Holds is whether every rule holds for moving node's want for m to m.FP, and if not, the first rule that does not,
+// with why (ADR 0429 §6). Rule 4, at most `step` others ahead, always holds: the mesh keeps no step, and step 0 is no
+// limit (ADR 0528 clause 3).
+func Holds(m Module, node string, n Nodes) (bool, int, string) {
+	switch {
+	case !m.Built:
+		return false, delivery.RuleBuildDone, fmt.Sprintf("the build of %s at %s is not done", m.Name, short(m.FP))
+	case m.Held:
+		return false, delivery.RuleNotHeld, fmt.Sprintf("%s is held at %s", m.Name, short(m.FP))
+	}
+	canary := Canary(m.Nodes, n.Online)
+	switch {
+	case canary == "":
+		return false, delivery.RuleCanary, fmt.Sprintf("none of the nodes of %s is online, so it has no canary", m.Name)
+	case node != canary && !healthy(n.Haves[canary][m.Name], m.FP):
+		return false, delivery.RuleCanary, fmt.Sprintf("the canary %s does not run %s healthy yet", canary, short(m.FP))
+	}
+	for _, provision := range m.Manifest.Requires {
+		if ok, why := providedHealthy(provision, node, n); !ok {
+			return false, delivery.RuleProviders, why
+		}
+	}
+	if !m.Granted {
+		return false, delivery.RuleGrant, fmt.Sprintf("the controller has not issued the credential of %s for %s", m.Name, short(m.FP))
+	}
+	return true, 0, ""
+}
+
+// providedHealthy is rule 5 for one provision: some module providing it runs healthy on the node, or, assigned
+// elsewhere only, at its canary. A provision no module provides is not a module's to judge (the mesh or the node
+// offers it) and holds.
+func providedHealthy(provision, node string, n Nodes) (bool, string) {
+	providers := n.Providers[provision]
+	if len(providers) == 0 {
+		return true, ""
+	}
+	names := make([]string, 0, len(providers))
+	for p := range providers {
+		names = append(names, p)
+	}
+	sort.Strings(names)
+	for _, p := range names {
+		nodes := providers[p]
+		at := node
+		if !slices.Contains(nodes, node) {
+			at = Canary(nodes, n.Online)
+		}
+		if h, ok := n.Haves[at][p]; ok && at != "" && h.Phase == delivery.PhaseRunning && h.Health == delivery.HealthOK {
+			return true, ""
+		}
+	}
+	return false, fmt.Sprintf("no provider of %s runs healthy on %s or at its canary", provision, node)
+}
+
+// keepsData says whether a module holds data a set-back would lose: an own item of a class that keeps (irreplaceable,
+// valuable or rebuildable; cache and none do not).
+func keepsData(m catalogue.Manifest) bool {
+	for _, it := range m.DataItems() {
+		if it.Class == catalogue.ClassIrreplaceable || it.Class == catalogue.ClassValuable || it.Class == catalogue.ClassRebuildable {
+			return true
+		}
+	}
+	return false
+}
+
+// Outcome is what one module's pass decides: each node's want to write (only those that change), and a hold to write.
+type Outcome struct {
+	Wants map[string]delivery.Want
+	// Held is the hold of m.FP to write, when a node's health check failed on it and it is not held yet.
+	Held *delivery.Held
+	// Rules is, by node, the rule holding the node back from m.FP and why, for the comparison.
+	Rules map[string]Holding
+}
+
+// Holding is a rule holding a node back, and why.
+type Holding struct {
+	Rule  int
+	Words string
+}
+
+// Wants is the pass of one module m: for each of its nodes, the want by the six rules, starting from the want written
+// before (wants, by node); lastHealthy is, by node, the newest fingerprint other than m.FP the node ran healthy. A failed
+// health check of m.FP on a node holds it: every node wanting m.FP is set back to its last healthy fingerprint, but a
+// module holding data is not set back (in release 5 it is asked about from release 6 on: wants are only compared). A
+// node that wants m but is no longer among its nodes gets its want written removed, never deleted (ADR 0408 §4).
+func Wants(m Module, n Nodes, wants map[string]delivery.Want, lastHealthy map[string]string) Outcome {
+	out := Outcome{Wants: map[string]delivery.Want{}, Rules: map[string]Holding{}}
+	held := m.Held
+	if !held && m.FP != "" {
+		for _, node := range slices.Sorted(slices.Values(m.Nodes)) {
+			if h, ok := n.Haves[node][m.Name]; ok && h.FP == m.FP && h.Health == delivery.HealthFailed {
+				out.Held = &delivery.Held{Node: node, Words: h.Detail}
+				held = true
+				break
+			}
+		}
+	}
+	mm := m
+	mm.Held = held
+	for _, node := range m.Nodes {
+		if m.FP == "" {
+			break
+		}
+		before, had := wants[node]
+		var next delivery.Want
+		switch ok, rule, words := Holds(mm, node, n); {
+		case ok:
+			next = delivery.Want{FP: m.FP}
+		case held && had && before.FP == m.FP:
+			out.Rules[node] = Holding{Rule: rule, Words: words}
+			last := lastHealthy[node]
+			switch {
+			case keepsData(m.Manifest):
+				next = before
+				next.Words = fmt.Sprintf("%s holds data, so it is not set back from %s: the operator is asked from release 6", m.Name, short(m.FP))
+			case last == "":
+				next = before
+				next.Words = fmt.Sprintf("%s is held at %s and %s ran no other fingerprint healthy to set it back to", m.Name, short(m.FP), node)
+			default:
+				next = delivery.Want{FP: last, Newest: m.FP, Rule: rule, Words: words}
+			}
+		default:
+			out.Rules[node] = Holding{Rule: rule, Words: words}
+			if !had || before.Removed {
+				continue
+			}
+			next = delivery.Want{FP: before.FP, Newest: m.FP, Rule: rule, Words: words}
+			if before.FP == m.FP {
+				next = delivery.Want{FP: m.FP}
+			}
+		}
+		if !had || !delivery.SameWant(normal(before), normal(next)) {
+			out.Wants[node] = next
+		}
+	}
+	for node, before := range wants {
+		if !slices.Contains(m.Nodes, node) && !before.Removed {
+			out.Wants[node] = delivery.Want{Removed: true, Words: fmt.Sprintf("%s is no longer assigned to %s", m.Name, node)}
+		}
+	}
+	return out
+}
+
+// normal is a want without its version, as a decoded and a composed one are compared.
+func normal(w delivery.Want) delivery.Want {
+	w.V = 0
+	return w
+}
+
+func short(fp string) string {
+	part, err := delivery.FingerprintKeyPart(fp)
+	if err != nil || len(part) < 12 {
+		return fp
+	}
+	return part[:12]
+}

modules/mesh-delivery-assigner/internal/assign/wants_test.go

@@ -0,0 +1,139 @@
+package assign
+
+import (
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+func fpOf(c byte) string { return delivery.SourcePrefix2 + strings.Repeat(string(c), 64) }
+
+var (
+	fNew = fpOf('b')
+	fOld = fpOf('a')
+)
+
+// ready is a module mail at fNew on ace and g14 for which every rule holds: built, not held, granted, its provider
+// store healthy on ace and the canary ace running fNew healthy.
+func ready() (Module, Nodes) {
+	m := Module{Name: "mail", FP: fNew, Built: true, Granted: true, Nodes: []string{"g14", "ace"},
+		Manifest: catalogue.Manifest{Module: "mail", Requires: []string{"database"}}}
+	n := Nodes{
+		Online: map[string]bool{"ace": true, "g14": true},
+		Haves: map[string]map[string]delivery.Have{
+			"ace": {"mail": {FP: fNew, Phase: delivery.PhaseRunning, Health: delivery.HealthOK}, "store": {FP: fpOf('s'), Phase: delivery.PhaseRunning, Health: delivery.HealthOK}},
+			"g14": {"mail": {FP: fOld, Phase: delivery.PhaseRunning, Health: delivery.HealthOK}},
+		},
+		Providers: map[string]map[string][]string{"database": {"store": {"ace"}}},
+	}
+	return m, n
+}
+
+func wantedOld() map[string]delivery.Want {
+	return map[string]delivery.Want{"ace": {FP: fOld}, "g14": {FP: fOld}}
+}
+
+// 1297/B4: with every rule holding, both nodes' wants move to the new fingerprint (the canary ace runs it healthy, so
+// g14 follows at once: step 0, ADR 0528 clause 3).
+func TestEveryRuleHoldsSoTheWantsMove(t *testing.T) {
+	m, n := ready()
+	out := Wants(m, n, wantedOld(), nil)
+	for _, node := range []string{"ace", "g14"} {
+		if out.Wants[node].FP != fNew || out.Wants[node].Rule != 0 {
+			t.Errorf("%s's want = %+v, want %s", node, out.Wants[node], fNew)
+		}
+	}
+}
+
+// 1297/B4, one test per rule: given every rule but N holds, no want moves to F, and the rule N is named.
+func TestEachRuleHoldsTheWantBack(t *testing.T) {
+	for rule, breakIt := range map[int]func(*Module, *Nodes){
+		delivery.RuleBuildDone: func(m *Module, _ *Nodes) { m.Built = false },
+		delivery.RuleNotHeld:   func(m *Module, _ *Nodes) { m.Held = true },
+		delivery.RuleCanary: func(_ *Module, n *Nodes) {
+			n.Haves["ace"]["mail"] = delivery.Have{FP: fOld, Phase: delivery.PhaseRunning, Health: delivery.HealthOK}
+		},
+		delivery.RuleProviders: func(_ *Module, n *Nodes) {
+			n.Haves["ace"]["store"] = delivery.Have{FP: fpOf('s'), Phase: delivery.PhaseRunning, Health: delivery.HealthWaits}
+		},
+		delivery.RuleGrant: func(m *Module, _ *Nodes) { m.Granted = false },
+	} {
+		m, n := ready()
+		breakIt(&m, &n)
+		out := Wants(m, n, wantedOld(), nil)
+		if w, ok := out.Wants["g14"]; ok && w.FP == fNew {
+			t.Errorf("rule %d broken: g14's want moved to F", rule)
+		}
+		if got := out.Rules["g14"].Rule; got != rule {
+			t.Errorf("rule %d broken: g14 is held back by rule %d (%s)", rule, got, out.Rules["g14"].Words)
+		}
+		if w := out.Wants["g14"]; w.FP != "" && (w.FP != fOld || w.Newest != fNew || w.Rule != rule) {
+			t.Errorf("rule %d broken: g14's want is %+v", rule, w)
+		}
+	}
+}
+
+// 1297/B4, ADR 0435 §3: a canary that is offline is passed over: the next node by name is the canary, and moves first.
+func TestAnOfflineCanaryIsPassedOver(t *testing.T) {
+	m, n := ready()
+	n.Online["ace"] = false
+	n.Haves["ace"]["mail"] = delivery.Have{FP: fOld, Phase: delivery.PhaseRunning, Health: delivery.HealthOK}
+	n.Providers["database"]["store"] = []string{"ace", "g14"}
+	n.Haves["g14"]["store"] = delivery.Have{FP: fpOf('s'), Phase: delivery.PhaseRunning, Health: delivery.HealthOK}
+	if c := Canary(m.Nodes, n.Online); c != "g14" {
+		t.Fatalf("canary = %q, want g14", c)
+	}
+	out := Wants(m, n, wantedOld(), nil)
+	if out.Wants["g14"].FP != fNew {
+		t.Errorf("the canary g14's want = %+v", out.Wants["g14"])
+	}
+	if out.Rules["ace"].Rule != delivery.RuleCanary {
+		t.Errorf("ace, behind the canary g14, is held back by %+v", out.Rules["ace"])
+	}
+}
+
+// 1297/B4: a failed health check of F holds F and sets the nodes that want it back to their last healthy fingerprint.
+func TestAFailedHealthHoldsAndSetsBack(t *testing.T) {
+	m, n := ready()
+	n.Haves["ace"]["mail"] = delivery.Have{FP: fNew, Phase: delivery.PhaseRunning, Health: delivery.HealthFailed, Detail: "connection refused"}
+	out := Wants(m, n, map[string]delivery.Want{"ace": {FP: fNew}, "g14": {FP: fOld}}, map[string]string{"ace": fOld})
+	if out.Held == nil || out.Held.Node != "ace" || out.Held.Words != "connection refused" {
+		t.Fatalf("held = %+v", out.Held)
+	}
+	if w := out.Wants["ace"]; w.FP != fOld || w.Newest != fNew || w.Rule != delivery.RuleNotHeld {
+		t.Errorf("ace's want = %+v, want set back to the last healthy fingerprint", w)
+	}
+	if w, ok := out.Wants["g14"]; ok && w.FP == fNew {
+		t.Errorf("g14 moved to a held fingerprint: %+v", w)
+	}
+}
+
+// 1297/B4: a module holding data is not set back; its want stays and says why.
+func TestADataModuleIsNotSetBack(t *testing.T) {
+	m, n := ready()
+	m.Manifest.Data = &catalogue.Data{Own: []catalogue.DataItem{{ID: "mail", Class: catalogue.ClassIrreplaceable}}}
+	n.Haves["ace"]["mail"] = delivery.Have{FP: fNew, Phase: delivery.PhaseRunning, Health: delivery.HealthFailed}
+	out := Wants(m, n, map[string]delivery.Want{"ace": {FP: fNew}}, map[string]string{"ace": fOld})
+	if out.Held == nil {
+		t.Fatal("F was not held")
+	}
+	if w := out.Wants["ace"]; w.FP != fNew || !strings.Contains(w.Words, "holds data") {
+		t.Errorf("ace's want = %+v, want it left at F, saying it holds data", w)
+	}
+}
+
+// 1297/B4, ADR 0408 §4: a node that leaves the module's nodes gets its want written removed, never deleted; a want that
+// is already as the rules give it is not written again.
+func TestALeavingNodeIsRemovedAndNothingIsWrittenTwice(t *testing.T) {
+	m, n := ready()
+	m.Nodes = []string{"ace"}
+	out := Wants(m, n, map[string]delivery.Want{"ace": {V: 1, FP: fNew}, "g14": {FP: fOld}}, nil)
+	if w := out.Wants["g14"]; !w.Removed {
+		t.Errorf("g14's want = %+v, want removed", w)
+	}
+	if _, ok := out.Wants["ace"]; ok {
+		t.Errorf("ace's want, unchanged, was written again: %+v", out.Wants["ace"])
+	}
+}

modules/mesh-delivery-assigner/manifest_test.go

@@ -0,0 +1,61 @@
+package manifest
+
+import (
+	"os"
+	"reflect"
+	"slices"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+)
+
+func load(t *testing.T) catalogue.Manifest {
+	t.Helper()
+	raw, err := os.ReadFile("module.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	m, err := catalogue.ParseManifest(raw)
+	if err != nil {
+		t.Fatalf("mesh-sdk's manifest reader refuses the manifest: %v", err)
+	}
+	return m
+}
+
+// 1297/B2a: the controller's reader (mesh-sdk catalogue, which the controller reads manifests with) takes the
+// manifest; it reads exactly the buckets the assigner opens (the program's list, held equal in its own test), keeps
+// its three states, and holds a credential of its own.
+func TestManifest(t *testing.T) {
+	m := load(t)
+	if m.Module != "mesh-delivery-assigner" {
+		t.Errorf("module = %q", m.Module)
+	}
+	reads := slices.Clone(m.Reads)
+	slices.Sort(reads)
+	want := []string{"mesh-build-go.steps", "mesh-controller.assignments", "mesh-controller.builds", "mesh-controller.grants",
+		"mesh-delivery-builder.builds", "mesh-delivery-indexer.candidates", "mesh-delivery-indexer.manifests",
+		"mesh-delivery-indexer.modules", "mesh-delivery-watchman.presence", "node-engine.have"}
+	if !reflect.DeepEqual(reads, want) {
+		t.Errorf("reads = %v, want exactly %v", reads, want)
+	}
+	states := map[string]int{}
+	for _, s := range m.State {
+		states[s.Name] = s.History
+	}
+	if want := map[string]int{"asks": 5, "compositions": 5, "differences": 64, "wants": 20}; !reflect.DeepEqual(states, want) {
+		t.Errorf("state = %v, want %v", states, want)
+	}
+	if _, ok := m.OwnSecrets["broker"]; !ok || len(m.OwnSecrets) != 1 {
+		t.Errorf("own-secrets = %v, want exactly broker (or no credential is issued)", m.OwnSecrets)
+	}
+	if m.SecretsOwner != "mesh-delivery-assigner" {
+		t.Errorf("secrets-owner = %q", m.SecretsOwner)
+	}
+	// 1622: the assigner puts its compose asks on the Go build seat, as the checker puts its checks.
+	if !slices.Equal(m.Uses, []string{"node-build-go"}) {
+		t.Errorf("uses = %v, want exactly node-build-go", m.Uses)
+	}
+	if len(m.Claims) != 0 || len(m.Tools) != 0 || len(m.Invokes) != 0 {
+		t.Errorf("the assigner claims, serves or calls something: claims %v, tools %v, invokes %v", m.Claims, m.Tools, m.Invokes)
+	}
+}

modules/mesh-delivery-assigner/module.json

@@ -0,0 +1,75 @@
+{
+  "module": "mesh-delivery-assigner",
+  "version": "1",
+  "slug": "assigner",
+  "reads": [
+    "mesh-build-go.steps",
+    "mesh-controller.assignments",
+    "mesh-controller.builds",
+    "mesh-controller.grants",
+    "mesh-delivery-builder.builds",
+    "mesh-delivery-indexer.candidates",
+    "mesh-delivery-indexer.manifests",
+    "mesh-delivery-indexer.modules",
+    "mesh-delivery-watchman.presence",
+    "node-engine.have"
+  ],
+  "uses": [
+    "node-build-go"
+  ],
+  "state": [
+    { "name": "asks", "history": 5 },
+    { "name": "compositions", "history": 5 },
+    { "name": "differences", "history": 64 },
+    { "name": "wants", "history": 20 }
+  ],
+  "own-secrets": {
+    "broker": "${dir:state}/broker"
+  },
+  "secrets-owner": "mesh-delivery-assigner",
+  "resources": [
+    {
+      "id": "account",
+      "type": "user",
+      "name": "mesh-delivery-assigner",
+      "shell": "/usr/bin/nologin",
+      "home": "/var/lib/mesh-delivery-assigner"
+    },
+    {
+      "id": "state",
+      "type": "directory",
+      "mode": "0700",
+      "owner": "mesh-delivery-assigner",
+      "place": ".",
+      "unknown": "program"
+    },
+    {
+      "id": "assigner",
+      "type": "process",
+      "name": "mesh-delivery-assigner",
+      "artifact": "program",
+      "run": [
+        "./mesh-delivery-assigner"
+      ],
+      "env": {
+        "MESH_BROKER_FILE": "${dir:state}/broker"
+      },
+      "user": "mesh-delivery-assigner",
+      "health": {
+        "kind": "unit"
+      }
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "program",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/mesh-delivery-assigner",
+        "binary": "mesh-delivery-assigner"
+      }
+    ]
+  }
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/bus.go

@@ -0,0 +1,122 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-builder/internal/build"
+)
+
+// bucketOpener is the part of the bus the watches use.
+type bucketOpener interface {
+	KeyValue(ctx context.Context, bucket string) (jetstream.KeyValue, error)
+}
+
+// kvStore is the builds bucket as the builder's store: create and compare-and-set.
+type kvStore struct{ kv jetstream.KeyValue }
+
+func conflict(err error) error {
+	if errors.Is(err, jetstream.ErrKeyExists) || errors.Is(err, jetstream.ErrKeyRevisionMismatch) {
+		return build.ErrConflict
+	}
+	return err
+}
+
+func (s kvStore) Get(ctx context.Context, key string) ([]byte, uint64, bool, error) {
+	e, err := s.kv.Get(ctx, key)
+	if errors.Is(err, jetstream.ErrKeyNotFound) {
+		return nil, 0, false, nil
+	}
+	if err != nil {
+		return nil, 0, false, err
+	}
+	return e.Value(), e.Revision(), true, nil
+}
+
+func (s kvStore) Create(ctx context.Context, key string, value []byte) (uint64, error) {
+	rev, err := s.kv.Create(ctx, key, value)
+	return rev, conflict(err)
+}
+
+func (s kvStore) Update(ctx context.Context, key string, value []byte, revision uint64) (uint64, error) {
+	rev, err := s.kv.Update(ctx, key, value, revision)
+	return rev, conflict(err)
+}
+
+func (s kvStore) Keys(ctx context.Context) ([]string, error) {
+	keys, err := s.kv.Keys(ctx)
+	if errors.Is(err, jetstream.ErrNoKeysFound) {
+		return nil, nil
+	}
+	return keys, err
+}
+
+func opOf(e jetstream.KeyValueEntry) bool { return e.Operation() == jetstream.KeyValuePut }
+
+// settle reads the entries a watcher holds now, up to its mark of the last values, and returns the watcher for the
+// changes that follow.
+func settle(ctx context.Context, kv jetstream.KeyValue, each func(jetstream.KeyValueEntry)) (jetstream.KeyWatcher, error) {
+	w, err := kv.WatchAll(ctx)
+	if err != nil {
+		return nil, err
+	}
+	for {
+		select {
+		case <-ctx.Done():
+			w.Stop()
+			return nil, ctx.Err()
+		case e, ok := <-w.Updates():
+			if !ok {
+				return nil, errors.New("the watch ended")
+			}
+			if e == nil {
+				return w, nil
+			}
+			each(e)
+		}
+	}
+}
+
+// follow hands each change of a watcher to each until ctx ends; a watch that ends is an error, and the process manager
+// starts the program again.
+func follow(ctx context.Context, w jetstream.KeyWatcher, each func(jetstream.KeyValueEntry)) error {
+	defer w.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case e, ok := <-w.Updates():
+			if !ok {
+				return errors.New("a watch ended")
+			}
+			if e != nil {
+				each(e)
+			}
+		}
+	}
+}
+
+// manifestReader reads manifests.<digest> of the indexer and parses the manifest it holds.
+type manifestReader struct{ kv jetstream.KeyValue }
+
+func (m manifestReader) Manifest(ctx context.Context, digest string) (catalogue.Manifest, error) {
+	key, err := delivery.ManifestsKey(digest)
+	if err != nil {
+		return catalogue.Manifest{}, err
+	}
+	e, err := m.kv.Get(ctx, key)
+	if err != nil {
+		return catalogue.Manifest{}, fmt.Errorf("manifests.%s: %w", key, err)
+	}
+	kept, err := delivery.DecodeManifest(e.Value())
+	if err != nil {
+		return catalogue.Manifest{}, err
+	}
+	return catalogue.ParseManifestForInputs([]byte(kept.JSON))
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/held.go

@@ -0,0 +1,76 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// heldOnTheBus says whether an ask a build key names is on its build seat's stream, or a build node wrote a step for it
+// (issue 1910): read once, at the take-over of a key at start, never polled.
+type heldOnTheBus struct{ js jetstream.JetStream }
+
+// Held is build.Builder's Held: a step key `<node>.<ask id>` in the build module's steps, or a message of the stream under
+// the ask's subject whose Nats-Msg-Id is the ask's id.
+func (h heldOnTheBus) Held(ctx context.Context, a delivery.StepAsk) (bool, error) {
+	module, err := delivery.BuildModuleOf(a.Language)
+	if err != nil {
+		return false, err
+	}
+	pattern, err := delivery.AskStepWatch(a.ID)
+	if err != nil {
+		return false, err
+	}
+	steps, err := h.js.KeyValue(ctx, delivery.StepsBucket(module))
+	if err != nil {
+		return false, fmt.Errorf("the bucket %s: %w", delivery.StepsBucket(module), err)
+	}
+	keys, err := steps.ListKeysFiltered(ctx, pattern)
+	if err != nil {
+		return false, err
+	}
+	for range keys.Keys() {
+		keys.Stop()
+		return true, nil // a node took it
+	}
+	subject, err := delivery.AskSubject(a.Language, a.Kind)
+	if err != nil {
+		return false, err
+	}
+	// The seat's stream by its name (delivery.AskStream), as the broker grants the builder its information and its
+	// messages by sequence and nothing wider (issue 1910).
+	name, err := delivery.AskStream(a.Language)
+	if err != nil {
+		return false, err
+	}
+	stream, err := h.js.Stream(ctx, name)
+	if errors.Is(err, jetstream.ErrStreamNotFound) {
+		return false, nil
+	}
+	if err != nil {
+		return false, err
+	}
+	// A seat's stream is a work queue, which takes no second consumer over its subjects: its messages are read by sequence
+	// instead, each a direct read that consumes nothing.
+	info, err := stream.Info(ctx)
+	if err != nil {
+		return false, err
+	}
+	for seq := info.State.FirstSeq; seq != 0 && seq <= info.State.LastSeq; seq++ {
+		m, err := stream.GetMsg(ctx, seq)
+		if errors.Is(err, jetstream.ErrMsgNotFound) {
+			continue // taken and acknowledged, or removed
+		}
+		if err != nil {
+			return false, err
+		}
+		if m.Subject == subject && m.Header.Get(jetstream.MsgIDHeader) == a.ID {
+			return true, nil
+		}
+	}
+	return false, nil
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/integration_test.go

@@ -0,0 +1,823 @@
+//go:build integration
+
+package main
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats-server/v2/server"
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// busConf is the shape of the composed accounts file (mesh-controller internal/broker): one account with JetStream, the
+// controller's user and the builder's own principals <node>.<module> (two instances, for the test of one build).
+const busConf = `
+listen: 127.0.0.1:-1
+jetstream { store_dir: %q }
+accounts {
+  MESH {
+    jetstream: enabled
+    users = [
+      { user: "ctl", password: "pw" }
+      { user: "n1.mesh-delivery-builder", password: "pw" }
+      { user: "n2.mesh-delivery-builder", password: "pw" }
+    ]
+  }
+}
+`
+
+const (
+	commit = "7a74cee83f88e6585a5511c3cc53bdf0f5303d20"
+	fp     = "src2:3333333333333333333333333333333333333333333333333333333333333333"
+)
+
+// fakeBuildModules are the build modules on the nodes as the real ones run since R4g (ADR 0525; issue 1887 A4): each pulls
+// its build seat's asks on its nodes (buildstep.Puller over the seat's workers) and runs an ask's job with step bodies that
+// answer as the real tools do, ending the step on <node>.<ask id> of its steps bucket.
+type fakeBuildModules struct {
+	js        jetstream.JetStream
+	ctx       context.Context
+	failBuild atomic.Bool
+	// refusePush makes every bundle and archive build fail as a push the artifact store refused (ADR 0498 clause 2).
+	refusePush atomic.Bool
+	mu         sync.Mutex
+	calls      map[string]int // by `<module>.<tool>`
+	fetches    []map[string]any
+	builds     []map[string]any // the arguments of every build call
+	// closed, while set, keeps every node's capacity at 0: no ask is pulled until open is called (a test of the asks
+	// waiting in their streams).
+	closed  atomic.Bool
+	pullers []*buildstep.Puller
+}
+
+// open lets the nodes pull again and wakes their pullers.
+func (f *fakeBuildModules) open() {
+	f.closed.Store(false)
+	f.mu.Lock()
+	ps := append([]*buildstep.Puller(nil), f.pullers...)
+	f.mu.Unlock()
+	for _, p := range ps {
+		p.Wake()
+	}
+}
+
+func (f *fakeBuildModules) count(tool string) int {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return f.calls[tool]
+}
+
+// digestOf is what every node builds an artifact to.
+func digestOf(artifact string) string {
+	sum := sha256.Sum256([]byte(artifact))
+	return "sha256:" + hex.EncodeToString(sum[:])
+}
+
+var prefixOf = map[string]string{"mesh-build-go": "build_go_", "mesh-build-node": "build_node_", "mesh-build-image": "build_image_"}
+
+// step is one tool's answer, as the real module's.
+func (f *fakeBuildModules) step(module, name string, args map[string]any) (any, error) {
+	tool := prefixOf[module] + name
+	f.mu.Lock()
+	f.calls[module+"."+tool]++
+	if name == "fetch" {
+		f.fetches = append(f.fetches, args)
+	} else {
+		f.builds = append(f.builds, args)
+	}
+	f.mu.Unlock()
+	switch {
+	case name == "fetch":
+		merge := ""
+		if args["base"] != nil { // a fetch with a base answers the merge commit (mesh-build-go FetchResult)
+			merge = `,"merge":"` + strings.Repeat("9", 40) + `"`
+		}
+		return json.RawMessage(`{"workspace":"w` + buildstep.NewID() + `","commit":"` + commit + `"` + merge + `}`), nil
+	case f.failBuild.Load() && tool != "build_image_copy": // the build fails wherever it runs
+		return nil, fmt.Errorf("go build of %v: boom", args["artifact"])
+	case tool == "build_image_copy": // the upstream copy answers the digest and the registry's reference (ADR 0498 clause 4)
+		d := digestOf(fmt.Sprint(args["artifact"]))
+		return json.RawMessage(`{"artifact":"` + fmt.Sprint(args["artifact"]) + `","digest":"` + d + `","reference":"registry.example/` + fmt.Sprint(args["module"]) + `/` + fmt.Sprint(args["artifact"]) + `@` + d + `","pushed":true}`), nil
+	case tool != "build_image_build" && f.refusePush.Load():
+		return nil, fmt.Errorf("%s%v: the artifact store answered 507 Insufficient Storage", delivery.NotStored, args["artifact"])
+	case tool != "build_image_build": // a bundle or an archive is pushed and its reference answered (ADR 0498 clause 1)
+		d := digestOf(fmt.Sprint(args["artifact"]))
+		return json.RawMessage(`{"digest":"` + d + `","reference":"artifact-store://` + filepath.Base(fmt.Sprint(args["module"])) + `/` + fmt.Sprint(args["artifact"]) + `/blobs/` + d + `"}`), nil
+	case tool == "build_image_build" && args["publish"] == true: // a trunk image is pushed: the digest and the reference
+		d := digestOf(fmt.Sprint(args["artifact"]))
+		return json.RawMessage(`{"digest":"` + d + `","reference":"registry.example/imaged/server@` + d + `"}`), nil
+	default:
+		return json.RawMessage(`{"digest":"` + digestOf(fmt.Sprint(args["artifact"])) + `"}`), nil
+	}
+}
+
+// serve makes module's steps bucket and its build seat's stream and workers, and pulls its asks on nodes.
+func (f *fakeBuildModules) serve(t *testing.T, module string, nodes ...string) {
+	kv, err := f.js.CreateKeyValue(f.ctx, jetstream.KeyValueConfig{Bucket: delivery.StepsBucket(module), History: 1})
+	if err != nil {
+		t.Fatal(err)
+	}
+	language := strings.TrimPrefix(module, "mesh-build-")
+	if err := buildstep.DeclareAskWorkers(f.ctx, f.js, language, 30*time.Second); err != nil {
+		t.Fatal(err)
+	}
+	put := func(key string, value any) (uint64, error) {
+		raw, _ := value.(json.RawMessage)
+		return kv.Put(f.ctx, key, raw)
+	}
+	call := func(name string) buildstep.StepFunc {
+		return func(ctx context.Context, args map[string]any) (any, error) { return f.step(module, name, args) }
+	}
+	steps := buildstep.AskSteps{Fetch: call("fetch"), Build: call("build"), Copy: call("copy")}
+	for _, node := range nodes {
+		p := &buildstep.Puller{Source: &buildstep.JetStreamAsks{JS: f.js, Language: language}, Language: language, Node: node, Put: put,
+			Capacity: func() int {
+				if f.closed.Load() {
+					return 0
+				}
+				return 2
+			}, PullWait: 200 * time.Millisecond,
+			Run: func(ctx context.Context, a delivery.StepAsk) (any, error) { return buildstep.RunAsk(ctx, steps, a) }}
+		f.mu.Lock()
+		f.pullers = append(f.pullers, p)
+		f.mu.Unlock()
+		go func() { _ = p.Pull(f.ctx) }()
+	}
+}
+
+type bed struct {
+	ctx        context.Context
+	js         jetstream.JetStream
+	modules    jetstream.KeyValue
+	candidates jetstream.KeyValue
+	builds     jetstream.KeyValue
+	tools      map[string]jetstream.KeyValue
+	instances  jetstream.KeyValue
+	stop       func() // stops the builder started last
+	fake       *fakeBuildModules
+	srvURL     string
+	dir        string
+}
+
+// startBed starts the bus, the buckets the controller makes from the builder's and the build modules' manifests, the
+// build modules' streams and the builder's durable consumers on them, two nodes' toolchains, the indexer's manifests, and
+// the fake build modules. It runs no builder.
+func startBed(t *testing.T) *bed { return startBedWith(t, false) }
+
+// startBedWith is startBed with the nodes' capacity 0 from the start when closed: a puller that reads its capacity before a
+// test could close the nodes may be in a pull already and takes the first ask put (issue 1928).
+func startBedWith(t *testing.T, closed bool) *bed {
+	dir, err := os.MkdirTemp(os.Getenv("TMPDIR"), "b")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { os.RemoveAll(dir) })
+	conf := filepath.Join(dir, "bus.conf")
+	if err := os.WriteFile(conf, []byte(fmt.Sprintf(busConf, filepath.Join(dir, "js"))), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	opts, err := server.ProcessConfigFile(conf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	opts.NoLog, opts.NoSigs = true, true
+	srv, err := server.NewServer(opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+	go srv.Start()
+	if !srv.ReadyForConnections(10 * time.Second) {
+		t.Fatal("the bus did not come up")
+	}
+	t.Cleanup(srv.Shutdown)
+	ctl, err := nats.Connect(srv.ClientURL(), nats.UserInfo("ctl", "pw"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(ctl.Close)
+	js, err := jetstream.New(ctl)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 90*time.Second)
+	t.Cleanup(cancel)
+	b := &bed{ctx: ctx, js: js, tools: map[string]jetstream.KeyValue{}, srvURL: srv.ClientURL(), dir: dir}
+	for module, stream := range toolchainStreams {
+		if _, err := js.CreateStream(ctx, jetstream.StreamConfig{Name: stream, Subjects: []string{"mesh.stream." + module + ".event.toolchain.reported"}}); err != nil {
+			t.Fatal(err)
+		}
+		for _, node := range []string{"n1", "n2"} {
+			if _, err := js.CreateOrUpdateConsumer(ctx, stream, jetstream.ConsumerConfig{Durable: node + "_mesh-delivery-builder", AckPolicy: jetstream.AckExplicitPolicy}); err != nil {
+				t.Fatal(err)
+			}
+		}
+		kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: delivery.ToolchainsBucket(module), History: 1})
+		if err != nil {
+			t.Fatal(err)
+		}
+		b.tools[module] = kv
+	}
+	mk := func(name string, history int) jetstream.KeyValue {
+		kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: name, History: uint8(history)})
+		if err != nil {
+			t.Fatal(err)
+		}
+		return kv
+	}
+	b.modules = mk(delivery.ModulesBucket, delivery.ModulesHistory)
+	b.candidates = mk(delivery.CandidatesBucket, delivery.CandidatesHistory)
+	mk(delivery.ManifestsBucket, delivery.ManifestsHistory)
+	b.builds = mk(delivery.BuilderBuildsBucket, delivery.BuilderBuildsHistory)
+	b.instances = mk(instancesBucket, 1)
+	b.fake = &fakeBuildModules{js: js, ctx: ctx, calls: map[string]int{}}
+	b.fake.closed.Store(closed)
+	b.fake.serve(t, "mesh-build-go", "n1", "n2")
+	b.fake.serve(t, "mesh-build-node", "n1", "n2")
+	b.fake.serve(t, "mesh-build-image", "n1") // the image build module runs on n1 only
+	b.report(t, "mesh-build-go", "n1", "go", "go1.27.1", "1")
+	b.report(t, "mesh-build-go", "n2", "go", "go1.27.1", "1")
+	b.report(t, "mesh-build-node", "n1", "typescript", "tsc5", "1")
+	b.report(t, "mesh-build-node", "n2", "typescript", "tsc5", "1")
+	return b
+}
+
+// report writes a node's toolchains key of a build module and says so on the module's stream, as the module does.
+func (b *bed) report(t *testing.T, module, node, language, version, recipe string) {
+	t.Helper()
+	data, err := delivery.EncodeToolchain(delivery.Toolchain{Language: language, Version: version, Recipe: recipe, At: time.Now().UTC()})
+	if err != nil {
+		t.Fatal(err)
+	}
+	key, _ := delivery.ToolchainKey(node, language)
+	if _, err := b.tools[module].Put(b.ctx, key, data); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := b.js.Publish(b.ctx, "mesh.stream."+module+".event.toolchain.reported", []byte(`{}`)); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// module writes modules.<name> as the indexer does for a module with a new-form fingerprint, and its manifest by digest.
+func (b *bed) module(t *testing.T, name, fixture, path string) string {
+	return b.moduleWith(t, name, fixture, path, map[string]delivery.ToolchainUsed{"go": {Version: "go1.27.1", Recipe: "1"}, "typescript": {Version: "tsc5", Recipe: "1"}})
+}
+
+// moduleWith is module with the toolchains its fingerprint was computed with.
+func (b *bed) moduleWith(t *testing.T, name, fixture, path string, toolchains map[string]delivery.ToolchainUsed) string {
+	return b.moduleCommit(t, name, fixture, path, toolchains, commit)
+}
+
+func (b *bed) moduleCommit(t *testing.T, name, fixture, path string, toolchains map[string]delivery.ToolchainUsed, at string) string {
+	t.Helper()
+	raw, err := os.ReadFile(filepath.Join("testdata", fixture))
+	if err != nil {
+		t.Fatal(err)
+	}
+	digest := delivery.ManifestDigest(raw)
+	manifests, err := b.js.KeyValue(b.ctx, delivery.ManifestsBucket)
+	if err != nil {
+		t.Fatal(err)
+	}
+	mv, err := delivery.EncodeManifest(delivery.Manifest{Module: name, JSON: string(raw)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := manifests.Put(b.ctx, digest, mv); err != nil {
+		t.Fatal(err)
+	}
+	data, err := delivery.EncodeModule(delivery.Module{Repository: "novox/mesh-catalog", Commit: at, FP: "src1:" + strings.Repeat("f", 64), FP2: fp,
+		Manifest: digest, Path: path, Toolchains: toolchains})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := b.modules.Put(b.ctx, name, data); err != nil {
+		t.Fatal(err)
+	}
+	return digest
+}
+
+// archive writes modules.<name> as the real indexer does for a module of an archive only: its fingerprint names no
+// toolchain (mesh-delivery-indexer internal/index inputs.go languagesOf gives an archive no language), so Toolchains is empty.
+func (b *bed) archive(t *testing.T, name, path, at string) string {
+	t.Helper()
+	return b.moduleCommit(t, name, "catalogue-a67f0196-ca-trust.module.json", path, nil, at)
+}
+
+// start runs the program as the builder of a node.
+func (b *bed) start(t *testing.T, node string, env map[string]string) {
+	t.Helper()
+	broker := filepath.Join(t.TempDir(), "broker")
+	cred, _ := json.Marshal(credential{URL: b.srvURL, Node: node, Module: "mesh-delivery-builder", User: node + ".mesh-delivery-builder", Password: "pw"})
+	if err := os.WriteFile(broker, cred, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	e := map[string]string{"MESH_BROKER_FILE": broker}
+	for k, v := range env {
+		e[k] = v
+	}
+	runCtx, stop := context.WithCancel(b.ctx)
+	done := make(chan error, 1)
+	go func() { done <- run(runCtx, func(k string) string { return e[k] }, io.Discard) }()
+	var once sync.Once
+	b.stop = func() { once.Do(func() { stop(); <-done }) }
+	t.Cleanup(b.stop)
+}
+
+// await reads the build key until pred holds of it, within 20 s.
+func (b *bed) await(t *testing.T, module string, pred func(delivery.BuilderBuild) bool) delivery.BuilderBuild {
+	t.Helper()
+	key, err := delivery.BuilderBuildKey(module, fp)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var last delivery.BuilderBuild
+	for deadline := time.Now().Add(20 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+		e, err := b.builds.Get(b.ctx, key)
+		if err != nil {
+			continue
+		}
+		if last, err = delivery.DecodeBuilderBuild(e.Value()); err == nil && pred(last) {
+			return last
+		}
+	}
+	t.Fatalf("builds.%s = %+v within 20 s", key, last)
+	return last
+}
+
+func isState(state string) func(delivery.BuilderBuild) bool {
+	return func(v delivery.BuilderBuild) bool { return v.State == state }
+}
+
+// TestBuilderMakesADoneKeyWithTheDigests: modules.netcheck (a Go and a TypeScript bundle) and its manifest are in the
+// indexer's buckets, and two nodes report each build module's toolchain; the program writes builds.netcheck.<fp> done,
+// the digests of both bundles, both build modules' toolchains, after a fetch and a build on one node (ADR 0478 clause 4).
+func TestBuilderMakesADoneKeyWithTheDigests(t *testing.T) { // 1607/AC7
+	b := startBed(t)
+	digest := b.module(t, "netcheck", "catalogue-a67f0196-netcheck.module.json", "modules/netcheck")
+	b.start(t, "n1", nil)
+	v := b.await(t, "netcheck", isState(delivery.BuildDone))
+	if v.By != "n1.mesh-delivery-builder" || v.Manifest != digest || len(v.Artifacts) != 2 {
+		t.Fatalf("build = %+v", v)
+	}
+	for _, a := range v.Artifacts {
+		if a.Digest != digestOf(a.Name) || a.Kind != "bundle" || a.Reference != "artifact-store://netcheck/"+a.Name+"/blobs/"+a.Digest {
+			t.Errorf("artifact = %+v, want the digest every node built and the reference its push answered (ADR 0498 clause 1)", a)
+		}
+	}
+	if v.Toolchains["go"].Version != "go1.27.1" || v.Toolchains["typescript"].Version != "tsc5" {
+		t.Errorf("toolchains = %+v", v.Toolchains)
+	}
+	for tool, want := range map[string]int{"mesh-build-go.build_go_fetch": 1, "mesh-build-go.build_go_build": 1, "mesh-build-node.build_node_fetch": 1, "mesh-build-node.build_node_build": 1} {
+		if got := b.fake.count(tool); got != want {
+			t.Errorf("%s called %d times, want %d (on one node, ADR 0478 clause 4)", tool, got, want)
+		}
+	}
+}
+
+// TestTwoBuilderInstancesStartingTogetherEndWithOneDoneKey: two builders on two nodes start together on one module key of an
+// archive only (no toolchain named, as the indexer writes it); the second takes over the key the first holds building
+// (ADR 0478 clause 6), and the key ends done, written once.
+func TestTwoBuilderInstancesStartingTogetherEndWithOneDoneKey(t *testing.T) { // 1607/AC7
+	b := startBed(t)
+	b.archive(t, "ca-trust", "modules/ca-trust", commit)
+	b.start(t, "n1", nil)
+	b.start(t, "n2", nil)
+	v := b.await(t, "ca-trust", isState(delivery.BuildDone))
+	if len(v.Artifacts) != 1 || v.Artifacts[0].Kind != "archive" || v.Artifacts[0].Digest != digestOf("files") {
+		t.Fatalf("build = %+v, want the archive's digest", v)
+	}
+	if n := b.fake.count("mesh-build-go.build_go_build"); n < 1 { // each instance that built, on one node
+		t.Errorf("build_go_build was called %d times, want one for each instance that built", n)
+	}
+}
+
+// TestAnArchiveOnlyModuleNamingNoToolchainIsBuilt: the indexer gives an archive no language, so modules.ca-trust has no
+// toolchains; the builder builds it on the build module's nodes all the same (review round 4).
+func TestAnArchiveOnlyModuleNamingNoToolchainIsBuilt(t *testing.T) {
+	b := startBed(t)
+	b.archive(t, "ca-trust", "modules/ca-trust", commit)
+	b.start(t, "n1", nil)
+	v := b.await(t, "ca-trust", isState(delivery.BuildDone))
+	if len(v.Toolchains) != 0 || len(v.Artifacts) != 1 || strings.HasPrefix(v.Step, "one node (") {
+		t.Errorf("build = %+v, want done naming no toolchain", v)
+	}
+}
+
+// TestAFailedKeyIsBuiltAgainAsANewRevisionFromANewModulesValueWithTheSameFingerprint: a build step fails, so the key is
+// failed naming it; the indexer writing modules.<m> again with the same fingerprint wakes the builder, which builds
+// the key again as a new revision of the same key, now done.
+func TestAFailedKeyIsBuiltAgainAsANewRevisionFromANewModulesValueWithTheSameFingerprint(t *testing.T) { // 1607/AC6, AC7
+	b := startBed(t)
+	b.fake.failBuild.Store(true)
+	b.archive(t, "ca-trust", "modules/ca-trust", commit)
+	b.start(t, "n1", nil)
+	v := b.await(t, "ca-trust", isState(delivery.BuildFailed))
+	if !strings.Contains(v.Error, " on n") || !strings.Contains(v.Error, "boom") {
+		t.Errorf("build = %+v, want failed naming the node and the step's reason", v)
+	}
+	key, _ := delivery.BuilderBuildKey("ca-trust", fp)
+	failed, err := b.builds.Get(b.ctx, key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	b.fake.failBuild.Store(false)
+	// The indexer writes the module again (here at a later commit), with the same fingerprint.
+	b.archive(t, "ca-trust", "modules/ca-trust", "89abcdef0123456789abcdef0123456789abcdef")
+	b.await(t, "ca-trust", isState(delivery.BuildDone))
+	done, err := b.builds.Get(b.ctx, key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if done.Revision() <= failed.Revision() {
+		t.Errorf("revision %d, was %d: the key was not written as a new revision", done.Revision(), failed.Revision())
+	}
+}
+
+// TestAToolchainChangeDoesNotBuildTheOldFingerprint: the fingerprint names go1.27.1, the nodes then agree on go1.27.2 (a
+// report of both nodes), and the builder writes no key for the old fingerprint although it was woken by the report; a
+// module value naming go1.27.2 (the new fingerprint, computed by the indexer) is built.
+func TestAToolchainChangeDoesNotBuildTheOldFingerprint(t *testing.T) { // 1615/AC4
+	b := startBed(t)
+	b.report(t, "mesh-build-go", "n1", "go", "go1.27.2", "1")
+	b.report(t, "mesh-build-go", "n2", "go", "go1.27.2", "1")
+	b.module(t, "netcheck", "catalogue-a67f0196-netcheck.module.json", "modules/netcheck") // names go1.27.1
+	b.start(t, "n1", nil)
+	// Another module, whose fingerprint names the new toolchain, is built; by then the old one has been looked at.
+	b.moduleCommit(t, "netcheck2", "catalogue-a67f0196-netcheck.module.json", "modules/netcheck",
+		map[string]delivery.ToolchainUsed{"go": {Version: "go1.27.2", Recipe: "1"}, "typescript": {Version: "tsc5", Recipe: "1"}}, commit)
+	b.await(t, "netcheck2", isState(delivery.BuildDone))
+	if _, err := b.builds.Get(b.ctx, mustKey(t, "netcheck")); err == nil {
+		t.Error("the old fingerprint, naming go1.27.1, was built with go1.27.2")
+	}
+	if n := b.fake.count("mesh-build-go.build_go_build"); n != 1 {
+		t.Errorf("build_go_build was called %d times, want 1 (the new fingerprint on one node only)", n)
+	}
+}
+
+// TestARootModuleIsBuilt: a module whose path is "." is given to the build tools as it is.
+func TestARootModuleIsBuilt(t *testing.T) { // 1615/AC4
+	b := startBed(t)
+	b.archive(t, "ca-trust", delivery.RootPath, commit)
+	b.start(t, "n1", nil)
+	b.await(t, "ca-trust", isState(delivery.BuildDone))
+}
+
+func mustKey(t *testing.T, module string) string {
+	k, err := delivery.BuilderBuildKey(module, fp)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return k
+}
+
+// moduleAt is module with the go toolchain version the fingerprint names and the commit it was computed at.
+func (b *bed) moduleAt(t *testing.T, name, fixture, path, goVersion, at string) {
+	t.Helper()
+	b.moduleCommit(t, name, fixture, path, map[string]delivery.ToolchainUsed{"go": {Version: goVersion, Recipe: "1"}}, at)
+}
+
+// TestAKeyLeftBuildingForAModuleThatIsGoneIsClosedAtStart: the builds bucket holds a key left building by another node for
+// a module the indexer no longer has; the program, at start, fails it naming why (issue 1660, ADR 0478 clause 6).
+func TestAKeyLeftBuildingForAModuleThatIsGoneIsClosedAtStart(t *testing.T) {
+	b := startBed(t)
+	data, err := delivery.EncodeBuilderBuild(delivery.BuilderBuild{State: delivery.BuildBuilding, By: "n2.mesh-delivery-builder", Manifest: strings.Repeat("a", 64)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := b.builds.Put(b.ctx, mustKey(t, "ghost"), data); err != nil {
+		t.Fatal(err)
+	}
+	b.start(t, "n1", nil)
+	v := b.await(t, "ghost", isState(delivery.BuildFailed))
+	if !strings.Contains(v.Error, "no longer has this fingerprint") || !strings.Contains(v.Error, "n2.mesh-delivery-builder") {
+		t.Errorf("build = %+v, want it closed naming who left it", v)
+	}
+}
+
+// TestBuilderBuildsACandidatesFingerprintFromTheHeadMergedOntoTheTrunk: the trunk's record of netcheck carries a fingerprint of its
+// own; a candidate the indexer wrote gives netcheck the fingerprint fp at a pull request's head; the program writes
+// builds.netcheck.<fp> done, its fetch given the head, the ref that carries it and the trunk commit (issue 1684).
+func TestBuilderBuildsACandidatesFingerprintFromTheHeadMergedOntoTheTrunk(t *testing.T) { // N7/AC1
+	b := startBed(t)
+	other := "src2:" + strings.Repeat("e", 64)
+	digest := b.module(t, "netcheck", "catalogue-a67f0196-netcheck.module.json", "modules/netcheck")
+	data, err := delivery.EncodeModule(delivery.Module{Repository: "novox/mesh-catalog", Commit: commit, FP: "src1:" + strings.Repeat("f", 64), FP2: other,
+		Manifest: digest, Path: "modules/netcheck", Toolchains: map[string]delivery.ToolchainUsed{"go": {Version: "go1.27.1", Recipe: "1"}, "typescript": {Version: "tsc5", Recipe: "1"}}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := b.modules.Put(b.ctx, "netcheck", data); err != nil {
+		t.Fatal(err)
+	}
+	const head = "1111111111111111111111111111111111111111"
+	pulls := []delivery.CandidatePull{{Head: delivery.Head{Repository: "novox/mesh-catalog", Number: 7, Head: head}, Modules: []string{"netcheck"},
+		Fps: map[string]delivery.CandidateModule{"netcheck": {FP2: fp, Manifest: digest}}}}
+	hash, _ := delivery.HeadsHash([]delivery.Head{pulls[0].Head})
+	cand, err := delivery.EncodeCandidate(delivery.Candidate{V: delivery.Version, Group: "feat/x", HeadsHash: hash, Pulls: pulls, FPSet: delivery.FingerprintSet(pulls)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	ckey, err := delivery.CandidatesKey("feat/x")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := b.candidates.Put(b.ctx, ckey, cand); err != nil {
+		t.Fatal(err)
+	}
+	b.start(t, "n1", nil)
+	v := b.await(t, "netcheck", isState(delivery.BuildDone))
+	if len(v.Artifacts) != 2 {
+		t.Fatalf("build = %+v", v)
+	}
+	b.fake.mu.Lock()
+	defer b.fake.mu.Unlock()
+	found := false
+	for _, f := range b.fake.fetches {
+		if f["commit"] == head && f["ref"] == "refs/pull/7/head" && f["base"] == commit {
+			found = true
+		}
+	}
+	if !found {
+		t.Errorf("fetches = %v, want one of the candidate's head with its ref and the trunk commit", b.fake.fetches)
+	}
+}
+
+// TestAnImageIsBuiltOnOneNodeAndOnlyATrunkKeyPublishes: modules.imaged (one image artifact) is built on n1, where
+// mesh-build-image runs: a trunk record's key is done with the digest and the reference, its build call carrying publish; a
+// candidate's key for the same module is built first with no publish and no reference; when the pull request is merged and the
+// trunk's record names the candidate's fingerprint, the key is built again with publish and ends with a reference
+// (ADR 0487 clauses 5 and 12).
+func TestAnImageIsBuiltOnOneNodeAndOnlyATrunkKeyPublishes(t *testing.T) { // 1705
+	b := startBed(t)
+	other := "src2:" + strings.Repeat("e", 64)
+	digest := b.moduleCommit(t, "imaged", "catalogue-a67f0196-imaged.module.json", "modules/imaged", nil, commit)
+	// The trunk carries `other`; its key is built and published.
+	trunk := func(fp2 string) {
+		data, err := delivery.EncodeModule(delivery.Module{Repository: "novox/mesh-catalog", Commit: commit, FP: "src1:" + strings.Repeat("f", 64), FP2: fp2,
+			Manifest: digest, Path: "modules/imaged"})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if _, err := b.modules.Put(b.ctx, "imaged", data); err != nil {
+			t.Fatal(err)
+		}
+	}
+	trunk(other)
+	b.start(t, "n1", nil)
+	okey, _ := delivery.BuilderBuildKey("imaged", other)
+	awaitKey := func(key string, pred func(delivery.BuilderBuild) bool) delivery.BuilderBuild {
+		var last delivery.BuilderBuild
+		for deadline := time.Now().Add(20 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+			if e, err := b.builds.Get(b.ctx, key); err == nil {
+				if last, err = delivery.DecodeBuilderBuild(e.Value()); err == nil && pred(last) {
+					return last
+				}
+			}
+		}
+		t.Fatalf("builds.%s = %+v within 20 s", key, last)
+		return last
+	}
+	v := awaitKey(okey, isState(delivery.BuildDone))
+	if len(v.Artifacts) != 1 || v.Artifacts[0].Digest != digestOf("server") || !strings.HasSuffix(v.Artifacts[0].Reference, "@"+digestOf("server")) {
+		t.Fatalf("trunk build = %+v, want the digest and the reference", v)
+	}
+	// The candidate carries fp: built, not published.
+	const head = "1111111111111111111111111111111111111111"
+	pulls := []delivery.CandidatePull{{Head: delivery.Head{Repository: "novox/mesh-catalog", Number: 7, Head: head}, Modules: []string{"imaged"},
+		Fps: map[string]delivery.CandidateModule{"imaged": {FP2: fp, Manifest: digest}}}}
+	hash, _ := delivery.HeadsHash([]delivery.Head{pulls[0].Head})
+	cand, err := delivery.EncodeCandidate(delivery.Candidate{V: delivery.Version, Group: "feat/x", HeadsHash: hash, Pulls: pulls, FPSet: delivery.FingerprintSet(pulls)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	ckey, _ := delivery.CandidatesKey("feat/x")
+	if _, err := b.candidates.Put(b.ctx, ckey, cand); err != nil {
+		t.Fatal(err)
+	}
+	v = b.await(t, "imaged", isState(delivery.BuildDone))
+	if len(v.Artifacts) != 1 || v.Artifacts[0].Reference != "" {
+		t.Fatalf("candidate build = %+v, want done with no reference", v)
+	}
+	b.fake.mu.Lock()
+	if len(b.fake.builds) != 2 || b.fake.builds[0]["publish"] != true || b.fake.builds[1]["publish"] != nil {
+		t.Errorf("builds = %v, want the trunk's with publish, then the candidate's with none", b.fake.builds)
+	}
+	b.fake.mu.Unlock()
+	// The pull request is merged: the trunk's record names fp, and its key ends published, built once more with publish.
+	trunk(fp)
+	v = b.await(t, "imaged", func(v delivery.BuilderBuild) bool {
+		return v.State == delivery.BuildDone && len(v.Artifacts) == 1 && v.Artifacts[0].Reference != ""
+	})
+	if v.Artifacts[0].Digest != digestOf("server") {
+		t.Errorf("merged build = %+v", v)
+	}
+	b.fake.mu.Lock()
+	defer b.fake.mu.Unlock()
+	published := 0
+	for _, a := range b.fake.builds {
+		if a["publish"] == true {
+			published++
+		}
+	}
+	if len(b.fake.builds) != 3 || published != 2 {
+		t.Errorf("builds = %v, want three, two of them with publish (the trunk's two fingerprints)", b.fake.builds)
+	}
+}
+
+// TestEveryDoneKeyNamesItsReferencesAndARefusedPushIsBuiltAgain: with the artifact store refusing pushes, the key of an
+// archive module ends failed opening "not stored:"; once it takes them, a new modules value builds the key again, done, its
+// every artifact naming a reference (issue 1587, B8, ADR 0498 clauses 1, 2 and 8).
+func TestEveryDoneKeyNamesItsReferencesAndARefusedPushIsBuiltAgain(t *testing.T) {
+	b := startBed(t)
+	b.fake.refusePush.Store(true)
+	b.archive(t, "ca-trust", "modules/ca-trust", commit)
+	b.start(t, "n1", nil)
+	v := b.await(t, "ca-trust", isState(delivery.BuildFailed))
+	if !strings.HasPrefix(v.Error, delivery.NotStored) || !strings.Contains(v.Error, "507") {
+		t.Fatalf("build = %+v, want failed opening %q with the store's words", v, delivery.NotStored)
+	}
+	b.fake.refusePush.Store(false)
+	b.archive(t, "ca-trust", "modules/ca-trust", "89abcdef0123456789abcdef0123456789abcdef")
+	v = b.await(t, "ca-trust", isState(delivery.BuildDone))
+	if ok, missing := v.Referenced(); !ok {
+		t.Errorf("build = %+v, artifacts naming no reference: %v", v, missing)
+	}
+}
+
+// TestAPinnedUpstreamIsCopiedByTheImageBuildModule: hello-web's manifest (captured from mesh-catalog 49caf17f) names an
+// upstream image pinned by its digest and an archive; the upstream is copied on n1, where mesh-build-image runs, with no
+// fetch of the image module, and the key ends done with both references (issue 1587, B8, ADR 0498 clause 4).
+func TestAPinnedUpstreamIsCopiedByTheImageBuildModule(t *testing.T) {
+	b := startBed(t)
+	b.moduleCommit(t, "hello-web", "catalogue-49caf17f-hello-web.module.json", "modules/hello-web", nil, commit)
+	b.start(t, "n1", nil)
+	v := b.await(t, "hello-web", isState(delivery.BuildDone))
+	if ok, missing := v.Referenced(); !ok {
+		t.Fatalf("build = %+v, artifacts naming no reference: %v", v, missing)
+	}
+	if n := b.fake.count("mesh-build-image.build_image_copy"); n != 1 {
+		t.Errorf("build_image_copy called %d times, want once", n)
+	}
+	if n := b.fake.count("mesh-build-image.build_image_fetch"); n != 0 {
+		t.Errorf("build_image_fetch called %d times, want none for a copy", n)
+	}
+}
+
+// TestAManifestFallingBackToAPredefinedKeyIsBuilt: claude-code's manifest (mesh-catalog 835bf22b) has a config value falling
+// back to a predefined key; the builder, which holds no published list of them, reads it and builds the key done (issue
+// 1751, mesh-sdk catalogue.ParseManifestForInputs).
+func TestAManifestFallingBackToAPredefinedKeyIsBuilt(t *testing.T) {
+	b := startBed(t)
+	b.module(t, "claude-code", "catalogue-835bf22b-claude-code.module.json", "modules/claude-code")
+	b.start(t, "n1", nil)
+	v := b.await(t, "claude-code", func(v delivery.BuilderBuild) bool {
+		return v.State == delivery.BuildDone || v.State == delivery.BuildFailed
+	})
+	if v.State != delivery.BuildDone {
+		t.Errorf("build = %+v, want done: the manifest is read", v)
+	}
+}
+
+// 1886/AC5: a builder on n1 whose Go, Node and image build modules each answered a reference says under n1, in its bucket
+// of instances, that it writes references, and takes the say away when it stops: the controller delivers from its keys
+// only while it holds.
+func TestABuilderWhoseBuildModulesAnsweredReferencesSaysItAndStoppedSaysNothing(t *testing.T) {
+	b := startBed(t)
+	b.module(t, "netcheck", "catalogue-a67f0196-netcheck.module.json", "modules/netcheck")              // a Go and a TypeScript bundle
+	b.moduleCommit(t, "imaged", "catalogue-a67f0196-imaged.module.json", "modules/imaged", nil, commit) // an image, for the trunk
+	b.start(t, "n1", nil)
+	var said string
+	for deadline := time.Now().Add(20 * time.Second); time.Now().Before(deadline) && said == ""; time.Sleep(50 * time.Millisecond) {
+		if e, err := b.instances.Get(b.ctx, "n1"); err == nil {
+			said = string(e.Value())
+		}
+	}
+	if !strings.Contains(said, `"writes":["references"]`) {
+		t.Fatalf("the builder said %q", said)
+	}
+	b.stop()
+	if _, err := b.instances.Get(b.ctx, "n1"); !errors.Is(err, jetstream.ErrKeyNotFound) {
+		t.Fatalf("the stopped builder still says: %v", err)
+	}
+}
+
+// 1887/AC1, AC2 on the real bus: the builder puts the trunk fingerprint's build as asks on the build seats' delivery
+// streams and calls no node's tool; the build modules that pulled them wrote the steps, and the key is done naming the
+// references.
+func TestTheBuilderAsksTheBuildSeatsAndCallsNoNode(t *testing.T) {
+	b := startBed(t)
+	b.module(t, "netcheck", "catalogue-a67f0196-netcheck.module.json", "modules/netcheck")
+	sub, err := nats.Connect(b.srvURL, nats.UserInfo("ctl", "pw"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer sub.Close()
+	var calls atomic.Int64
+	s, err := sub.Subscribe("mesh.mod.*.call.>", func(*nats.Msg) { calls.Add(1) })
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer s.Unsubscribe()
+	asked := b.asksPut(t, sub)
+	b.start(t, "n1", nil)
+	v := b.await(t, "netcheck", isState(delivery.BuildDone))
+	for _, a := range v.Artifacts {
+		if a.Reference == "" {
+			t.Errorf("artifact %s names no reference", a.Name)
+		}
+	}
+	if n := calls.Load(); n != 0 {
+		t.Errorf("%d tool calls reached a build module", n)
+	}
+	// 1887/AC1: one ask per build module the build needs (netcheck: a Go and a TypeScript bundle), each on its seat's
+	// delivery stream.
+	got := asked()
+	if len(got) != 2 {
+		t.Fatalf("asks put = %+v, want one Go and one Node delivery ask", got)
+	}
+	for _, a := range got {
+		if a.Kind != delivery.AskDelivery || a.Build == nil || a.Build.FP != fp {
+			t.Errorf("ask %+v, want a delivery ask of the fingerprint", a)
+		}
+	}
+}
+
+// asksPut hears every ask put on a build seat's accept subjects (a core subscription beside the stream) and answers the
+// asks heard so far.
+func (b *bed) asksPut(t *testing.T, nc *nats.Conn) func() []delivery.StepAsk {
+	t.Helper()
+	var mu sync.Mutex
+	var asks []delivery.StepAsk
+	s, err := nc.Subscribe("mesh.seat.*.accept.>", func(m *nats.Msg) {
+		if a, err := delivery.DecodeStepAsk(m.Data); err == nil {
+			mu.Lock()
+			asks = append(asks, a)
+			mu.Unlock()
+		}
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = s.Unsubscribe() })
+	return func() []delivery.StepAsk {
+		mu.Lock()
+		defer mu.Unlock()
+		return append([]delivery.StepAsk(nil), asks...)
+	}
+}
+
+// 1887/AC3: a builder that started again while its asks waited in the streams (no node had a free slot) puts no second
+// ask: it waits for the asks its building key names, and the key is done once a node took them.
+func TestARestartedBuilderPutsNoSecondAsk(t *testing.T) {
+	b := startBedWith(t, true) // 1928/AC1: no node can take an ask from the start, so no pull in hand takes the first one
+	b.module(t, "netcheck", "catalogue-a67f0196-netcheck.module.json", "modules/netcheck")
+	sub, err := nats.Connect(b.srvURL, nats.UserInfo("ctl", "pw"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer sub.Close()
+	asked := b.asksPut(t, sub)
+	b.start(t, "n1", nil)
+	v := b.await(t, "netcheck", func(v delivery.BuilderBuild) bool { return v.State == delivery.BuildBuilding && len(v.Asks) == 2 })
+	for deadline := time.Now().Add(20 * time.Second); len(asked()) < 2; time.Sleep(20 * time.Millisecond) {
+		if time.Now().After(deadline) {
+			t.Fatalf("asks put = %+v within 20 s, want the two the key names", asked())
+		}
+	}
+	b.stop()
+	b.start(t, "n1", nil) // the same builder, started again, while both asks wait
+	b.fake.open()
+	done := b.await(t, "netcheck", isState(delivery.BuildDone))
+	if got := asked(); len(got) != 2 {
+		t.Fatalf("asks put = %d (%+v), want the two the key named and none again", len(got), got)
+	}
+	for lang, id := range v.Asks {
+		found := false
+		for _, a := range asked() {
+			found = found || a.ID == id
+		}
+		if !found {
+			t.Errorf("the %s ask %s the key named was never put", lang, id)
+		}
+	}
+	if len(done.Artifacts) != 2 {
+		t.Errorf("done = %+v", done)
+	}
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/main.go

@@ -0,0 +1,246 @@
+// Command mesh-delivery-builder is delivery's builder (novox/hq ADR 0453 clause 4, ADR 0478, issue 1607): it builds every
+// new-form fingerprint the indexer writes, dark, into its own build keys (builds.<module>.<fingerprint>), through the build
+// modules' fetch and build tools. Nothing reads its keys to deliver until release R4e. It serves no request subject and
+// holds no timer: every reaction is a watch or a bus event (ADR 0437 §8).
+package main
+
+import (
+	"context"
+	"crypto/sha256"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+	"io"
+	"log"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+	"time"
+
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-builder/internal/build"
+)
+
+const (
+	// defaultStepBound is how long one ask's step may run once a build node took it (a fetch downloads the Go modules, a
+	// build compiles): from its start, never from its put, so an ask waiting in its stream for a free slot is not failed
+	// (buildrun.Asker.Bound; ADR 0525 §3, §6).
+	defaultStepBound = 30 * time.Minute
+)
+
+func main() {
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	if err := run(ctx, os.Getenv, os.Stderr); err != nil {
+		fmt.Fprintln(os.Stderr, "mesh-delivery-builder:", err)
+		os.Exit(1)
+	}
+}
+
+// credential is the broker file the controller issues to the module: JSON of the bus address, the certificate
+// fingerprint to pin, the principal and its password (as the indexer reads it; issue 1242 moves this into the SDK).
+type credential struct {
+	URL         string `json:"url"`
+	Fingerprint string `json:"fingerprint"`
+	Node        string `json:"node"`
+	Module      string `json:"module"`
+	User        string `json:"user"`
+	Password    string `json:"password"`
+}
+
+func readCredential(path string) (credential, error) {
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		return credential{}, err
+	}
+	var c credential
+	if err := json.Unmarshal(raw, &c); err != nil {
+		return credential{}, fmt.Errorf("the broker credential is not one: %w", err)
+	}
+	if c.URL == "" || c.User == "" {
+		return credential{}, errors.New("the broker credential names no bus address or user")
+	}
+	return c, nil
+}
+
+// pinned accepts exactly the certificate with this SHA-256 and no other.
+func pinned(want string) *tls.Config {
+	return &tls.Config{
+		InsecureSkipVerify: true, //nolint:gosec // replaced by the pin below, which is stricter
+		MinVersion:         tls.VersionTLS12,
+		VerifyPeerCertificate: func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
+			if len(rawCerts) == 0 {
+				return errors.New("the bus presented no certificate")
+			}
+			sum := sha256.Sum256(rawCerts[0])
+			if got := "sha256:" + hex.EncodeToString(sum[:]); got != want {
+				return fmt.Errorf("the bus presented a certificate this mesh does not know (%.23s…)", got)
+			}
+			return nil
+		},
+	}
+}
+
+// run is the program: it returns when ctx ends or the bus cannot be used.
+func run(ctx context.Context, getenv func(string) string, logOut io.Writer) error {
+	logger := log.New(logOut, "mesh-delivery-builder: ", log.LstdFlags)
+	path := strings.TrimSpace(getenv("MESH_BROKER_FILE"))
+	if path == "" {
+		return errors.New("MESH_BROKER_FILE is not set, so there is no credential to hear the bus with")
+	}
+	cred, err := readCredential(path)
+	if err != nil {
+		return err
+	}
+	opts := []nats.Option{
+		nats.Name(cred.Node + "." + cred.Module),
+		nats.UserInfo(cred.User, cred.Password),
+		nats.CustomInboxPrefix("_INBOX." + cred.User),
+		nats.MaxReconnects(-1),
+		nats.RetryOnFailedConnect(true),
+	}
+	if strings.TrimSpace(cred.Fingerprint) != "" {
+		opts = append(opts, nats.Secure(pinned(cred.Fingerprint)))
+	}
+	conn, err := nats.Connect(cred.URL, opts...)
+	if err != nil {
+		return fmt.Errorf("connecting to the bus: %w", err)
+	}
+	defer conn.Close()
+	js, err := jetstream.New(conn)
+	if err != nil {
+		return err
+	}
+	bucket := func(name string) (jetstream.KeyValue, error) {
+		kv, err := js.KeyValue(ctx, name)
+		if err != nil {
+			return nil, fmt.Errorf("the bucket %s: %w", name, err)
+		}
+		return kv, nil
+	}
+	builds, err := bucket(delivery.BuilderBuildsBucket)
+	if err != nil {
+		return err
+	}
+	modules, err := bucket(delivery.ModulesBucket)
+	if err != nil {
+		return err
+	}
+	manifests, err := bucket(delivery.ManifestsBucket)
+	if err != nil {
+		return err
+	}
+	candidates, err := bucket(delivery.CandidatesBucket)
+	if err != nil {
+		return err
+	}
+	bound := defaultStepBound
+	if v := strings.TrimSpace(getenv("MESH_BUILDER_STEP_BOUND")); v != "" {
+		if bound, err = time.ParseDuration(v); err != nil {
+			return fmt.Errorf("MESH_BUILDER_STEP_BOUND: %w", err)
+		}
+	}
+	tools := &buildrun.ToolchainSet{}
+	// Each build module's part of a build is an ask on its build seat's stream, pulled by a build node with a free slot
+	// (novox/hq ADR 0525): the builder chooses no node, so it reads neither presence nor have and holds no capacity.
+	asks := buildrun.JetStreamAsks{JS: js}
+	b := &build.Builder{
+		Claimer:    build.Claimer{Store: kvStore{builds}, By: cred.Node + "." + cred.Module},
+		Asks:       buildrun.Asker{Publisher: asks, Waiter: asks, Bound: bound},
+		Held:       heldOnTheBus{js},
+		Toolchains: tools,
+		Manifests:  manifestReader{manifests},
+		Logf:       logger.Printf,
+	}
+	// **Said once every build module answered a reference, taken away when stopped** (issue 1886, ADR 0522): the
+	// controller delivers from this builder's keys only while an instance says it writes references. A bucket not there
+	// yet (the manifest's state not made) is said, and the controller's plan waits for the keys, named (no build-agent
+	// is asked since R4g, ADR 0524 §7).
+	switch kv, err := js.KeyValue(ctx, instancesBucket); {
+	case errors.Is(err, jetstream.ErrBucketNotFound):
+		logger.Printf("the bucket %s does not exist yet: the controller is not told that this builder writes references until it starts again", instancesBucket)
+	case err != nil:
+		return fmt.Errorf("the bucket %s: %w", instancesBucket, err)
+	default:
+		says := newSayer(ctx, kv, cred.Node, []string{buildrun.GoBuildModule, buildrun.NodeBuildModule, build.ImageBuildModule}, logger.Printf)
+		b.Answered = says.Answered
+		defer func() {
+			stopping, cancel := context.WithTimeout(context.WithoutCancel(ctx), 5*time.Second)
+			defer cancel()
+			if err := says.unsay(stopping); err != nil {
+				logger.Printf("%v", err)
+			}
+		}()
+	}
+	// The toolchains first, so a build that starts from the first modules value finds the nodes.
+	watch := newToolchainWatch(ctx, js, tools, b.NodesChanged, logger)
+	if err := watch.start(); err != nil {
+		return err
+	}
+	// A build module says each time it wrote its toolchains key: its stream, and the builder's durable consumer on it, are
+	// made by the controller. Where the stream is not there yet the builder says so and is started again with the build
+	// module.
+	for _, module := range []string{buildrun.GoBuildModule, buildrun.NodeBuildModule} {
+		stream := toolchainStreams[module]
+		cons, err := js.Consumer(ctx, stream, cred.Node+"_"+cred.Module)
+		if err != nil {
+			logger.Printf("the consumer %s_%s on %s does not exist yet, so %s's reports are not heard until the builder starts again: %v", cred.Node, cred.Module, stream, module, err)
+			continue
+		}
+		cc, err := cons.Consume(func(m jetstream.Msg) { watch.Reported(m) },
+			jetstream.ConsumeErrHandler(func(_ jetstream.ConsumeContext, err error) { logger.Printf("hearing the bus: %v", err) }))
+		if err != nil {
+			return err
+		}
+		defer cc.Stop()
+	}
+	each := func(e jetstream.KeyValueEntry) {
+		if opOf(e) {
+			b.Module(ctx, e.Key(), e.Value())
+		} else {
+			b.Forget(e.Key())
+		}
+	}
+	w, err := settle(ctx, modules, each)
+	if err != nil {
+		return err
+	}
+	// A key left building for a fingerprint its module no longer has is closed (issue 1660); the modules are all known now.
+	if err := b.Sweep(ctx); err != nil {
+		return err
+	}
+	// The fingerprints the indexer gives the candidates' modules are built too (issue 1684), once the trunk's modules are known.
+	eachCandidate := func(e jetstream.KeyValueEntry) {
+		if opOf(e) {
+			b.Candidate(ctx, e.Key(), e.Value())
+		} else {
+			b.ForgetCandidate(e.Key())
+		}
+	}
+	cw, err := settle(ctx, candidates, eachCandidate)
+	if err != nil {
+		return err
+	}
+	logger.Printf("started on %s", cred.Node)
+	errs := make(chan error, 2)
+	go func() { errs <- follow(ctx, w, each) }()
+	go func() { errs <- follow(ctx, cw, eachCandidate) }()
+	select {
+	case <-ctx.Done():
+		b.Wait()
+		return nil
+	case err := <-errs:
+		return err
+	case err := <-watch.errs:
+		return err
+	}
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/says.go

@@ -0,0 +1,79 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"sync"
+
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+// What the builder says it writes (novox/hq issue 1886, ADR 0522): each running instance keeps a key, named by its node,
+// in its own bucket of instances (`mesh-delivery-builder_instances`, the manifest's state `instances`), saying that every
+// done key it writes names where its artifacts are (ADR 0498 §1). The references come from the build modules' own pushes,
+// so an instance says it only once a step of every build module it calls answered one since it started: a builder beside
+// a build module from before R4e says nothing. The controller delivers from the builder's keys only while an instance
+// says so; since R4g it asks no build-agent, and a module whose key is not yet done waits, named (ADR 0524 §7). The bucket is read by the controller alone, so its name and shape
+// are not in mesh-sdk.
+const (
+	instancesBucket  = "mesh-delivery-builder_instances"
+	writesReferences = `{"v":1,"writes":["references"]}`
+)
+
+// sayStore is the bucket of instances as the builder writes it.
+type sayStore interface {
+	Put(ctx context.Context, key string, value []byte) (uint64, error)
+	Delete(ctx context.Context, key string, opts ...jetstream.KVDeleteOpt) error
+}
+
+// sayer puts this instance's say once every build module in need answered a reference, and takes it away at the stop.
+type sayer struct {
+	ctx   context.Context
+	store sayStore
+	node  string
+	need  []string
+	logf  func(string, ...any)
+
+	mu       sync.Mutex
+	answered map[string]bool
+	said     bool
+}
+
+func newSayer(ctx context.Context, store sayStore, node string, need []string, logf func(string, ...any)) *sayer {
+	return &sayer{ctx: ctx, store: store, node: node, need: need, logf: logf, answered: map[string]bool{}}
+}
+
+// Answered is told the build module whose step answered a reference (build.Builder.Answered).
+func (s *sayer) Answered(module string) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.answered[module] = true
+	if s.said {
+		return
+	}
+	for _, m := range s.need {
+		if !s.answered[m] {
+			return
+		}
+	}
+	if _, err := s.store.Put(s.ctx, s.node, []byte(writesReferences)); err != nil {
+		s.logf("saying in %s that this builder writes references: %v; said again at the next reference", instancesBucket, err)
+		return
+	}
+	s.said = true
+	s.logf("every build module answered a reference: said in %s that this builder writes references", instancesBucket)
+}
+
+// unsay takes the say away, if it was made: a builder replaced by one that does not write references leaves none.
+func (s *sayer) unsay(ctx context.Context) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if !s.said {
+		return nil
+	}
+	if err := s.store.Delete(ctx, s.node); err != nil {
+		return fmt.Errorf("taking away the say in %s: %w", instancesBucket, err)
+	}
+	s.said = false
+	return nil
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/says_test.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+type saysOf map[string]string
+
+func (s saysOf) Put(_ context.Context, key string, value []byte) (uint64, error) {
+	s[key] = string(value)
+	return 1, nil
+}
+
+func (s saysOf) Delete(_ context.Context, key string, _ ...jetstream.KVDeleteOpt) error {
+	delete(s, key)
+	return nil
+}
+
+// 1886/AC5: a builder says, under its node, that it writes references only once every build module it calls answered
+// one; stopped, it says nothing any more.
+func TestTheBuilderSaysItWritesReferencesOnceEveryBuildModuleAnsweredOne(t *testing.T) {
+	s := saysOf{}
+	say := newSayer(t.Context(), s, "shanks", []string{"mesh-build-go", "mesh-build-node", "mesh-build-image"}, t.Logf)
+	say.Answered("mesh-build-go")
+	say.Answered("mesh-build-node")
+	if v, ok := s["shanks"]; ok {
+		t.Fatalf("said before the image build module answered a reference: %q", v)
+	}
+	say.Answered("mesh-build-image")
+	var v struct {
+		Writes []string `json:"writes"`
+	}
+	if err := json.Unmarshal([]byte(s["shanks"]), &v); err != nil || len(v.Writes) != 1 || v.Writes[0] != "references" {
+		t.Fatalf("the builder's say: %q %v", s["shanks"], err)
+	}
+	if err := say.unsay(t.Context()); err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := s["shanks"]; ok {
+		t.Fatalf("the stopped builder still says: %v", s)
+	}
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/testdata/catalogue-49caf17f-hello-web.module.json

@@ -0,0 +1,82 @@
+{
+  "module": "hello-web",
+  "slug": "hello",
+  "version": "1",
+  "capabilities": [
+    "container-runtime"
+  ],
+  "requires": [
+    "route"
+  ],
+  "contributes": {
+    "route": {
+      "label": "hello",
+      "endpoint": "web"
+    }
+  },
+  "binds": {
+    "route": "${dir:state}/route.json"
+  },
+  "listens": [
+    {
+      "name": "web",
+      "port": 8080,
+      "protocol": "tcp",
+      "from": "mesh",
+      "why": "the demo web page; only the route-proxy reaches it, and the public name is a route grant"
+    }
+  ],
+  "resources": [
+    {
+      "id": "state",
+      "type": "directory",
+      "mode": "0700",
+      "place": ".",
+      "unknown": "program"
+    },
+    {
+      "id": "page",
+      "type": "file",
+      "path": "${dir:state}/index.html",
+      "mode": "0644",
+      "template": "files/index.html"
+    },
+    {
+      "id": "net",
+      "type": "network",
+      "name": "hello-web"
+    },
+    {
+      "id": "server",
+      "type": "container",
+      "name": "hello-web",
+      "network": "hello-web",
+      "ports": [
+        "8080"
+      ],
+      "volumes": [
+        "${dir:state}/index.html:/www/index.html:ro"
+      ],
+      "args": [
+        "sh",
+        "-c",
+        "while true; do { printf 'HTTP/1.1 200 OK\\r\\nContent-Type: text/plain\\r\\nConnection: close\\r\\n\\r\\n'; cat /www/index.html; } | nc -l -p 8080; done"
+      ],
+      "artifact": "server"
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "server",
+        "kind": "upstream",
+        "from": "alpine@sha256:28bd5fe8b56d1bd048e5babf5b10710ebe0bae67db86916198a6eec434943f8b"
+      },
+      {
+        "name": "files",
+        "kind": "archive",
+        "from": "files"
+      }
+    ]
+  }
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/testdata/catalogue-835bf22b-claude-code.module.json

@@ -0,0 +1,249 @@
+{
+  "module": "claude-code",
+  "version": "1",
+  "moved": true,
+  "slug": "agent",
+  "capabilities": [
+    "package-manager"
+  ],
+  "requires": [
+    "mcp-endpoint",
+    {
+      "name": "gitea-read",
+      "optional": true
+    }
+  ],
+  "binds": {
+    "mcp-endpoint": "${dir:state}/mcp-endpoint.json"
+  },
+  "secrets": {
+    "gitea-read": "${dir:state}/gitea-read.secret"
+  },
+  "uses": [
+    "operator-channel"
+  ],
+  "state": [
+    "servers",
+    "holdings",
+    "config",
+    "proposals",
+    "questions",
+    "memory",
+    "waits"
+  ],
+  "reads": [
+    "claude-licence-manager.bindings"
+  ],
+  "tools": [
+    "claude_code_status",
+    "claude_code_render",
+    "claude_code_guard",
+    "claude_code_pull",
+    "claude_code_grant",
+    "claude_code_add_api_key",
+    "claude_code_registrations",
+    "claude_code_memory",
+    "claude_code_mcp_list",
+    "claude_code_mcp_register",
+    "claude_code_mcp_unregister",
+    "claude_code_skill_list",
+    "claude_code_skill_register",
+    "claude_code_skill_unregister",
+    "claude_code_agent_list",
+    "claude_code_agent_register",
+    "claude_code_agent_unregister",
+    "claude_code_command_list",
+    "claude_code_command_register",
+    "claude_code_command_unregister",
+    "claude_code_hook_list",
+    "claude_code_hook_register",
+    "claude_code_hook_unregister",
+    "claude_code_output_style_list",
+    "claude_code_output_style_register",
+    "claude_code_output_style_unregister",
+    "claude_code_instructions_list",
+    "claude_code_instructions_register",
+    "claude_code_instructions_unregister",
+    "claude_code_instructions_propose",
+    "claude_code_proposals",
+    "claude_code_ask",
+    "claude_code_answer",
+    "claude_code_wait",
+    "claude_code_settings_get",
+    "claude_code_settings_set",
+    "claude_code_settings_clear",
+    "claude_code_permission_add",
+    "claude_code_permission_remove",
+    "claude_code_config_list",
+    "claude_code_config_show",
+    "claude_code_config_status",
+    "claude_code_config_import",
+    "claude_code_home_show",
+    "claude_code_home_remove",
+    "claude_code_home_removed",
+    "claude_code_home_restore",
+    "claude_code_judge",
+    "claude_code_judged"
+  ],
+  "data": {
+    "own": [
+      {
+        "id": "agent-home",
+        "path": "${dir:agent-home}",
+        "class": "valuable",
+        "why": "the operator's agent's own files: its memory, history and projects"
+      }
+    ]
+  },
+  "config": {
+    "role": {
+      "type": "string",
+      "description": "What this machine is for, in a sentence, written into the instructions every Claude Code session on it reads; empty says nothing.",
+      "trusted": true,
+      "default": ""
+    },
+    "mcp_servers": {
+      "type": "object",
+      "description": "The tool servers every session on this machine is given beside the mesh's own, by name, each as Claude Code's managed MCP configuration takes it; empty adds none.",
+      "trusted": true,
+      "default": {}
+    },
+    "managed_settings": {
+      "type": "object",
+      "description": "Keys of Claude Code's managed settings every session on this machine obeys, such as spinnerTipsEnabled, laid over the mesh's own; empty adds none. Falls back to agent-managed-settings, the mesh's or this node's.",
+      "trusted": true,
+      "predefined": "agent-managed-settings",
+      "default": {}
+    },
+    "instructions": {
+      "type": "object",
+      "description": "The instructions every session on this machine reads, by name, each a text as one line or a list of its lines; empty adds none.",
+      "trusted": true,
+      "default": {}
+    },
+    "output_styles": {
+      "type": "object",
+      "description": "The output styles offered to every session on this machine, by name, each a text as one line or a list of its lines; empty adds none.",
+      "trusted": true,
+      "default": {}
+    },
+    "skills": {
+      "type": "object",
+      "description": "The skills offered to every session on this machine, by name, each its files by path, a text as one line or a list of its lines; a skill without its SKILL.md is left out; empty adds none.",
+      "trusted": true,
+      "default": {}
+    },
+    "commands": {
+      "type": "object",
+      "description": "The slash commands offered to every session on this machine, by name, each a text as one line or a list of its lines; empty adds none.",
+      "trusted": true,
+      "default": {}
+    },
+    "agents": {
+      "type": "object",
+      "description": "The agents offered to every session on this machine, by name, each a text as one line or a list of its lines; empty adds none.",
+      "trusted": true,
+      "default": {}
+    }
+  },
+  "resources": [
+    {
+      "id": "package",
+      "type": "package",
+      "package": "claude-code"
+    },
+    {
+      "id": "managed",
+      "type": "directory",
+      "path": "/etc/claude-code",
+      "mode": "0755",
+      "unknown": "program"
+    },
+    {
+      "id": "start",
+      "type": "file",
+      "path": "/usr/local/bin/claude-agent",
+      "mode": "0755",
+      "template": "files/claude-agent"
+    },
+    {
+      "id": "agent-account-name",
+      "type": "file",
+      "path": "/etc/claude-code/agent-account",
+      "mode": "0644",
+      "template": "files/agent-account"
+    },
+    {
+      "id": "agent-account",
+      "type": "user",
+      "name": "${machine:agent-account}",
+      "home": "${machine:agent-home}",
+      "root": "${machine:agent-root}"
+    },
+    {
+      "id": "agent-home",
+      "type": "directory",
+      "path": "${machine:agent-home}/.claude",
+      "mode": "0700",
+      "owner": "${machine:agent-account}",
+      "unknown": "module"
+    },
+    {
+      "id": "state",
+      "type": "directory",
+      "mode": "0700",
+      "owner": "${machine:account}",
+      "place": ".",
+      "unknown": "program"
+    },
+    {
+      "id": "facts",
+      "type": "file",
+      "path": "${dir:state}/facts.json",
+      "mode": "0600",
+      "owner": "${machine:account}",
+      "template": "files/facts.json"
+    },
+    {
+      "id": "settings",
+      "type": "file",
+      "path": "${dir:state}/settings.json",
+      "mode": "0600",
+      "owner": "${machine:account}",
+      "takes-config": ["role", "mcp_servers", "managed_settings", "instructions", "output_styles", "skills", "commands", "agents"],
+      "merge": "json",
+      "template": "files/settings.json"
+    }
+  ],
+  "items": [
+    {
+      "collection": "shell:zsh:normal",
+      "template": "files/zsh-normal"
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "tools",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/claude-code",
+        "binary": "claude-code",
+        "loads": [
+          "claude-code"
+        ],
+        "env": {
+          "MESH_CLAUDE_CODE_STATE": "${dir:state}",
+          "MESH_CLAUDE_CODE_FACTS": "${dir:state}/facts.json",
+          "MESH_CLAUDE_CODE_SETTINGS": "${dir:state}/settings.json"
+        }
+      },
+      {
+        "name": "files",
+        "kind": "archive",
+        "from": "files"
+      }
+    ]
+  }
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/testdata/catalogue-a67f0196-ca-trust.module.json

@@ -0,0 +1,66 @@
+{
+  "module": "ca-trust",
+  "version": "1",
+  "slug": "catrust",
+  "capabilities": [
+    "service-manager"
+  ],
+  "requires": [
+    "internal-acme-ca"
+  ],
+  "seats": [
+    {
+      "name": "the-mesh-trust-anchor",
+      "scope": "node"
+    }
+  ],
+  "claims": [
+    {
+      "name": "the-mesh-trust-anchor",
+      "scope": "node"
+    }
+  ],
+  "resources": [
+    {
+      "id": "state",
+      "type": "directory",
+      "mode": "0700",
+      "place": ".",
+      "unknown": "program"
+    },
+    {
+      "id": "anchor",
+      "type": "file",
+      "path": "${dir:state}/anchor",
+      "mode": "0755",
+      "template": "files/anchor"
+    },
+    {
+      "id": "unit",
+      "type": "file",
+      "path": "/etc/systemd/system/mesh-ca-trust.service",
+      "mode": "0644",
+      "template": "files/mesh-ca-trust.service"
+    },
+    {
+      "id": "trust",
+      "type": "service",
+      "unit": "mesh-ca-trust.service",
+      "state": "running",
+      "boot": "enabled",
+      "restart-on": [
+        "anchor",
+        "unit"
+      ]
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "files",
+        "kind": "archive",
+        "from": "files"
+      }
+    ]
+  }
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/testdata/catalogue-a67f0196-imaged.module.json

@@ -0,0 +1,14 @@
+{
+  "module": "imaged",
+  "version": "1",
+  "slug": "imaged",
+  "build": {
+    "artifacts": [
+      {
+        "name": "server",
+        "kind": "image",
+        "from": "Dockerfile"
+      }
+    ]
+  }
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/testdata/catalogue-a67f0196-netcheck.module.json

@@ -0,0 +1,57 @@
+{
+  "module": "netcheck",
+  "version": "1",
+  "emits": [
+    "tunnel.endpoint-changed",
+    "tunnel.handshake-stale",
+    "tunnel.handshake-fresh"
+  ],
+  "tools": [
+    "netcheck_tunnel",
+    "netcheck_tcp",
+    "netcheck_dns",
+    "netcheck_http",
+    "netcheck_listening"
+  ],
+  "replaces": {
+    "netcheck_listening": [
+      "ss -lunt",
+      "ss -ltn",
+      "netstat -lnt"
+    ],
+    "netcheck_dns": [
+      "dig",
+      "nslookup"
+    ],
+    "netcheck_tunnel": [
+      "wg show",
+      "wg show mesh0 dump"
+    ]
+  },
+  "build": {
+    "artifacts": [
+      {
+        "name": "tools-go",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/netcheck",
+        "binary": "netcheck",
+        "loads": [
+          "netcheck"
+        ]
+      },
+      {
+        "name": "tools-typescript",
+        "kind": "bundle",
+        "language": "typescript",
+        "entrypoints": [
+          "tools/index.js"
+        ],
+        "loads": [
+          "tools/index.js"
+        ]
+      }
+    ]
+  }
+}

modules/mesh-delivery-builder/cmd/mesh-delivery-builder/toolchains.go

@@ -0,0 +1,103 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+	"log"
+	"strings"
+	"sync"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// toolchainStreams are the stream each build module carries its toolchain.reported event on, as the bus names it
+// (declared by the build modules, heard by this module through consumes).
+var toolchainStreams = map[string]string{buildrun.GoBuildModule: "TOOLCHAINS_GO", buildrun.NodeBuildModule: "TOOLCHAINS_NODE"}
+
+// toolchainWatch keeps the build modules' toolchains in a buildrun.ToolchainSet and tells the builder when one changed. A
+// build module's bucket is made when it is assigned, after the builder started, and the builder holds no timer (ADR 0437
+// §8): it watches the buckets that exist at start, and a build module says each time it wrote its toolchains key
+// (toolchain.reported, handled by Reported); a bucket not watched yet is then watched.
+type toolchainWatch struct {
+	ctx     context.Context
+	js      bucketOpener
+	set     *buildrun.ToolchainSet
+	changed func(ctx context.Context) // a language's entries changed: the failed builds are tried again
+	logger  *log.Logger
+	errs    chan error
+	mu      sync.Mutex
+	watched map[string]bool
+}
+
+func newToolchainWatch(ctx context.Context, js bucketOpener, set *buildrun.ToolchainSet, changed func(context.Context), logger *log.Logger) *toolchainWatch {
+	return &toolchainWatch{ctx: ctx, js: js, set: set, changed: changed, logger: logger, errs: make(chan error, len(buildrun.LanguageOf)), watched: map[string]bool{}}
+}
+
+// start watches the buckets that exist now; a missing one is said and waits for its build module's event.
+func (w *toolchainWatch) start() error {
+	for module := range buildrun.LanguageOf {
+		if err := w.ensure(module); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (w *toolchainWatch) ensure(module string) error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if w.watched[module] {
+		return nil
+	}
+	name := delivery.ToolchainsBucket(module)
+	kv, err := w.js.KeyValue(w.ctx, name)
+	switch {
+	case errors.Is(err, jetstream.ErrBucketNotFound):
+		w.logger.Printf("the bucket %s does not exist yet: it is watched when %s reports a toolchain", name, module)
+		return nil
+	case err != nil:
+		return fmt.Errorf("the bucket %s: %w", name, err)
+	}
+	watcher, err := settle(w.ctx, kv, func(e jetstream.KeyValueEntry) { w.set.Put(module, e.Key(), e.Value(), !opOf(e)) })
+	if err != nil {
+		return err
+	}
+	w.watched[module] = true
+	go func() {
+		w.errs <- follow(w.ctx, watcher, func(e jetstream.KeyValueEntry) {
+			if w.set.Put(module, e.Key(), e.Value(), !opOf(e)) {
+				w.changed(w.ctx)
+			}
+		})
+	}()
+	w.changed(w.ctx) // what the settle read is new to the builder
+	return nil
+}
+
+// delivered is the part of a JetStream message the watch uses.
+type delivered interface {
+	Subject() string
+	Ack() error
+	Term() error
+}
+
+// Reported takes one toolchain.reported event of a build module in: the module is read off the subject,
+// mesh.stream.<module>.event.toolchain.reported, and its bucket is watched if it is not. A subject of no build module is
+// terminated; a failure stays unacknowledged, and the server delivers it again.
+func (w *toolchainWatch) Reported(m delivered) {
+	module, _, _ := strings.Cut(strings.TrimPrefix(m.Subject(), "mesh.stream."), ".event.")
+	if _, known := buildrun.LanguageOf[module]; !known || !strings.HasPrefix(m.Subject(), "mesh.stream.") {
+		w.logger.Printf("%s: not a build module's event, dropped", m.Subject())
+		_ = m.Term()
+		return
+	}
+	if err := w.ensure(module); err != nil {
+		w.logger.Printf("%s: left for redelivery: %v", m.Subject(), err)
+		return
+	}
+	_ = m.Ack()
+}

modules/mesh-delivery-builder/go.mod

@@ -0,0 +1,22 @@
+module mesh-delivery-builder
+
+go 1.26.0
+
+require (
+	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261023150321-a2c813a6b468
+	github.com/nats-io/nats-server/v2 v2.11.17
+	github.com/nats-io/nats.go v1.54.0
+)
+
+require (
+	github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op // indirect
+	github.com/google/go-tpm v0.9.8 // indirect
+	github.com/klauspost/compress v1.20.0 // indirect
+	github.com/minio/highwayhash v1.0.4 // indirect
+	github.com/nats-io/jwt/v2 v2.8.1 // indirect
+	github.com/nats-io/nkeys v0.4.16 // indirect
+	github.com/nats-io/nuid v1.0.1 // indirect
+	golang.org/x/crypto v0.57.0 // indirect
+	golang.org/x/sys v0.48.0 // indirect
+	golang.org/x/time v0.15.0 // indirect
+)

modules/mesh-delivery-builder/go.sum

@@ -0,0 +1,27 @@
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261023150321-a2c813a6b468 h1:UcMee+IV2ii5E4dRZdQUaSaeh9IedTFYumuQbBiB0k0=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261023150321-a2c813a6b468/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op h1:Z/MZK75wC/NSrkgqeNIa7jexam9uWzhLmFTSCPI/kn0=
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op/go.mod h1:FQyySiasQQM8735Ddel3MRojmy4dA1IqCeyJ5jmPMbI=
+github.com/google/go-tpm v0.9.8 h1:slArAR9Ft+1ybZu0lBwpSmpwhRXaa85hWtMinMyRAWo=
+github.com/google/go-tpm v0.9.8/go.mod h1:h9jEsEECg7gtLis0upRBQU+GhYVH6jMjrFxI8u6bVUY=
+github.com/klauspost/compress v1.20.0 h1:a3C1ke2ohxFymNlb2HWAHjDeKCI90scRskErZkR0ezA=
+github.com/klauspost/compress v1.20.0/go.mod h1:LUdAzn7YLVvxLpc7y3V1m40wESHTgc1422pwwBSKYuI=
+github.com/minio/highwayhash v1.0.4 h1:asJizugGgchQod2ja9NJlGOWq4s7KsAWr5XUc9Clgl4=
+github.com/minio/highwayhash v1.0.4/go.mod h1:GGYsuwP/fPD6Y9hMiXuapVvlIUEhFhMTh0rxU3ik1LQ=
+github.com/nats-io/jwt/v2 v2.8.1 h1:V0xpGuD/N8Mi+fQNDynXohVvp7ZztevW5io8CUWlPmU=
+github.com/nats-io/jwt/v2 v2.8.1/go.mod h1:nWnOEEiVMiKHQpnAy4eXlizVEtSfzacZ1Q43LIRavZg=
+github.com/nats-io/nats-server/v2 v2.11.17 h1:GKEghcFK6A+aFx11Yf1LjgLC3txAwvyhnYzhBIQZA8I=
+github.com/nats-io/nats-server/v2 v2.11.17/go.mod h1:B1sFVz4StNosQ903ak4N1G01Fl/9f8e06mXpFIE2K24=
+github.com/nats-io/nats.go v1.54.0 h1:vsXoOxjHp/GmPUN+EcI7uOf/uB+iAP+kEsAFNQN0yzA=
+github.com/nats-io/nats.go v1.54.0/go.mod h1:y+DZoD1oBOYfZTU681eTUiUjI0vbqYGixNVFHcjHJ0k=
+github.com/nats-io/nkeys v0.4.16 h1:rd5oAuLOb8mnAycB0xleuEBNS1pVVnN0fv/FF34Eypg=
+github.com/nats-io/nkeys v0.4.16/go.mod h1:llLgWoI0o4z/Q57q2R1kHfmocyhGV6VG/U18Glg1Afs=
+github.com/nats-io/nuid v1.0.1 h1:5iA8DT8V7q8WK2EScv2padNa/rTESc1KdnPw4TC2paw=
+github.com/nats-io/nuid v1.0.1/go.mod h1:19wcPz3Ph3q0Jbyiqsd0kePYG7A95tJPxeL+1OSON2c=
+golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
+golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
+golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
+golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
+golang.org/x/time v0.15.0 h1:bbrp8t3bGUeFOx08pvsMYRTCVSMk89u4tKbNOZbp88U=
+golang.org/x/time v0.15.0/go.mod h1:Y4YMaQmXwGQZoFaVFk4YpCt4FLQMYKZe9oeV/f4MSno=

modules/mesh-delivery-builder/internal/build/candidates.go

@@ -0,0 +1,108 @@
+package build
+
+import (
+	"context"
+	"fmt"
+	"sort"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+// How a candidate's fingerprint is built (novox/hq ADR 0484 clause 3, issue 1684): the indexer writes, for each module a
+// pull request touches, the fingerprint of the new form it has at the head merged onto the trunk (candidates.<group>), and
+// the builder builds each, once, as a key of its own (builds.<module>.<fingerprint>) that the checker's line reads. The
+// build is the trunk module's: the same build modules, the same nodes and capacity; what differs is where the source comes
+// from: the fetch step is given the pull request's head, the ref that carries it and the trunk commit to merge it onto, as
+// the checker's fetch is, and builds the merge's module directory.
+
+// via is how a build's fetch step reaches its source when it is a candidate's: the ref that carries the head and the trunk
+// commit the head is merged onto.
+type via struct{ Ref, Base string }
+
+// Candidate takes one value of the indexer's candidates bucket in (the key is the group) and builds the fingerprints it
+// carries. A value that is not a candidate is said and left.
+func (b *Builder) Candidate(ctx context.Context, key string, value []byte) {
+	b.init()
+	c, err := delivery.DecodeCandidate(value)
+	if err != nil {
+		b.logf("candidates.%s holds what is not a candidate, left: %v", key, err)
+		return
+	}
+	b.mu.Lock()
+	b.cands[key] = c
+	b.mu.Unlock()
+	b.considerCandidate(ctx, c)
+}
+
+// ForgetCandidate takes a candidate out (its key was deleted).
+func (b *Builder) ForgetCandidate(key string) {
+	b.init()
+	b.mu.Lock()
+	delete(b.cands, key)
+	b.mu.Unlock()
+}
+
+func (b *Builder) considerCandidate(ctx context.Context, c delivery.Candidate) {
+	for _, p := range c.Pulls {
+		names := make([]string, 0, len(p.Fps))
+		for name := range p.Fps {
+			names = append(names, name)
+		}
+		sort.Strings(names)
+		for _, name := range names {
+			cm := p.Fps[name]
+			if cm.FP2 == "" || cm.Manifest == "" {
+				continue // no fingerprint of the new form for it (a reason in none2) or no manifest to build by
+			}
+			b.mu.Lock()
+			trunk, known := b.known[name]
+			b.mu.Unlock()
+			if !known || trunk.Path == "" {
+				b.logf("candidates.%s: the module %s has no record of the trunk yet, so its fingerprint %s is not built", c.Group, name, cm.FP2)
+				continue
+			}
+			key, err := delivery.BuilderBuildKey(name, cm.FP2)
+			if err != nil {
+				b.logf("candidates.%s: %v", c.Group, err)
+				continue
+			}
+			m := delivery.Module{Repository: p.Repository, Commit: p.Head.Head, FP2: cm.FP2, Manifest: cm.Manifest, Path: trunk.Path,
+				Toolchains: b.agreedFor(ctx, cm.Manifest)}
+			if len(cm.Paths) > 0 {
+				// The named paths' objects the preview gave it: the fetch names the paths (runLane, ADR 0499 clause 4).
+				m.Inputs2 = &delivery.KeptInputs2{Paths: cm.Paths}
+			}
+			b.mu.Lock()
+			if _, onTrunk := b.trunkFP[key]; !onTrunk {
+				b.via[key] = via{Ref: fmt.Sprintf("refs/pull/%d/head", p.Number), Base: trunk.Commit}
+			}
+			b.mu.Unlock()
+			b.consider(ctx, name, m)
+		}
+	}
+}
+
+// agreedFor are the toolchains the build nodes agree on now, for the languages of the manifest's plan: the toolchains the
+// candidate's fingerprint was computed with, as the indexer recomputes it whenever they change. A language with none agreed
+// is left out, and the build then waits for it as the trunk's does.
+func (b *Builder) agreedFor(ctx context.Context, manifest string) map[string]delivery.ToolchainUsed {
+	plan, err, _ := b.planOf(ctx, manifest)
+	if err != nil {
+		return nil
+	}
+	out := map[string]delivery.ToolchainUsed{}
+	for _, bm := range plan.Modules() {
+		if !plan.NeedsToolchain(bm) {
+			continue
+		}
+		language := buildrun.LanguageOf[bm]
+		if tc, none := delivery.AgreedToolchain(b.Toolchains.Entries(language)); none == "" {
+			out[language] = delivery.ToolchainUsed{Version: tc.Version, Recipe: tc.Recipe}
+		}
+	}
+	if len(out) == 0 {
+		return nil
+	}
+	return out
+}

modules/mesh-delivery-builder/internal/build/candidates_test.go

@@ -0,0 +1,114 @@
+package build
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// trunkModule writes the trunk's record of the module m at a fingerprint of its own, so that the candidate's fingerprint (fp1)
+// is one the trunk does not carry.
+func trunkModule(t *testing.T, r *rig) {
+	t.Helper()
+	data, err := delivery.EncodeModule(delivery.Module{Repository: "novox/mesh-catalog", Commit: "7a74cee83f88e6585a5511c3cc53bdf0f5303d20", FP: "src1:" + hex64('f'),
+		FP2: "src2:" + hex64('e'), Manifest: mdigest('a'), Path: "modules/m", Toolchains: agreedToolchains})
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.b.Module(context.Background(), "m", data)
+	r.b.Wait()
+	r.bm.mu.Lock()
+	r.bm.calls = nil
+	r.bm.mu.Unlock()
+}
+
+func candidateValue(t *testing.T, group string, number int, head string) []byte {
+	t.Helper()
+	pulls := []delivery.CandidatePull{{Head: delivery.Head{Repository: "novox/mesh-catalog", Number: number, Head: head}, Modules: []string{"m"},
+		Fps: map[string]delivery.CandidateModule{"m": {FP2: fp1, Manifest: mdigest('a')}}}}
+	hash, err := delivery.HeadsHash([]delivery.Head{pulls[0].Head})
+	if err != nil {
+		t.Fatal(err)
+	}
+	data, err := delivery.EncodeCandidate(delivery.Candidate{V: delivery.Version, Group: group, HeadsHash: hash, Pulls: pulls, FPSet: delivery.FingerprintSet(pulls)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return data
+}
+
+const (
+	headX = "1111111111111111111111111111111111111111"
+	headY = "2222222222222222222222222222222222222222"
+)
+
+func TestACandidatesFingerprintIsBuiltOnceAsAKeyOfItsOwnFromTheHeadMergedOntoTheTrunk(t *testing.T) { // N7/AC1, N7/AC2 (issue 1684)
+	r := newRig(t, goBundle)
+	trunkModule(t, r)
+	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	r.b.Wait()
+	v := valueOf(t, r.st, r.key)
+	if v.State != delivery.BuildDone || len(v.Artifacts) != 1 {
+		t.Fatalf("build = %+v, want the candidate's fingerprint built", v)
+	}
+	fetches := r.bm.callsOf("build_go_fetch")
+	if len(fetches) != 1 { // one node per fingerprint (ADR 0478 clause 4)
+		t.Fatalf("%d fetches, want one", len(fetches))
+	}
+	f := fetches[0].body.(map[string]any)
+	if f["commit"] != headX || f["ref"] != "refs/pull/7/head" || f["base"] != "7a74cee83f88e6585a5511c3cc53bdf0f5303d20" || f["repository"] != "novox/mesh-catalog" {
+		t.Errorf("fetch args = %+v, want the head, its ref and the trunk commit to merge onto", f)
+	}
+	if b := r.bm.callsOf("build_go_build")[0].body.(map[string]any); b["module"] != "modules/m" {
+		t.Errorf("build args = %+v", b)
+	}
+	// Two heads carrying one fingerprint are one build.
+	r.b.Candidate(context.Background(), "feat%2Fy", candidateValue(t, "feat/y", 8, headY))
+	r.b.Wait()
+	if n := len(r.bm.callsOf("build_go_fetch")); n != 1 {
+		t.Errorf("%d fetches after a second head with the same fingerprint, want no more", n)
+	}
+}
+
+func TestACandidateWhoseModuleHasNoTrunkRecordIsNotBuilt(t *testing.T) {
+	r := newRig(t, goBundle)
+	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	r.b.Wait()
+	if _, ok := r.st.vals[r.key]; ok {
+		t.Error("a build key was written for a module the builder knows no directory of")
+	}
+}
+
+func TestAFingerprintTheTrunkCarriesIsBuiltFromTheTrunksCommit(t *testing.T) { // the trunk's source wins
+	r := newRig(t, goBundle)
+	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m")) // the trunk now carries fp1
+	r.b.Wait()
+	for _, c := range r.bm.callsOf("build_go_fetch") {
+		if f := c.body.(map[string]any); f["ref"] != nil || f["base"] != nil {
+			t.Errorf("fetch args = %+v: a trunk fingerprint is built from the trunk's commit alone", f)
+		}
+	}
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone {
+		t.Errorf("build = %+v", v)
+	}
+}
+
+func TestACandidateWhoseHeadDoesNotMergeIsFailedAndNoTrunkBuildIsStoredUnderIt(t *testing.T) { // review D4
+	for name, set := range map[string]func(*rig){
+		"conflict": func(r *rig) { r.bm.conflicts = "go.mod" },
+		"no merge": func(r *rig) { r.bm.noMerge = true },
+	} {
+		r := newRig(t, goBundle)
+		trunkModule(t, r)
+		set(r)
+		r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+		r.b.Wait()
+		v := valueOf(t, r.st, r.key)
+		if v.State != delivery.BuildFailed || (name == "conflict" && !strings.Contains(v.Error, "go.mod")) || len(r.bm.callsOf("build_go_build")) != 0 {
+			t.Errorf("%s: build = %+v, builds %d, want failed and nothing built", name, v, len(r.bm.callsOf("build_go_build")))
+		}
+	}
+}

modules/mesh-delivery-builder/internal/build/claim.go

@@ -0,0 +1,206 @@
+package build
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"sort"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+// ErrConflict is what a Store answers when a Create finds the key or an Update finds another revision than the one given.
+var ErrConflict = errors.New("the key exists or changed")
+
+// Store is the builder's bucket (builds): create and compare-and-set, each answering the key's new revision. Only the
+// builder's credential writes it (ADR 0429 clause 5).
+type Store interface {
+	Get(ctx context.Context, key string) (value []byte, revision uint64, found bool, err error)
+	Create(ctx context.Context, key string, value []byte) (uint64, error)
+	Update(ctx context.Context, key string, value []byte, revision uint64) (uint64, error)
+	// Keys are every key of the bucket.
+	Keys(ctx context.Context) ([]string, error)
+}
+
+// Claimer claims fingerprints for the builder instance By (ADR 0429 clause 5: a builder claims a fingerprint by creating
+// its key and moves it by compare-and-set).
+type Claimer struct {
+	Store Store
+	By    string
+}
+
+// Claim is a build the builder holds: its key, the revision the next write must be made at and the value last written.
+type Claim struct {
+	Key   string
+	Rev   uint64
+	Build delivery.BuilderBuild
+}
+
+// ClaimOptions say what the builder knows about the moment of a claim.
+type ClaimOptions struct {
+	// TakeOver takes a key found building whoever holds it: the builder has just started and looks at the key for the first
+	// time, and a build left building by a builder that is gone, on this node or another, is nobody's (ADR 0478 clause 6).
+	TakeOver bool
+	// ImageBuilder says whether a node runs a healthy image build module now: a key failed for NoImageBuilderPrefix is taken
+	// again only then. Nil means none does.
+	ImageBuilder func() bool
+	// Trunk is whether the trunk's record names this fingerprint. A done key whose image or package has no reference was
+	// built as a candidate's, which never pushes or publishes (ADR 0487 clause 12, ADR 0498 clauses 5 and 6); on the trunk it
+	// is taken again to publish them, an image only when an image builder runs (ImageBuilder).
+	Trunk bool
+	// Published says whether a package version `<name>@<version>` is published: one of the builder's done keys names it as
+	// a package's reference. A key queued waiting for a version (BuilderBuild.Waits) is taken only once it is (ADR 0500
+	// clause 6). Nil means none is.
+	Published func(ref string) bool
+}
+
+// Unpublished is whether a done build holds an image built without a push or a package built without a publish: it has
+// no reference (a candidate's, ADR 0487 clause 12, ADR 0498 clauses 5 and 6).
+func Unpublished(b delivery.BuilderBuild) bool { return len(UnpublishedModules(b)) > 0 }
+
+// UnpublishedModules are the build modules that publish what a done build holds unpublished: the image build module for
+// an image, the Node build module for a package; sorted, none when it holds nothing unpublished.
+func UnpublishedModules(b delivery.BuilderBuild) []string {
+	if b.State != delivery.BuildDone {
+		return nil
+	}
+	var image, pkg bool
+	for _, a := range b.Artifacts {
+		image = image || (a.Kind == catalogue.ArtifactImage && a.Reference == "")
+		pkg = pkg || (a.Kind == catalogue.ArtifactPackage && a.Reference == "")
+	}
+	var out []string
+	if image {
+		out = append(out, ImageBuildModule)
+	}
+	if pkg {
+		out = append(out, buildrun.NodeBuildModule)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// publishable are the build modules of UnpublishedModules that can publish now: the image build module only while a node
+// runs it (imageBuilder).
+func publishable(b delivery.BuilderBuild, imageBuilder func() bool) []string {
+	var out []string
+	for _, bm := range UnpublishedModules(b) {
+		if bm != ImageBuildModule || (imageBuilder != nil && imageBuilder()) {
+			out = append(out, bm)
+		}
+	}
+	return out
+}
+
+// Unreferenced is whether a done build holds a bundle, an archive or an upstream copy that names no reference: a key done
+// before R4e, whose artifacts stayed on their build nodes (ADR 0498 clause 8). An artifact of no kind (a key written before
+// kinds) is one too. Claim takes such a key again, once: its new revision names them.
+func Unreferenced(b delivery.BuilderBuild) bool {
+	if b.State != delivery.BuildDone {
+		return false
+	}
+	for _, a := range b.Artifacts {
+		if a.Reference == "" && (a.Kind == "" || stored(a.Kind)) {
+			return true
+		}
+	}
+	return false
+}
+
+// Claim takes the build of module at fingerprint, or answers nil when it is not this builder's to build now:
+//   - no key: it is created building, by this builder; a create that finds the key made meanwhile gets nothing;
+//   - a done key is not taken again (the same source is never built twice), except one whose bundle, archive or upstream
+//     copy names no reference (Unreferenced, a key done before R4e: ADR 0498 clause 8), which is claimed building as a new
+//     revision and built whole, and one whose image or package was built unpublished as a candidate's once the trunk
+//     names it (ClaimOptions.Trunk): that is taken as it stands, with the done value, and its builder writes the new
+//     revision when the publishing build ends (ADR 0498 clause 6). From R4e one node builds each fingerprint (ADR 0478
+//     clause 4), so a key built on one node is never built again for a second;
+//   - a failed key is taken again as a new revision of the same key (ADR 0429 clause 18), except one failed for a kind no
+//     builder builds, for an upstream pinned by no digest or a package version taken (delivery.FailedUntilChanged: ADR 0478
+//     clause 2, ADR 0498 clauses 4 and 5) or for digests that differ (buildrun.DigestsDifferPrefix, clause 4),
+//     which wait for another fingerprint, and one failed for want of an image builder (NoImageBuilderPrefix), which waits for
+//     another fingerprint or a node that runs the image build module (ClaimOptions.ImageBuilder);
+//   - a key queued waiting for a package version (Waits) is claimed building as a new revision once that version is
+//     published (ClaimOptions.Published, ADR 0500 clause 6), and not before;
+//   - a key left queued or building by this builder is taken as it stands (ADR 0478 clause 5: a stopped builder takes its
+//     own again when it starts), and so is one left by another builder when ClaimOptions.TakeOver (clause 6).
+func (c Claimer) Claim(ctx context.Context, module, fingerprint, manifest string, opt ClaimOptions) (*Claim, error) {
+	key, err := delivery.BuilderBuildKey(module, fingerprint)
+	if err != nil {
+		return nil, err
+	}
+	building := delivery.BuilderBuild{State: delivery.BuildBuilding, By: c.By, Step: "claimed", Manifest: manifest}
+	value, rev, found, err := c.Store.Get(ctx, key)
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", key, err)
+	}
+	if !found {
+		return c.write(ctx, key, building, func(data []byte) (uint64, error) { return c.Store.Create(ctx, key, data) })
+	}
+	cur, err := delivery.DecodeBuilderBuild(value)
+	if err != nil {
+		return nil, fmt.Errorf("%s holds what is not a build: %w", key, err)
+	}
+	switch {
+	case cur.State == delivery.BuildDone:
+		if Unreferenced(cur) {
+			return c.write(ctx, key, building, func(data []byte) (uint64, error) { return c.Store.Update(ctx, key, data, rev) })
+		}
+		if opt.Trunk && len(publishable(cur, opt.ImageBuilder)) > 0 {
+			return &Claim{Key: key, Rev: rev, Build: cur}, nil
+		}
+		return nil, nil
+	case cur.State == delivery.BuildFailed && (delivery.FailedUntilChanged(cur.Error) || strings.HasPrefix(cur.Error, buildrun.DigestsDifferPrefix)):
+		return nil, nil
+	case cur.State == delivery.BuildFailed && strings.HasPrefix(cur.Error, NoImageBuilderPrefix) && (opt.ImageBuilder == nil || !opt.ImageBuilder()):
+		return nil, nil
+	case cur.State == delivery.BuildFailed:
+		return c.write(ctx, key, building, func(data []byte) (uint64, error) { return c.Store.Update(ctx, key, data, rev) })
+	case cur.State == delivery.BuildQueued && cur.Waits != "":
+		if opt.Published == nil || !opt.Published(cur.Waits) {
+			return nil, nil // the package it waits for is not published yet
+		}
+		return c.write(ctx, key, building, func(data []byte) (uint64, error) { return c.Store.Update(ctx, key, data, rev) })
+	case cur.By == c.By || opt.TakeOver:
+		return &Claim{Key: key, Rev: rev, Build: cur}, nil
+	}
+	return nil, nil
+}
+
+func (c Claimer) write(_ context.Context, key string, b delivery.BuilderBuild, put func([]byte) (uint64, error)) (*Claim, error) {
+	data, err := delivery.EncodeBuilderBuild(b)
+	if err != nil {
+		return nil, err
+	}
+	rev, err := put(data)
+	if errors.Is(err, ErrConflict) {
+		return nil, nil // another builder made it first
+	}
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", key, err)
+	}
+	b.V = delivery.Version
+	return &Claim{Key: key, Rev: rev, Build: b}, nil
+}
+
+// Finish moves the claimed key to b by compare-and-set at the claim's revision, and writes nothing when b is the value
+// the key holds. A key that changed meanwhile is ErrConflict: the claim is no longer this builder's.
+func (c Claimer) Finish(ctx context.Context, cl *Claim, b delivery.BuilderBuild) error {
+	b.V = delivery.Version
+	if delivery.SameBuilderBuild(cl.Build, b) {
+		return nil
+	}
+	data, err := delivery.EncodeBuilderBuild(b)
+	if err != nil {
+		return err
+	}
+	rev, err := c.Store.Update(ctx, cl.Key, data, cl.Rev)
+	if err != nil {
+		return fmt.Errorf("%s: %w", cl.Key, err)
+	}
+	cl.Rev, cl.Build = rev, b
+	return nil
+}

modules/mesh-delivery-builder/internal/build/claim_test.go

@@ -0,0 +1,219 @@
+package build
+
+import (
+	"context"
+	"errors"
+	"sync"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// memStore is a bucket's create and compare-and-set in memory, with a revision per write.
+type memStore struct {
+	mu     sync.Mutex
+	vals   map[string][]byte
+	revs   map[string]uint64
+	next   uint64
+	writes int
+	// before runs once ahead of the next write, so a test changes the key under the writer.
+	before func()
+}
+
+func newMem() *memStore { return &memStore{vals: map[string][]byte{}, revs: map[string]uint64{}} }
+
+func (m *memStore) Get(_ context.Context, key string) ([]byte, uint64, bool, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	v, ok := m.vals[key]
+	return v, m.revs[key], ok, nil
+}
+
+func (m *memStore) Keys(_ context.Context) ([]string, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	var keys []string
+	for k := range m.vals {
+		keys = append(keys, k)
+	}
+	return keys, nil
+}
+
+func (m *memStore) hook() {
+	if h := m.before; h != nil {
+		m.before = nil
+		h()
+	}
+}
+
+func (m *memStore) put(key string, value []byte) uint64 {
+	m.next++
+	m.writes++
+	m.vals[key], m.revs[key] = value, m.next
+	return m.next
+}
+
+func (m *memStore) Create(_ context.Context, key string, value []byte) (uint64, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.hook()
+	if _, ok := m.vals[key]; ok {
+		return 0, ErrConflict
+	}
+	return m.put(key, value), nil
+}
+
+func (m *memStore) Update(_ context.Context, key string, value []byte, rev uint64) (uint64, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.hook()
+	if _, ok := m.vals[key]; !ok || m.revs[key] != rev {
+		return 0, ErrConflict
+	}
+	return m.put(key, value), nil
+}
+
+const (
+	fp1    = "src2:1111111111111111111111111111111111111111111111111111111111111111"
+	digest = "sha256:2222222222222222222222222222222222222222222222222222222222222222"
+)
+
+func seed(t *testing.T, st *memStore, b delivery.BuilderBuild) string {
+	t.Helper()
+	key, err := delivery.BuilderBuildKey("m", fp1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	data, err := delivery.EncodeBuilderBuild(b)
+	if err != nil {
+		t.Fatal(err)
+	}
+	st.put(key, data)
+	return key
+}
+
+func valueOf(t *testing.T, st *memStore, key string) delivery.BuilderBuild {
+	t.Helper()
+	b, err := delivery.DecodeBuilderBuild(st.vals[key])
+	if err != nil {
+		t.Fatal(err)
+	}
+	return b
+}
+
+func TestClaimCreatesTheKeyBuildingAndASecondBuilderGetsNothing(t *testing.T) { // 1607/AC3
+	st := newMem()
+	a, b := Claimer{Store: st, By: "novox.a"}, Claimer{Store: st, By: "novox.b"}
+	got, err := a.Claim(context.Background(), "m", fp1, hex64('a'), ClaimOptions{})
+	if err != nil || got == nil {
+		t.Fatalf("first claim = %v, %v, want a claim", got, err)
+	}
+	if v := valueOf(t, st, got.Key); v.State != delivery.BuildBuilding || v.By != "novox.a" || v.Manifest != hex64('a') {
+		t.Errorf("the key holds %+v, want building by novox.a with the manifest digest", v)
+	}
+	if second, err := b.Claim(context.Background(), "m", fp1, hex64('a'), ClaimOptions{}); err != nil || second != nil {
+		t.Errorf("second builder's claim = %v, %v, want none: the same source is never built twice", second, err)
+	}
+}
+
+func TestClaimLosingTheCreateRaceGetsNothing(t *testing.T) { // 1607/AC3
+	st := newMem()
+	st.before = func() { seed(t, st, delivery.BuilderBuild{State: delivery.BuildBuilding, By: "novox.b"}) }
+	got, err := Claimer{Store: st, By: "novox.a"}.Claim(context.Background(), "m", fp1, "", ClaimOptions{})
+	if err != nil || got != nil {
+		t.Errorf("claim = %v, %v, want none: the create failed because the key exists", got, err)
+	}
+}
+
+func TestADoneKeyIsNeverTakenAgain(t *testing.T) { // 1607/AC3; a key whose artifacts name references (ADR 0498 clause 8)
+	st := newMem()
+	seed(t, st, delivery.BuilderBuild{State: delivery.BuildDone, By: "novox.a", Manifest: hex64('a'), Artifacts: []delivery.BuiltArtifact{{Name: "x", Kind: "bundle", Digest: digest, Reference: "artifact-store://m/x/blobs/" + digest}}})
+	writes := st.writes
+	got, err := Claimer{Store: st, By: "novox.a"}.Claim(context.Background(), "m", fp1, hex64('a'), ClaimOptions{})
+	if err != nil || got != nil || st.writes != writes {
+		t.Errorf("claim = %v, %v, writes %d (was %d), want none and no write", got, err, st.writes, writes)
+	}
+}
+
+func TestAFailedKeyIsTakenAgainAsANewRevisionExceptARefusedKind(t *testing.T) { // 1607/AC3, ADR 0478 clause 2
+	st := newMem()
+	key := seed(t, st, delivery.BuilderBuild{State: delivery.BuildFailed, By: "novox.a", Error: "the step failed"})
+	rev := st.revs[key]
+	got, err := Claimer{Store: st, By: "novox.a"}.Claim(context.Background(), "m", fp1, hex64('a'), ClaimOptions{})
+	if err != nil || got == nil || st.revs[key] <= rev {
+		t.Fatalf("claim = %v, %v, revision %d (was %d), want a claim as a new revision of the same key", got, err, st.revs[key], rev)
+	}
+	if v := valueOf(t, st, key); v.State != delivery.BuildBuilding || v.Error != "" {
+		t.Errorf("the key holds %+v, want building with no error", v)
+	}
+
+	st = newMem()
+	key = seed(t, st, delivery.BuilderBuild{State: delivery.BuildFailed, By: "novox.a", Error: delivery.RefusedKind + "package of language \"python\" (artifact x)"})
+	writes := st.writes
+	if got, err := (Claimer{Store: st, By: "novox.a"}).Claim(context.Background(), "m", fp1, "", ClaimOptions{}); err != nil || got != nil || st.writes != writes {
+		t.Errorf("a refused kind: claim = %v, %v, writes %d (was %d), want none and no write", got, err, st.writes, writes)
+	}
+	for _, e := range []string{delivery.NotPinned + "up: nats:2 names no digest", delivery.VersionTaken + "@novox/mesh-sdk@0.1.15"} { // B3, B5: ADR 0498 clauses 4, 5
+		st = newMem()
+		seed(t, st, delivery.BuilderBuild{State: delivery.BuildFailed, By: "novox.a", Error: e})
+		writes = st.writes
+		if got, err := (Claimer{Store: st, By: "novox.a"}).Claim(context.Background(), "m", fp1, "", ClaimOptions{}); err != nil || got != nil || st.writes != writes {
+			t.Errorf("%s: claim = %v, %v, writes %d (was %d), want none until the fingerprint changes", e, got, err, st.writes, writes)
+		}
+	}
+}
+
+func TestAKeyFailedForNoImageBuilderIsTakenAgainOnlyWhenANodeHasTheModule(t *testing.T) { // 1705b
+	st := newMem()
+	key := seed(t, st, delivery.BuilderBuild{State: delivery.BuildFailed, By: "novox.a", Error: NoImageBuilderPrefix + " no node has mesh-build-image"})
+	writes := st.writes
+	c := Claimer{Store: st, By: "novox.a"}
+	for _, opt := range []ClaimOptions{{}, {ImageBuilder: func() bool { return false }}} {
+		if got, err := c.Claim(context.Background(), "m", fp1, "", opt); err != nil || got != nil || st.writes != writes {
+			t.Errorf("claim = %v, %v, writes %d (was %d), want none and no write", got, err, st.writes, writes)
+		}
+	}
+	got, err := c.Claim(context.Background(), "m", fp1, hex64('a'), ClaimOptions{ImageBuilder: func() bool { return true }})
+	if err != nil || got == nil || valueOf(t, st, key).State != delivery.BuildBuilding {
+		t.Errorf("claim = %v, %v, want a claim with the key building", got, err)
+	}
+}
+
+func TestFinishMovesTheKeyByCompareAndSetAndWritesOnlyADifferentValue(t *testing.T) { // 1607/AC3
+	st := newMem()
+	c := Claimer{Store: st, By: "novox.a"}
+	got, _ := c.Claim(context.Background(), "m", fp1, hex64('a'), ClaimOptions{})
+	done := delivery.BuilderBuild{State: delivery.BuildDone, By: "novox.a", Manifest: hex64('a'), Artifacts: []delivery.BuiltArtifact{{Name: "x", Kind: "archive", Digest: digest}}}
+	if err := c.Finish(context.Background(), got, done); err != nil {
+		t.Fatal(err)
+	}
+	if v := valueOf(t, st, got.Key); v.State != delivery.BuildDone || v.Artifacts[0].Digest != digest {
+		t.Errorf("the key holds %+v", v)
+	}
+	writes := st.writes
+	if err := c.Finish(context.Background(), got, done); err != nil && !errors.Is(err, ErrConflict) {
+		t.Fatal(err)
+	}
+	if st.writes != writes {
+		t.Errorf("the same value was written again (%d writes, was %d)", st.writes, writes)
+	}
+}
+
+func TestFinishAfterTheKeyChangedIsAConflictNotAnOverwrite(t *testing.T) { // 1607/AC3
+	st := newMem()
+	c := Claimer{Store: st, By: "novox.a"}
+	got, _ := c.Claim(context.Background(), "m", fp1, "", ClaimOptions{})
+	st.put(got.Key, []byte(`{"v":1,"state":"failed","error":"someone else"}`))
+	err := c.Finish(context.Background(), got, delivery.BuilderBuild{State: delivery.BuildFailed, Error: "mine"})
+	if !errors.Is(err, ErrConflict) {
+		t.Errorf("Finish = %v, want ErrConflict", err)
+	}
+}
+
+func hex64(c byte) string {
+	b := make([]byte, 64)
+	for i := range b {
+		b[i] = c
+	}
+	return string(b)
+}

modules/mesh-delivery-builder/internal/build/fakes_test.go

@@ -0,0 +1,94 @@
+package build
+
+// The fakes of the build modules the builder tests run against: a caller answering a long tool at once with the step and its key,
+// and the steps watch. The caller, the steps watch and the runner themselves are the SDK's (mesh-sdk go/delivery/buildrun, issue 1671).
+
+import (
+	"context"
+	"encoding/json"
+	"sync"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+type call struct {
+	node, key string
+	body      any
+}
+
+// fakeCaller answers a long tool as the build modules do: at once, with the step and its key.
+type fakeCaller struct {
+	calls  []call
+	answer string
+	err    error
+}
+
+func (f *fakeCaller) CallOn(node, key string, body any) (json.RawMessage, error) {
+	f.calls = append(f.calls, call{node, key, body})
+	if f.err != nil {
+		return nil, f.err
+	}
+	return json.RawMessage(f.answer), nil
+}
+
+// fakeSteps holds the steps values by `<module>/<key>`; Wait on a key it does not hold blocks until the context ends.
+type fakeSteps struct {
+	mu    sync.Mutex
+	steps map[string]delivery.Step
+	// during, when set, is called as a wait starts and the function it answers as the wait ends.
+	during func(key string) func()
+}
+
+func (f *fakeSteps) Wait(ctx context.Context, module, key string) (delivery.Step, error) {
+	f.mu.Lock()
+	s, ok := f.steps[module+"/"+key]
+	during := f.during
+	f.mu.Unlock()
+	if ok {
+		if during != nil {
+			defer during(key)()
+		}
+		return s, nil
+	}
+	<-ctx.Done()
+	return delivery.Step{}, context.Cause(ctx)
+}
+
+func stepAt(node, id, state, reason string, result string) delivery.Step {
+	s := delivery.Step{ID: id, Tool: "build_go_fetch", Node: node, State: state, Reason: reason}
+	if result != "" {
+		s.Result = json.RawMessage(result)
+	}
+	return s
+}
+
+// presenceValue is a watchman presence value, as its writer encodes it (mesh-sdk go/delivery EncodePresence).
+func presenceValue(t *testing.T, online bool) []byte {
+	t.Helper()
+	b, err := delivery.EncodePresence(delivery.Presence{Online: online})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return b
+}
+
+// tcValue is a toolchains value, as the build module's writer encodes it (mesh-sdk go/delivery EncodeToolchain).
+func tcValue(t *testing.T, language, version string) []byte {
+	t.Helper()
+	b, err := delivery.EncodeToolchain(delivery.Toolchain{Language: language, Version: version, Recipe: "1", At: time.Now()})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return b
+}
+
+// tcs are the toolchain entries of a language on nodes, as the toolchains set gives them.
+func tcs(language, version string, nodes ...string) []delivery.NodeToolchain {
+	var out []delivery.NodeToolchain
+	for _, n := range nodes {
+		out = append(out, delivery.NodeToolchain{Node: n, Toolchain: delivery.Toolchain{Language: language, Version: version, Recipe: "1"}})
+	}
+	return out
+}

modules/mesh-delivery-builder/internal/build/fixtures_test.go

@@ -0,0 +1,59 @@
+package build
+
+import (
+	"context"
+	"encoding/json"
+	"os"
+	"strings"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// result reads a captured step value of mesh-build-image (testdata/captured/README) and returns its result.
+func captured(t *testing.T, name string) json.RawMessage {
+	t.Helper()
+	raw, err := os.ReadFile("testdata/captured/" + name)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var step delivery.Step
+	if err := json.Unmarshal(raw, &step); err != nil {
+		t.Fatalf("%s: %v", name, err)
+	}
+	if step.State != delivery.StepPassed || len(step.Result) == 0 {
+		t.Fatalf("%s: state %q, result %s, want a passed step with a result", name, step.State, step.Result)
+	}
+	return step.Result
+}
+
+// The captured image steps, run as a pulled ask runs them (buildstep.RunAsk), answer what the builder reads: the trunk's
+// build its digest and reference, a candidate's its digest and no reference (issue 1887 A4a).
+func TestCapturedImageStepsDecodeWithTheBuildersOwnTypes(t *testing.T) { // review r2, mesh-catalog 2; ADR 0487 clause 1
+	for _, tc := range []struct {
+		build   string
+		publish bool
+		ref     bool
+	}{{"build-trunk.json", true, true}, {"build-candidate.json", false, false}} {
+		steps := buildstep.AskSteps{
+			Fetch: func(context.Context, map[string]any) (any, error) {
+				return json.RawMessage(captured(t, "fetch.json")), nil
+			},
+			Build: func(context.Context, map[string]any) (any, error) { return json.RawMessage(captured(t, tc.build)), nil },
+		}
+		ask := delivery.StepAsk{ID: buildstep.NewID(), Kind: delivery.AskDelivery, Language: delivery.AskImage, Asker: delivery.BuilderModule,
+			At: time.Now(), Build: &delivery.BuildJob{Module: "m", Path: "modules/m", Publish: tc.publish,
+				Fetch:     map[string]any{"repository": "novox/mesh-catalog", "commit": strings.Repeat("a", 40)},
+				Artifacts: []delivery.AskArtifact{{Artifact: "server"}}}}
+		out, err := buildstep.RunAsk(context.Background(), steps, ask)
+		if err != nil {
+			t.Fatalf("%s: %v", tc.build, err)
+		}
+		a := out.(delivery.BuildAnswer)
+		if len(a.Artifacts) != 1 || a.Artifacts[0].Digest == "" || (a.Artifacts[0].Reference != "") != tc.ref {
+			t.Errorf("%s answered %+v, want a digest and a reference only for the trunk", tc.build, a)
+		}
+	}
+}

modules/mesh-delivery-builder/internal/build/followups_test.go

@@ -0,0 +1,46 @@
+package build
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// 1660: at start the builder closes a key left building for a fingerprint the module no longer has.
+func TestAKeyLeftBuildingForAFingerprintTheModuleNoLongerHasIsClosedAtStart(t *testing.T) { // issue 1660
+	r := newRig(t, goBundle)
+	stale := seed(t, r.st, delivery.BuilderBuild{State: delivery.BuildBuilding, By: "ace.builder", Manifest: manifestD}) // m at fp1
+	other, _ := delivery.BuilderBuildKey("gone", fp1)
+	data, _ := delivery.EncodeBuilderBuild(delivery.BuilderBuild{State: delivery.BuildBuilding, By: "ace.builder", Manifest: manifestD})
+	r.st.put(other, data)
+	// The module m has moved on to another fingerprint.
+	moved := delivery.Module{Repository: "novox/mesh-catalog", Commit: "7a74cee83f88e6585a5511c3cc53bdf0f5303d20", FP: "src1:" + hex64('f'),
+		FP2: "src2:" + hex64('7'), Manifest: manifestD, Path: "modules/m", Toolchains: agreedToolchains}
+	enc, _ := delivery.EncodeModule(moved)
+	r.b.Module(context.Background(), "m", enc)
+	r.b.Wait()
+	if err := r.b.Sweep(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	for _, k := range []string{stale, other} {
+		v := valueOf(t, r.st, k)
+		if v.State != delivery.BuildFailed || !strings.Contains(v.Error, "no longer") || !strings.Contains(v.Error, "ace.builder") {
+			t.Errorf("%s = %+v, want it closed as failed, naming why and who left it", k, v)
+		}
+	}
+}
+
+func TestSweepLeavesAKeyOfTheModulesCurrentFingerprintForTheBuildToTakeOver(t *testing.T) { // issue 1660
+	r := newRig(t, goBundle)
+	seed(t, r.st, delivery.BuilderBuild{State: delivery.BuildBuilding, By: "ace.builder", Manifest: manifestD})
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m")) // takes it over and builds it
+	r.b.Wait()
+	if err := r.b.Sweep(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone || v.By != "novox.builder" {
+		t.Errorf("build = %+v, want done by novox.builder", v)
+	}
+}

modules/mesh-delivery-builder/internal/build/manifests.go

@@ -0,0 +1,12 @@
+package build
+
+import (
+	"context"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+)
+
+// Manifests reads a module's manifest by its digest, the key of the indexer's manifests bucket.
+type Manifests interface {
+	Manifest(ctx context.Context, digest string) (catalogue.Manifest, error)
+}

modules/mesh-delivery-builder/internal/build/plan.go

@@ -0,0 +1,118 @@
+// Package build is the builder's logic (novox/hq ADR 0453 clause 4, ADR 0478), apart from the bus: what a manifest asks
+// to be built and where, the claim of a build key, the choice of build nodes, the build modules' long steps and the run of
+// one build. The bus is reached through the small interfaces here, so each part is tested with fakes.
+package build
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+// ImageBuildModule is the build module that builds an image artifact (novox/hq ADR 0487): buildah, rootless, on the nodes that
+// run it. It has no toolchain language; the builder finds its nodes from the node-engine's have.
+const ImageBuildModule = "mesh-build-image"
+
+// NoImageBuilderPrefix opens the error of a build key failed because no node runs ImageBuildModule (ADR 0487 clause 5): such a
+// key is not built again as a new revision, only when a node reports the module (ClaimOptions.ImageBuilder) or the fingerprint
+// changes.
+const NoImageBuilderPrefix = "no image builder:"
+
+// Task is one artifact to build: its name and kind in the manifest, the build module that builds it and the language
+// of the toolchain it is built with.
+type Task struct {
+	Artifact string
+	Kind     string
+	Module   string
+	Language string
+	// From is, for an upstream artifact, the reference its manifest pins, which the image build module copies (ADR 0498
+	// clause 4).
+	From string
+}
+
+// Plan is what a manifest asks the builder to build, by artifact name.
+type Plan struct{ Tasks []Task }
+
+// Modules are the build modules the plan calls, sorted.
+func (p Plan) Modules() []string {
+	seen := map[string]bool{}
+	var out []string
+	for _, t := range p.Tasks {
+		if !seen[t.Module] {
+			seen[t.Module] = true
+			out = append(out, t.Module)
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+// NeedsToolchain is whether any task the build module builds is built with a toolchain: a bundle is, an archive is not
+// (the indexer gives an archive no language, so a fingerprint names no toolchain for it; ADR 0478 clause 1).
+func (p Plan) NeedsToolchain(module string) bool {
+	for _, t := range p.Tasks {
+		if t.Module == module && t.Kind != catalogue.ArtifactArchive && t.Kind != catalogue.ArtifactImage && t.Kind != catalogue.ArtifactUpstream {
+			return true
+		}
+	}
+	return false
+}
+
+// Refused is the error of a plan the builder does not build: an artifact of a kind (or of a language) no build module
+// builds. It opens delivery.RefusedKind, so its key is not built again until the fingerprint changes.
+type Refused struct{ Artifact, What string }
+
+func (r *Refused) Error() string {
+	return fmt.Sprintf("%s%s (artifact %s): no build module builds it; the builder builds Go and TypeScript bundles, archives, images, upstream copies and TypeScript packages", delivery.RefusedKind, r.What, r.Artifact)
+}
+
+// NotPinned is the error of a plan with an upstream artifact whose reference names no digest (ADR 0498 clause 4): it opens
+// delivery.NotPinned, so its key is not built again until the fingerprint changes.
+type NotPinned struct{ Artifact, From string }
+
+func (n *NotPinned) Error() string {
+	return fmt.Sprintf("%s%s: %q names no digest (@sha256:), so what would be copied is whatever its tag means today", delivery.NotPinned, n.Artifact, n.From)
+}
+
+// PlanOf is the plan of a manifest (ADR 0478 clauses 1 and 2, ADR 0498 clauses 4 and 5): a Go bundle and an archive are
+// built by the Go build module, an image by the image build module (ADR 0487), which also copies an upstream image pinned
+// by its digest, and a TypeScript bundle or package by the Node one, each in the order of the artifacts' names. A manifest
+// with an upstream artifact pinned by no digest, or a bundle or a package of another language, or a kind no build module
+// builds, is refused as a whole, naming the first such artifact by name. A manifest with no artifact has an empty plan.
+func PlanOf(m catalogue.Manifest) (Plan, error) {
+	if m.Build == nil {
+		return Plan{}, nil
+	}
+	artifacts := append([]catalogue.Artifact(nil), m.Build.Artifacts...)
+	sort.Slice(artifacts, func(i, j int) bool { return artifacts[i].Name < artifacts[j].Name })
+	var p Plan
+	for _, a := range artifacts {
+		switch {
+		case a.Kind == catalogue.ArtifactArchive:
+			p.Tasks = append(p.Tasks, Task{Artifact: a.Name, Kind: a.Kind, Module: buildrun.GoBuildModule, Language: "go"})
+		case a.Kind == catalogue.ArtifactBundle && a.Language == "go":
+			p.Tasks = append(p.Tasks, Task{Artifact: a.Name, Kind: a.Kind, Module: buildrun.GoBuildModule, Language: "go"})
+		case a.Kind == catalogue.ArtifactBundle && a.Language == "typescript":
+			p.Tasks = append(p.Tasks, Task{Artifact: a.Name, Kind: a.Kind, Module: buildrun.NodeBuildModule, Language: "typescript"})
+		case a.Kind == catalogue.ArtifactImage:
+			p.Tasks = append(p.Tasks, Task{Artifact: a.Name, Kind: a.Kind, Module: ImageBuildModule})
+		case a.Kind == catalogue.ArtifactUpstream && !strings.Contains(a.From, "@sha256:"):
+			return Plan{}, &NotPinned{Artifact: a.Name, From: a.From}
+		case a.Kind == catalogue.ArtifactUpstream:
+			p.Tasks = append(p.Tasks, Task{Artifact: a.Name, Kind: a.Kind, Module: ImageBuildModule, From: a.From})
+		case a.Kind == catalogue.ArtifactPackage && a.Language == "typescript":
+			p.Tasks = append(p.Tasks, Task{Artifact: a.Name, Kind: a.Kind, Module: buildrun.NodeBuildModule, Language: "typescript"})
+		case a.Kind == catalogue.ArtifactBundle:
+			return Plan{}, &Refused{Artifact: a.Name, What: fmt.Sprintf("bundle of language %q", a.Language)}
+		case a.Kind == catalogue.ArtifactPackage:
+			return Plan{}, &Refused{Artifact: a.Name, What: fmt.Sprintf("package of language %q", a.Language)}
+		default:
+			return Plan{}, &Refused{Artifact: a.Name, What: a.Kind}
+		}
+	}
+	return p, nil
+}

modules/mesh-delivery-builder/internal/build/plan_test.go

@@ -0,0 +1,96 @@
+package build
+
+import (
+	"errors"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+)
+
+// manifestOf is a manifest holding these artifacts: the plan reads only their name, kind and language.
+func manifestOf(artifacts ...catalogue.Artifact) catalogue.Manifest {
+	return catalogue.Manifest{Module: "m", Build: &catalogue.Build{Artifacts: artifacts}}
+}
+
+func TestPlanRoutesEachKindToItsBuildModule(t *testing.T) { // 1607/AC2
+	m := manifestOf(
+		catalogue.Artifact{Name: "tool", Kind: "bundle", Language: "go"},
+		catalogue.Artifact{Name: "web", Kind: "bundle", Language: "typescript"},
+		catalogue.Artifact{Name: "files", Kind: "archive"})
+	p, err := PlanOf(m)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []Task{
+		{Artifact: "files", Kind: "archive", Module: buildrun.GoBuildModule, Language: "go"},
+		{Artifact: "tool", Kind: "bundle", Module: buildrun.GoBuildModule, Language: "go"},
+		{Artifact: "web", Kind: "bundle", Module: buildrun.NodeBuildModule, Language: "typescript"},
+	}
+	if len(p.Tasks) != len(want) {
+		t.Fatalf("tasks = %+v, want %+v", p.Tasks, want)
+	}
+	for i := range want {
+		if p.Tasks[i] != want[i] {
+			t.Errorf("task %d = %+v, want %+v", i, p.Tasks[i], want[i])
+		}
+	}
+	if modules := p.Modules(); len(modules) != 2 || modules[0] != buildrun.GoBuildModule || modules[1] != buildrun.NodeBuildModule {
+		t.Errorf("modules = %v", modules)
+	}
+}
+
+const pinned = "nats:2.11.17-alpine@sha256:3333333333333333333333333333333333333333333333333333333333333333"
+
+func TestPlanSendsAPinnedUpstreamToTheImageBuildModulesCopyAndRefusesAnUnpinnedOne(t *testing.T) { // B3, ADR 0498 clause 4
+	p, err := PlanOf(manifestOf(catalogue.Artifact{Name: "ok", Kind: "archive"}, catalogue.Artifact{Name: "up", Kind: "upstream", From: pinned}))
+	if err != nil || len(p.Tasks) != 2 {
+		t.Fatalf("plan %+v, error %v", p, err)
+	}
+	if up := p.Tasks[1]; up.Artifact != "up" || up.Kind != "upstream" || up.Module != ImageBuildModule || up.From != pinned || up.Language != "" {
+		t.Errorf("task = %+v, want the upstream sent to %s with its pinned reference and no toolchain", up, ImageBuildModule)
+	}
+	if p.NeedsToolchain(ImageBuildModule) {
+		t.Error("a copy needs no toolchain")
+	}
+	_, err = PlanOf(manifestOf(catalogue.Artifact{Name: "up", Kind: "upstream", From: "nats:2.11.17-alpine"}))
+	if err == nil || !strings.HasPrefix(err.Error(), delivery.NotPinned+"up") || !delivery.FailedUntilChanged(err.Error()) {
+		t.Errorf("an upstream with no digest: error = %v, want it to open %q naming the artifact", err, delivery.NotPinned)
+	}
+}
+
+func TestPlanRefusesAPackageOfAnotherLanguageByName(t *testing.T) { // ADR 0498 clause 5
+	_, err := PlanOf(manifestOf(catalogue.Artifact{Name: "ok", Kind: "archive"}, catalogue.Artifact{Name: "pkg", Kind: "package", Language: "python"}))
+	var r *Refused
+	if err == nil || !asRefused(err, &r) || !strings.HasPrefix(err.Error(), delivery.RefusedKind) || !strings.Contains(err.Error(), "python") || !strings.Contains(err.Error(), "pkg") {
+		t.Errorf("error = %v, want it to open %q naming the artifact and its language", err, delivery.RefusedKind)
+	}
+}
+
+func TestPlanRefusesABundleOfAnotherLanguageAndAModuleWithNoArtifact(t *testing.T) {
+	if _, err := PlanOf(manifestOf(catalogue.Artifact{Name: "x", Kind: "bundle", Language: "python"})); err == nil || !strings.HasPrefix(err.Error(), delivery.RefusedKind) {
+		t.Errorf("a python bundle: error = %v, want a refusal", err)
+	}
+	p, err := PlanOf(manifestOf())
+	if err != nil || len(p.Tasks) != 0 {
+		t.Errorf("no artifact: plan %+v error %v, want an empty plan", p, err)
+	}
+}
+
+func asRefused(err error, target **Refused) bool { return errors.As(err, target) }
+
+func TestPlanSendsAnImageToMeshBuildImageWithNoToolchain(t *testing.T) { // 1705a, ADR 0487 clause 5
+	p, err := PlanOf(manifestOf(catalogue.Artifact{Name: "img", Kind: "image"}, catalogue.Artifact{Name: "files", Kind: "archive"}))
+	if err != nil || len(p.Tasks) != 2 {
+		t.Fatalf("plan %+v, error %v", p, err)
+	}
+	if p.Tasks[1].Artifact != "img" || p.Tasks[1].Module != ImageBuildModule {
+		t.Errorf("task = %+v, want the image on %s", p.Tasks[1], ImageBuildModule)
+	}
+	if p.NeedsToolchain(ImageBuildModule) {
+		t.Error("an image needs no toolchain")
+	}
+}

modules/mesh-delivery-builder/internal/build/r4e_test.go

@@ -0,0 +1,403 @@
+package build
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// R4e: references in the key (novox/hq ADR 0498), upstream copies, packages published from the trunk, the package wait
+// (ADR 0500 clause 6) and one node per fingerprint (ADR 0478 clause 4).
+
+func TestACandidatesBundleKeyNamesItsReferenceAndTheTrunkBuildsItNoMore(t *testing.T) { // B1, ADR 0498 clause 3 and its check 3
+	r := newRig(t, goBundle, archiveA)
+	trunkModule(t, r)
+	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	r.b.Wait()
+	v := valueOf(t, r.st, r.key)
+	if v.State != delivery.BuildDone {
+		t.Fatalf("build = %+v, want done", v)
+	}
+	if ok, missing := v.Referenced(); !ok {
+		t.Fatalf("a candidate's bundle and archive name no reference: %v (%+v)", missing, v.Artifacts)
+	}
+	rev := r.st.revs[r.key]
+	r.bm.mu.Lock()
+	r.bm.calls = nil
+	r.bm.mu.Unlock()
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m")) // the merge: the trunk now names the same fingerprint
+	r.b.Wait()
+	if n := len(r.bm.calls); n != 0 || r.st.revs[r.key] != rev {
+		t.Errorf("the trunk built its candidate's fingerprint again: %d calls, revision %d (was %d)", n, r.st.revs[r.key], rev)
+	}
+}
+
+func TestABundleWhosePushAnsweredNoReferenceFailsNotStoredAndIsBuiltAgain(t *testing.T) { // B1, ADR 0498 clauses 1 and 2
+	r := newRig(t, goBundle)
+	r.bm.noRef["ace/tool"] = true
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildFailed || !strings.HasPrefix(v.Error, delivery.NotStored) || !strings.Contains(v.Error, "tool") {
+		t.Fatalf("build = %+v, want failed opening %q and naming the artifact", v, delivery.NotStored)
+	}
+	delete(r.bm.noRef, "ace/tool")
+	if v = r.consider(t, "modules/m"); v.State != delivery.BuildDone {
+		t.Errorf("build = %+v, want a not-stored key built again as a new revision", v)
+	}
+}
+
+func TestAPushRefusedByTheStoreFailsTheKeyOpeningNotStored(t *testing.T) { // B1, ADR 0498 clause 2
+	r := newRig(t, goBundle)
+	r.bm.fails["ace/build_go_build"] = delivery.NotStored + "tool: the artifact store answered 507 insufficient storage"
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildFailed || !strings.HasPrefix(v.Error, delivery.NotStored) || !strings.Contains(v.Error, "507") || !strings.Contains(v.Error, "ace") {
+		t.Fatalf("build = %+v, want failed opening %q with the store's words and the node", v, delivery.NotStored)
+	}
+}
+
+func TestOnlyATrunkKeysBuildsAreAskedToPublish(t *testing.T) { // B1, the lead's interface (a): publish only for a trunk key
+	r := newRig(t, goBundle)
+	r.consider(t, "modules/m")
+	for _, c := range r.bm.callsOf("build_go_build") {
+		if c.body.(map[string]any)["publish"] != true {
+			t.Errorf("trunk build args = %+v, want publish", c.body)
+		}
+	}
+	c := newRig(t, goBundle)
+	trunkModule(t, c)
+	c.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	c.b.Wait()
+	for _, call := range c.bm.callsOf("build_go_build") {
+		if _, ok := call.body.(map[string]any)["publish"]; ok {
+			t.Errorf("candidate build args = %+v, want no publish", call.body)
+		}
+	}
+}
+
+// putBuild writes a builder key's value as the store would hold it.
+func putBuild(t *testing.T, st *memStore, key string, b delivery.BuilderBuild) uint64 {
+	t.Helper()
+	data, err := delivery.EncodeBuilderBuild(b)
+	if err != nil {
+		t.Fatal(err)
+	}
+	st.mu.Lock()
+	defer st.mu.Unlock()
+	return st.put(key, data)
+}
+
+func TestADoneKeyWrittenBeforeR4eIsBuiltAgainOnceAsANewRevision(t *testing.T) { // B2, ADR 0498 clause 8
+	r := newRig(t, goBundle, archiveA)
+	rev := putBuild(t, r.st, r.key, delivery.BuilderBuild{State: delivery.BuildDone, By: "novox.builder", Manifest: manifestD, Step: "built mesh-build-go on ace and novox",
+		Artifacts: []delivery.BuiltArtifact{{Name: "files", Kind: "archive", Digest: digest}, {Name: "tool", Kind: "bundle", Digest: digest}}})
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || r.st.revs[r.key] <= rev {
+		t.Fatalf("build = %+v at revision %d (was %d), want built again as a new revision", v, r.st.revs[r.key], rev)
+	}
+	if ok, missing := v.Referenced(); !ok {
+		t.Fatalf("the new revision names no reference for %v", missing)
+	}
+	rev = r.st.revs[r.key]
+	r.b.tried = map[string]bool{} // a builder started anew looks again
+	r.consider(t, "modules/m")
+	if r.st.revs[r.key] != rev {
+		t.Errorf("a key whose artifacts all name references was built again (revision %d, was %d): once only", r.st.revs[r.key], rev)
+	}
+}
+
+func TestAPinnedUpstreamIsCopiedOnceOnOneImageNodeWithNoFetchAndItsKeyNamesTheReference(t *testing.T) { // B4, ADR 0498 clause 4
+	up := catalogue.Artifact{Name: "up", Kind: "upstream", From: "nats:2.11.17-alpine@" + digest}
+	r := newRig(t, up)
+	r.puller = "ace"
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || len(v.Artifacts) != 1 {
+		t.Fatalf("build = %+v, want done with the copy", v)
+	}
+	if a := v.Artifacts[0]; a.Kind != "upstream" || a.Digest != digest || a.Reference != "registry.example/m/up@"+digest {
+		t.Errorf("artifact = %+v, want the upstream's digest and the registry's reference", a)
+	}
+	copies := r.bm.callsOf("build_image_copy")
+	if len(copies) != 1 {
+		t.Fatalf("%d copies, want one on one node", len(copies))
+	}
+	if args := copies[0].body.(map[string]any); args["module"] != "m" || args["artifact"] != "up" || args["from"] != up.From || len(args) != 3 {
+		t.Errorf("copy args = %+v, want the module's name, the artifact and the pinned reference", args)
+	}
+	if n := len(r.bm.callsOf("build_image_fetch")) + len(r.bm.callsOf("build_image_build")); n != 0 {
+		t.Errorf("%d fetch or build calls for a copy, want none", n)
+	}
+}
+
+func TestAnUpstreamBesideAnImageIsCopiedAndTheImageFetchedAndBuiltOnTheSameNode(t *testing.T) { // B4
+	r := newRig(t, imageArt, catalogue.Artifact{Name: "up", Kind: "upstream", From: "nats:2.11.17-alpine@" + digest})
+	r.puller = "ace"
+	v := r.consider(t, "modules/m")
+	if ok, missing := v.Referenced(); !ok {
+		t.Fatalf("build = %+v, missing references %v", v, missing)
+	}
+	if f, b, c := len(r.bm.callsOf("build_image_fetch")), len(r.bm.callsOf("build_image_build")), len(r.bm.callsOf("build_image_copy")); f != 1 || b != 1 || c != 1 {
+		t.Errorf("fetch %d, build %d, copy %d; want one each", f, b, c)
+	}
+}
+
+func TestACopyThatFailsNotStoredFailsTheKeyAndIsBuiltAgain(t *testing.T) { // B4, ADR 0498 clause 2
+	r := newRig(t, catalogue.Artifact{Name: "up", Kind: "upstream", From: "nats:2.11.17-alpine@" + digest})
+	r.puller = "ace"
+	r.bm.fails["ace/build_image_copy"] = delivery.NotStored + "up: the registry answered 500"
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildFailed || !strings.HasPrefix(v.Error, delivery.NotStored) || delivery.FailedUntilChanged(v.Error) {
+		t.Fatalf("build = %+v, want failed 'not stored:' and built again", v)
+	}
+	delete(r.bm.fails, "ace/build_image_copy")
+	if v = r.consider(t, "modules/m"); v.State != delivery.BuildDone {
+		t.Errorf("build = %+v, want done on the new revision", v)
+	}
+}
+
+var tsPackage = catalogue.Artifact{Name: "lib", Kind: "package", Language: "typescript"}
+
+func TestATypeScriptPackageIsBuiltByTheNodeModuleAndPublishedOnlyForTheTrunk(t *testing.T) { // B5, ADR 0498 clause 5, ADR 0500 clause 4
+	c := newRig(t, tsPackage)
+	c.bm.packages["lib"] = "@novox/mesh-sdk@0.1.15"
+	trunkModule(t, c)
+	c.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	c.b.Wait()
+	v := valueOf(t, c.st, c.key)
+	if v.State != delivery.BuildDone || len(v.Artifacts) != 1 || v.Artifacts[0].Kind != "package" || v.Artifacts[0].Reference != "" {
+		t.Fatalf("candidate build = %+v, want done with the packed digest and no reference", v)
+	}
+	for _, call := range c.bm.callsOf("build_node_build") {
+		if _, ok := call.body.(map[string]any)["publish"]; ok {
+			t.Errorf("a candidate's package build was asked to publish: %+v", call.body)
+		}
+	}
+
+	r := newRig(t, tsPackage)
+	r.bm.packages["lib"] = "@novox/mesh-sdk@0.1.15"
+	v = r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || v.Artifacts[0].Reference != "@novox/mesh-sdk@0.1.15" {
+		t.Fatalf("trunk build = %+v, want done naming the published version", v)
+	}
+	if n := len(r.bm.callsOf("build_node_build")); n == 0 {
+		t.Error("the package was not built by the Node build module")
+	}
+}
+
+func TestAVersionTakenFailsTheKeyUntilTheFingerprintChanges(t *testing.T) { // B5, ADR 0498 clause 5
+	r := newRig(t, tsPackage)
+	r.bm.packages["lib"] = "@novox/mesh-sdk@0.1.15"
+	r.bm.fails["ace/build_node_build"] = delivery.VersionTaken + "@novox/mesh-sdk@0.1.15 is published with another packed file"
+	r.bm.fails["novox/build_node_build"] = r.bm.fails["ace/build_node_build"]
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildFailed || !strings.HasPrefix(v.Error, delivery.VersionTaken) || !strings.Contains(v.Error, "0.1.15") {
+		t.Fatalf("build = %+v, want failed opening %q naming the version", v, delivery.VersionTaken)
+	}
+	writes := r.st.writes
+	r.consider(t, "modules/m")
+	if r.st.writes != writes {
+		t.Errorf("a version-taken key was built again (%d writes, was %d)", r.st.writes, writes)
+	}
+}
+
+func TestACandidatesPackageIsPublishedOnceWhenTheTrunkNamesItsFingerprint(t *testing.T) { // B6, ADR 0498 clause 6
+	r := newRig(t, tsPackage, tsBundle)
+	r.bm.packages["lib"] = "@novox/mesh-sdk@0.1.15"
+	trunkModule(t, r)
+	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone {
+		t.Fatalf("candidate build = %+v", v)
+	}
+	rev := r.st.revs[r.key]
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m")) // the merge names the candidate's fingerprint
+	r.b.Wait()
+	v := valueOf(t, r.st, r.key)
+	if r.st.revs[r.key] <= rev {
+		t.Fatalf("the trunk did not build the unpublished package again (revision %d, was %d)", r.st.revs[r.key], rev)
+	}
+	if ok, missing := v.Referenced(); !ok {
+		t.Fatalf("build = %+v, missing references %v", v, missing)
+	}
+	rev = r.st.revs[r.key]
+	r.b.tried = map[string]bool{}
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	r.b.Wait()
+	if r.st.revs[r.key] != rev {
+		t.Error("a published package was built again: once only")
+	}
+}
+
+func TestAPublishThatFailsVersionTakenOnTheTrunkKeepsThePrefixFirst(t *testing.T) { // B6, ADR 0498 clauses 5 and 6
+	r := newRig(t, tsPackage)
+	r.bm.packages["lib"] = "@novox/mesh-sdk@0.1.15"
+	trunkModule(t, r)
+	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	r.b.Wait()
+	for _, n := range []string{"ace", "novox"} {
+		r.bm.fails[n+"/build_node_build"] = delivery.VersionTaken + "@novox/mesh-sdk@0.1.15 is published with another packed file"
+	}
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildFailed || !strings.HasPrefix(v.Error, delivery.VersionTaken) {
+		t.Errorf("build = %+v, want failed opening %q", v, delivery.VersionTaken)
+	}
+}
+
+// sdkModule adds to the rig a module "sdk" whose manifest (digest b) holds the TypeScript package lib, published as ref.
+func sdkModule(t *testing.T, r *rig, ref string) []byte {
+	t.Helper()
+	r.mf.byDigest[mdigest('b')] = catalogue.Manifest{Module: "sdk", Build: &catalogue.Build{Artifacts: []catalogue.Artifact{tsPackage}}}
+	r.bm.packages["lib"] = ref
+	data, err := delivery.EncodeModule(delivery.Module{Repository: "novox/mesh-sdk", Commit: "8a74cee83f88e6585a5511c3cc53bdf0f5303d20", FP2: "src2:" + hex64('5'),
+		Manifest: mdigest('b'), Path: ".", Toolchains: agreedToolchains})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return data
+}
+
+func TestAModuleWhoseLockNamesAnUnpublishedPackageWaitsQueuedAndIsBuiltOncePublished(t *testing.T) { // B7, ADR 0500 clause 6
+	const ref = "@novox/mesh-sdk@0.1.15"
+	r := newRig(t, tsBundle)
+	for _, n := range []string{"ace", "novox"} {
+		r.bm.fails[n+"/build_node_fetch"] = waitsFor + ref + ": the lock names a version the registry does not hold"
+	}
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildQueued || v.Waits != ref || v.Error != "" {
+		t.Fatalf("build = %+v, want queued, waiting for %s, not failed", v, ref)
+	}
+	delete(r.bm.fails, "ace/build_node_fetch")
+	delete(r.bm.fails, "novox/build_node_fetch")
+	writes := r.st.writes
+	r.b.tried = map[string]bool{}
+	r.consider(t, "modules/m")
+	if r.st.writes != writes {
+		t.Fatalf("a key waiting for an unpublished package was claimed (%d writes, was %d)", r.st.writes, writes)
+	}
+	r.b.Module(context.Background(), "sdk", sdkModule(t, r, ref)) // the package's trunk key is built and published
+	r.b.Wait()
+	if v = valueOf(t, r.st, r.key); v.State != delivery.BuildDone || v.Waits != "" {
+		t.Errorf("build = %+v, want built once the package it waits for is published", v)
+	}
+}
+
+func TestAKeyWaitingForAPackageAlreadyPublishedIsBuiltWhenTheBuilderStarts(t *testing.T) { // B7: the scan at start
+	const ref = "@novox/mesh-sdk@0.1.15"
+	r := newRig(t, tsBundle)
+	putBuild(t, r.st, r.key, delivery.BuilderBuild{State: delivery.BuildQueued, By: "novox.builder", Manifest: manifestD, Waits: ref, Step: "waits"})
+	sdkKey, _ := delivery.BuilderBuildKey("sdk", "src2:"+hex64('5'))
+	putBuild(t, r.st, sdkKey, delivery.BuilderBuild{State: delivery.BuildDone, By: "novox.builder", Manifest: mdigest('b'), Step: "built",
+		Artifacts: []delivery.BuiltArtifact{{Name: "lib", Kind: "package", Digest: digest, Reference: ref}}})
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	if err := r.b.Sweep(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone {
+		t.Errorf("build = %+v, want built: the package it waits for was published before the builder started", v)
+	}
+}
+
+func TestTheFetchOfAModuleNamingItsPathsCarriesItsDirectoryAndThosePaths(t *testing.T) { // the lead's interface (c), ADR 0499 clause 4
+	r := newRig(t, tsPackage)
+	r.bm.packages["lib"] = "@novox/mesh-sdk@0.1.15"
+	paths := map[string]string{"src": hex40('1'), "package.json": hex40('2')}
+	tree, err := delivery.NamedTree(manifestD, paths)
+	if err != nil {
+		t.Fatal(err)
+	}
+	data, err := delivery.EncodeModule(delivery.Module{Repository: "novox/mesh-sdk", Commit: "7a74cee83f88e6585a5511c3cc53bdf0f5303d20", FP2: fp1, Manifest: manifestD, Path: ".",
+		Toolchains: agreedToolchains, Inputs2: &delivery.KeptInputs2{Tree: tree, Paths: paths}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.b.Module(context.Background(), "m", data)
+	r.b.Wait()
+	f := r.bm.callsOf("build_node_fetch")
+	if len(f) == 0 {
+		t.Fatal("no fetch")
+	}
+	req, err := buildstep.ParseFetchRequest(f[0].body.(map[string]any))
+	if err != nil || req.Dir != "." || strings.Join(req.Paths, ",") != "package.json,src" || req.Commit != "7a74cee83f88e6585a5511c3cc53bdf0f5303d20" {
+		t.Errorf("fetch request = %+v, %v; want dir . and the kept paths, sorted", req, err)
+	}
+	r2 := newRig(t, goBundle)
+	r2.consider(t, "modules/m")
+	if a := r2.bm.callsOf("build_go_fetch")[0].body.(map[string]any); a["dir"] != nil || a["paths"] != nil {
+		t.Errorf("fetch args = %+v, want no dir or paths for a module naming none", a)
+	}
+}
+
+func hex40(c byte) string { return strings.Repeat(string(c), 40) }
+
+func TestOneNodeBuildsEachFingerprint(t *testing.T) { // B9, ADR 0478 clause 4: "From R4e one node builds each fingerprint"
+	r := newRig(t, goBundle, archiveA, tsBundle) // ace and novox both qualify for both build modules
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || strings.Contains(v.Step, " and ") || strings.HasPrefix(v.Step, "one node (") {
+		t.Fatalf("build = %+v, want done on one node of each build module, unmarked", v)
+	}
+	if f, b := len(r.bm.callsOf("build_go_fetch")), len(r.bm.callsOf("build_go_build")); f != 1 || b != 2 {
+		t.Errorf("go fetches %d, builds %d; want one fetch and one build of each artifact, on one node", f, b)
+	}
+	if f := len(r.bm.callsOf("build_node_fetch")); f != 1 {
+		t.Errorf("node fetches %d, want one", f)
+	}
+}
+
+func TestAKeyDoneOnOneNodeIsNeverBuiltAgainForASecondNode(t *testing.T) { // B9: the second-node retake is gone
+	r := newRig(t, goBundle)
+	putBuild(t, r.st, r.key, delivery.BuilderBuild{State: delivery.BuildDone, By: "novox.builder", Manifest: manifestD,
+		Step:      "one node (mesh-build-go): built mesh-build-go on one node, novox",
+		Artifacts: []delivery.BuiltArtifact{{Name: "tool", Kind: "bundle", Digest: digest, Reference: "artifact-store://m/tool/blobs/" + digest}}})
+	writes := r.st.writes
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	r.b.NodesChanged(context.Background())
+	r.b.Wait()
+	if r.st.writes != writes || len(r.bm.calls) != 0 {
+		t.Errorf("a key done on one node was built again (%d writes, was %d; %d calls)", r.st.writes, writes, len(r.bm.calls))
+	}
+}
+
+func TestACandidatesFetchNamesTheNamedPathsTheIndexerGaveIt(t *testing.T) { // ADR 0499 clause 4, mesh-sdk CandidateModule.Paths
+	r := newRig(t, tsPackage)
+	r.bm.packages["lib"] = "@novox/mesh-sdk@0.1.15"
+	trunkModule(t, r)
+	pulls := []delivery.CandidatePull{{Head: delivery.Head{Repository: "novox/mesh-catalog", Number: 7, Head: headX}, Modules: []string{"m"},
+		Fps: map[string]delivery.CandidateModule{"m": {FP2: fp1, Manifest: mdigest('a'), Paths: map[string]string{"src": hex40('1'), "package.json": hex40('2')}}}}}
+	hash, _ := delivery.HeadsHash([]delivery.Head{pulls[0].Head})
+	data, err := delivery.EncodeCandidate(delivery.Candidate{V: delivery.Version, Group: "feat/x", HeadsHash: hash, Pulls: pulls, FPSet: delivery.FingerprintSet(pulls)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.b.Candidate(context.Background(), "feat%2Fx", data)
+	r.b.Wait()
+	f := r.bm.callsOf("build_node_fetch")
+	if len(f) == 0 {
+		t.Fatal("no fetch")
+	}
+	req, err := buildstep.ParseFetchRequest(f[0].body.(map[string]any))
+	if err != nil || req.Dir != "modules/m" || strings.Join(req.Paths, ",") != "package.json,src" || req.Base == "" {
+		t.Errorf("fetch request = %+v, %v; want the candidate's base, the module's directory and its named paths", req, err)
+	}
+}
+
+// 1886/AC5: the builder tells who answered a reference: the build module whose step named one, and none for a step that
+// answered a digest alone (a build module from before R4e).
+func TestTheBuilderTellsWhichBuildModuleAnsweredAReference(t *testing.T) {
+	r := newRig(t, goBundle)
+	var answered []string
+	r.b.Answered = func(module string) { answered = append(answered, module) }
+	r.bm.noRef["ace/tool"] = true
+	r.consider(t, "modules/m")
+	if len(answered) != 0 {
+		t.Fatalf("a step that answered no reference was told as one: %v", answered)
+	}
+	delete(r.bm.noRef, "ace/tool")
+	r.consider(t, "modules/m")
+	if len(answered) != 1 || answered[0] != "mesh-build-go" {
+		t.Fatalf("the build module that answered a reference: %v, want mesh-build-go", answered)
+	}
+}

modules/mesh-delivery-builder/internal/build/round4_test.go

@@ -0,0 +1,84 @@
+package build
+
+import (
+	"context"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+func haveValue(t *testing.T, phase delivery.Phase, health delivery.Health) []byte {
+	t.Helper()
+	b, err := delivery.EncodeHave(delivery.Have{Phase: phase, Health: health})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return b
+}
+
+// 1. A module of an archive only: the real indexer gives an archive no language (inputs.go languagesOf), so its
+// fingerprint names no toolchain, and the builder builds it on the build module's nodes with no toolchain agreed.
+func TestAnArchiveOnlyModuleIsBuiltAlthoughItsFingerprintNamesNoToolchain(t *testing.T) { // review round 4, 1
+	r := newRig(t, archiveA)
+	v := func() delivery.BuilderBuild {
+		r.b.Module(context.Background(), "m", moduleValueWith(t, "modules/m", nil))
+		r.b.Wait()
+		if _, ok := r.st.vals[r.key]; !ok {
+			t.Fatal("no build key was written for the archive-only module")
+		}
+		return valueOf(t, r.st, r.key)
+	}()
+	if v.State != delivery.BuildDone || len(v.Artifacts) != 1 || v.Artifacts[0].Kind != "archive" || len(v.Toolchains) != 0 {
+		t.Fatalf("build = %+v, want done with the archive and no toolchain named", v)
+	}
+	if n := len(r.bm.callsOf("build_go_build")); n != 1 {
+		t.Errorf("%d go builds, want one, on one node (ADR 0478 clause 4)", n)
+	}
+}
+
+func TestABundleAndAnArchiveOfOneBuildModuleStillNeedTheAgreedToolchain(t *testing.T) { // review round 4, 1
+	p, err := PlanOf(catalogue.Manifest{Module: "m", Build: &catalogue.Build{Artifacts: []catalogue.Artifact{goBundle, archiveA}}})
+	if err != nil || !p.NeedsToolchain(buildrun.GoBuildModule) {
+		t.Errorf("a plan with a Go bundle: %v, %v", p.NeedsToolchain(buildrun.GoBuildModule), err)
+	}
+	p, _ = PlanOf(catalogue.Manifest{Module: "m", Build: &catalogue.Build{Artifacts: []catalogue.Artifact{archiveA}}})
+	if p.NeedsToolchain(buildrun.GoBuildModule) {
+		t.Error("a plan of an archive needs a toolchain")
+	}
+}
+
+func TestClaimLeavesAKeyFailedForDifferingDigestsAlone(t *testing.T) { // review round 4, 2
+	st := newMem()
+	seed(t, st, delivery.BuilderBuild{State: delivery.BuildFailed, Error: buildrun.DigestsDifferPrefix + " the nodes built tool to different digests: ace x; novox y"})
+	writes := st.writes
+	got, err := (Claimer{Store: st, By: "novox.a"}).Claim(context.Background(), "m", fp1, "", ClaimOptions{TakeOver: true})
+	if err != nil || got != nil || st.writes != writes {
+		t.Errorf("claim = %v, %v, %d writes (was %d), want none and no write", got, err, st.writes, writes)
+	}
+}
+
+// 6. A key found building is taken over, whoever holds it.
+func TestABuildLeftBuildingByAnyBuilderIsTakenOverAtStart(t *testing.T) { // review round 4, 6; 1607/AC3, ADR 0478 clauses 5, 6
+	st := newMem()
+	seed(t, st, delivery.BuilderBuild{State: delivery.BuildBuilding, By: "novox.a"})
+	if got, err := (Claimer{Store: st, By: "novox.a"}).Claim(context.Background(), "m", fp1, "", ClaimOptions{}); err != nil || got == nil {
+		t.Errorf("own building key: claim = %v, %v, want it taken again", got, err)
+	}
+	if got, err := (Claimer{Store: st, By: "ace.b"}).Claim(context.Background(), "m", fp1, "", ClaimOptions{TakeOver: true}); err != nil || got == nil || got.Build.By != "novox.a" {
+		t.Errorf("another node's building key at start: claim = %v, %v, want it taken over", got, err)
+	}
+	if got, _ := (Claimer{Store: st, By: "ace.b"}).Claim(context.Background(), "m", fp1, "", ClaimOptions{}); got != nil {
+		t.Errorf("another builder's building key after the start was taken: a running builder's key is its own")
+	}
+}
+
+func TestABuilderFindingAKeyBuildingByAnotherNodeBuildsItOnStart(t *testing.T) { // review round 4, 6
+	r := newRig(t, goBundle)
+	seed(t, r.st, delivery.BuilderBuild{State: delivery.BuildBuilding, By: "ace.builder", Manifest: manifestD})
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || v.By != "novox.builder" {
+		t.Errorf("build = %+v, want it taken over and done by novox.builder", v)
+	}
+}

modules/mesh-delivery-builder/internal/build/run.go

@@ -0,0 +1,746 @@
+package build
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"maps"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+// ToolchainEntries are the nodes' toolchain entries of a language (buildrun.ToolchainSet).
+type ToolchainEntries interface {
+	Entries(language string) []delivery.NodeToolchain
+}
+
+// Builder builds, dark, every new-form fingerprint the indexer writes (novox/hq ADR 0453 clause 4, ADR 0478): it is
+// handed each modules value as the watch of the indexer's bucket sees it, and for each module with a fingerprint and an
+// artifact to build claims the fingerprint's build key, builds it by asking the build seats (one ask per build module,
+// pulled by whichever build node has a free slot: ADR 0525), and writes the key done or failed. It holds no timer; a build starts from a modules value or a
+// change of the toolchains.
+type Builder struct {
+	Claimer Claimer
+	// Asks puts each build module's part of a build as one ask on its build seat's stream and waits for its step (novox/hq
+	// ADR 0525 §1, §3, §6; issue 1887 A4): the builder chooses no node, whichever build node pulls the ask builds it.
+	Asks interface {
+		Put(ctx context.Context, a delivery.StepAsk) error
+		Wait(ctx context.Context, a delivery.StepAsk) (delivery.Step, error)
+	}
+	// Held says whether an ask a key names is on its stream or a build node wrote a step for it (issue 1910): a key taken
+	// over at start whose ask is neither was left by a builder that stopped between naming the ask and putting it, and
+	// the ask is put then, under the same id. Nil takes every named ask as held.
+	Held interface {
+		Held(ctx context.Context, a delivery.StepAsk) (bool, error)
+	}
+	Toolchains ToolchainEntries
+	Manifests  Manifests
+	// Limit is how many builds the builder has asked at once; their asks wait in the build seats' streams, which are the
+	// backlog (ADR 0525 §9), not here. 256 when 0.
+	Limit int
+	Logf  func(format string, args ...any)
+	// Answered is told the build module whose step answered a reference (issue 1886): what the builder says it writes
+	// rests on it. Nil tells nobody.
+	Answered func(buildModule string)
+
+	once     sync.Once
+	sem      chan struct{}
+	wg       sync.WaitGroup
+	mu       sync.Mutex
+	known    map[string]delivery.Module    // by modules key
+	inflight map[string]bool               // by build key
+	again    map[string]delivery.Module    // by build key: the newest value that arrived while the key was being built
+	plans    map[string]planned            // by manifest digest
+	cands    map[string]delivery.Candidate // by candidates key (candidates.go)
+	via      map[string]via                // by build key: a candidate's fetch (candidates.go)
+	trunkFP  map[string]bool               // by build key: a trunk module value carries this fingerprint
+	tried    map[string]bool               // by build key: looked at since this process started
+	// published are the package versions `<name>@<version>` a done key of this bucket names as a package's reference: a key
+	// waiting for one is built once it is here (ADR 0500 clause 6).
+	published map[string]bool
+}
+
+type planned struct {
+	plan Plan
+	err  error
+}
+
+func (b *Builder) init() {
+	b.once.Do(func() {
+		limit := b.Limit
+		if limit <= 0 {
+			limit = 256
+		}
+		b.sem = make(chan struct{}, limit)
+		b.cands, b.via, b.trunkFP = map[string]delivery.Candidate{}, map[string]via{}, map[string]bool{}
+		b.known, b.inflight, b.again, b.plans, b.tried = map[string]delivery.Module{}, map[string]bool{}, map[string]delivery.Module{}, map[string]planned{}, map[string]bool{}
+		b.published = map[string]bool{}
+	})
+}
+
+func (b *Builder) logf(format string, args ...any) {
+	if b.Logf != nil {
+		b.Logf(format, args...)
+	}
+}
+
+// Wait returns when every build started so far has ended.
+func (b *Builder) Wait() { b.wg.Wait() }
+
+// Module takes one value of the indexer's modules bucket in (the key is the module's name) and builds it if it is
+// to be built. A value that is not a module is said and left.
+func (b *Builder) Module(ctx context.Context, key string, value []byte) {
+	b.init()
+	m, err := delivery.DecodeModule(value)
+	if err != nil {
+		b.logf("modules.%s holds what is not a module, left: %v", key, err)
+		return
+	}
+	b.mu.Lock()
+	b.known[key] = m
+	if bk, err := delivery.BuilderBuildKey(key, m.FP2); err == nil && m.FP2 != "" {
+		// A fingerprint the trunk carries is built from the trunk's commit, whoever asked for it first.
+		b.trunkFP[bk] = true
+		delete(b.via, bk)
+	}
+	b.mu.Unlock()
+	b.consider(ctx, key, m)
+}
+
+// NodesChanged is Reconsider after a toolchain moved, so a build that waited for the nodes to agree on one may go on.
+func (b *Builder) NodesChanged(ctx context.Context) { b.Reconsider(ctx) }
+
+// Sweep reads, at start, every key of the bucket: it keeps the package versions done keys name as published (a key
+// waiting for one is then looked at again, ADR 0500 clause 6), and closes every key left building for a fingerprint its
+// module no longer has (issue 1660, ADR 0478 clause 6): the key can never be built, since nothing asks for it, and would
+// stay building for ever. It fails the key naming who left it. A key of the fingerprint the module has now is not
+// touched: the build takes it over. Call it once the modules bucket has been read, so every module is known.
+func (b *Builder) Sweep(ctx context.Context) error {
+	b.init()
+	keys, err := b.Claimer.Store.Keys(ctx)
+	if err != nil {
+		return err
+	}
+	b.mu.Lock()
+	current := map[string]bool{}
+	for name, m := range b.known {
+		if m.FP2 != "" {
+			if k, err := delivery.BuilderBuildKey(name, m.FP2); err == nil {
+				current[k] = true
+			}
+		}
+	}
+	b.mu.Unlock()
+	newly := false
+	for _, key := range keys {
+		value, rev, found, err := b.Claimer.Store.Get(ctx, key)
+		if err != nil || !found {
+			continue
+		}
+		cur, err := delivery.DecodeBuilderBuild(value)
+		if err != nil {
+			continue
+		}
+		newly = b.notePublished(cur) || newly
+		if current[key] || cur.State != delivery.BuildBuilding {
+			continue
+		}
+		closed := delivery.BuilderBuild{State: delivery.BuildFailed, By: b.Claimer.By, Manifest: cur.Manifest, Step: cur.Step,
+			Error: fmt.Sprintf("closed at start: left building by %s, and the module no longer has this fingerprint, so nothing will build it", cur.By)}
+		data, err := delivery.EncodeBuilderBuild(closed)
+		if err != nil {
+			return err
+		}
+		if _, err := b.Claimer.Store.Update(ctx, key, data, rev); err != nil && !errors.Is(err, ErrConflict) {
+			return fmt.Errorf("%s: %w", key, err)
+		}
+		b.logf("%s: closed, left building by %s for a fingerprint the module no longer has", key, cur.By)
+	}
+	if newly {
+		// A key read before the scan may wait for a package the scan found published (ADR 0500 clause 6).
+		b.Reconsider(ctx)
+	}
+	return nil
+}
+
+// notePublished keeps the package versions a done build names as references, and says whether one was new.
+func (b *Builder) notePublished(v delivery.BuilderBuild) bool {
+	if v.State != delivery.BuildDone {
+		return false
+	}
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	newly := false
+	for _, a := range v.Artifacts {
+		if a.Kind == catalogue.ArtifactPackage && a.Reference != "" && !b.published[a.Reference] {
+			b.published[a.Reference] = true
+			newly = true
+		}
+	}
+	return newly
+}
+
+func (b *Builder) isPublished(ref string) bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	return b.published[ref]
+}
+
+// Forget takes a module out (its key was deleted).
+func (b *Builder) Forget(key string) {
+	b.init()
+	b.mu.Lock()
+	delete(b.known, key)
+	b.mu.Unlock()
+}
+
+// Reconsider looks at every module again: the toolchains changed, so a build that failed for them may build now.
+func (b *Builder) Reconsider(ctx context.Context) {
+	b.init()
+	b.mu.Lock()
+	known := make(map[string]delivery.Module, len(b.known))
+	for k, m := range b.known {
+		known[k] = m
+	}
+	b.mu.Unlock()
+	for _, k := range sortedKeys(known) {
+		b.consider(ctx, k, known[k])
+	}
+	b.mu.Lock()
+	cands := make([]delivery.Candidate, 0, len(b.cands))
+	for _, c := range b.cands {
+		cands = append(cands, c)
+	}
+	b.mu.Unlock()
+	sort.Slice(cands, func(i, j int) bool { return cands[i].Group < cands[j].Group })
+	for _, c := range cands {
+		b.considerCandidate(ctx, c)
+	}
+}
+
+func sortedKeys(m map[string]delivery.Module) []string {
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}
+
+// planOf is the plan of the manifest with this digest, read once: a manifest by digest never changes. A manifest that
+// cannot be read is not kept, so it is read again when the module is.
+func (b *Builder) planOf(ctx context.Context, digest string) (Plan, error, bool) {
+	b.mu.Lock()
+	p, ok := b.plans[digest]
+	b.mu.Unlock()
+	if ok {
+		return p.plan, p.err, true
+	}
+	m, err := b.Manifests.Manifest(ctx, digest)
+	if err != nil {
+		return Plan{}, fmt.Errorf("its manifest %s cannot be read: %w", digest, err), false
+	}
+	plan, err := PlanOf(m)
+	b.mu.Lock()
+	b.plans[digest] = planned{plan, err}
+	b.mu.Unlock()
+	return plan, err, true
+}
+
+func (b *Builder) consider(ctx context.Context, module string, m delivery.Module) {
+	if m.FP2 == "" || m.Manifest == "" {
+		return
+	}
+	key, err := delivery.BuilderBuildKey(module, m.FP2)
+	if err != nil {
+		b.logf("modules.%s: %v", module, err)
+		return
+	}
+	b.mu.Lock()
+	if b.inflight[key] {
+		b.again[key] = m // looked at once more when the build ends, so a change is never lost
+		b.mu.Unlock()
+		return
+	}
+	b.inflight[key] = true
+	b.mu.Unlock()
+	b.wg.Add(1)
+	go func() {
+		defer b.wg.Done()
+		b.sem <- struct{}{}
+		defer func() { <-b.sem }()
+		for {
+			b.try(ctx, module, m)
+			b.mu.Lock()
+			next, more := b.again[key]
+			delete(b.again, key)
+			if !more || ctx.Err() != nil {
+				delete(b.inflight, key)
+				b.mu.Unlock()
+				return
+			}
+			b.mu.Unlock()
+			m = next
+		}
+	}()
+}
+
+// try claims the fingerprint and builds it, writing the key done or failed. A build that ends because ctx did is left
+// building by this builder: it takes it again when it starts (ADR 0478 clause 5).
+func (b *Builder) try(ctx context.Context, module string, m delivery.Module) {
+	plan, planErr, read := b.planOf(ctx, m.Manifest)
+	nothing := read && planErr == nil && len(plan.Tasks) == 0
+	if planErr == nil && !nothing {
+		if why := b.stale(m, plan); why != "" {
+			// The fingerprint names a toolchain the build nodes no longer agree on: a new fingerprint is coming, and a build
+			// now would be of this source with another toolchain (ADR 0477 clause 2). Nothing is written.
+			b.logf("%s at %s is not built: %s", module, m.FP2, why)
+			return
+		}
+	}
+	key, _ := delivery.BuilderBuildKey(module, m.FP2)
+	b.mu.Lock()
+	trunk := b.trunkFP[key]
+	first := !b.tried[key]
+	b.tried[key] = true
+	b.mu.Unlock()
+	cl, err := b.Claimer.Claim(ctx, module, m.FP2, m.Manifest, ClaimOptions{TakeOver: first, ImageBuilder: imageSeat, Trunk: trunk, Published: b.isPublished})
+	if err != nil {
+		b.logf("%s: %v", module, err)
+		return
+	}
+	if cl == nil {
+		return
+	}
+	// A done key taken again builds only what is missing: the image or the package built unpublished as a candidate's; the
+	// other artifacts stay as the done key has them (ADR 0487 clauses 5 and 8, ADR 0498 clause 6).
+	var prior *delivery.BuilderBuild
+	var only map[string]bool
+	publishing := false
+	if cl.Build.State == delivery.BuildDone {
+		prior, only = &cl.Build, map[string]bool{}
+		if trunk {
+			for _, bm := range publishable(cl.Build, imageSeat) {
+				only[bm] = true
+				publishing = true
+			}
+		}
+	}
+	var result delivery.BuilderBuild
+	if nothing {
+		// A manifest with no artifact is built by building nothing: its key is done with no artifact, claimed and written as
+		// any other, so the controller has a done key to register it from (issue 1613, ADR 0478 clause 1, ADR 0501 clause 1).
+		result = delivery.BuilderBuild{State: delivery.BuildDone, Step: "nothing to build: the manifest names no artifact"}
+	} else {
+		result = b.build(ctx, module, m, plan, planErr, prior, only, b.notes(cl))
+	}
+	if ctx.Err() != nil {
+		return
+	}
+	if result.State == "" {
+		b.logf("%s: left building, the toolchains moved under it", cl.Key)
+		return
+	}
+	result.By, result.Manifest = b.Claimer.By, m.Manifest
+	if publishing && result.State == delivery.BuildFailed {
+		// The trunk's image or package was built only as a candidate's and its push or publish failed: the key says so, so the builds view, the
+		// checker and the failed-key retake see it, and a look does not build the image again for nothing.
+		result.Error = keyError([]string{"publishing what the merged commit built failed: " + result.Error})
+	}
+	if err := b.Claimer.Finish(ctx, cl, result); err != nil {
+		b.logf("%s: the build could not be written: %v", cl.Key, err)
+		return
+	}
+	if result.State == delivery.BuildFailed {
+		b.logf("%s: failed: %s", cl.Key, result.Error)
+	}
+	if result.State == delivery.BuildQueued {
+		b.logf("%s: waits for the package %s to be published", cl.Key, result.Waits)
+	}
+	if b.notePublished(result) {
+		// A key may wait for the package this build published (ADR 0500 clause 6).
+		b.Reconsider(ctx)
+	}
+}
+
+// stale is why the module's fingerprint is not built now, or empty when it is: the toolchain each language of the plan
+// has agreed (novox/hq ADR 0465) must be the one the fingerprint was computed with (Module.Toolchains).
+func (b *Builder) stale(m delivery.Module, plan Plan) string {
+	for _, bm := range plan.Modules() {
+		if !plan.NeedsToolchain(bm) {
+			continue // an archive is packed with no toolchain
+		}
+		language := buildrun.LanguageOf[bm]
+		tc, none := delivery.AgreedToolchain(b.Toolchains.Entries(language))
+		if none != "" {
+			return fmt.Sprintf("the %s toolchain is not agreed: %s", language, none)
+		}
+		want, ok := m.Toolchains[language]
+		if !ok || want.Version != tc.Version || want.Recipe != tc.Recipe {
+			return fmt.Sprintf("the fingerprint names %s %s (recipe %s) and the nodes agree on %s (recipe %s)", language, want.Version, want.Recipe, tc.Version, tc.Recipe)
+		}
+	}
+	return ""
+}
+
+func failed(format string, args ...any) delivery.BuilderBuild {
+	return delivery.BuilderBuild{State: delivery.BuildFailed, Error: fmt.Sprintf(format, args...)}
+}
+
+// lane is the build of a plan's tasks of one build module on one node.
+type lane struct {
+	module, node string // node is the one that pulled the lane's ask
+	tasks        []Task
+	toolchain    *delivery.ToolchainUsed
+	digests      map[string]string // artifact -> digest
+	references   map[string]string // artifact -> the reference an image was pushed to (a trunk build only)
+	err          error
+}
+
+func (b *Builder) build(ctx context.Context, module string, m delivery.Module, plan Plan, planErr error, prior *delivery.BuilderBuild, only map[string]bool, asked *askNotes) delivery.BuilderBuild {
+	switch {
+	case planErr != nil:
+		return failed("%s", planErr)
+	case m.Path == "":
+		// Empty is not known (a root module's path is "."): the indexer writes it again (issue 1615).
+		return failed("the module's key names no directory (path), so the build tools cannot be told where %s lives", module)
+	}
+	repository := delivery.RepositoryName(m.Repository)
+	var lanes []*lane
+	used := map[string]delivery.ToolchainUsed{}
+	var kept []string // build modules whose artifacts stay as the prior done key has them
+	for _, bm := range plan.Modules() {
+		if prior != nil && len(only) > 0 && !only[bm] {
+			kept = append(kept, bm)
+			continue
+		}
+		var toolchain *delivery.ToolchainUsed
+		if bm != ImageBuildModule && plan.NeedsToolchain(bm) {
+			// The ask names the toolchain the fingerprint was computed with; a node building with another refuses it.
+			language := buildrun.LanguageOf[bm]
+			tc, none := delivery.AgreedToolchain(b.Toolchains.Entries(language))
+			if none != "" {
+				return failed("the %s toolchain is not agreed: %s", language, none)
+			}
+			if want := m.Toolchains[language]; want.Version != tc.Version || want.Recipe != tc.Recipe {
+				return delivery.BuilderBuild{} // the agreed toolchain moved since try looked: nothing is written
+			}
+			u := delivery.ToolchainUsed{Version: tc.Version, Recipe: tc.Recipe}
+			used[language], toolchain = u, &u
+		}
+		var tasks []Task
+		for _, t := range plan.Tasks {
+			if t.Module == bm {
+				tasks = append(tasks, t)
+			}
+		}
+		// One ask builds each fingerprint's part of a build module, on whichever node pulls it (ADR 0525 §3).
+		lanes = append(lanes, &lane{module: bm, tasks: tasks, toolchain: toolchain, digests: map[string]string{}, references: map[string]string{}})
+	}
+	var wg sync.WaitGroup
+	for _, l := range lanes {
+		wg.Add(1)
+		go func() { defer wg.Done(); b.runLane(ctx, l, repository, m, module, asked) }()
+	}
+	wg.Wait()
+	var errs []string
+	for _, l := range lanes {
+		if l.err != nil {
+			errs = append(errs, l.err.Error())
+		}
+	}
+	if len(errs) > 0 {
+		if ref := waitsOf(errs); ref != "" {
+			// The module's lock names a version of a package the registry does not hold yet: the key waits for it, queued, and
+			// is not failed (ADR 0500 clause 6).
+			return delivery.BuilderBuild{State: delivery.BuildQueued, Waits: ref, Step: "waits for the package " + ref + " to be published"}
+		}
+		return failed("%s", keyError(errs))
+	}
+	var artifacts []delivery.BuiltArtifact
+	keptModule := map[string]bool{}
+	for _, bm := range kept {
+		keptModule[bm] = true
+	}
+	for _, t := range plan.Tasks {
+		if keptModule[t.Module] {
+			found := false
+			for _, a := range prior.Artifacts {
+				if a.Name == t.Artifact {
+					artifacts, found = append(artifacts, a), true
+				}
+			}
+			if !found {
+				return failed("the done build holds no artifact %s to keep", t.Artifact)
+			}
+			continue
+		}
+		byNode := map[string]string{}
+		for _, l := range lanes {
+			if d, ok := l.digests[t.Artifact]; ok && l.module == t.Module {
+				byNode[l.node] = d
+			}
+		}
+		d, err := buildrun.Agree(t.Artifact, byNode)
+		if err != nil {
+			return failed("%s", err)
+		}
+		built := delivery.BuiltArtifact{Name: t.Artifact, Kind: t.Kind, Digest: d}
+		for _, l := range lanes {
+			if l.module != t.Module {
+				continue
+			}
+			r := l.references[t.Artifact]
+			if r == "" && stored(t.Kind) {
+				// A bundle, an archive or an upstream copy is done only when its push was answered with where it is (ADR 0498
+				// clause 1); a candidate's included (clause 3).
+				return failed("%s%s on %s: the build answered no reference, so its push to the artifact store was not answered", delivery.NotStored, t.Artifact, l.node)
+			}
+			if r != "" {
+				built.Reference = r
+			}
+		}
+		artifacts = append(artifacts, built)
+	}
+	var steps []string
+	for _, l := range lanes {
+		steps = append(steps, fmt.Sprintf("%s on %s", l.module, l.node))
+	}
+	for _, bm := range kept {
+		steps = append(steps, bm+" kept")
+		for lang, u := range prior.Toolchains {
+			if _, ok := used[lang]; !ok && buildrun.LanguageOf[bm] == lang {
+				used[lang] = u
+			}
+		}
+	}
+	step := "built " + strings.Join(steps, "; ")
+	if len(used) == 0 {
+		used = nil
+	}
+	done := delivery.BuilderBuild{State: delivery.BuildDone, By: b.Claimer.By, Manifest: m.Manifest, Step: step, Artifacts: artifacts, Toolchains: used}
+	if _, err := delivery.EncodeBuilderBuild(done); err != nil {
+		// A reference the build module answered that does not name the artifact and its digest is no reference.
+		return failed("%s%v", delivery.NotStored, err)
+	}
+	return done
+}
+
+// stored is whether an artifact of this kind is in the artifact store once built, a candidate's too, so its done key
+// names its reference (ADR 0498 clauses 1, 3 and 4); an image or a package names one only when built for the trunk.
+func stored(kind string) bool {
+	return kind == catalogue.ArtifactBundle || kind == catalogue.ArtifactArchive || kind == catalogue.ArtifactUpstream
+}
+
+// waitsFor opens the reason of a fetch step whose module's lock names a package version the registry does not hold, then
+// `<name>@<version>` (the Node build module's, ADR 0500 clause 6).
+const waitsFor = delivery.WaitsFor
+
+// waitsOf is the package version a lane's error says the module waits for, or "" when none does or what it names is not
+// `<name>@<version>`.
+func waitsOf(errs []string) string {
+	for _, e := range errs {
+		at := strings.Index(e, waitsFor)
+		if at < 0 {
+			continue
+		}
+		ref, _, _ := strings.Cut(e[at+len(waitsFor):], " ")
+		ref = strings.TrimRight(ref, ":;,")
+		if _, err := delivery.EncodeBuilderBuild(delivery.BuilderBuild{State: delivery.BuildQueued, Waits: ref}); err == nil {
+			return ref
+		}
+	}
+	return ""
+}
+
+// keyPrefixes are the errors a build module's step may open its reason with that the key's error must open with too, so
+// the claim reads them (delivery.FailedUntilChanged), first the ones not built again.
+var keyPrefixes = []string{delivery.NotPinned, delivery.VersionTaken, delivery.RefusedKind, delivery.NotStored}
+
+// keyError is the error of a key from its lanes' errors: when one names a prefix of keyPrefixes inside the step's words
+// (`<tool> on <node>: the step <key> failed: not stored: ...`), the key's error opens with that prefix, so a reader of the
+// key need not search for it.
+func keyError(errs []string) string {
+	for _, prefix := range keyPrefixes {
+		for i, e := range errs {
+			if strings.HasPrefix(e, prefix) {
+				return strings.Join(errs, "; ")
+			}
+			if at := strings.Index(e, prefix); at >= 0 {
+				rest := append([]string{prefix + e[:at] + e[at+len(prefix):]}, append(append([]string(nil), errs[:i]...), errs[i+1:]...)...)
+				return strings.Join(rest, "; ")
+			}
+		}
+	}
+	return strings.Join(errs, "; ")
+}
+
+// imageSeat says an image build is asked of the image build seat, which takes it when a node pulls it: a key failed for
+// want of an image builder before R4g is taken again (ADR 0525 §1).
+func imageSeat() bool { return true }
+
+// askLanguage is the build seat language of each build module (delivery.AskSubject).
+var askLanguage = map[string]string{buildrun.GoBuildModule: delivery.AskGo, buildrun.NodeBuildModule: delivery.AskNode, ImageBuildModule: delivery.AskImage}
+
+// askNotes writes a claimed key's asks into it, building, before each is put (ADR 0525 §1; issue 1887 A4b), and holds
+// the asks a key taken over at start already names, so they are waited for and never put again.
+type askNotes struct {
+	mu      sync.Mutex
+	b       *Builder
+	cl      *Claim
+	resumed map[string]string
+}
+
+func (b *Builder) notes(cl *Claim) *askNotes {
+	n := &askNotes{b: b, cl: cl}
+	if cl.Build.State == delivery.BuildBuilding && len(cl.Build.Asks) > 0 {
+		n.resumed = maps.Clone(cl.Build.Asks)
+	}
+	return n
+}
+
+// resume is the id of the ask a taken-over key names for language, or "".
+func (n *askNotes) resume(language string) string {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	return n.resumed[language]
+}
+
+// note writes the ask's id into the key, building, by compare-and-set at the claim's revision.
+func (n *askNotes) note(ctx context.Context, language, id, step string) error {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+	v := n.cl.Build
+	v.State, v.By, v.Step, v.Error, v.Artifacts = delivery.BuildBuilding, n.b.Claimer.By, step, "", nil
+	v.Asks = maps.Clone(v.Asks)
+	if v.Asks == nil {
+		v.Asks = map[string]string{}
+	}
+	v.Asks[language] = id
+	return n.b.Claimer.Finish(ctx, n.cl, v)
+}
+
+// runLane puts the lane's part of the build as one ask on its build seat's stream (the delivery stream for a trunk key, the
+// check stream for a candidate's) and reads what the node that pulled it built (ADR 0525 §1, §3, §6). An upstream artifact
+// is copied by its pinned reference with no fetch (ADR 0498 clause 4); a lane of copies alone fetches nothing. A lane of a
+// key taken over at start waits for the ask the key names and puts none.
+func (b *Builder) runLane(ctx context.Context, l *lane, repository string, m delivery.Module, module string, asked *askNotes) {
+	req := buildstep.FetchRequest{Repository: repository, Commit: m.Commit}
+	if key, err := delivery.BuilderBuildKey(module, m.FP2); err == nil {
+		b.mu.Lock()
+		v, candidate := b.via[key]
+		b.mu.Unlock()
+		if candidate {
+			req.Ref, req.Base = v.Ref, v.Base
+		}
+	}
+	if m.Inputs2 != nil && len(m.Inputs2.Paths) > 0 {
+		// A module whose every artifact names its paths is built from those alone (ADR 0499 clause 4): the paths come from
+		// the indexer's kept inputs, never from a manifest (the lead's decision L8 of R4e).
+		req.Dir = m.Path
+		for p := range m.Inputs2.Paths {
+			req.Paths = append(req.Paths, p)
+		}
+		sort.Strings(req.Paths)
+	}
+	candidate := req.Base != ""
+	language := askLanguage[l.module]
+	kind := delivery.AskDelivery
+	if candidate {
+		kind = delivery.AskCheck
+	}
+	job := &delivery.BuildJob{Module: module, Path: m.Path, FP: m.FP2, Toolchain: l.toolchain,
+		// Only a trunk key's build pushes an image or publishes a package; a candidate's never does (ADR 0487 clause 12,
+		// ADR 0498 clauses 5 and 6). A bundle or an archive is pushed either way (clause 3).
+		Publish: !candidate}
+	for _, t := range l.tasks {
+		a := delivery.AskArtifact{Artifact: t.Artifact}
+		if t.Kind == catalogue.ArtifactUpstream {
+			a.From = t.From // the copy runs no code of a change: the module's name, the artifact and its pin
+		}
+		job.Artifacts = append(job.Artifacts, a)
+	}
+	if needsFetch(l.tasks) {
+		job.Fetch = req.Args()
+	}
+	ask := delivery.StepAsk{ID: buildstep.NewID(), Kind: kind, Language: language, Asker: delivery.BuilderModule, At: time.Now(), Build: job}
+	if id := asked.resume(language); id != "" {
+		ask.ID = id // put before this builder started again: the stream holds it, or a node already ran it
+		if b.Held != nil {
+			held, err := b.Held.Held(ctx, ask)
+			if err != nil {
+				// Said, and the key is not failed: the ask may well be on its stream and its build finish (issue 1910).
+				b.logf("whether the ask %s of %s the key names is on its stream cannot be read, so it is waited for as put: %v", ask.ID, l.module, err)
+				held = true
+			}
+			if !held {
+				// The builder that named it stopped before it put it (issue 1910): put it now, under the same id.
+				b.logf("the ask %s of %s that the key names was never put: it is put now", ask.ID, l.module)
+				if err := b.Asks.Put(ctx, ask); err != nil {
+					l.err = err
+					return
+				}
+			}
+		}
+	} else {
+		if err := asked.note(ctx, language, ask.ID, "asked "+l.module); err != nil {
+			l.err = fmt.Errorf("the ask of %s could not be written to the key: %w", l.module, err)
+			return
+		}
+		if err := b.Asks.Put(ctx, ask); err != nil {
+			l.err = err
+			return
+		}
+	}
+	step, err := b.Asks.Wait(ctx, ask)
+	if err != nil {
+		l.err = fmt.Errorf("%s: %w", l.module, err)
+		return
+	}
+	l.node = step.Node
+	if step.State != delivery.StepPassed {
+		l.err = fmt.Errorf("%s on %s: the ask %s %s: %s", l.module, step.Node, ask.ID, step.State, step.Reason)
+		return
+	}
+	var answer delivery.BuildAnswer
+	if err := json.Unmarshal(step.Result, &answer); err != nil {
+		l.err = fmt.Errorf("the ask of %s on %s answered what is not a build: %s", l.module, step.Node, step.Result)
+		return
+	}
+	built := map[string]delivery.AskBuilt{}
+	for _, a := range answer.Artifacts {
+		built[a.Artifact] = a
+	}
+	for _, t := range l.tasks {
+		a, ok := built[t.Artifact]
+		if !ok || a.Digest == "" {
+			l.err = fmt.Errorf("the build of %s of %s on %s answered no digest: %s", t.Artifact, module, step.Node, step.Result)
+			return
+		}
+		l.digests[t.Artifact] = a.Digest
+		if a.Reference != "" && (stored(t.Kind) || !candidate) {
+			l.references[t.Artifact] = a.Reference
+		}
+		if a.Reference != "" && b.Answered != nil {
+			b.Answered(l.module)
+		}
+	}
+}
+
+// needsFetch is whether any of the tasks builds from the module's source: every one but an upstream copy.
+func needsFetch(tasks []Task) bool {
+	for _, t := range tasks {
+		if t.Kind != catalogue.ArtifactUpstream {
+			return true
+		}
+	}
+	return false
+}

modules/mesh-delivery-builder/internal/build/run_test.go

@@ -0,0 +1,699 @@
+package build
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// buildModules simulates the two build modules on the nodes: a long tool answers a step and key at once and writes the
+// step's end into the steps (as mesh-build-go and mesh-build-node do), with a digest by node and artifact, or a failure.
+type buildModules struct {
+	mu      sync.Mutex
+	n       int
+	calls   []call
+	steps   *fakeSteps
+	digests map[string]string // `<node>/<artifact>` -> digest; the default is `digest`
+	fails   map[string]string // `<node>/<tool>` -> the reason the step fails with
+	// noRef names `<node>/<artifact>` whose bundle or archive build answers no reference (its push not answered).
+	noRef map[string]bool
+	// packages are the package artifacts by name, each with the `<name>@<version>` its trunk build publishes (ADR 0498 clause 5).
+	packages map[string]string
+	// hold, when set before the builds start, blocks every call until it is closed; entered is sent to as a call arrives.
+	// conflicts, when set, is a file a fetch with a base reports in conflict; noMerge makes it answer neither a merge nor a conflict.
+	conflicts string
+	noMerge   bool
+	hold      chan struct{}
+	entered   chan struct{}
+}
+
+func newBuildModules() *buildModules {
+	return &buildModules{steps: &fakeSteps{steps: map[string]delivery.Step{}}, digests: map[string]string{}, fails: map[string]string{}, noRef: map[string]bool{}, packages: map[string]string{}}
+}
+
+func (b *buildModules) CallOn(node, key string, body any) (json.RawMessage, error) {
+	if b.hold != nil {
+		select {
+		case b.entered <- struct{}{}:
+		default:
+		}
+		<-b.hold
+	}
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.calls = append(b.calls, call{node, key, body})
+	b.n++
+	id := fmt.Sprintf("s%d", b.n)
+	module, tool, _ := strings.Cut(key, ".")
+	args, _ := body.(map[string]any)
+	step := delivery.Step{ID: id, Tool: tool, Node: node, State: delivery.StepPassed}
+	if reason, ok := b.fails[node+"/"+tool]; ok {
+		step.State, step.Reason = delivery.StepFailed, reason
+	} else if strings.HasSuffix(tool, "_fetch") {
+		step.Result = json.RawMessage(`{"workspace":"w-` + node + `"}`)
+		if args["base"] != nil { // a fetch with a base answers the merge, or the files in conflict (mesh-build-go FetchResult)
+			if b.conflicts != "" {
+				step.Result = json.RawMessage(`{"workspace":"w-` + node + `","base":"` + fmt.Sprint(args["base"]) + `","conflicts":["` + b.conflicts + `"]}`)
+			} else if !b.noMerge {
+				step.Result = json.RawMessage(`{"workspace":"w-` + node + `","base":"` + fmt.Sprint(args["base"]) + `","merge":"` + strings.Repeat("9", 40) + `"}`)
+			}
+		}
+	} else {
+		d := digest
+		if v, ok := b.digests[node+"/"+fmt.Sprint(args["artifact"])]; ok {
+			d = v
+		}
+		if tool == "build_image_copy" { // mesh-build-image's copy answers the digest and where it copied to (ADR 0498 clause 4)
+			step.Result = json.RawMessage(`{"artifact":"` + fmt.Sprint(args["artifact"]) + `","digest":"` + d + `","reference":"registry.example/` + fmt.Sprint(args["module"]) + `/` + fmt.Sprint(args["artifact"]) + `@` + d + `","pushed":true}`)
+		} else if pkg, ok := b.packages[fmt.Sprint(args["artifact"])]; ok { // a package names its version only when published
+			step.Result = json.RawMessage(`{"digest":"` + d + `"}`)
+			if args["publish"] == true {
+				step.Result = json.RawMessage(`{"digest":"` + d + `","reference":"` + pkg + `"}`)
+			}
+		} else if tool == "build_image_build" && args["publish"] == true {
+			step.Result = json.RawMessage(`{"digest":"` + d + `","reference":"registry.example/m/` + fmt.Sprint(args["artifact"]) + `@` + d + `"}`)
+		} else if tool != "build_image_build" && !b.noRef[node+"/"+fmt.Sprint(args["artifact"])] {
+			// A bundle or an archive is pushed to the artifact store and its reference answered (ADR 0498 clause 1).
+			step.Result = json.RawMessage(`{"digest":"` + d + `","reference":"artifact-store://m/` + fmt.Sprint(args["artifact"]) + `/blobs/` + d + `"}`)
+		} else {
+			step.Result = json.RawMessage(`{"digest":"` + d + `"}`)
+		}
+	}
+	sk, _ := delivery.StepKey(node, id)
+	b.steps.mu.Lock()
+	b.steps.steps[module+"/"+sk] = step
+	b.steps.mu.Unlock()
+	return json.RawMessage(`{"step":"` + id + `","key":"` + sk + `","state":"running"}`), nil
+}
+
+func (b *buildModules) callsOf(tool string) (out []call) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	for _, c := range b.calls {
+		if strings.HasSuffix(c.key, "."+tool) {
+			out = append(out, c)
+		}
+	}
+	return out
+}
+
+type fakeManifests struct {
+	byDigest map[string]catalogue.Manifest
+}
+
+func (f *fakeManifests) Manifest(_ context.Context, d string) (catalogue.Manifest, error) {
+	m, ok := f.byDigest[d]
+	if !ok {
+		return catalogue.Manifest{}, fmt.Errorf("manifests.%s is not there", d)
+	}
+	return m, nil
+}
+
+func mdigest(c byte) string { return hex64(c) }
+
+type rig struct {
+	b     *Builder
+	st    *memStore
+	bm    *buildModules
+	tools *buildrun.ToolchainSet
+	mf    *fakeManifests
+	key   string
+	// asks are the build seats' streams; puller is the node that pulls every ask ("ace" when empty).
+	asks   *buildrun.FakeAsks
+	puller string
+}
+
+// toolPrefix is the start of each build module's tool names, as the fake build modules answer them.
+var toolPrefix = map[string]string{buildrun.GoBuildModule: "build_go_", buildrun.NodeBuildModule: "build_node_", ImageBuildModule: "build_image_"}
+
+// answer runs an ask as the build module that pulls it does (buildstep.RunAsk), with the fake build modules' tools on the
+// rig's pulling node, and answers the step that node writes.
+func (r *rig) answer(a delivery.StepAsk) delivery.Step {
+	node := r.puller
+	if node == "" {
+		node = "ace"
+	}
+	module, _ := delivery.BuildModuleOf(a.Language)
+	runner := buildrun.Runner{Caller: r.bm, Steps: r.bm.steps, Bound: time.Second}
+	tool := func(name string) buildstep.StepFunc {
+		return func(ctx context.Context, args map[string]any) (any, error) {
+			raw, err := runner.Run(ctx, module, node, toolPrefix[module]+name, args)
+			if err != nil {
+				return nil, err
+			}
+			return raw, nil
+		}
+	}
+	steps := buildstep.AskSteps{Fetch: tool("fetch"), Build: tool("build"), Copy: tool("copy")}
+	out, err := buildstep.RunAsk(context.Background(), steps, a)
+	step := delivery.Step{ID: a.ID, Tool: a.Kind + " ask", Node: node, State: delivery.StepPassed}
+	if err != nil {
+		step.State, step.Reason = delivery.StepFailed, err.Error()
+		return step
+	}
+	step.Result, _ = json.Marshal(out)
+	return step
+}
+
+func newRig(t *testing.T, artifacts ...catalogue.Artifact) *rig {
+	t.Helper()
+	r := &rig{st: newMem(), bm: newBuildModules(), tools: &buildrun.ToolchainSet{}, mf: &fakeManifests{byDigest: map[string]catalogue.Manifest{mdigest('a'): {Module: "m", Build: &catalogue.Build{Artifacts: artifacts}}}}}
+	for _, n := range []string{"ace", "novox"} {
+		r.tools.Put(buildrun.GoBuildModule, n+".go", tcValue(t, "go", "go1.27.1"), false)
+		r.tools.Put(buildrun.NodeBuildModule, n+".typescript", tcValue(t, "typescript", "tsc5"), false)
+	}
+	r.asks = &buildrun.FakeAsks{Answer: r.answer}
+	r.b = &Builder{
+		Claimer: Claimer{Store: r.st, By: "novox.builder"}, Asks: buildrun.Asker{Publisher: r.asks, Waiter: r.asks, Bound: 2 * time.Second},
+		Toolchains: r.tools, Manifests: r.mf, Logf: t.Logf,
+	}
+	var err error
+	if r.key, err = delivery.BuilderBuildKey("m", fp1); err != nil {
+		t.Fatal(err)
+	}
+	return r
+}
+
+// agreedToolchains are what the rig's nodes report, and so what a fingerprint computed now names.
+var agreedToolchains = map[string]delivery.ToolchainUsed{"go": {Version: "go1.27.1", Recipe: "1"}, "typescript": {Version: "tsc5", Recipe: "1"}}
+
+func moduleValue(t *testing.T, path string) []byte { return moduleValueWith(t, path, agreedToolchains) }
+
+func moduleValueWith(t *testing.T, path string, toolchains map[string]delivery.ToolchainUsed) []byte {
+	t.Helper()
+	data, err := delivery.EncodeModule(delivery.Module{Repository: "novox/mesh-catalog", Commit: "7a74cee83f88e6585a5511c3cc53bdf0f5303d20", FP: "src1:" + hex64('f'), FP2: fp1, Manifest: mdigest('a'), Path: path, Toolchains: toolchains})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return data
+}
+
+func (r *rig) consider(t *testing.T, path string) delivery.BuilderBuild {
+	t.Helper()
+	r.b.Module(context.Background(), "m", moduleValue(t, path))
+	r.b.Wait()
+	if _, ok := r.st.vals[r.key]; !ok {
+		t.Fatal("no build key was written")
+	}
+	return valueOf(t, r.st, r.key)
+}
+
+var (
+	goBundle  = catalogue.Artifact{Name: "tool", Kind: "bundle", Language: "go"}
+	tsBundle  = catalogue.Artifact{Name: "web", Kind: "bundle", Language: "typescript"}
+	archiveA  = catalogue.Artifact{Name: "files", Kind: "archive"}
+	imageArt  = catalogue.Artifact{Name: "img", Kind: "image"}
+	manifestD = mdigest('a')
+)
+
+func TestABundleAndAnArchiveAreBuiltOnOneNodeAndDone(t *testing.T) { // 1607/AC7, ADR 0478 clauses 1, 4
+	r := newRig(t, goBundle, archiveA, tsBundle)
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || v.By != "novox.builder" || v.Manifest != manifestD || len(v.Artifacts) != 3 {
+		t.Fatalf("build = %+v, want done by novox.builder with three artifacts", v)
+	}
+	for i, want := range []string{"files", "tool", "web"} {
+		if a := v.Artifacts[i]; a.Name != want || a.Digest != digest || a.Reference != "artifact-store://m/"+want+"/blobs/"+digest {
+			t.Errorf("artifact %d = %+v, want %s with the digest and its artifact-store reference (ADR 0498 clause 1)", i, a, want)
+		}
+	}
+	if v.Artifacts[0].Kind != "archive" || v.Artifacts[1].Kind != "bundle" {
+		t.Errorf("kinds = %+v", v.Artifacts)
+	}
+	if got := v.Toolchains["go"]; got.Version != "go1.27.1" || got.Recipe != "1" {
+		t.Errorf("toolchains = %+v, want go and typescript named", v.Toolchains)
+	}
+	if got := v.Toolchains["typescript"]; got.Version != "tsc5" {
+		t.Errorf("toolchains = %+v", v.Toolchains)
+	}
+	// One fetch per build module, on one node (ADR 0478 clause 4); every build names the module's directory.
+	if n := len(r.bm.callsOf("build_go_fetch")); n != 1 {
+		t.Errorf("%d go fetches, want one", n)
+	}
+	if n := len(r.bm.callsOf("build_go_build")); n != 2 { // tool and files
+		t.Errorf("%d go builds, want 2", n)
+	}
+	if n := len(r.bm.callsOf("build_node_build")); n != 1 {
+		t.Errorf("%d node builds, want 1", n)
+	}
+	c := r.bm.callsOf("build_go_build")[0]
+	if args := c.body.(map[string]any); args["module"] != "modules/m" || !strings.HasPrefix(fmt.Sprint(args["workspace"]), "w-") {
+		t.Errorf("build args = %+v, want the module's path and the fetch's workspace", args)
+	}
+	f := r.bm.callsOf("build_go_fetch")[0].body.(map[string]any)
+	if f["repository"] != "novox/mesh-catalog" || f["commit"] != "7a74cee83f88e6585a5511c3cc53bdf0f5303d20" {
+		t.Errorf("fetch args = %+v", f)
+	}
+}
+
+// 1887/AC1, AC2: a trunk fingerprint with no key is one ask on the Go seat's delivery stream, named in the building key
+// before it is put, and the builder calls no node; the step a node wrote for it makes the key done naming its reference.
+func TestATrunkFingerprintIsOneAskOnTheDeliveryStream(t *testing.T) {
+	r := newRig(t, goBundle)
+	r.asks.Answer = nil // no node has pulled it yet
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	var asks []delivery.StepAsk
+	for deadline := time.Now().Add(2 * time.Second); len(asks) == 0; time.Sleep(time.Millisecond) {
+		if time.Now().After(deadline) {
+			t.Fatal("no ask was put")
+		}
+		asks = r.asks.Asks()
+	}
+	a := asks[0]
+	if len(asks) != 1 || a.Kind != delivery.AskDelivery || a.Language != delivery.AskGo || a.Build == nil || a.Build.FP != fp1 {
+		t.Fatalf("asks = %+v, want one Go delivery ask of the fingerprint", asks)
+	}
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildBuilding || v.Asks[delivery.AskGo] != a.ID {
+		t.Fatalf("the key = %+v, want building naming the ask %s", v, a.ID)
+	}
+	if n := len(r.bm.callsOf("build_go_build")) + len(r.bm.callsOf("build_go_fetch")); n != 0 {
+		t.Fatalf("the builder called a node %d times", n)
+	}
+	r.asks.End(r.answer(a)) // a node pulled it and ran it
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone || !strings.Contains(v.Step, "on ace") || v.Artifacts[0].Reference == "" || len(v.Asks) != 0 {
+		t.Fatalf("the key = %+v, want done on ace naming the reference", v)
+	}
+}
+
+// 1887/AC3: a builder that starts again while its ask waits puts no second ask: it waits for the step of the ask the
+// building key names.
+func TestARestartedBuilderWaitsForTheAskTheKeyNames(t *testing.T) {
+	r := newRig(t, goBundle)
+	const id = "mvl0frv18d1957"
+	data, _ := delivery.EncodeBuilderBuild(delivery.BuilderBuild{State: delivery.BuildBuilding, By: "novox.builder", Manifest: manifestD,
+		Step: "asked mesh-build-go", Asks: map[string]string{delivery.AskGo: id}})
+	r.st.vals[r.key] = data
+	r.asks.Answer = nil
+	r.asks.End(delivery.Step{ID: id, Node: "shanks", State: delivery.StepPassed,
+		Result: []byte(`{"artifacts":[{"artifact":"tool","digest":"` + digest + `","reference":"artifact-store://m/tool/blobs/` + digest + `"}]}`)})
+	v := r.consider(t, "modules/m")
+	if n := len(r.asks.Asks()); n != 0 {
+		t.Fatalf("%d asks put again", n)
+	}
+	if v.State != delivery.BuildDone || !strings.Contains(v.Step, "on shanks") {
+		t.Fatalf("the key = %+v, want done from the ask's step on shanks", v)
+	}
+}
+
+func TestAFailingStepFailsTheBuildWithItsReasonAndNodeAndIsTriedAgainAsANewRevision(t *testing.T) { // 1607/AC7, ADR 0429 clause 18
+	r := newRig(t, goBundle)
+	r.bm.fails["ace/build_go_build"] = "go build of tool: undefined: x"
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildFailed || !strings.Contains(v.Error, "ace") || !strings.Contains(v.Error, "undefined: x") {
+		t.Fatalf("build = %+v, want failed with the node and the reason", v)
+	}
+	rev := r.st.revs[r.key]
+	delete(r.bm.fails, "ace/build_go_build")
+	v = r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || r.st.revs[r.key] <= rev {
+		t.Errorf("build = %+v at revision %d (was %d), want done as a new revision of the same key", v, r.st.revs[r.key], rev)
+	}
+}
+
+func TestAnImageGoesToOneNodeAndGetsOneDoneKeyWithItsReference(t *testing.T) { // 1705a, ADR 0487 clause 5
+	r := newRig(t, imageArt)
+	r.puller = "ace" // two nodes qualify; an image still builds on one
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || len(v.Artifacts) != 1 || v.Artifacts[0].Kind != "image" || v.Artifacts[0].Digest != digest {
+		t.Fatalf("build = %+v, want done with one image artifact and its digest", v)
+	}
+	if v.Artifacts[0].Reference == "" {
+		t.Errorf("a trunk image has no reference: %+v", v.Artifacts[0])
+	}
+	if n := len(r.bm.callsOf("build_image_fetch")); n != 1 {
+		t.Errorf("%d image fetches, want one", n)
+	}
+	writes := r.st.writes
+	r.consider(t, "modules/m")
+	if r.st.writes != writes || len(r.bm.callsOf("build_image_build")) != 1 {
+		t.Errorf("a done image key was built again")
+	}
+}
+
+func TestABundleAndAnImageOfOneModuleBuildOnOneNodeEach(t *testing.T) { // 1705a
+	r := newRig(t, goBundle, imageArt)
+	r.puller = "ace"
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || len(v.Artifacts) != 2 {
+		t.Fatalf("build = %+v", v)
+	}
+	if n := len(r.bm.callsOf("build_go_build")); n != 1 {
+		t.Errorf("%d go builds, want 1 (one node per fingerprint, ADR 0478 clause 4)", n)
+	}
+	if n := len(r.bm.callsOf("build_image_build")); n != 1 {
+		t.Errorf("%d image builds, want 1", n)
+	}
+}
+
+func TestACandidatesImageCallCarriesNoPublishAndItsKeyNoReference(t *testing.T) { // 1705b, lead's decision
+	r := newRig(t, imageArt)
+	r.puller = "ace"
+	trunkModule(t, r)
+	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	r.b.Wait()
+	v := valueOf(t, r.st, r.key)
+	if v.State != delivery.BuildDone || len(v.Artifacts) != 1 || v.Artifacts[0].Reference != "" {
+		t.Fatalf("build = %+v, want done with no reference", v)
+	}
+	calls := r.bm.callsOf("build_image_build")
+	if len(calls) != 1 {
+		t.Fatalf("%d image builds, want 1", len(calls))
+	}
+	if _, has := calls[0].body.(map[string]any)["publish"]; has {
+		t.Errorf("a candidate's image call carries publish: %+v", calls[0].body)
+	}
+}
+
+func TestATrunkImageCallCarriesPublish(t *testing.T) { // 1705b
+	r := newRig(t, imageArt)
+	r.puller = "ace"
+	r.consider(t, "modules/m")
+	calls := r.bm.callsOf("build_image_build")
+	if len(calls) != 1 || calls[0].body.(map[string]any)["publish"] != true {
+		t.Errorf("calls = %+v, want publish true", calls)
+	}
+}
+
+func TestAnUnpinnedUpstreamFailsNotPinnedAndIsNeverBuiltAgain(t *testing.T) { // B3, ADR 0498 clause 4
+	r := newRig(t, archiveA, catalogue.Artifact{Name: "up", Kind: "upstream", From: "nats:2.11.17-alpine"})
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildFailed || !strings.HasPrefix(v.Error, delivery.NotPinned) || !strings.Contains(v.Error, "up") {
+		t.Fatalf("build = %+v, want failed 'not pinned:' naming the artifact", v)
+	}
+	if len(r.bm.calls) != 0 {
+		t.Errorf("%d calls, want none for an unpinned upstream", len(r.bm.calls))
+	}
+	writes := r.st.writes
+	r.consider(t, "modules/m")
+	if r.st.writes != writes {
+		t.Errorf("an unpinned upstream's key was written again (%d writes, was %d)", r.st.writes, writes)
+	}
+}
+
+func TestAModuleKeyWithNoPathFailsNamingThatReason(t *testing.T) { // 1607/AC8, ADR 0478 clause 8
+	r := newRig(t, goBundle)
+	v := r.consider(t, "")
+	if v.State != delivery.BuildFailed || !strings.Contains(v.Error, "path") || len(r.bm.calls) != 0 {
+		t.Errorf("build = %+v with %d calls, want failed naming the missing path and nothing called", v, len(r.bm.calls))
+	}
+}
+
+func TestAnUnreadableManifestFailsTheBuild(t *testing.T) {
+	r := newRig(t, goBundle)
+	delete(r.mf.byDigest, mdigest('a'))
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildFailed || !strings.Contains(v.Error, "manifest") {
+		t.Errorf("build = %+v, want failed naming the manifest", v)
+	}
+}
+
+func TestAModuleWithNoFingerprintIsNotBuilt(t *testing.T) { // 1607/AC2
+	r := newRig(t)
+	data, _ := delivery.EncodeModule(delivery.Module{Repository: "novox/r", Commit: "c", FP: "src1:" + hex64('f'), None2: "toolchain not yet reported"})
+	r.b.Module(context.Background(), "n", data)
+	r.b.Wait()
+	if len(r.st.vals) != 0 {
+		t.Errorf("keys %v were written: a module with no new-form fingerprint has nothing to build", r.st.vals)
+	}
+}
+
+func TestAModuleWithNoArtifactGetsADoneKeyWithNoArtifactAndNoBuildCall(t *testing.T) { // issue 1613, ADR 0478 clause 1
+	for name, manifest := range map[string]catalogue.Manifest{"no build": {Module: "m"}, "no artifact": {Module: "m", Build: &catalogue.Build{}}} {
+		r := newRig(t)
+		r.mf.byDigest[mdigest('a')] = manifest
+		v := r.consider(t, "") // a module with nothing to build needs no directory
+		if v.State != delivery.BuildDone || len(v.Artifacts) != 0 || v.Manifest != manifestD || v.By != "novox.builder" {
+			t.Errorf("%s: build = %+v, want done with no artifact", name, v)
+		}
+		if len(r.bm.calls) != 0 {
+			t.Errorf("%s: %d build module calls, want none", name, len(r.bm.calls))
+		}
+		writes := r.st.writes
+		r.b.tried = map[string]bool{}
+		r.consider(t, "")
+		if r.st.writes != writes {
+			t.Errorf("%s: the done key was written again", name)
+		}
+	}
+}
+
+func TestAKeyTheBuilderLeftBuildingIsBuiltAtStartAndDoneKeysAreNotBuiltTwice(t *testing.T) { // 1607/AC3, AC7
+	r := newRig(t, goBundle)
+	seed(t, r.st, delivery.BuilderBuild{State: delivery.BuildBuilding, By: "novox.builder", Manifest: manifestD})
+	if v := r.consider(t, "modules/m"); v.State != delivery.BuildDone {
+		t.Fatalf("build = %+v, want the builder's own building key built", v)
+	}
+	calls := len(r.bm.calls)
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	r.b.Reconsider(context.Background())
+	r.b.Wait()
+	if len(r.bm.calls) != calls {
+		t.Errorf("a done key was built again (%d calls, was %d)", len(r.bm.calls), calls)
+	}
+}
+
+// Two instances that start together on one key: the second finds the key building and takes it over (ADR 0478 clause 6:
+// a key found building at start is taken over, whoever holds it), so both may build; the key is written once, by the one
+// whose compare-and-set comes first, and the other's write is refused, never overwriting it.
+func TestTwoInstancesStartingTogetherEndWithOneDoneKey(t *testing.T) { // 1607/AC7, review round 4
+	r := newRig(t, goBundle)
+	other := &Builder{Claimer: Claimer{Store: r.st, By: "ace.builder"}, Asks: r.b.Asks, Toolchains: r.tools, Manifests: r.mf, Logf: t.Logf}
+	value := moduleValue(t, "modules/m")
+	var wg sync.WaitGroup
+	for _, b := range []*Builder{r.b, other} {
+		wg.Add(1)
+		go func() { defer wg.Done(); b.Module(context.Background(), "m", value); b.Wait() }()
+	}
+	wg.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone || len(v.Artifacts) != 1 {
+		t.Errorf("build = %+v, want one done key", v)
+	}
+	if n := len(r.bm.callsOf("build_go_build")); n < 1 {
+		t.Errorf("%d builds, want one for each instance that built", n)
+	}
+}
+
+func TestAModulesValueThatArrivesWhileItsKeyIsBeingBuiltIsLookedAtAgainWhenItEnds(t *testing.T) { // 1607/AC6 (no event is dropped, no timer)
+	r := newRig(t, goBundle)
+	r.bm.fails["ace/build_go_build"] = "go build of tool: boom"
+	r.bm.hold, r.bm.entered = make(chan struct{}), make(chan struct{}, 8)
+	value := moduleValue(t, "modules/m")
+	r.b.Module(context.Background(), "m", value)
+	<-r.bm.entered // the first build is under way
+	r.b.Module(context.Background(), "m", value)
+	r.b.Reconsider(context.Background())
+	delete(r.bm.fails, "ace/build_go_build") // what the event is about: the build can succeed now
+	close(r.bm.hold)
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone {
+		t.Errorf("build = %+v, want the failed key built again as a new revision after the first build ended", v)
+	}
+}
+
+func TestAKeyIsBuiltOnlyWithTheToolchainItsFingerprintNamesAndNothingIsWrittenOtherwise(t *testing.T) { // 1615/AC4
+	r := newRig(t, goBundle)
+	old := map[string]delivery.ToolchainUsed{"go": {Version: "go1.26.0", Recipe: "1"}}
+	r.b.Module(context.Background(), "m", moduleValueWith(t, "modules/m", old))
+	r.b.Wait()
+	if len(r.st.vals) != 0 || len(r.bm.calls) != 0 {
+		t.Errorf("keys %v and %d calls for a fingerprint of go1.26.0 while the nodes agree on go1.27.1, want neither", r.st.vals, len(r.bm.calls))
+	}
+	// A recipe that differs is a different toolchain too, and a value that names none (written before) is not built.
+	r.b.Module(context.Background(), "m", moduleValueWith(t, "modules/m", map[string]delivery.ToolchainUsed{"go": {Version: "go1.27.1", Recipe: "0"}}))
+	r.b.Module(context.Background(), "m", moduleValueWith(t, "modules/m", nil))
+	r.b.Wait()
+	if len(r.st.vals) != 0 || len(r.bm.calls) != 0 {
+		t.Errorf("keys %v and %d calls for a recipe that differs or a value that names no toolchain", r.st.vals, len(r.bm.calls))
+	}
+	// The toolchain moves under a key that is not built yet: the old fingerprint stays unbuilt, the new one builds.
+	r.tools.Put(buildrun.GoBuildModule, "ace.go", tcValue(t, "go", "go1.27.2"), false)
+	r.tools.Put(buildrun.GoBuildModule, "novox.go", tcValue(t, "go", "go1.27.2"), false)
+	r.b.Reconsider(context.Background())
+	r.b.Wait()
+	if len(r.st.vals) != 0 {
+		t.Errorf("keys %v: the old fingerprint was built with the new toolchain", r.st.vals)
+	}
+	r.b.Module(context.Background(), "m", moduleValueWith(t, "modules/m", map[string]delivery.ToolchainUsed{"go": {Version: "go1.27.2", Recipe: "1"}}))
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone || v.Toolchains["go"].Version != "go1.27.2" {
+		t.Errorf("build = %+v, want done with go1.27.2", v)
+	}
+}
+
+func TestNodesTheyDisagreeOnLeaveTheKeyUnwritten(t *testing.T) { // 1615/AC4
+	r := newRig(t, goBundle)
+	r.tools.Put(buildrun.GoBuildModule, "ace.go", tcValue(t, "go", "go1.26.0"), false)
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	r.b.Wait()
+	if len(r.st.vals) != 0 || len(r.bm.calls) != 0 {
+		t.Errorf("keys %v and %d calls while the nodes disagree", r.st.vals, len(r.bm.calls))
+	}
+}
+
+func TestARootModulesPathIsDotAndIsGivenToTheBuildTools(t *testing.T) { // 1615/AC4
+	r := newRig(t, goBundle)
+	if v := r.consider(t, delivery.RootPath); v.State != delivery.BuildDone {
+		t.Fatalf("build = %+v, want done for a root module", v)
+	}
+	if args := r.bm.callsOf("build_go_build")[0].body.(map[string]any); args["module"] != "." {
+		t.Errorf("build args = %+v, want module \".\"", args)
+	}
+}
+
+func TestACandidatesImageIsPublishedOnceWhenTheTrunkNamesItsFingerprint(t *testing.T) { // review r1, mesh-delivery 1; ADR 0487 clause 5
+	r := newRig(t, imageArt)
+	r.puller = "ace"
+	trunkModule(t, r) // the trunk carries another fingerprint; fp1 is the candidate's
+	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	r.b.Wait()
+	v := valueOf(t, r.st, r.key)
+	if v.State != delivery.BuildDone || v.Artifacts[0].Reference != "" {
+		t.Fatalf("candidate build = %+v, want done with no reference", v)
+	}
+	if n := len(r.bm.callsOf("build_image_build")); n != 1 {
+		t.Fatalf("%d image builds after the candidate, want 1", n)
+	}
+	// The pull request is merged: the trunk's record names the candidate's fingerprint.
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	r.b.Wait()
+	v = valueOf(t, r.st, r.key)
+	if v.State != delivery.BuildDone || len(v.Artifacts) != 1 || v.Artifacts[0].Reference == "" {
+		t.Fatalf("trunk build = %+v, want done with a reference", v)
+	}
+	calls := r.bm.callsOf("build_image_build")
+	published := 0
+	for _, c := range calls {
+		if c.body.(map[string]any)["publish"] == true {
+			published++
+		}
+	}
+	if len(calls) != 2 || published != 1 {
+		t.Errorf("%d image builds, %d with publish, want 2 and exactly 1", len(calls), published)
+	}
+	// Written once more only: looking again builds nothing.
+	rev := r.st.revs[r.key]
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	r.b.Wait()
+	if r.st.revs[r.key] != rev || len(r.bm.callsOf("build_image_build")) != 2 {
+		t.Error("a published key was built again")
+	}
+}
+
+func TestAFailedPublishOfACandidatesImageIsWrittenToTheKey(t *testing.T) { // review r2, mesh-delivery 1; ADR 0487 clause 5
+	r := newRig(t, imageArt)
+	r.puller = "ace"
+	trunkModule(t, r)
+	r.b.Candidate(context.Background(), "feat%2Fx", candidateValue(t, "feat/x", 7, headX))
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone {
+		t.Fatalf("candidate build = %+v", v)
+	}
+	r.bm.fails["ace/build_image_build"] = "push to the registry: connection refused"
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m")) // the merge: the trunk names the fingerprint
+	r.b.Wait()
+	v := valueOf(t, r.st, r.key)
+	if v.State != delivery.BuildFailed || !strings.Contains(v.Error, "connection refused") || !strings.Contains(v.Error, "publish") {
+		t.Fatalf("build = %+v, want failed naming the publish and its reason", v)
+	}
+	// The failed key is retaken as any failed key is, and ends published once the registry answers.
+	delete(r.bm.fails, "ace/build_image_build")
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone || v.Artifacts[0].Reference == "" {
+		t.Errorf("build = %+v, want done with a reference", v)
+	}
+}
+
+// Review round 2 item 1: a build ask that waits in its stream longer than the step bound is not failed and not asked
+// again; the key is done when a node takes it.
+func TestABuildAskWaitingInItsStreamIsNotBounded(t *testing.T) {
+	r := newRig(t, goBundle)
+	r.asks.Answer = nil
+	r.b.Asks = buildrun.Asker{Publisher: r.asks, Waiter: r.asks, Bound: 20 * time.Millisecond}
+	r.b.Module(context.Background(), "m", moduleValue(t, "modules/m"))
+	for deadline := time.Now().Add(2 * time.Second); len(r.asks.Asks()) == 0; time.Sleep(time.Millisecond) {
+		if time.Now().After(deadline) {
+			t.Fatal("no ask was put")
+		}
+	}
+	time.Sleep(100 * time.Millisecond)
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildBuilding {
+		t.Fatalf("the key = %+v while its ask waits, want building", v)
+	}
+	r.asks.End(r.answer(r.asks.Asks()[0]))
+	r.b.Wait()
+	if v := valueOf(t, r.st, r.key); v.State != delivery.BuildDone || len(r.asks.Asks()) != 1 {
+		t.Fatalf("the key = %+v after %d asks, want done from the one ask", v, len(r.asks.Asks()))
+	}
+}
+
+// heldAsks says an ask is held when its id is among held.
+type heldAsks map[string]bool
+
+func (h heldAsks) Held(_ context.Context, a delivery.StepAsk) (bool, error) { return h[a.ID], nil }
+
+// 1910: a builder that stopped between naming the ask in its key and putting it left a key naming an ask neither the
+// stream holds nor any node ran: started again, the builder puts that ask, under the same id, once, and the key is
+// built from its step; an ask the stream holds is not put again.
+func TestAnAskTheKeyNamesAndNobodyPutIsPutAtStart(t *testing.T) {
+	for _, held := range []bool{false, true} {
+		r := newRig(t, goBundle)
+		const id = "mvl0frv18d1958"
+		data, _ := delivery.EncodeBuilderBuild(delivery.BuilderBuild{State: delivery.BuildBuilding, By: "novox.builder", Manifest: manifestD,
+			Step: "asked mesh-build-go", Asks: map[string]string{delivery.AskGo: id}})
+		r.st.vals[r.key] = data
+		r.b.Held = heldAsks{id: held}
+		if held {
+			r.asks.Answer = nil
+			r.asks.End(delivery.Step{ID: id, Node: "shanks", State: delivery.StepPassed,
+				Result: []byte(`{"artifacts":[{"artifact":"tool","digest":"` + digest + `","reference":"artifact-store://m/tool/blobs/` + digest + `"}]}`)})
+		}
+		v := r.consider(t, "modules/m")
+		asks := r.asks.Asks()
+		switch {
+		case held && len(asks) != 0:
+			t.Errorf("an ask the stream holds was put again: %+v", asks)
+		case !held && (len(asks) != 1 || asks[0].ID != id):
+			t.Errorf("the ask nobody put: asks %+v, want one under %s", asks, id)
+		}
+		if v.State != delivery.BuildDone {
+			t.Errorf("held %v: the key = %+v, want done", held, v)
+		}
+	}
+}
+
+// unreadableHeld cannot tell whether an ask is held.
+type unreadableHeld struct{}
+
+func (unreadableHeld) Held(context.Context, delivery.StepAsk) (bool, error) {
+	return false, errors.New("permissions violation for publish to $JS.API.STREAM.INFO.SEAT_NODE_BUILD_GO")
+}
+
+// 1910: a take-over that cannot read whether the ask its key names is on its stream says so and waits for the ask's step:
+// the key is not failed, and the build finishes when a node ran the ask.
+func TestATakeOverThatCannotReadTheStreamWaitsForTheAsk(t *testing.T) {
+	r := newRig(t, goBundle)
+	const id = "mvl0frv18d1959"
+	data, _ := delivery.EncodeBuilderBuild(delivery.BuilderBuild{State: delivery.BuildBuilding, By: "novox.builder", Manifest: manifestD,
+		Step: "asked mesh-build-go", Asks: map[string]string{delivery.AskGo: id}})
+	r.st.vals[r.key] = data
+	r.b.Held = unreadableHeld{}
+	r.asks.Answer = nil
+	r.asks.End(delivery.Step{ID: id, Node: "shanks", State: delivery.StepPassed,
+		Result: []byte(`{"artifacts":[{"artifact":"tool","digest":"` + digest + `","reference":"artifact-store://m/tool/blobs/` + digest + `"}]}`)})
+	v := r.consider(t, "modules/m")
+	if v.State != delivery.BuildDone || len(r.asks.Asks()) != 0 {
+		t.Fatalf("the key = %+v after %d asks, want done from the ask's step, none put", v, len(r.asks.Asks()))
+	}
+}

modules/mesh-delivery-builder/internal/build/testdata/captured/README

@@ -0,0 +1,4 @@
+Captured step values of mesh-build-image (fetch, a candidate's build, a trunk's build), copied from
+novox/mesh-catalog modules/mesh-build-image/cmd/mesh-build-image/testdata/captured/. Both copies must change together: the
+module's capture test writes them, and the builder's TestCapturedImageStepsDecodeWithTheBuildersOwnTypes (internal/build,
+fixtures_test.go) decodes these with the types the builder reads results with and fails on a missing field.

modules/mesh-delivery-builder/internal/build/testdata/captured/build-candidate.json

@@ -0,0 +1,14 @@
+{
+  "ended": "2026-10-22T08:00:01Z",
+  "id": "STEPID",
+  "node": "ace",
+  "result": {
+    "artifact": "server",
+    "digest": "sha256:1111111111111111111111111111111111111111111111111111111111111111",
+    "pushed": false
+  },
+  "started": "2026-10-22T08:00:00Z",
+  "state": "passed",
+  "tool": "build_image_build",
+  "v": 1
+}

modules/mesh-delivery-builder/internal/build/testdata/captured/build-trunk.json

@@ -0,0 +1,15 @@
+{
+  "ended": "2026-10-22T08:00:01Z",
+  "id": "STEPID",
+  "node": "ace",
+  "result": {
+    "artifact": "server",
+    "digest": "sha256:1111111111111111111111111111111111111111111111111111111111111111",
+    "pushed": true,
+    "reference": "REGISTRY/fixture-image/server@sha256:1111111111111111111111111111111111111111111111111111111111111111"
+  },
+  "started": "2026-10-22T08:00:00Z",
+  "state": "passed",
+  "tool": "build_image_build",
+  "v": 1
+}

modules/mesh-delivery-builder/internal/build/testdata/captured/fetch.json

@@ -0,0 +1,13 @@
+{
+  "ended": "2026-10-22T08:00:01Z",
+  "id": "STEPID",
+  "node": "ace",
+  "result": {
+    "commit": "COMMIT",
+    "workspace": "WORKSPACE"
+  },
+  "started": "2026-10-22T08:00:00Z",
+  "state": "passed",
+  "tool": "build_image_fetch",
+  "v": 1
+}

modules/mesh-delivery-builder/manifest_test.go

@@ -0,0 +1,185 @@
+package manifest
+
+import (
+	"bytes"
+	"encoding/json"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"reflect"
+	"slices"
+	"strings"
+	"testing"
+)
+
+// The controller's manifest reader is mesh-controller internal/catalogue (Manifest, manifest.go: Consumes :521,
+// Invokes :590, Streams :613, Reads :659; StreamDeclaration, streams.go), an internal package of another repository.
+// These tests decode the manifest strictly into the fields those types name (DisallowUnknownFields) and hold the
+// rules of issue 1607 (ADR 0453 §4, ADR 0478). The merge gate's module check proves the controller takes the manifest.
+
+type state struct {
+	Name    string `json:"name"`
+	History int    `json:"history,omitempty"`
+}
+
+type artifact struct {
+	Name     string `json:"name"`
+	Kind     string `json:"kind"`
+	Language string `json:"language"`
+	System   string `json:"system"`
+	From     string `json:"from"`
+	Binary   string `json:"binary"`
+}
+
+type manifest struct {
+	Module   string   `json:"module"`
+	Version  string   `json:"version"`
+	Slug     string   `json:"slug"`
+	Consumes []string `json:"consumes"`
+	State    []state  `json:"state"`
+	Reads    []string `json:"reads"`
+	Uses     []string `json:"uses"`
+	Invokes  []string `json:"invokes"`
+	Config   map[string]struct {
+		Type        string `json:"type"`
+		Description string `json:"description"`
+		Pattern     string `json:"pattern"`
+		Default     string `json:"default"`
+	} `json:"config"`
+	OwnSecrets   map[string]string `json:"own-secrets"`
+	SecretsOwner string            `json:"secrets-owner"`
+	Resources    []map[string]any  `json:"resources"`
+	Build        struct {
+		Artifacts []artifact `json:"artifacts"`
+	} `json:"build"`
+}
+
+func load(t *testing.T) (manifest, map[string]json.RawMessage) {
+	t.Helper()
+	raw, err := os.ReadFile("module.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var m manifest
+	dec := json.NewDecoder(bytes.NewReader(raw))
+	dec.DisallowUnknownFields()
+	if err := dec.Decode(&m); err != nil {
+		t.Fatalf("the controller's reader refuses a key this manifest has: %v", err)
+	}
+	var top map[string]json.RawMessage
+	if err := json.Unmarshal(raw, &top); err != nil {
+		t.Fatal(err)
+	}
+	return m, top
+}
+
+func sorted(s []string) []string {
+	s = slices.Clone(s)
+	slices.Sort(s)
+	return s
+}
+
+func TestManifestDeclarations(t *testing.T) { // 1607/AC1
+	m, top := load(t)
+	if m.Module != "mesh-delivery-builder" {
+		t.Errorf("module = %q", m.Module)
+	}
+	if want := []state{{Name: "builds", History: 5}, {Name: "instances", History: 1}}; !reflect.DeepEqual(m.State, want) { // delivery.BuilderBuildsHistory
+		t.Errorf("state = %+v, want %+v", m.State, want)
+	}
+	// 1887/A4c: the builder chooses no node, so it reads neither presence nor have, invokes no build module's tool and
+	// holds no capacity; it puts asks on the three build seats and reads their steps (ADR 0525 §1, §4, §5).
+	if want := []string{"mesh-build-go.steps", "mesh-build-go.toolchains", "mesh-build-image.steps", "mesh-build-node.steps", "mesh-build-node.toolchains",
+		"mesh-delivery-indexer.candidates", "mesh-delivery-indexer.manifests", "mesh-delivery-indexer.modules"}; !reflect.DeepEqual(sorted(m.Reads), want) {
+		t.Errorf("reads = %v, want %v", m.Reads, want)
+	}
+	if want := []string{"node-build-go", "node-build-image", "node-build-node"}; !reflect.DeepEqual(sorted(m.Uses), want) {
+		t.Errorf("uses = %v, want the three build seats", m.Uses)
+	}
+	if len(m.Invokes) != 0 || len(m.Config) != 0 {
+		t.Errorf("invokes = %v, config = %v, want none: no tool call from the builder and no capacity", m.Invokes, m.Config)
+	}
+	// The builder is woken by a build module's report of a toolchain, as the indexer is: the bucket may not exist when it starts.
+	if want := []string{"mesh-build-go.toolchain.reported", "mesh-build-node.toolchain.reported"}; !reflect.DeepEqual(sorted(m.Consumes), want) {
+		t.Errorf("consumes = %v, want %v", m.Consumes, want)
+	}
+	if b, ok := m.OwnSecrets["broker"]; !ok || len(m.OwnSecrets) != 1 || b != "${dir:state}/broker" {
+		t.Errorf("own-secrets = %v, want exactly broker", m.OwnSecrets)
+	}
+	if m.SecretsOwner != "mesh-delivery-builder" {
+		t.Errorf("secrets-owner = %q", m.SecretsOwner)
+	}
+	for _, k := range []string{"streams", "logs", "emits", "claims", "provides", "requires", "defines-seats", "tools", "seat", "seats", "bus", "invokes", "config"} {
+		if _, ok := top[k]; ok {
+			t.Errorf("the manifest declares %q: the builder has none", k)
+		}
+	}
+}
+
+func TestManifestProcess(t *testing.T) { // 1607/AC1
+	m, _ := load(t)
+	var procs []map[string]any
+	for _, r := range m.Resources {
+		if r["type"] == "process" {
+			procs = append(procs, r)
+		}
+		if r["type"] == "tool" || r["type"] == "seat" {
+			t.Errorf("resource %v: the builder serves no tool and holds no seat", r)
+		}
+	}
+	if len(procs) != 1 {
+		t.Fatalf("%d process resources, want one", len(procs))
+	}
+	p := procs[0]
+	if p["artifact"] != "program" || !reflect.DeepEqual(p["run"], []any{"./mesh-delivery-builder"}) {
+		t.Errorf("process = %v", p)
+	}
+	env, _ := p["env"].(map[string]any)
+	if len(env) != 1 || env["MESH_BROKER_FILE"] != "${dir:state}/broker" {
+		t.Errorf("env = %v, want the broker file alone", p["env"])
+	}
+	for _, r := range m.Resources {
+		if r["id"] == "settings" {
+			t.Errorf("a settings resource %v: the builder holds no setting since the capacity is the build modules' (ADR 0525 §5)", r)
+		}
+	}
+	if _, bus := p["bus"]; bus {
+		t.Errorf("the process declares a bus: it runs on its own broker credential")
+	}
+	if len(m.Build.Artifacts) != 1 {
+		t.Fatalf("artifacts = %+v, want the program alone", m.Build.Artifacts)
+	}
+	a := m.Build.Artifacts[0]
+	if st, err := os.Stat(a.From); err != nil || !st.IsDir() || a.Binary != "mesh-delivery-builder" || !strings.HasSuffix(a.From, a.Binary) || a.Kind != "bundle" || a.Language != "go" {
+		t.Errorf("artifact = %+v", a)
+	}
+}
+
+func TestServesNoRequestSubjectAndHoldsNoTicker(t *testing.T) { // 1607/AC6 (ADR 0437 §8: no timer, a wait is a context's bound)
+	forbidden := []string{"Subscribe(", "QueueSubscribe", "ChanSubscribe", "time.NewTicker", "time.Tick", "time.NewTimer", "time.AfterFunc", "time.After(", "time.Sleep"}
+	var files int
+	for _, root := range []string{"cmd", "internal"} {
+		err := filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
+			if err != nil || d.IsDir() || !strings.HasSuffix(path, ".go") || strings.HasSuffix(path, "_test.go") {
+				return err
+			}
+			files++
+			src, err := os.ReadFile(path)
+			if err != nil {
+				return err
+			}
+			for _, f := range forbidden {
+				if strings.Contains(string(src), f) {
+					t.Errorf("%s holds %s: the builder serves no request subject and holds no timer", path, f)
+				}
+			}
+			return nil
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+	if files < 1 {
+		t.Fatalf("read %d source files, want the program's", files)
+	}
+}

modules/mesh-delivery-builder/module.json

@@ -0,0 +1,78 @@
+{
+  "module": "mesh-delivery-builder",
+  "version": "1",
+  "slug": "builder",
+  "consumes": [
+    "mesh-build-go.toolchain.reported",
+    "mesh-build-node.toolchain.reported"
+  ],
+  "state": [
+    { "name": "builds", "history": 5 },
+    { "name": "instances", "history": 1 }
+  ],
+  "reads": [
+    "mesh-build-go.steps",
+    "mesh-build-go.toolchains",
+    "mesh-build-image.steps",
+    "mesh-build-node.steps",
+    "mesh-build-node.toolchains",
+    "mesh-delivery-indexer.candidates",
+    "mesh-delivery-indexer.manifests",
+    "mesh-delivery-indexer.modules"
+  ],
+  "uses": [
+    "node-build-go",
+    "node-build-image",
+    "node-build-node"
+  ],
+
+  "own-secrets": {
+    "broker": "${dir:state}/broker"
+  },
+  "secrets-owner": "mesh-delivery-builder",
+  "resources": [
+    {
+      "id": "account",
+      "type": "user",
+      "name": "mesh-delivery-builder",
+      "shell": "/usr/bin/nologin",
+      "home": "/var/lib/mesh-delivery-builder"
+    },
+    {
+      "id": "state",
+      "type": "directory",
+      "mode": "0700",
+      "owner": "mesh-delivery-builder",
+      "place": ".",
+      "unknown": "program"
+    },
+    {
+      "id": "builder",
+      "type": "process",
+      "name": "mesh-delivery-builder",
+      "artifact": "program",
+      "run": [
+        "./mesh-delivery-builder"
+      ],
+      "env": {
+        "MESH_BROKER_FILE": "${dir:state}/broker"
+      },
+      "user": "mesh-delivery-builder",
+      "health": {
+        "kind": "unit"
+      }
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "program",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/mesh-delivery-builder",
+        "binary": "mesh-delivery-builder"
+      }
+    ]
+  }
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main.go

@@ -0,0 +1,191 @@
+// Command mesh-delivery-checker-tools serves the checker's read tools (novox/hq ADR 0484 clause 13, issue 1686): the runtime
+// launches it for a call, it reads the checker's verdicts and kept states and the indexer's candidates through the checker's
+// state and reads, and writes nothing. The checker is the other program: it serves no tool (ADR 0437 §4).
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"time"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+func read(s stdio.KeptState) check.StateRead {
+	return check.StateRead{Keys: s.Keys, Get: func(key string) (json.RawMessage, error) {
+		e, err := s.Get(key)
+		if err != nil || e == nil {
+			return nil, err
+		}
+		return e.Value, nil
+	}}
+}
+
+// stateStore is a state the tools write: the tries.
+type stateStore struct {
+	check.StateRead
+	create func(key string, value []byte) error
+}
+
+func (s stateStore) Keys() ([]string, error)                 { return s.StateRead.Keys() }
+func (s stateStore) Get(key string) (json.RawMessage, error) { return s.StateRead.Get(key) }
+func (s stateStore) Create(key string, value []byte) error   { return s.create(key, value) }
+
+// Trying is what the try's tools work on: the tries, and the gate's trunk heads.
+type Trying struct {
+	Tries  check.TryStore
+	Trunks func() (map[string]string, error)
+	Now    func() time.Time
+}
+
+// TryTools are the try's two tools (ADR 0501 §5): ask one, read one. mesh-controller's try calls them.
+func TryTools(tr Trying) []stdio.Tool {
+	str := func(args map[string]any, k string) string { s, _ := args[k].(string); return s }
+	return []stdio.Tool{
+		{Name: check.TryTool,
+			Description: "Try a pushed head before its pull request is opened: the checker judges it as it judges a pull request's head, merged onto its trunk's head, " +
+				"its unit and integration levels through the build modules, and owes the forge nothing. Answers the try's id at once; " + check.TryReadTool + " reads " +
+				"where it stands. A try of the same head that waits or runs is the answer to a second ask; at most 4 wait or run at once, mesh-wide. A repository " +
+				"the checker checks no level of (one whose trunk the gate does not name) is refused.",
+			Input: map[string]any{"type": "object", "required": []string{"repository", "head"}, "properties": map[string]any{
+				"repository": map[string]any{"type": "string", "description": "<owner>/<name>"},
+				"head":       map[string]any{"type": "string", "description": "the full commit to try, 40 or 64 hex digits"},
+				"trunk":      map[string]any{"type": "string", "description": "the trunk commit to merge it onto, or the trunk's branch for its head now; the trunk's head when absent"},
+				"tests":      map[string]any{"type": "string", "description": "a go test -run pattern: only those tests run, and nothing is kept"},
+				"level":      map[string]any{"type": "string", "enum": []string{"unit", "integration"}, "description": "only this level; both when absent"}}},
+			Run: func(args map[string]any) (any, error) {
+				if tr.Tries == nil || tr.Trunks == nil {
+					return nil, fmt.Errorf("the tries state cannot be written here")
+				}
+				trunks, err := tr.Trunks()
+				if err != nil {
+					return nil, fmt.Errorf("the trunk heads cannot be read: %w", err)
+				}
+				now := time.Now
+				if tr.Now != nil {
+					now = tr.Now
+				}
+				id, err := check.AskTry(tr.Tries, trunks, check.TryAsk{Repository: str(args, "repository"), Head: str(args, "head"),
+					Trunk: str(args, "trunk"), Tests: str(args, "tests"), Level: str(args, "level")}, now())
+				if err != nil {
+					return nil, err
+				}
+				return map[string]any{"id": id}, nil
+			}},
+		{Name: check.TryReadTool,
+			Description: "Where a try stands, as stored: queued, running, or its end (pass, fail, or error when it could not run), with what was said of it, " +
+				"the head and the trunk commit it was merged onto, the time it took and what failed first. Read-only.",
+			Input: map[string]any{"type": "object", "required": []string{"id"}, "properties": map[string]any{
+				"id": map[string]any{"type": "string", "description": "the try's id, try-<digits>"}}},
+			Run: func(args map[string]any) (any, error) {
+				if tr.Tries == nil {
+					return nil, fmt.Errorf("the tries state cannot be read here")
+				}
+				return check.ReadTry(tr.Tries, str(args, "id"))
+			}},
+	}
+}
+
+// Tools are the read tools over the checker's states.
+func Tools(r check.Reader) []stdio.Tool {
+	return []stdio.Tool{
+		{Name: check.VerdictsReadTool,
+			Description: "The verdicts the checker holds, each as stored under verdicts.<group>.<heads>: its state, what failed first, the tests run, kept and skipped per level, the time of each part, the trunk heads it judged against and the composition, with the full " +
+				"report of the status each pull request carries (the line the forge shows is cut at 140 characters, this is not). With a group, that group's only. Read-only.",
+			Input: map[string]any{"type": "object", "properties": map[string]any{
+				"group": map[string]any{"type": "string", "description": "the delivery group's branch name"}}},
+			Run: func(args map[string]any) (any, error) {
+				group, _ := args["group"].(string)
+				vs, err := r.Verdicts(group)
+				return map[string]any{"verdicts": vs}, err
+			}},
+		{Name: check.PullReadTool,
+			Description: "The verdict that judges one pull request and the full report of its status mesh/check. Read-only.",
+			Input: map[string]any{"type": "object", "required": []string{"repository", "number"}, "properties": map[string]any{
+				"repository": map[string]any{"type": "string", "description": "<owner>/<name>"},
+				"number":     map[string]any{"type": "integer", "description": "the pull request's number"}}},
+			Run: func(args map[string]any) (any, error) {
+				repository, _ := args["repository"].(string)
+				n, _ := args["number"].(float64)
+				return r.Pull(repository, int(n))
+			}},
+		{Name: check.KeptReadTool,
+			Description: "The kept verdicts of passing packages, each as stored under kept.<level>.<digest>: the package, its tests, the time they took, the toolchain " +
+				"and when it was kept. With a level, that level's; with a level and a digest, that one. Read-only.",
+			Input: map[string]any{"type": "object", "properties": map[string]any{
+				"level":  map[string]any{"type": "string", "enum": []string{"unit", "integration"}, "description": "the level"},
+				"digest": map[string]any{"type": "string", "description": "the package's digest, with a level"}}},
+			Run: func(args map[string]any) (any, error) {
+				level, _ := args["level"].(string)
+				digest, _ := args["digest"].(string)
+				kept, err := r.Kept(level, digest)
+				return map[string]any{"kept": kept}, err
+			}},
+		{Name: check.PreviewsReadTool,
+			Description: "The merge previews the checker holds, each as stored under previews.<repository>.<head>.<trunk>: the merge commit, per module directory " +
+				"its tree, manifest digest and lock hashes, or the files in conflict. With a repository, that repository's; with a head (7 or more characters) " +
+				"only that head's. Keys that are no preview key are listed as unreadable. Read-only.",
+			Input: map[string]any{"type": "object", "properties": map[string]any{
+				"repository": map[string]any{"type": "string", "description": "<owner>/<name>"},
+				"head":       map[string]any{"type": "string", "description": "a pull request head commit, or a prefix of at least 7 characters"}}},
+			Run: func(args map[string]any) (any, error) {
+				repository, _ := args["repository"].(string)
+				head, _ := args["head"].(string)
+				if head != "" && len(head) < 7 {
+					return nil, fmt.Errorf("the head %q is too short: give at least 7 characters", head)
+				}
+				ps, bad, err := r.Previews(repository, head)
+				return map[string]any{"previews": ps, "unreadable": bad}, err
+			}},
+		{Name: check.StatusReadTool,
+			Description: "What runs: the steps in flight on the build modules by node, the candidates without a verdict for their heads, " +
+				"and the candidates whose check is owed by kind (waiting_by_kind: new, nodes, and trunk, a re-judge pulled after the other two). A key a " +
+				"build module left running (started past the step bound, or its build module not running on its node) is listed apart under " +
+				"left_running with why, and not counted. Nothing holds the checker and it has no capacity of its own: a check is an ask on the " +
+				"build seats' streams, whose backlog the delivery view shows (novox/hq ADR 0525). Read-only.",
+			Input: map[string]any{"type": "object", "properties": map[string]any{}},
+			Run:   func(map[string]any) (any, error) { return r.Status() }},
+	}
+}
+
+// stepBound is the checker's step bound as the checker reads it (MESH_CHECKER_STEP_BOUND), its default when unset or not a
+// duration.
+func stepBound() time.Duration {
+	if d, err := time.ParseDuration(os.Getenv("MESH_CHECKER_STEP_BOUND")); err == nil && d > 0 {
+		return d
+	}
+	return check.DefaultStepBound
+}
+
+func main() {
+	r := check.Reader{VerdictState: read(stdio.State("verdicts")), KeptState: read(stdio.State("kept")), CandidateState: read(stdio.State("mesh-delivery-indexer.candidates")),
+		PreviewState: read(stdio.State("previews")),
+		StepStates:   map[string]check.StateRead{"mesh-build-go": read(stdio.State("mesh-build-go.steps")), "mesh-build-node": read(stdio.State("mesh-build-node.steps"))},
+		HaveState:    read(stdio.State("node-engine.have")), StepBound: stepBound()}
+	tries := stdio.State(check.TriesState)
+	source := stdio.State("mesh-delivery-gate.source")
+	trunks := func() (map[string]string, error) {
+		e, err := source.Get(delivery.SourceMainKey)
+		if err != nil || e == nil {
+			return nil, err
+		}
+		s, err := delivery.DecodeSource(e.Value)
+		return s.Heads, err
+	}
+	r.Trunks = trunks
+	trying := Trying{
+		Tries: stateStore{StateRead: read(tries), create: func(key string, value []byte) error {
+			_, err := tries.Create(key, json.RawMessage(value))
+			return err
+		}},
+		Trunks: trunks,
+	}
+	if err := stdio.Serve("", append(Tools(r), TryTools(trying)...)); err != nil {
+		fmt.Fprintf(os.Stderr, "[mesh-delivery-checker-tools] %v\n", err)
+		os.Exit(1)
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main_test.go

@@ -0,0 +1,81 @@
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"slices"
+	"strings"
+	"testing"
+	"time"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+func TestTheToolsServedAreTheFiveReadTools(t *testing.T) {
+	var names []string
+	for _, tl := range Tools(check.Reader{}) {
+		names = append(names, tl.Name)
+		if tl.Description == "" || tl.Run == nil {
+			t.Errorf("%s has no description or no run", tl.Name)
+		}
+	}
+	want := []string{check.VerdictsReadTool, check.PullReadTool, check.KeptReadTool, check.PreviewsReadTool, check.StatusReadTool}
+	if !slices.Equal(names, want) {
+		t.Errorf("tools = %v, want %v", names, want)
+	}
+	// With nothing to read from a tool says so and changes nothing.
+	for _, tl := range Tools(check.Reader{}) {
+		if tl.Name == check.StatusReadTool {
+			continue // it answers from what it can read, and says what it could not
+		}
+		if _, err := tl.Run(map[string]any{"repository": "novox/x", "number": float64(1)}); err == nil {
+			t.Errorf("%s answered with no state to read", tl.Name)
+		}
+	}
+}
+
+// memStore is a tries state in memory.
+type memStore struct{ vals map[string]json.RawMessage }
+
+func (m *memStore) Keys() ([]string, error) {
+	var out []string
+	for k := range m.vals {
+		out = append(out, k)
+	}
+	return out, nil
+}
+func (m *memStore) Get(key string) (json.RawMessage, error) { return m.vals[key], nil }
+func (m *memStore) Create(key string, value []byte) error {
+	if _, ok := m.vals[key]; ok {
+		return errors.New("exists")
+	}
+	m.vals[key] = value
+	return nil
+}
+
+func TestTheTryToolsAskAndReadATry(t *testing.T) { // ADR 0501 §5, the agreed interface with mesh-controller's try
+	store := &memStore{vals: map[string]json.RawMessage{}}
+	tools := TryTools(Trying{Tries: store, Now: func() time.Time { return time.Unix(1, 5) },
+		Trunks: func() (map[string]string, error) {
+			return map[string]string{"novox/mesh-delivery": strings.Repeat("a", 40)}, nil
+		}})
+	if len(tools) != 2 || tools[0].Name != "checker_try" || tools[1].Name != "checker_try_read" {
+		t.Fatalf("tools = %+v", tools)
+	}
+	out, err := tools[0].Run(map[string]any{"repository": "novox/mesh-delivery", "head": strings.Repeat("1", 40), "trunk": "main"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	id := out.(map[string]any)["id"].(string)
+	if id != "try-1000000005" {
+		t.Errorf("id = %q", id)
+	}
+	raw, err := tools[1].Run(map[string]any{"id": id})
+	if err != nil || !strings.Contains(string(raw.(json.RawMessage)), `"state":"queued"`) {
+		t.Errorf("read = %s, %v", raw, err)
+	}
+	if _, err := tools[0].Run(map[string]any{"repository": "novox/hq", "head": strings.Repeat("1", 40)}); err == nil ||
+		err.Error() != "no level of novox/hq is checked by the checker" {
+		t.Errorf("hq: %v", err)
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/bus.go

@@ -0,0 +1,125 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+// bucketOpener is the part of the bus the watches use.
+type bucketOpener interface {
+	KeyValue(ctx context.Context, bucket string) (jetstream.KeyValue, error)
+}
+
+// kvStore is the builds bucket as the builder's store: create and compare-and-set.
+type kvStore struct{ kv jetstream.KeyValue }
+
+func conflict(err error) error {
+	if errors.Is(err, jetstream.ErrKeyExists) || errors.Is(err, jetstream.ErrKeyRevisionMismatch) {
+		return check.ErrConflict
+	}
+	return err
+}
+
+func (s kvStore) Get(ctx context.Context, key string) ([]byte, uint64, bool, error) {
+	e, err := s.kv.Get(ctx, key)
+	if errors.Is(err, jetstream.ErrKeyNotFound) {
+		return nil, 0, false, nil
+	}
+	if err != nil {
+		return nil, 0, false, err
+	}
+	return e.Value(), e.Revision(), true, nil
+}
+
+func (s kvStore) Create(ctx context.Context, key string, value []byte) (uint64, error) {
+	rev, err := s.kv.Create(ctx, key, value)
+	return rev, conflict(err)
+}
+
+func (s kvStore) Update(ctx context.Context, key string, value []byte, revision uint64) (uint64, error) {
+	rev, err := s.kv.Update(ctx, key, value, revision)
+	return rev, conflict(err)
+}
+
+func (s kvStore) Keys(ctx context.Context) ([]string, error) {
+	keys, err := s.kv.Keys(ctx)
+	if errors.Is(err, jetstream.ErrNoKeysFound) {
+		return nil, nil
+	}
+	return keys, err
+}
+
+// Delete removes a key (an ended try past its keeping).
+func (s kvStore) Delete(ctx context.Context, key string) error { return s.kv.Delete(ctx, key) }
+
+func opOf(e jetstream.KeyValueEntry) bool { return e.Operation() == jetstream.KeyValuePut }
+
+// settle reads the entries a watcher holds now, up to its mark of the last values, and returns the watcher for the
+// changes that follow.
+func settle(ctx context.Context, kv jetstream.KeyValue, each func(jetstream.KeyValueEntry)) (jetstream.KeyWatcher, error) {
+	w, err := kv.WatchAll(ctx)
+	if err != nil {
+		return nil, err
+	}
+	for {
+		select {
+		case <-ctx.Done():
+			w.Stop()
+			return nil, ctx.Err()
+		case e, ok := <-w.Updates():
+			if !ok {
+				return nil, errors.New("the watch ended")
+			}
+			if e == nil {
+				return w, nil
+			}
+			each(e)
+		}
+	}
+}
+
+// follow hands each change of a watcher to each until ctx ends; a watch that ends is an error, and the process manager
+// starts the program again.
+func follow(ctx context.Context, w jetstream.KeyWatcher, each func(jetstream.KeyValueEntry)) error {
+	defer w.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case e, ok := <-w.Updates():
+			if !ok {
+				return errors.New("a watch ended")
+			}
+			if e != nil {
+				each(e)
+			}
+		}
+	}
+}
+
+// manifestReader reads manifests.<digest> of the indexer and parses the manifest it holds.
+type manifestReader struct{ kv jetstream.KeyValue }
+
+func (m manifestReader) Manifest(ctx context.Context, digest string) (catalogue.Manifest, error) {
+	key, err := delivery.ManifestsKey(digest)
+	if err != nil {
+		return catalogue.Manifest{}, err
+	}
+	e, err := m.kv.Get(ctx, key)
+	if err != nil {
+		return catalogue.Manifest{}, fmt.Errorf("manifests.%s: %w", key, err)
+	}
+	kept, err := delivery.DecodeManifest(e.Value())
+	if err != nil {
+		return catalogue.Manifest{}, err
+	}
+	return catalogue.ParseManifest([]byte(kept.JSON))
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/composition_line_integration_test.go

@@ -0,0 +1,63 @@
+//go:build integration
+
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// assignerWrote raises the assigner's compositions bucket, the assigner online in the watchman's presence, and its verdict
+// under the check's key, as the assigner leaves them on the bus.
+func (b *bed) assignerWrote(t *testing.T, key string, v delivery.CompositionVerdict) {
+	t.Helper()
+	kv, err := b.js.CreateKeyValue(b.ctx, jetstream.KeyValueConfig{Bucket: delivery.AssignerCompositionsBucket, History: delivery.AssignerCompositionsHistory})
+	if err != nil {
+		t.Fatal(err)
+	}
+	pkey, _ := delivery.PresencePartKey(delivery.AssignerModule, "novox")
+	on, _ := delivery.EncodePresence(delivery.Presence{Online: true})
+	if _, err := b.buckets[delivery.PresenceBucket].Put(b.ctx, pkey, on); err != nil {
+		t.Fatal(err)
+	}
+	data, err := delivery.EncodeCompositionVerdict(v)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := kv.Put(b.ctx, key, data); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// 1297/AC3: started whole with the assigner's verdict on the bus, the checker's line says the composition's verdict, not
+// "not yet run": a pass names its machine, a fail fails the check with the assigner's words.
+func TestTheCheckersLineSaysTheAssignersComposition(t *testing.T) {
+	for _, c := range []struct {
+		state, owed, words string
+	}{
+		{delivery.CompositionPass, "success", "composition passed"},
+		{delivery.CompositionFail, "failure", "g14 runs web, which the change removes from its source"},
+	} {
+		b := startBed(t)
+		key := b.candidate(t, "feat/x", pull(repo, 7, head1))
+		group, heads, _ := delivery.ParseCheckerVerdictKey(key)
+		v := delivery.CompositionVerdict{Group: group, Heads: heads, State: c.state, SDK: "v0.1.14-x", Machines: []string{"g14"}}
+		if c.state == delivery.CompositionFail {
+			v.Machine, v.Words = "g14", c.words
+		}
+		b.assignerWrote(t, key, v)
+		b.start(t, nil)
+		got := b.verdict(t, key, ended)
+		if got.Composition == nil || got.Composition.State != c.state {
+			t.Fatalf("%s: the verdict's composition is %+v", c.state, got.Composition)
+		}
+		o := b.owed(t, 7, head1, c.owed)
+		if !strings.Contains(o.Text, c.words) || strings.Contains(o.Text, "not yet run") {
+			t.Errorf("%s: the line says %q", c.state, o.Text)
+		}
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/compositions.go

@@ -0,0 +1,131 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"sync"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+// compositionWatch reads the assigner's composition of a check (ADR 0528 clause 5) by watching its key and the
+// assigner's presence: no poll and no timer. With no assigner online it answers check.ErrAssignerNotRunning at once.
+type compositionWatch struct {
+	kv jetstream.KeyValue
+	// presence is the watchman's presence bucket; nil (not there) counts as no assigner online.
+	presence jetstream.KeyValue
+}
+
+// Await answers the composition under key once the assigner wrote one that does not wait (check.AwaitComposition).
+func (c compositionWatch) Await(ctx context.Context, key string) (delivery.CompositionVerdict, error) {
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+	comps := make(chan check.CompositionEvent)
+	presence := make(chan check.PresenceEvent)
+	cw, err := c.kv.Watch(ctx, key)
+	if err != nil {
+		return delivery.CompositionVerdict{}, err
+	}
+	defer cw.Stop()
+	go func() {
+		for e := range cw.Updates() {
+			ev := check.CompositionEvent{Settled: e == nil}
+			if e != nil && e.Operation() == jetstream.KeyValuePut {
+				ev.Value = e.Value()
+			}
+			select {
+			case comps <- ev:
+			case <-ctx.Done():
+				return
+			}
+		}
+	}()
+	if c.presence == nil {
+		go func() {
+			select {
+			case presence <- check.PresenceEvent{Settled: true}:
+			case <-ctx.Done():
+			}
+		}()
+	} else {
+		pw, err := c.presence.Watch(ctx, "part."+delivery.AssignerModule+".*")
+		if err != nil {
+			return delivery.CompositionVerdict{}, err
+		}
+		defer pw.Stop()
+		go func() {
+			for e := range pw.Updates() {
+				ev := check.PresenceEvent{Settled: e == nil}
+				if e != nil {
+					ev.Key = e.Key()
+					if e.Operation() == jetstream.KeyValuePut {
+						if p, err := delivery.DecodePresence(e.Value()); err == nil {
+							ev.Online = p.Online
+						}
+					}
+				}
+				select {
+				case presence <- ev:
+				case <-ctx.Done():
+					return
+				}
+			}
+		}()
+	}
+	return check.AwaitComposition(ctx, presence, comps)
+}
+
+// followCompositions hands the checker each composition the assigner writes from now on, so a verdict that said its
+// composition was not judged takes it in when the assigner starts (event-driven).
+func followCompositions(ctx context.Context, kv jetstream.KeyValue, ch *check.Checker) error {
+	w, err := kv.WatchAll(ctx, jetstream.UpdatesOnly())
+	if err != nil {
+		return err
+	}
+	go func() {
+		defer w.Stop()
+		for e := range w.Updates() {
+			if e == nil || e.Operation() != jetstream.KeyValuePut {
+				continue
+			}
+			if comp, err := delivery.DecodeCompositionVerdict(e.Value()); err == nil {
+				ch.Composed(ctx, comp)
+			}
+		}
+	}()
+	return nil
+}
+
+// lazyCompositions opens the assigner's compositions when a check first asks for one and the bucket is there: until it
+// is, no assigner ever ran, so the check says at once that its composition is not judged (check.ErrAssignerNotRunning),
+// and the next check looks again. No timer: each look is a check asking.
+type lazyCompositions struct {
+	open func(ctx context.Context) (check.CompositionReader, error)
+
+	mu     sync.Mutex
+	reader check.CompositionReader
+}
+
+// Await is the opened reader's Await, opening it first when it is not yet.
+func (l *lazyCompositions) Await(ctx context.Context, key string) (delivery.CompositionVerdict, error) {
+	l.mu.Lock()
+	r := l.reader
+	if r == nil {
+		opened, err := l.open(ctx)
+		switch {
+		case errors.Is(err, jetstream.ErrBucketNotFound):
+			l.mu.Unlock()
+			return delivery.CompositionVerdict{}, check.ErrAssignerNotRunning
+		case err != nil:
+			l.mu.Unlock()
+			return delivery.CompositionVerdict{}, err
+		}
+		l.reader, r = opened, opened
+	}
+	l.mu.Unlock()
+	return r.Await(ctx, key)
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/compositions_integration_test.go

@@ -0,0 +1,106 @@
+//go:build integration
+
+package main
+
+import (
+	"context"
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats-server/v2/server"
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+// 1297/AC3 (its bus half): on the real bus, the checker's read of the assigner's composition waits while the key is
+// absent and while the assigner says it waits, and answers the verdict the assigner then writes under the check's key.
+func TestTheCheckerAwaitsTheAssignersComposition(t *testing.T) {
+	dir, err := os.MkdirTemp(os.Getenv("TMPDIR"), "comp")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { os.RemoveAll(dir) })
+	srv, err := server.NewServer(&server.Options{Host: "127.0.0.1", Port: -1, JetStream: true, StoreDir: filepath.Join(dir, "js"), NoLog: true, NoSigs: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	go srv.Start()
+	if !srv.ReadyForConnections(10 * time.Second) {
+		t.Fatal("the bus did not come up")
+	}
+	t.Cleanup(srv.Shutdown)
+	nc, err := nats.Connect(srv.ClientURL())
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(nc.Close)
+	js, _ := jetstream.New(nc)
+	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
+	defer cancel()
+	kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: delivery.AssignerCompositionsBucket, History: delivery.AssignerCompositionsHistory})
+	if err != nil {
+		t.Fatal(err)
+	}
+	pkv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: delivery.PresenceBucket, History: 5})
+	if err != nil {
+		t.Fatal(err)
+	}
+	pkey, _ := delivery.PresencePartKey(delivery.AssignerModule, "novox")
+	on, _ := delivery.EncodePresence(delivery.Presence{Online: true})
+	if _, err := pkv.Put(ctx, pkey, on); err != nil {
+		t.Fatal(err)
+	}
+	// With no assigner online the wait answers at once (a second key, before the assigner of this test is online).
+	off, _ := delivery.EncodePresence(delivery.Presence{Online: false})
+	if _, err := pkv.Put(ctx, pkey, off); err != nil {
+		t.Fatal(err)
+	}
+	other, _ := delivery.CompositionKey("feat/y", "0123456789ab")
+	if _, err := (compositionWatch{kv: kv, presence: pkv}).Await(ctx, other); !errors.Is(err, check.ErrAssignerNotRunning) {
+		t.Fatalf("with no assigner online the wait answered %v", err)
+	}
+	if _, err := pkv.Put(ctx, pkey, on); err != nil {
+		t.Fatal(err)
+	}
+	key, _ := delivery.CompositionKey("feat/x", "0123456789ab")
+	got := make(chan delivery.CompositionVerdict, 1)
+	go func() {
+		v, err := compositionWatch{kv: kv, presence: pkv}.Await(ctx, key)
+		if err != nil {
+			t.Error(err)
+		}
+		got <- v
+	}()
+	put := func(v delivery.CompositionVerdict) {
+		data, err := delivery.EncodeCompositionVerdict(v)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if _, err := kv.Put(ctx, key, data); err != nil {
+			t.Fatal(err)
+		}
+	}
+	time.Sleep(200 * time.Millisecond)
+	put(delivery.CompositionVerdict{Group: "feat/x", Heads: "0123456789ab", State: delivery.CompositionWaits, Words: "the indexer holds no candidates yet"})
+	select {
+	case v := <-got:
+		t.Fatalf("a waiting composition was answered: %+v", v)
+	case <-time.After(300 * time.Millisecond):
+	}
+	put(delivery.CompositionVerdict{Group: "feat/x", Heads: "0123456789ab", State: delivery.CompositionPass, SDK: "x", Machines: []string{"g14"}})
+	select {
+	case v := <-got:
+		if v.State != delivery.CompositionPass || v.Machines[0] != "g14" {
+			t.Errorf("answered %+v", v)
+		}
+	case <-time.After(5 * time.Second):
+		t.Fatal("the composition written was not answered")
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/compositions_test.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+type answering struct{ v delivery.CompositionVerdict }
+
+func (a answering) Await(context.Context, string) (delivery.CompositionVerdict, error) {
+	return a.v, nil
+}
+
+// 1297 review item 3: the compositions bucket missing when the checker starts is looked up again at the next check: while
+// it is missing a check says at once the assigner is not running; once it is there the check reads its composition, and
+// it is opened once.
+func TestTheCompositionsBucketIsLookedUpAtEachCheck(t *testing.T) {
+	opens, there := 0, false
+	l := &lazyCompositions{open: func(context.Context) (check.CompositionReader, error) {
+		opens++
+		if !there {
+			return nil, jetstream.ErrBucketNotFound
+		}
+		return answering{delivery.CompositionVerdict{State: delivery.CompositionPass, SDK: "x"}}, nil
+	}}
+	if _, err := l.Await(context.Background(), "k"); !errors.Is(err, check.ErrAssignerNotRunning) {
+		t.Fatalf("without the bucket: %v", err)
+	}
+	there = true
+	for range 2 {
+		v, err := l.Await(context.Background(), "k")
+		if err != nil || v.State != delivery.CompositionPass {
+			t.Fatalf("with the bucket: %+v, %v", v, err)
+		}
+	}
+	if opens != 2 {
+		t.Errorf("opened %d times, want twice (missing, then once)", opens)
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge.go

@@ -0,0 +1,104 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/nats-io/nats.go"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+// The forge's tools the checker reads with (mesh-catalog modules/gitea): gitea_get_file answers {file: {content}}, the text
+// of a file at a ref, and gitea_compare answers {total_commits, commits}, what head holds that base does not. The checker
+// writes nothing to the forge: the forge bridge sets the statuses (ADR 0484 clause 2).
+const (
+	getFileTool = "gitea.gitea_get_file"
+	compareTool = "gitea.gitea_compare"
+	commitsTool = "gitea.gitea_commits"
+)
+
+// notFoundStatus is the 404 of the forge's error, `Gitea API <path>: <status> <body>`.
+var notFoundStatus = regexp.MustCompile(`: 404( |$)`)
+
+// forgeReads reads the forge through call (mesh-sdk process.Conn.Call as the checker's own account).
+type forgeReads struct {
+	call func(key string, body any) (json.RawMessage, error)
+}
+
+// ask calls a forge tool; a call that reached nobody (no responders: the forge's tool runner re-serving, or the forge
+// down) is marked Unheard, so the check fails at the forge and is judged again when the nodes change (issue 1624).
+func (f forgeReads) ask(key string, body any) (json.RawMessage, error) {
+	raw, err := f.call(key, body)
+	if errors.Is(err, nats.ErrNoResponders) || errors.Is(err, nats.ErrTimeout) || errors.Is(err, context.DeadlineExceeded) {
+		return nil, &check.Unheard{Err: err}
+	}
+	return raw, err
+}
+
+func ownerRepo(repository string) (string, string) {
+	owner, repo, _ := strings.Cut(repository, "/")
+	return owner, repo
+}
+
+// File is the text of a file of a repository at a ref.
+func (f forgeReads) File(_ context.Context, repository, path, ref string) (string, error) {
+	owner, repo := ownerRepo(repository)
+	raw, err := f.ask(getFileTool, map[string]string{"owner": owner, "repo": repo, "path": path, "ref": ref})
+	if err != nil {
+		if notFoundStatus.MatchString(err.Error()) {
+			// The forge answers 404 for a file the ref does not hold (issue 1845). The status is matched in its own place,
+			// after the path's colon: the path carries a sha that may hold the digits 404.
+			return "", fmt.Errorf("%w: %v", check.ErrNotFound, err)
+		}
+		return "", err
+	}
+	var a struct {
+		File *struct {
+			Content *string `json:"content"`
+		} `json:"file"`
+	}
+	if err := json.Unmarshal(raw, &a); err != nil || a.File == nil || a.File.Content == nil {
+		return "", fmt.Errorf("the answer of %s is not {file: {content}}: %v", getFileTool, err)
+	}
+	return *a.File.Content, nil
+}
+
+// OnTrunk says whether the commit is already on the repository's main: main holds it when the commit holds nothing main does
+// not.
+func (f forgeReads) OnTrunk(_ context.Context, repository, commit string) (bool, error) {
+	owner, repo := ownerRepo(repository)
+	raw, err := f.ask(compareTool, map[string]string{"owner": owner, "repo": repo, "base": "main", "head": commit})
+	if err != nil {
+		return false, err
+	}
+	var a struct {
+		Total *int `json:"total_commits"`
+	}
+	if err := json.Unmarshal(raw, &a); err != nil || a.Total == nil {
+		return false, fmt.Errorf("the answer of %s is not {total_commits}: %v", compareTool, err)
+	}
+	return *a.Total == 0, nil
+}
+
+// FullSHA is the whole sha of a commit named by its first digits: the newest commit of the history at that ref.
+func (f forgeReads) FullSHA(_ context.Context, repository, commit string) (string, error) {
+	owner, repo := ownerRepo(repository)
+	raw, err := f.ask(commitsTool, map[string]any{"owner": owner, "repo": repo, "ref": commit, "limit": 1})
+	if err != nil {
+		return "", err
+	}
+	var a struct {
+		Commits []struct {
+			SHA string `json:"sha"`
+		} `json:"commits"`
+	}
+	if err := json.Unmarshal(raw, &a); err != nil || len(a.Commits) == 0 || len(a.Commits[0].SHA) != 40 || !strings.HasPrefix(a.Commits[0].SHA, commit) {
+		return "", fmt.Errorf("the answer of %s for %s is not a commit that starts with it: %v", commitsTool, commit, err)
+	}
+	return a.Commits[0].SHA, nil
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge_test.go

@@ -0,0 +1,105 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/nats-io/nats.go"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+// capturedAnswer is what the forge's tool answered (internal/check/testdata/captured/README).
+func capturedAnswer(t *testing.T, name string) json.RawMessage {
+	t.Helper()
+	raw, err := os.ReadFile(filepath.Join("..", "..", "internal", "check", "testdata", "captured", name+".json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	return raw
+}
+
+func TestTheForgeReadsParseWhatTheForgeAnswered(t *testing.T) { // 1624/AC4
+	var asked []string
+	f := forgeReads{call: func(key string, body any) (json.RawMessage, error) {
+		b, _ := json.Marshal(body)
+		asked = append(asked, key+" "+string(b))
+		switch {
+		case key == getFileTool:
+			return capturedAnswer(t, "forge-get-file-go-mod"), nil
+		case strings.Contains(string(b), "cb54756c3865"):
+			return capturedAnswer(t, "forge-compare-trunk"), nil
+		}
+		return capturedAnswer(t, "forge-compare-branch"), nil
+	}}
+	text, err := f.File(context.Background(), "novox/mesh-delivery", "modules/mesh-delivery-builder/go.mod", "main")
+	if err != nil || !strings.Contains(text, "git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261021100209-cb54756c3865") {
+		t.Errorf("file = %q, %v", text, err)
+	}
+	if on, err := f.OnTrunk(context.Background(), "novox/mesh-sdk", "cb54756c3865"); err != nil || !on {
+		t.Errorf("a commit on the trunk: %v, %v", on, err)
+	}
+	if on, err := f.OnTrunk(context.Background(), "novox/mesh-sdk", "9aaa5c80ac5c"); err != nil || on {
+		t.Errorf("a commit of the branch: %v, %v", on, err)
+	}
+	if len(asked) != 3 || !strings.Contains(asked[0], `"owner":"novox"`) || !strings.Contains(asked[2], `"base":"main"`) {
+		t.Errorf("asked %v", asked)
+	}
+	bad := forgeReads{call: func(string, any) (json.RawMessage, error) { return json.RawMessage(`{}`), nil }}
+	if _, err := bad.File(context.Background(), "novox/x", "go.mod", "main"); err == nil {
+		t.Error("an answer with no file was taken")
+	}
+	if _, err := bad.OnTrunk(context.Background(), "novox/x", "abc"); err == nil {
+		t.Error("an answer with no total was taken")
+	}
+}
+
+func TestTheForgeNamesTheWholeShaOfAShortCommit(t *testing.T) { // review D2
+	f := forgeReads{call: func(key string, body any) (json.RawMessage, error) {
+		if key != commitsTool {
+			t.Errorf("called %s", key)
+		}
+		return capturedAnswer(t, "forge-commits"), nil
+	}}
+	if sha, err := f.FullSHA(context.Background(), "novox/mesh-sdk", "cb54756c3865"); err != nil || sha != "cb54756c3865df5ac9c0dc0481ad9ebe2bf013a1" {
+		t.Errorf("sha = %q, %v", sha, err)
+	}
+	if _, err := f.FullSHA(context.Background(), "novox/mesh-sdk", "deadbeefdead"); err == nil {
+		t.Error("a commit that does not start with the pin was taken")
+	}
+}
+
+func TestAFileTheRefDoesNotHoldIsNotFoundAndOtherFailuresAreNot(t *testing.T) { // 1845/AC1, AC4
+	f := forgeReads{call: func(string, any) (json.RawMessage, error) {
+		return nil, errors.New("Gitea API contents/checks/particulars/go.mod?ref=98ca97fc: 404 object does not exist")
+	}}
+	if _, err := f.File(context.Background(), "novox/mesh-catalog", "checks/particulars/go.mod", "98ca97fc"); !errors.Is(err, check.ErrNotFound) {
+		t.Errorf("a 404 is %v, want ErrNotFound", err)
+	}
+	f = forgeReads{call: func(string, any) (json.RawMessage, error) {
+		return nil, errors.New("Gitea API contents/go.mod?ref=1111111111111111111111111111111404abcde: 500 internal error")
+	}}
+	if _, err := f.File(context.Background(), "novox/mesh-catalog", "go.mod", "main"); err == nil || errors.Is(err, check.ErrNotFound) {
+		t.Errorf("a 500 is %v, want a failure that is not ErrNotFound", err)
+	}
+}
+
+func TestAForgeReadThatReachesNobodyIsUnheard(t *testing.T) { // 1624 C7: "nats: no responders" on mesh-catalog #293
+	f := forgeReads{call: func(string, any) (json.RawMessage, error) { return nil, nats.ErrNoResponders }}
+	_, err := f.File(context.Background(), "novox/mesh-catalog", "checks/agenthome/go.mod", "950e37a46e8d")
+	var u *check.Unheard
+	if !errors.As(err, &u) {
+		t.Errorf("err = %v, want it marked as reaching nobody", err)
+	}
+	if _, err := f.OnTrunk(context.Background(), "novox/mesh-sdk", "abc"); !errors.As(err, &u) {
+		t.Errorf("compare: %v", err)
+	}
+	if _, err := f.FullSHA(context.Background(), "novox/mesh-sdk", "abc"); !errors.As(err, &u) {
+		t.Errorf("commits: %v", err)
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/integration_test.go

@@ -0,0 +1,708 @@
+//go:build integration
+
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats-server/v2/server"
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/announce"
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+// busConf is the shape of the composed accounts file (mesh-controller internal/broker): one account with JetStream, the
+// controller's user and the checker's own principal <node>.<module>. It carries no per-principal permissions: the grants
+// the controller composes from the manifest's state and reads (only the checker writes its buckets) are the controller's,
+// and are proved by its own module check, not here.
+const busConf = `
+listen: 127.0.0.1:-1
+jetstream { store_dir: %q }
+accounts {
+  MESH {
+    jetstream: enabled
+    users = [
+      { user: "ctl", password: "pw" }
+      { user: "n1.mesh-delivery-checker", password: "pw" }
+    ]
+  }
+}
+`
+
+const (
+	repo   = "novox/mesh-delivery"
+	head1  = "1111111111111111111111111111111111111111"
+	head2  = "2222222222222222222222222222222222222222"
+	trunk  = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+	merged = "fedcba9876543210fedcba9876543210fedcba98" // the merge commit of the captured fetch answer
+	digU   = "aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11"
+	digI   = "bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22"
+)
+
+var captured = filepath.Join("..", "..", "internal", "check", "testdata", "captured")
+
+func readCaptured(t *testing.T, name string) map[string]any {
+	t.Helper()
+	raw, err := os.ReadFile(filepath.Join(captured, name+".json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var v map[string]any
+	if err := json.Unmarshal(raw, &v); err != nil {
+		t.Fatal(err)
+	}
+	return v
+}
+
+// fakeBuildModules serve the tools of mesh-build-go and mesh-build-node as the real ones do (ADR 0469 clause 2): a call on
+// mesh.mod.<module>.call.<tool>.<node>.<caller> answers at once with the step and its key, and the step's end is written to
+// the key <node>.<id> of the module's steps bucket. What the steps end with are the results the build modules' own code
+// marshalled (internal/check/testdata/captured, README).
+type fakeBuildModules struct {
+	js       jetstream.JetStream
+	ctx      context.Context
+	conflict atomic.Bool
+	mu       sync.Mutex
+	calls    map[string]int // by `<module>.<tool>`
+	testTool *testing.T
+	// beside is, by workspace, the siblings the fetch placed in it as `<owner/repo> <commit>`, sorted: a digest echoes them
+	// (1929/AC2; mesh-sdk buildstep.besideOf), or the level runs whole and keeps nothing.
+	beside map[string][]string
+}
+
+func (f *fakeBuildModules) count(tool string) int {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return f.calls[tool]
+}
+
+func (f *fakeBuildModules) result(t *testing.T, tool string, args map[string]any) json.RawMessage {
+	level, _ := args["level"].(string)
+	var v any
+	switch {
+	case strings.HasSuffix(tool, "_fetch"):
+		name := "go-fetch-clean"
+		if f.conflict.Load() {
+			name = "go-fetch-conflict"
+		}
+		fetched := readCaptured(t, name)
+		fetched["commit"], fetched["base"] = args["commit"], args["base"]
+		var refs []struct {
+			Repository string `json:"repository"`
+			Commit     string `json:"commit"`
+		}
+		raw, _ := json.Marshal(args["beside"])
+		_ = json.Unmarshal(raw, &refs)
+		var lines []string
+		for _, r := range refs {
+			lines = append(lines, r.Repository+" "+r.Commit)
+		}
+		sort.Strings(lines)
+		f.mu.Lock()
+		if f.beside == nil {
+			f.beside = map[string][]string{}
+		}
+		f.beside[fmt.Sprint(fetched["workspace"])] = lines
+		f.mu.Unlock()
+		v = fetched
+	case strings.HasSuffix(tool, "_digest"):
+		d := map[string]string{"unit": digU, "integration": digI}[level]
+		f.mu.Lock()
+		beside := f.beside[fmt.Sprint(args["workspace"])]
+		f.mu.Unlock()
+		v = map[string]any{"level": level, "packages": map[string]string{"fixture/slow": d}, "beside": beside}
+	case strings.HasSuffix(tool, "_test"):
+		r := readCaptured(t, "go-test-slow")
+		r["level"] = level
+		v = r
+	}
+	data, _ := json.Marshal(v)
+	return data
+}
+
+// serve makes module's steps bucket and its build seat's stream and workers, and pulls its asks on n1 as the real module
+// does since R4g (ADR 0525; issue 1887 A5): each ask's job runs with step bodies answering the captured results, and a
+// check takes the kept verdicts of the checker's kept bucket by their digests.
+func (f *fakeBuildModules) serve(t *testing.T, module string, kept jetstream.KeyValue) {
+	kv, err := f.js.CreateKeyValue(f.ctx, jetstream.KeyValueConfig{Bucket: delivery.StepsBucket(module), History: 1})
+	if err != nil {
+		t.Fatal(err)
+	}
+	language := strings.TrimPrefix(module, "mesh-build-")
+	if err := buildstep.DeclareAskWorkers(f.ctx, f.js, language, 30*time.Second); err != nil {
+		t.Fatal(err)
+	}
+	prefix := map[string]string{"mesh-build-go": "build_go_", "mesh-build-node": "build_node_"}[module]
+	call := func(name string) buildstep.StepFunc {
+		return func(ctx context.Context, args map[string]any) (any, error) {
+			tool := prefix + name
+			f.mu.Lock()
+			f.calls[module+"."+tool]++
+			f.mu.Unlock()
+			return f.result(t, tool, args), nil
+		}
+	}
+	steps := buildstep.AskSteps{Fetch: call("fetch"), Test: call("test"),
+		Kept: func(ctx context.Context, level, digest string) (int, bool, error) {
+			key, err := delivery.KeptKey(level, digest)
+			if err != nil {
+				return 0, false, err
+			}
+			e, err := kept.Get(ctx, key)
+			if errors.Is(err, jetstream.ErrKeyNotFound) {
+				return 0, false, nil
+			}
+			if err != nil {
+				return 0, false, err
+			}
+			v, err := delivery.DecodeKept(e.Value())
+			return v.Tests, err == nil, err
+		}}
+	if module == "mesh-build-go" {
+		steps.Digest = call("digest")
+	}
+	put := func(key string, value any) (uint64, error) {
+		raw, _ := value.(json.RawMessage)
+		return kv.Put(f.ctx, key, raw)
+	}
+	p := &buildstep.Puller{Source: &buildstep.JetStreamAsks{JS: f.js, Language: language}, Language: language, Node: "n1", Put: put,
+		Capacity: func() int { return 2 }, PullWait: 200 * time.Millisecond,
+		Run: func(ctx context.Context, a delivery.StepAsk) (any, error) { return buildstep.RunAsk(ctx, steps, a) }}
+	go func() { _ = p.Pull(f.ctx) }()
+}
+
+// serveForge answers the forge's two reads as its tools do, with the answers the forge gave (internal/check/testdata/captured):
+// the go.mod of the captured file, whose mesh-sdk pin is cb54756c3865, and gitea_compare for the pin: on the trunk, unless the
+// pin is the one the test set as stale.
+func (b *bed) serveForge(t *testing.T, nc *nats.Conn) {
+	reply := func(m *nats.Msg, name string) {
+		var result map[string]any
+		_ = json.Unmarshal(mustRead(t, name), &result)
+		answer, _ := json.Marshal(map[string]any{"result": result, "error": "", "node": "n0"})
+		_ = m.Respond(answer)
+	}
+	for _, tool := range []string{"gitea_get_file", "gitea_compare"} {
+		tool := tool
+		sub, err := nc.Subscribe("mesh.mod.gitea.tool."+tool, func(m *nats.Msg) {
+			var a map[string]string
+			_ = json.Unmarshal(m.Data, &a)
+			switch {
+			case tool == "gitea_get_file" && b.stalePin.Load():
+				content := strings.Replace(string(mustRead(t, "forge-get-file-go-mod")), "cb54756c3865", "9aaa5c80ac5c", 1)
+				var result map[string]any
+				_ = json.Unmarshal([]byte(content), &result)
+				answer, _ := json.Marshal(map[string]any{"result": result, "error": "", "node": "n0"})
+				_ = m.Respond(answer)
+			case tool == "gitea_get_file":
+				reply(m, "forge-get-file-go-mod")
+			case strings.HasPrefix(a["head"], "9aaa5c80ac5c"):
+				reply(m, "forge-compare-branch")
+			default:
+				reply(m, "forge-compare-trunk")
+			}
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+		t.Cleanup(func() { _ = sub.Unsubscribe() })
+	}
+}
+
+func mustRead(t *testing.T, name string) []byte {
+	t.Helper()
+	raw, err := os.ReadFile(filepath.Join(captured, name+".json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	return raw
+}
+
+type bed struct {
+	stalePin atomic.Bool
+	ctx      context.Context
+	js       jetstream.JetStream
+	buckets  map[string]jetstream.KeyValue
+	tools    map[string]jetstream.KeyValue
+	fake     *fakeBuildModules
+	srvURL   string
+	announce []string
+	mu       sync.Mutex
+}
+
+// startBed starts the bus, the buckets the controller makes from the checker's and the other parts' manifests, the build
+// modules' streams and the checker's durable consumers on them, one node's toolchains, the gate's source naming the trunk, and
+// the fake build modules. It runs no checker.
+func startBed(t *testing.T) *bed {
+	dir, err := os.MkdirTemp(os.Getenv("TMPDIR"), "c")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { os.RemoveAll(dir) })
+	conf := filepath.Join(dir, "bus.conf")
+	if err := os.WriteFile(conf, []byte(fmt.Sprintf(busConf, filepath.Join(dir, "js"))), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	opts, err := server.ProcessConfigFile(conf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	opts.NoLog, opts.NoSigs = true, true
+	srv, err := server.NewServer(opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+	go srv.Start()
+	if !srv.ReadyForConnections(10 * time.Second) {
+		t.Fatal("the bus did not come up")
+	}
+	t.Cleanup(srv.Shutdown)
+	ctl, err := nats.Connect(srv.ClientURL(), nats.UserInfo("ctl", "pw"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(ctl.Close)
+	js, err := jetstream.New(ctl)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 90*time.Second)
+	t.Cleanup(cancel)
+	b := &bed{ctx: ctx, js: js, buckets: map[string]jetstream.KeyValue{}, tools: map[string]jetstream.KeyValue{}, srvURL: srv.ClientURL()}
+	for module, stream := range toolchainStreams {
+		if _, err := js.CreateStream(ctx, jetstream.StreamConfig{Name: stream, Subjects: []string{"mesh.stream." + module + ".event.toolchain.reported"}}); err != nil {
+			t.Fatal(err)
+		}
+		if _, err := js.CreateOrUpdateConsumer(ctx, stream, jetstream.ConsumerConfig{Durable: "n1_mesh-delivery-checker", AckPolicy: jetstream.AckExplicitPolicy}); err != nil {
+			t.Fatal(err)
+		}
+		kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: delivery.ToolchainsBucket(module), History: 1})
+		if err != nil {
+			t.Fatal(err)
+		}
+		b.tools[module] = kv
+	}
+	// The checker's stream of events, which the indexer and the forge bridge hear.
+	if _, err := js.CreateStream(ctx, jetstream.StreamConfig{Name: "CHECKS", Subjects: []string{"mesh.stream.mesh-delivery-checker.event.>"}}); err != nil {
+		t.Fatal(err)
+	}
+	for name, history := range map[string]int{delivery.CheckerVerdictsBucket: delivery.CheckerVerdictsHistory, delivery.CheckerKeptBucket: delivery.CheckerKeptHistory,
+		delivery.CheckerOwedBucket: delivery.CheckerOwedHistory, delivery.PreviewsBucket: delivery.PreviewsHistory, delivery.CandidatesBucket: delivery.CandidatesHistory,
+		delivery.ModulesBucket: delivery.ModulesHistory, delivery.ManifestsBucket: delivery.ManifestsHistory, delivery.SourceBucket: delivery.SourceHistory,
+		delivery.PresenceBucket: delivery.PresenceHistory, delivery.HaveBucket: delivery.HaveHistory, check.TriesBucket: 1} {
+		kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: name, History: uint8(history)})
+		if err != nil {
+			t.Fatal(err)
+		}
+		b.buckets[name] = kv
+	}
+	// 1929/AC1: the indexer's value of the repository's module, with no TypeScript manifest, so the Go build module alone
+	// judges the repository (an unknown repository is judged by both, issue 1887 A12).
+	known, err := delivery.EncodeModule(delivery.Module{Repository: repo, Commit: trunk, Path: "modules/m", None2: "the fingerprint is computed with its chain"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := b.buckets[delivery.ModulesBucket].Put(ctx, "m", known); err != nil {
+		t.Fatal(err)
+	}
+	b.setOnline(t, "n1", true)
+	for _, module := range []string{"mesh-build-go", "mesh-build-node"} {
+		b.setHealth(t, "n1", module)
+	}
+	b.serveForge(t, ctl)
+	b.fake = &fakeBuildModules{js: js, ctx: ctx, calls: map[string]int{}}
+	b.fake.serve(t, "mesh-build-go", b.buckets[delivery.CheckerKeptBucket])
+	b.fake.serve(t, "mesh-build-node", b.buckets[delivery.CheckerKeptBucket])
+	b.report(t, "mesh-build-go", "n1", "go", "go1.27.1", "1")
+	b.report(t, "mesh-build-node", "n1", "typescript", "tsc5", "1")
+	b.setTrunk(t, map[string]string{repo: trunk})
+	return b
+}
+
+func (b *bed) setTrunk(t *testing.T, heads map[string]string) {
+	t.Helper()
+	data, err := delivery.EncodeSource(delivery.Source{Group: "g", Heads: heads})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := b.buckets[delivery.SourceBucket].Put(b.ctx, delivery.SourceMainKey, data); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func (b *bed) setOnline(t *testing.T, node string, online bool) {
+	t.Helper()
+	data, _ := delivery.EncodePresence(delivery.Presence{Online: online})
+	if _, err := b.buckets[delivery.PresenceBucket].Put(b.ctx, node, data); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func (b *bed) setHealth(t *testing.T, node, module string) {
+	t.Helper()
+	data, err := delivery.EncodeHave(delivery.Have{Phase: delivery.PhaseRunning, Health: delivery.HealthOK})
+	if err != nil {
+		t.Fatal(err)
+	}
+	key, _ := delivery.HaveKey(node, module)
+	if _, err := b.buckets[delivery.HaveBucket].Put(b.ctx, key, data); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func (b *bed) report(t *testing.T, module, node, language, version, recipe string) {
+	t.Helper()
+	data, err := delivery.EncodeToolchain(delivery.Toolchain{Language: language, Version: version, Recipe: recipe, At: time.Now().UTC()})
+	if err != nil {
+		t.Fatal(err)
+	}
+	key, _ := delivery.ToolchainKey(node, language)
+	if _, err := b.tools[module].Put(b.ctx, key, data); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := b.js.Publish(b.ctx, "mesh.stream."+module+".event.toolchain.reported", []byte(`{}`)); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// candidate writes candidates.<group> as the indexer does (the SDK's EncodeCandidate is the indexer's own encoder).
+func (b *bed) candidate(t *testing.T, group string, pulls ...delivery.CandidatePull) string {
+	t.Helper()
+	heads := make([]delivery.Head, len(pulls))
+	for i, p := range pulls {
+		heads[i] = p.Head
+	}
+	hash, err := delivery.HeadsHash(heads)
+	if err != nil {
+		t.Fatal(err)
+	}
+	data, err := delivery.EncodeCandidate(delivery.Candidate{V: delivery.Version, Group: group, HeadsHash: hash, Pulls: pulls, FPSet: delivery.FingerprintSet(pulls)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	key, _ := delivery.CandidatesKey(group)
+	if _, err := b.buckets[delivery.CandidatesBucket].Put(b.ctx, key, data); err != nil {
+		t.Fatal(err)
+	}
+	vk, _ := delivery.CheckerVerdictKey(group, hash)
+	return vk
+}
+
+func pull(repository string, number int, head string) delivery.CandidatePull {
+	return delivery.CandidatePull{Head: delivery.Head{Repository: repository, Number: number, Head: head}, Modules: []string{}}
+}
+
+// start runs the program as the checker of a node.
+func (b *bed) start(t *testing.T, env map[string]string) {
+	t.Helper()
+	broker := filepath.Join(t.TempDir(), "broker")
+	cred, _ := json.Marshal(credential{URL: b.srvURL, Node: "n1", Module: "mesh-delivery-checker", User: "n1.mesh-delivery-checker", Password: "pw"})
+	if err := os.WriteFile(broker, cred, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	e := map[string]string{"MESH_BROKER_FILE": broker}
+	for k, v := range env {
+		e[k] = v
+	}
+	runCtx, stop := context.WithCancel(b.ctx)
+	done := make(chan error, 1)
+	go func() { done <- run(runCtx, func(k string) string { return e[k] }, io.Discard) }()
+	t.Cleanup(func() { stop(); <-done })
+}
+
+// verdict reads the verdict key until pred holds of it, within 20 s.
+func (b *bed) verdict(t *testing.T, key string, pred func(delivery.Verdict) bool) delivery.Verdict {
+	t.Helper()
+	var last delivery.Verdict
+	for deadline := time.Now().Add(20 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+		e, err := b.buckets[delivery.CheckerVerdictsBucket].Get(b.ctx, key)
+		if err != nil {
+			continue
+		}
+		if last, err = delivery.DecodeVerdict(e.Value()); err == nil && pred(last) {
+			return last
+		}
+	}
+	t.Fatalf("verdicts.%s = %+v within 20 s", key, last)
+	return last
+}
+
+func ended(v delivery.Verdict) bool { return v.State != delivery.VerdictRunning }
+
+// owed reads the status the checker owes on a head.
+func (b *bed) owed(t *testing.T, number int, head, state string) delivery.Owed {
+	t.Helper()
+	key, err := delivery.CheckerOwedKey(repo, number, head)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var last delivery.Owed
+	for deadline := time.Now().Add(20 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+		e, err := b.buckets[delivery.CheckerOwedBucket].Get(b.ctx, key)
+		if err != nil {
+			continue
+		}
+		if last, err = delivery.DecodeCheckerOwed(e.Value()); err == nil && last.State == state {
+			return last
+		}
+	}
+	t.Fatalf("owed.%s = %+v within 20 s, want the state %s", key, last, state)
+	return last
+}
+
+// TestCheckerJudgesACandidateAndOwesItsStatus: a candidate the indexer wrote, one pull request of mesh-delivery, is fetched
+// merged onto the trunk the gate names, digested and tested at both levels on the node, kept, previewed; the verdict passes
+// with the counts of both levels and the composition not run, and the status mesh/check is owed on the head as success.
+func TestCheckerJudgesACandidateAndOwesItsStatus(t *testing.T) { // N6/AC5, 1300/AC5, 1445/AC1, 1929/AC1
+	b := startBed(t)
+	key := b.candidate(t, "feat/x", pull(repo, 7, head1))
+	b.start(t, nil)
+	v := b.verdict(t, key, ended)
+	if v.State != delivery.VerdictPass || v.Levels[delivery.LevelUnit].Run != 2 || v.Levels[delivery.LevelIntegration].Run != 2 || v.Trunk[repo] != trunk {
+		t.Fatalf("verdict = %+v", v)
+	}
+	if v.Composition == nil || v.Composition.State != delivery.CompositionNotRun || len(v.Machines) != 1 || v.Machines[0] != "n1" {
+		t.Errorf("composition %+v machines %v", v.Composition, v.Machines)
+	}
+	o := b.owed(t, 7, head1, "success")
+	if o.Context != delivery.StatusContextCheck || !strings.HasPrefix(o.Text, "pass 111111111111 on aaaaaaaaaaaa") || !strings.Contains(o.Text, "unit 2 run") {
+		t.Errorf("owed = %+v", o)
+	}
+	for tool, want := range map[string]int{"mesh-build-go.build_go_fetch": 1, "mesh-build-go.build_go_digest": 2, "mesh-build-go.build_go_test": 2} {
+		if got := b.fake.count(tool); got != want {
+			t.Errorf("%s called %d times, want %d", tool, got, want)
+		}
+	}
+	// What passed is kept once under each level's digest.
+	for _, k := range []string{"unit." + digU, "integration." + digI} {
+		if _, err := b.buckets[delivery.CheckerKeptBucket].Get(b.ctx, k); err != nil {
+			t.Errorf("kept.%s: %v", k, err)
+		}
+	}
+	// The preview of the head merged onto the trunk, with the tree and the manifest digest the fetch named.
+	pk, _ := delivery.PreviewKey(repo, head1, trunk)
+	e, err := b.buckets[delivery.PreviewsBucket].Get(b.ctx, pk)
+	if err != nil {
+		t.Fatalf("previews.%s: %v", pk, err)
+	}
+	pv, err := delivery.DecodePreview(e.Value())
+	if err != nil || pv.Merge != merged || pv.Modules["modules/m"].Tree != "1111111111111111111111111111111111111111" {
+		t.Errorf("preview = %+v, %v", pv, err)
+	}
+}
+
+// TestACheckOfEqualInputsRunsNothing: a second candidate (another head, the same digests) is checked with every package
+// taken from the first's kept verdicts: no test step runs and no second kept key appears.
+func TestACheckOfEqualInputsRunsNothing(t *testing.T) { // 1287/AC5, 1288/AC6, 1929/AC2
+	b := startBed(t)
+	first := b.candidate(t, "feat/x", pull(repo, 7, head1))
+	b.start(t, nil)
+	b.verdict(t, first, ended)
+	tests, kept := b.fake.count("mesh-build-go.build_go_test"), keptCount(t, b)
+	second := b.candidate(t, "feat/y", pull(repo, 8, head2))
+	v := b.verdict(t, second, ended)
+	if v.State != delivery.VerdictPass || v.Levels[delivery.LevelUnit].Run != 0 || v.Levels[delivery.LevelUnit].Kept != 2 || v.Levels[delivery.LevelIntegration].Run != 0 {
+		t.Fatalf("verdict = %+v, want everything taken from the kept verdicts", v)
+	}
+	if got := b.fake.count("mesh-build-go.build_go_test"); got != tests {
+		t.Errorf("build_go_test called %d times, was %d: a test ran for equal inputs", got, tests)
+	}
+	if got := keptCount(t, b); got != kept {
+		t.Errorf("%d kept keys, was %d", got, kept)
+	}
+}
+
+func keptCount(t *testing.T, b *bed) int {
+	t.Helper()
+	keys, err := b.buckets[delivery.CheckerKeptBucket].Keys(b.ctx)
+	if err != nil {
+		return 0
+	}
+	return len(keys)
+}
+
+// TestAHeadThatDoesNotMergeFailsNamingTheFilesAndRunsNoTest: the fetch answers the files in conflict; the verdict fails naming
+// them, no test or digest step is run, a preview of the conflicts alone is written and the status is owed as failure.
+func TestAHeadThatDoesNotMergeFailsNamingTheFilesAndRunsNoTest(t *testing.T) { // 1289/AC4
+	b := startBed(t)
+	b.fake.conflict.Store(true)
+	key := b.candidate(t, "feat/x", pull(repo, 7, head1))
+	b.start(t, nil)
+	v := b.verdict(t, key, ended)
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "files in conflict: a.go, sub/b.go") {
+		t.Fatalf("verdict = %+v", v)
+	}
+	if o := b.owed(t, 7, head1, "failure"); !strings.HasPrefix(o.Text, "failed: n1: ") || !strings.Contains(o.Text, "files in conflict: a.go, sub/b.go") {
+		t.Errorf("owed = %+v", o)
+	}
+	if n := b.fake.count("mesh-build-go.build_go_digest") + b.fake.count("mesh-build-go.build_go_test"); n != 0 {
+		t.Errorf("%d digest and test steps ran after a conflict", n)
+	}
+	pk, _ := delivery.PreviewKey(repo, head1, trunk)
+	if e, err := b.buckets[delivery.PreviewsBucket].Get(b.ctx, pk); err != nil {
+		t.Errorf("previews.%s: %v", pk, err)
+	} else if pv, err := delivery.DecodePreview(e.Value()); err != nil || strings.Join(pv.Conflicts, ",") != "a.go,sub/b.go" || pv.Merge != "" {
+		t.Errorf("preview = %+v, %v, want the files in conflict alone", pv, err)
+	}
+}
+
+// TestAnHqPullRequestGetsNoVerdictAndAnotherDoes: hq's pull request is judged by no one (ADR 0484 clause 8), the other one in
+// the same run is.
+// 1887/A10, ADR 0527 §2: a pull request into hq gets a verdict and a mesh/check from the checker, as any repository's.
+func TestAnHqPullRequestGetsAVerdictAndAStatus(t *testing.T) {
+	b := startBed(t)
+	b.setTrunk(t, map[string]string{repo: trunk, "novox/hq": trunk})
+	hq := b.candidate(t, "feat/hq", pull("novox/hq", 3, head1))
+	b.start(t, nil)
+	if v := b.verdict(t, hq, ended); v.State != delivery.VerdictPass {
+		t.Fatalf("hq's verdict = %+v", v)
+	}
+	key, _ := delivery.CheckerOwedKey("novox/hq", 3, head1)
+	for deadline := time.Now().Add(20 * time.Second); ; time.Sleep(50 * time.Millisecond) {
+		if e, err := b.buckets[delivery.CheckerOwedBucket].Get(b.ctx, key); err == nil {
+			if o, err := delivery.DecodeCheckerOwed(e.Value()); err == nil && o.State == "success" {
+				return
+			}
+		}
+		if time.Now().After(deadline) {
+			t.Fatalf("hq#3 owes no success within 20 s")
+		}
+	}
+}
+
+// TestACheckLeftRunningIsTakenOverWhenTheCheckerStarts: the verdict key holds running, left by a checker that stopped; the
+// started checker judges it again and ends it (ADR 0478 clause 6, as the builder's).
+func TestACheckLeftRunningIsTakenOverWhenTheCheckerStarts(t *testing.T) { // N6/AC2
+	b := startBed(t)
+	key := b.candidate(t, "feat/x", pull(repo, 7, head1))
+	group, heads, _ := delivery.ParseCheckerVerdictKey(key)
+	left, err := delivery.EncodeVerdict(delivery.Verdict{Group: group, Heads: heads, Trunk: map[string]string{repo: trunk}, State: delivery.VerdictRunning})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := b.buckets[delivery.CheckerVerdictsBucket].Create(b.ctx, key, left); err != nil {
+		t.Fatal(err)
+	}
+	b.start(t, nil)
+	if v := b.verdict(t, key, ended); v.State != delivery.VerdictPass {
+		t.Errorf("verdict = %+v", v)
+	}
+}
+
+// TestAMemberNamingAMeshSDKCommitOffTheTrunkFailsNamingTheCommit: the go.mod the forge answers names a commit that main does not
+// hold; the verdict fails naming the member and the commit and no test runs (ADR 0484 clause 9).
+func TestAMemberNamingAMeshSDKCommitOffTheTrunkFailsNamingTheCommit(t *testing.T) { // 1624/AC2, 1929/AC3
+	b := startBed(t)
+	b.stalePin.Store(true)
+	key := b.candidate(t, "feat/x", pull(repo, 7, head1))
+	b.start(t, nil)
+	v := b.verdict(t, key, ended)
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "9aaa5c80ac5c") || !strings.Contains(v.Failed.Words, repo+"#7") {
+		t.Fatalf("verdict = %+v", v)
+	}
+	// 1929/AC3: no assertion that no test ran: one ask runs fetch, digest and tests (ADR 0525 §3).
+}
+
+// triesStore is the tries bucket as the tools write it.
+type triesStore struct {
+	kv  jetstream.KeyValue
+	ctx context.Context
+}
+
+func (s triesStore) Keys() ([]string, error) {
+	keys, err := s.kv.Keys(s.ctx)
+	if err == jetstream.ErrNoKeysFound {
+		return nil, nil
+	}
+	return keys, err
+}
+func (s triesStore) Get(key string) (json.RawMessage, error) {
+	e, err := s.kv.Get(s.ctx, key)
+	if err == jetstream.ErrKeyNotFound {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return e.Value(), nil
+}
+func (s triesStore) Create(key string, value []byte) error {
+	_, err := s.kv.Create(s.ctx, key, value)
+	return err
+}
+
+// TestATryIsJudgedAndItsEndWrittenWithNoStatusOwed: a try written as checker_try writes it is taken by the running checker,
+// judged through the build modules as a pull request's head merged onto its trunk, and ended pass in its key, with no
+// verdict and no status owed (ADR 0501 §5).
+func TestATryIsJudgedAndItsEndWrittenWithNoStatusOwed(t *testing.T) {
+	b := startBed(t)
+	b.start(t, nil)
+	store := triesStore{b.buckets[check.TriesBucket], b.ctx}
+	id, err := check.AskTry(store, map[string]string{repo: trunk}, check.TryAsk{Repository: repo, Head: head1}, time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	var last check.Try
+	for deadline := time.Now().Add(20 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+		raw, _ := store.Get(id)
+		if last, err = check.DecodeTry(raw); err == nil && last.Over() {
+			break
+		}
+	}
+	if last.State != check.TryPass || last.Trunk != trunk || last.Took == "" {
+		t.Fatalf("try = %+v, want passed on the trunk", last)
+	}
+	if b.fake.count("mesh-build-go.build_go_fetch") == 0 {
+		t.Errorf("the try fetched nothing")
+	}
+	for _, name := range []string{delivery.CheckerOwedBucket, delivery.CheckerVerdictsBucket, delivery.PreviewsBucket} {
+		if keys, _ := b.buckets[name].Keys(b.ctx); len(keys) != 0 {
+			t.Errorf("a try wrote %s: %v", name, keys)
+		}
+	}
+}
+
+// TestTheCheckerSaysOwedReadableOnTheBus: started, the checker says on its own states subject what it keeps, owed among
+// the readable ones, which is what grants the forge module its read of owed (ADR 0495 §2-§3, ADR 0521; R4e finding R2-1).
+func TestTheCheckerSaysOwedReadableOnTheBus(t *testing.T) { // R2-1
+	b := startBed(t)
+	if _, err := b.js.CreateStream(b.ctx, jetstream.StreamConfig{Name: "EVENTS", Subjects: []string{"mesh.mod.*.event.>"}}); err != nil {
+		t.Fatal(err)
+	}
+	b.start(t, nil)
+	events, err := b.js.Stream(b.ctx, "EVENTS")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var said announce.States
+	for deadline := time.Now().Add(10 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+		m, err := events.GetLastMsgForSubject(b.ctx, announce.Subject("mesh-delivery-checker"))
+		if err != nil {
+			continue
+		}
+		if err := json.Unmarshal(m.Data, &said); err != nil {
+			t.Fatal(err)
+		}
+		break
+	}
+	if said.Module != "mesh-delivery-checker" || said.Node != "n1" || !said.Keeps("owed") || !said.Readable("owed") ||
+		!said.Readable("previews") || !said.Readable("verdicts") || !said.Readable("kept") || said.Readable("tries") || len(said.States) != 5 {
+		t.Fatalf("the checker said %+v, want its five states with kept, owed, previews and verdicts readable (1929/AC4; 1887 A5b)", said)
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge.go

@@ -0,0 +1,191 @@
+package main
+
+import (
+	"context"
+	"sort"
+	"strings"
+	"sync"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+// judgeDeps are the parts the judge of a check is made of.
+type judgeDeps struct {
+	asks     check.Asks
+	tools    *buildrun.ToolchainSet
+	trunks   *check.Trunks
+	kept     check.KV
+	previews check.KV
+	repos    *repoModules
+	forge    check.Forge
+	announce check.Announcer
+	builds   check.BuildStates
+	// compositions is the assigner's bucket of compositions; nil leaves every composition not run.
+	compositions check.CompositionReader
+	logf         func(format string, args ...any)
+}
+
+func newJudge(d judgeDeps) check.Judge {
+	return &check.Examiner{Compositions: d.compositions, Asks: d.asks, Toolchains: d.tools,
+		Kept: check.Kept{Store: d.kept}, Previews: d.previews, Modules: d.repos, Packages: d.repos, Forge: d.forge, Runs: d.repos, Builds: d.builds, Announce: d.announce, Trunks: d.trunks, Logf: d.logf}
+}
+
+// manifestKV reads a manifest by its digest.
+type manifestKV interface {
+	Get(ctx context.Context, key string) (value []byte, revision uint64, found bool, err error)
+}
+
+// repoModules knows which build modules judge a repository, from the indexer's modules and their manifests: the Go build
+// module always (a repository's go.mod files are its own), the Node one when a module of the repository has a TypeScript
+// artifact (ADR 0484 clause 10). Safe for use from the watch and from a check at once.
+type repoModules struct {
+	manifests manifestKV
+	logf      func(format string, args ...any)
+
+	mu     sync.Mutex
+	langs  map[string]map[string]bool     // by manifest digest: the languages of its artifacts
+	tsPkgs map[string][]string            // by manifest digest: the names of its TypeScript package artifacts
+	path   map[string]string              // by module: its directory in its repository
+	named  map[string]map[string][]string // by module: each artifact's named paths, as the indexer keeps them
+	repoOf map[string]string              // by module: its repository
+	commit map[string]string              // by module: the commit its record was computed at (the commit the mesh runs)
+	typed  map[string]string              // by module: its manifest digest
+}
+
+// Put takes a change of the indexer's modules bucket in: a module's repository and the languages its manifest names.
+func (r *repoModules) Put(ctx context.Context, key string, value []byte, deleted bool) {
+	r.mu.Lock()
+	if r.repoOf == nil {
+		r.repoOf, r.typed, r.langs, r.commit = map[string]string{}, map[string]string{}, map[string]map[string]bool{}, map[string]string{}
+		r.tsPkgs, r.path, r.named = map[string][]string{}, map[string]string{}, map[string]map[string][]string{}
+	}
+	if deleted {
+		delete(r.repoOf, key)
+		delete(r.typed, key)
+		delete(r.commit, key)
+		delete(r.path, key)
+		delete(r.named, key)
+		r.mu.Unlock()
+		return
+	}
+	r.mu.Unlock()
+	m, err := delivery.DecodeModule(value)
+	if err != nil {
+		return
+	}
+	r.mu.Lock()
+	r.repoOf[key] = m.Repository
+	r.typed[key] = m.Manifest
+	r.commit[key] = m.Commit
+	r.path[key] = m.Path
+	r.named[key] = m.ArtifactPaths
+	_, known := r.langs[m.Manifest]
+	r.mu.Unlock()
+	if m.Manifest == "" || known {
+		return
+	}
+	set := map[string]bool{}
+	var pkgs []string
+	if mk, err := delivery.ManifestsKey(m.Manifest); err == nil {
+		if raw, _, found, err := r.manifests.Get(ctx, mk); err == nil && found {
+			if kept, err := delivery.DecodeManifest(raw); err == nil {
+				if man, err := catalogue.ParseManifest([]byte(kept.JSON)); err == nil && man.Build != nil {
+					for _, a := range man.Build.Artifacts {
+						if a.Language != "" {
+							set[a.Language] = true
+						}
+						if a.Kind == "package" && a.Language == "typescript" {
+							pkgs = append(pkgs, a.Name)
+						}
+					}
+				} else if err != nil && r.logf != nil {
+					r.logf("the manifest %s cannot be read, so its module counts as no TypeScript: %v", m.Manifest, err)
+				}
+			}
+		}
+	}
+	r.mu.Lock()
+	r.langs[m.Manifest] = set
+	r.tsPkgs[m.Manifest] = pkgs
+	r.mu.Unlock()
+}
+
+// PackagePaths are the paths, relative to the repository, that the TypeScript package artifacts of a repository's modules
+// are built from, sorted: the named paths the indexer keeps in each module's value (delivery.Module.ArtifactPaths; only the
+// indexer reads them from a manifest, the lead's decision L8), under the module's directory. None for a module whose value
+// holds no paths.
+func (r *repoModules) PackagePaths(repository string) []string {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	var out []string
+	for module, repo := range r.repoOf {
+		if repo != repository {
+			continue
+		}
+		dir := strings.Trim(r.path[module], "/")
+		for _, name := range r.tsPkgs[r.typed[module]] {
+			for _, p := range r.named[module][name] {
+				p = strings.Trim(strings.TrimPrefix(p, "./"), "/")
+				if dir != "" && dir != delivery.RootPath {
+					p = dir + "/" + p
+				}
+				out = append(out, p)
+			}
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+// BuildModules are the build modules that judge a repository, sorted: the Go build module always, and the Node build
+// module when a module of the repository builds TypeScript. A repository of which the mesh knows no module (mesh-lab, hq)
+// is judged by both, each finding its own directories in the tree (go.mod files; package.json files), so a repository
+// with tests in either language and no manifest is judged whole (issue 1887 A12).
+func (r *repoModules) BuildModules(repository string) []string {
+	out := []string{buildrun.GoBuildModule}
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	known := false
+	for module, repo := range r.repoOf {
+		if repo != repository {
+			continue
+		}
+		known = true
+		if r.langs[r.typed[module]]["typescript"] {
+			out = append(out, buildrun.NodeBuildModule)
+			break
+		}
+	}
+	if !known {
+		out = append(out, buildrun.NodeBuildModule)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// buildReader reads the builder's build of a module at a fingerprint (mesh-delivery-builder_builds).
+type buildReader struct{ kv kvStore }
+
+func (r buildReader) Build(ctx context.Context, module, fp2 string) (delivery.BuilderBuild, bool, error) {
+	key, err := delivery.BuilderBuildKey(module, fp2)
+	if err != nil {
+		return delivery.BuilderBuild{}, false, err
+	}
+	value, _, found, err := r.kv.Get(ctx, key)
+	if err != nil || !found {
+		return delivery.BuilderBuild{}, false, err
+	}
+	b, err := delivery.DecodeBuilderBuild(value)
+	return b, err == nil, err
+}
+
+// CommitOf is the commit the indexer's record of the module was computed at: the commit of its repository the mesh runs.
+func (r *repoModules) CommitOf(module string) string {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return r.commit[module]
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge_test.go

@@ -0,0 +1,114 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"os"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+type memManifests map[string][]byte
+
+func (m memManifests) Get(_ context.Context, key string) ([]byte, uint64, bool, error) {
+	v, ok := m[key]
+	return v, 1, ok, nil
+}
+
+func putModule(t *testing.T, r *repoModules, name, repository, manifest string) {
+	t.Helper()
+	data, err := delivery.EncodeModule(delivery.Module{Repository: repository, Commit: strings.Repeat("a", 40), FP: "src1:" + strings.Repeat("a", 64), Manifest: delivery.ManifestDigest([]byte(manifest))})
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.Put(context.Background(), name, data, false)
+}
+
+func TestARepositoryWithATypeScriptModuleIsJudgedByTheNodeBuildModuleToo(t *testing.T) { // 1292/AC2
+	own, err := os.ReadFile("../../module.json") // a manifest with a Go bundle: this module's own
+	if err != nil {
+		t.Fatal(err)
+	}
+	goManifest := string(own)
+	// A TypeScript bundle names neither a system nor a directory it is built from (the catalogue's parser says so).
+	var doc map[string]any
+	if err := json.Unmarshal(own, &doc); err != nil {
+		t.Fatal(err)
+	}
+	artifacts := doc["build"].(map[string]any)["artifacts"].([]any)
+	program := artifacts[0].(map[string]any)
+	program["language"] = "typescript"
+	delete(program, "system")
+	delete(program, "from")
+	delete(program, "binary")
+	tsRaw, err := json.Marshal(doc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tsManifest := string(tsRaw)
+	store := memManifests{}
+	for _, m := range []string{goManifest, tsManifest} {
+		data, err := delivery.EncodeManifest(delivery.Manifest{Module: "demo", JSON: m})
+		if err != nil {
+			t.Fatal(err)
+		}
+		store[delivery.ManifestDigest([]byte(m))] = data
+	}
+	r := &repoModules{manifests: store}
+	putModule(t, r, "mesh-delivery-checker", "novox/mesh-delivery", goManifest)
+	putModule(t, r, "mesh-ui", "novox/mesh-catalog", tsManifest)
+	if got := r.BuildModules("novox/mesh-delivery"); strings.Join(got, ",") != buildrun.GoBuildModule {
+		t.Errorf("mesh-delivery: %v, want the Go build module alone", got)
+	}
+	if got := r.BuildModules("novox/mesh-catalog"); strings.Join(got, ",") != buildrun.GoBuildModule+","+buildrun.NodeBuildModule {
+		t.Errorf("mesh-catalog: %v, want both", got)
+	}
+	if got := r.CommitOf("mesh-delivery-checker"); got != strings.Repeat("a", 40) || r.CommitOf("gone") != "" {
+		t.Errorf("the commit the mesh runs = %q", got)
+	}
+	// 1887/A12: a repository with no module the mesh knows (mesh-lab: nested go.mod files and a root package.json) is
+	// judged by both build modules.
+	if got := r.BuildModules("novox/mesh-lab"); strings.Join(got, ",") != buildrun.GoBuildModule+","+buildrun.NodeBuildModule {
+		t.Errorf("a repository with no module: %v, want both build modules", got)
+	}
+}
+
+// sdkManifest is mesh-sdk's own manifest (its module.json at feat/r4e-sdk): one TypeScript package naming its paths.
+const sdkManifest = `{"module":"mesh-sdk","version":"1","slug":"sdk","build":{"artifacts":[{"name":"lib","kind":"package","language":"typescript",` +
+	`"paths":["src","test","package.json","package-lock.json","tsconfig.json"]}]},"resources":[]}`
+
+func TestTheTypeScriptPackagesPathsComeFromTheIndexersModulesNotTheManifest(t *testing.T) { // ADR 0500 §5 with lead decision L8
+	store := memManifests{}
+	data, err := delivery.EncodeManifest(delivery.Manifest{Module: "mesh-sdk", JSON: sdkManifest})
+	if err != nil {
+		t.Fatal(err)
+	}
+	store[delivery.ManifestDigest([]byte(sdkManifest))] = data
+	r := &repoModules{manifests: store}
+	put := func(path string, paths map[string][]string) {
+		v, err := delivery.EncodeModule(delivery.Module{Repository: "novox/mesh-sdk", Commit: strings.Repeat("a", 40), FP: "src1:" + strings.Repeat("a", 64),
+			Manifest: delivery.ManifestDigest([]byte(sdkManifest)), Path: path, ArtifactPaths: paths})
+		if err != nil {
+			t.Fatal(err)
+		}
+		r.Put(context.Background(), "mesh-sdk", v, false)
+	}
+	put(".", map[string][]string{"lib": {"src", "package.json"}}) // the indexer's word, not the manifest's five paths
+	if got := strings.Join(r.PackagePaths("novox/mesh-sdk"), ","); got != "package.json,src" {
+		t.Errorf("paths = %q, want the indexer's, at the repository's root", got)
+	}
+	put("ts", map[string][]string{"lib": {"src"}})
+	if got := strings.Join(r.PackagePaths("novox/mesh-sdk"), ","); got != "ts/src" {
+		t.Errorf("paths = %q, want them under the module's directory", got)
+	}
+	put(".", nil) // a value written before the indexer kept paths: nothing to serve by
+	if got := r.PackagePaths("novox/mesh-sdk"); len(got) != 0 {
+		t.Errorf("paths = %v, want none", got)
+	}
+	if got := r.PackagePaths("novox/mesh-delivery"); len(got) != 0 {
+		t.Errorf("another repository: %v", got)
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/kept_test.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"sort"
+	"testing"
+)
+
+// The checker says on the bus which states it keeps and which others may read (novox/hq ADR 0495 clauses 2 and 3): a
+// reader is granted from that announcement. owed is read by the forge module, which writes mesh/check from it (ADR 0521,
+// R4e round 2 finding R2-1), and by the forge bridge; previews by the indexer; verdicts by the gate. The list names every
+// state of the manifest, so no state is refused at the call for want of being announced (clause 5).
+func TestTheCheckerAnnouncesEveryStateItKeepsAndOwedReadable(t *testing.T) { // R2-1, ADR 0495 §2-§3, ADR 0521
+	raw, err := os.ReadFile("../../module.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var m struct {
+		State []struct{ Name string } `json:"state"`
+	}
+	if err := json.Unmarshal(raw, &m); err != nil {
+		t.Fatal(err)
+	}
+	var manifest, announced, readable []string
+	for _, s := range m.State {
+		manifest = append(manifest, s.Name)
+	}
+	for _, s := range keptStates {
+		announced = append(announced, s.Name)
+		if s.Readable {
+			readable = append(readable, s.Name)
+		}
+	}
+	sort.Strings(manifest)
+	sort.Strings(announced)
+	if !equal(manifest, announced) {
+		t.Errorf("announced %v, the manifest keeps %v", announced, manifest)
+	}
+	// kept is read by the Go build module for a check ask (issue 1887 design limit 1).
+	if want := []string{"kept", "owed", "previews", "verdicts"}; !equal(readable, want) {
+		t.Errorf("readable %v, want %v", readable, want)
+	}
+}
+
+func equal(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/main.go

@@ -0,0 +1,375 @@
+// Command mesh-delivery-checker is delivery's checker (novox/hq ADR 0453 clause 4, ADR 0447, ADR 0484, issues 1678 to 1686): for
+// each candidate the indexer writes it judges every pull request's head merged onto its trunk, through the build modules'
+// fetch, digest and test steps, keeps the passing packages' verdicts, writes the verdict, and owes the forge the status
+// `mesh/check`, which the forge bridge sets. It runs dark: nothing reads its answers to merge or deliver (ADR 0453 clause 4).
+// It serves no request subject and holds no timer: every reaction is a watch or a bus event (ADR 0437 §8).
+package main
+
+import (
+	"context"
+	"crypto/sha256"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"os/signal"
+	"strings"
+	"syscall"
+	"time"
+
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/announce"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+	"git.novox.be/novox/mesh-sdk/go/process"
+
+	"mesh-delivery-checker/internal/check"
+)
+
+// eventSubject is the subject of an event of the checker's stream checks (the bus names the stream CHECKS): the indexer's
+// watch of the previews bucket and the forge bridge's watch of the owed bucket are woken by them.
+func eventSubject(event string) string {
+	return "mesh.stream." + delivery.CheckerModule + ".event." + event
+}
+
+const (
+	// defaultLink is the base of the address a status points at; the verdict key follows.
+	defaultLink = "mesh-delivery-view/checks"
+)
+
+func main() {
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	if err := run(ctx, os.Getenv, os.Stderr); err != nil {
+		fmt.Fprintln(os.Stderr, "mesh-delivery-checker:", err)
+		os.Exit(1)
+	}
+}
+
+// credential is the broker file the controller issues to the module: JSON of the bus address, the certificate
+// fingerprint to pin, the principal and its password (as the indexer reads it; issue 1242 moves this into the SDK).
+type credential struct {
+	URL         string `json:"url"`
+	Fingerprint string `json:"fingerprint"`
+	Node        string `json:"node"`
+	Module      string `json:"module"`
+	User        string `json:"user"`
+	Password    string `json:"password"`
+}
+
+func readCredential(path string) (credential, error) {
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		return credential{}, err
+	}
+	var c credential
+	if err := json.Unmarshal(raw, &c); err != nil {
+		return credential{}, fmt.Errorf("the broker credential is not one: %w", err)
+	}
+	if c.URL == "" || c.User == "" {
+		return credential{}, errors.New("the broker credential names no bus address or user")
+	}
+	return c, nil
+}
+
+// pinned accepts exactly the certificate with this SHA-256 and no other.
+func pinned(want string) *tls.Config {
+	return &tls.Config{
+		InsecureSkipVerify: true, //nolint:gosec // replaced by the pin below, which is stricter
+		MinVersion:         tls.VersionTLS12,
+		VerifyPeerCertificate: func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
+			if len(rawCerts) == 0 {
+				return errors.New("the bus presented no certificate")
+			}
+			sum := sha256.Sum256(rawCerts[0])
+			if got := "sha256:" + hex.EncodeToString(sum[:]); got != want {
+				return fmt.Errorf("the bus presented a certificate this mesh does not know (%.23s…)", got)
+			}
+			return nil
+		},
+	}
+}
+
+// durationEnv reads a duration setting from the environment, def when it is not set.
+func durationEnv(getenv func(string) string, name string, def time.Duration) (time.Duration, error) {
+	v := strings.TrimSpace(getenv(name))
+	if v == "" {
+		return def, nil
+	}
+	d, err := time.ParseDuration(v)
+	if err != nil || d <= 0 {
+		return 0, fmt.Errorf("%s: %q is not a duration of more than 0", name, v)
+	}
+	return d, nil
+}
+
+// run is the program: it returns when ctx ends or the bus cannot be used.
+// keptStates is every state the checker keeps and which others may read (ADR 0495 §2-§3): owed by the forge module,
+// which writes mesh/check from it (ADR 0521), and by the forge bridge; previews by the indexer; verdicts by the gate.
+var keptStates = []announce.State{
+	// The kept verdicts are read by the Go build module, which takes them for a check ask's unchanged packages (issue 1887's
+	// design limit 1); the checker alone writes them (ADR 0444 clause 5).
+	{Name: "kept", Readable: true},
+	{Name: "owed", Readable: true},
+	{Name: "previews", Readable: true},
+	{Name: "tries"},
+	{Name: "verdicts", Readable: true},
+}
+
+func run(ctx context.Context, getenv func(string) string, logOut io.Writer) error {
+	logger := log.New(logOut, "mesh-delivery-checker: ", log.LstdFlags)
+	path := strings.TrimSpace(getenv("MESH_BROKER_FILE"))
+	if path == "" {
+		return errors.New("MESH_BROKER_FILE is not set, so there is no credential to hear the bus with")
+	}
+	cred, err := readCredential(path)
+	if err != nil {
+		return err
+	}
+	opts := []nats.Option{
+		nats.Name(cred.Node + "." + cred.Module),
+		nats.UserInfo(cred.User, cred.Password),
+		nats.CustomInboxPrefix("_INBOX." + cred.User),
+		nats.MaxReconnects(-1),
+		nats.RetryOnFailedConnect(true),
+	}
+	if strings.TrimSpace(cred.Fingerprint) != "" {
+		opts = append(opts, nats.Secure(pinned(cred.Fingerprint)))
+	}
+	conn, err := nats.Connect(cred.URL, opts...)
+	if err != nil {
+		return fmt.Errorf("connecting to the bus: %w", err)
+	}
+	defer conn.Close()
+	js, err := jetstream.New(conn)
+	if err != nil {
+		return err
+	}
+	bucket := func(name string) (jetstream.KeyValue, error) {
+		kv, err := js.KeyValue(ctx, name)
+		if err != nil {
+			return nil, fmt.Errorf("the bucket %s: %w", name, err)
+		}
+		return kv, nil
+	}
+	buckets := map[string]jetstream.KeyValue{}
+	for _, name := range []string{delivery.CheckerVerdictsBucket, delivery.CheckerKeptBucket, delivery.CheckerOwedBucket, delivery.PreviewsBucket,
+		delivery.CandidatesBucket, delivery.ModulesBucket, delivery.ManifestsBucket, check.TriesBucket} {
+		if buckets[name], err = bucket(name); err != nil {
+			return err
+		}
+	}
+	// Calls to the build modules go out as this module's own account, naming the machine (mesh-sdk process.CallOn); the
+	// buckets are read and written on the connection above.
+	account, err := process.ReadAccount(path)
+	if err != nil {
+		return err
+	}
+	caller, err := process.Connect(account, nats.Name(cred.Node+"."+cred.Module+".calls"), nats.RetryOnFailedConnect(true))
+	if err != nil {
+		return err
+	}
+	defer caller.Close()
+	// What the checker keeps, said on the bus (ADR 0495 §2-§3): a reader is granted from it. Not fatal when it cannot be said
+	// now: process.Conn says it again at every reconnect.
+	if err := caller.Keeps(keptStates...); err != nil {
+		logger.Printf("what the checker keeps could not be said on the bus, so readers of owed, previews and verdicts are not granted until it is: %v", err)
+	}
+
+	stepBound, err := durationEnv(getenv, "MESH_CHECKER_STEP_BOUND", check.DefaultStepBound)
+	if err != nil {
+		return err
+	}
+	checkBound, err := durationEnv(getenv, "MESH_CHECKER_BOUND", check.DefaultBound)
+	if err != nil {
+		return err
+	}
+	link := strings.TrimSpace(getenv("MESH_CHECKER_LINK"))
+	if link == "" {
+		link = defaultLink
+	}
+	tools := &buildrun.ToolchainSet{}
+	presence := &buildrun.PresenceSet{}
+	trunks := &check.Trunks{}
+	// A check is one ask per pull request and build module on the build seats' check stream, pulled by a build node with a
+	// free slot (novox/hq ADR 0525 §1, §3): the checker chooses no node and starts no step.
+	asks := buildrun.JetStreamAsks{JS: js}
+	ch := &check.Checker{
+		Verdicts: kvStore{buckets[delivery.CheckerVerdictsBucket]},
+		Owed:     kvStore{buckets[delivery.CheckerOwedBucket]},
+		Trunks:   trunks,
+		Bound:    checkBound,
+		Link:     link,
+		Logf:     logger.Printf,
+	}
+	// The builder's builds say how the candidates' fingerprints stand (issue 1684); where its bucket is not there yet the line
+	// says nothing of the builds, until the checker starts again.
+	var builds check.BuildStates
+	switch kv, err := js.KeyValue(ctx, delivery.BuilderBuildsBucket); {
+	case errors.Is(err, jetstream.ErrBucketNotFound):
+		logger.Printf("the bucket %s does not exist yet: the line says nothing of the builds until the checker starts again", delivery.BuilderBuildsBucket)
+	case err != nil:
+		return fmt.Errorf("the bucket %s: %w", delivery.BuilderBuildsBucket, err)
+	default:
+		builds = buildReader{kvStore{kv}}
+	}
+	// The assigner's compositions (ADR 0528 clause 5, issue 1297): their bucket is looked up at each check until it is
+	// there, so an assigner delivered after the checker started is read at the next check, and followed from then on.
+	compositions := &lazyCompositions{open: func(at context.Context) (check.CompositionReader, error) {
+		kv, err := js.KeyValue(at, delivery.AssignerCompositionsBucket)
+		if err != nil {
+			return nil, err
+		}
+		cw := compositionWatch{kv: kv}
+		if pkv, err := js.KeyValue(at, delivery.PresenceBucket); err == nil {
+			cw.presence = pkv
+		}
+		if err := followCompositions(ctx, kv, ch); err != nil {
+			return nil, fmt.Errorf("the bucket %s cannot be watched: %w", delivery.AssignerCompositionsBucket, err)
+		}
+		logger.Printf("the assigner's compositions are read from %s", delivery.AssignerCompositionsBucket)
+		return cw, nil
+	}}
+	// The tries (ADR 0501 §5) are judged by the same judge, held by the same deliveries.
+	tryer := &check.Tryer{Tries: kvStore{buckets[check.TriesBucket]}, Bound: checkBound, Logf: logger.Printf}
+	announce := func(ctx context.Context, event, key string) {
+		body, _ := json.Marshal(map[string]string{"key": key})
+		if _, err := js.Publish(ctx, eventSubject(event), body); err != nil {
+			logger.Printf("%s of %s was written and the part that reads it could not be told: %v", event, key, err)
+		}
+	}
+	repos := &repoModules{manifests: kvStore{buckets[delivery.ManifestsBucket]}, logf: logger.Printf}
+	ch.Judge = newJudge(judgeDeps{
+		asks: buildrun.Asker{Publisher: asks, Waiter: asks, Bound: stepBound}, tools: tools, trunks: trunks,
+		kept: kvStore{buckets[delivery.CheckerKeptBucket]}, previews: kvStore{buckets[delivery.PreviewsBucket]},
+		repos: repos, builds: builds, forge: forgeReads{call: caller.Call}, logf: logger.Printf,
+		announce: announce, compositions: compositions,
+	})
+	ch.Announce = announce
+	tryer.Judge = ch.Judge
+
+	// The toolchains first, so a check that starts from the first candidate finds the nodes.
+	watch := newToolchainWatch(ctx, js, tools, ch.NodesChanged, logger)
+	if err := watch.start(); err != nil {
+		return err
+	}
+	// A build module says each time it wrote its toolchains key: its stream, and the checker's durable consumer on it, are
+	// made by the controller. Where the stream is not there yet the checker says so and is started again with the build
+	// module.
+	for _, module := range []string{buildrun.GoBuildModule, buildrun.NodeBuildModule} {
+		stream := toolchainStreams[module]
+		cons, err := js.Consumer(ctx, stream, cred.Node+"_"+cred.Module)
+		if err != nil {
+			logger.Printf("the consumer %s_%s on %s does not exist yet, so %s's reports are not heard until the checker starts again: %v", cred.Node, cred.Module, stream, module, err)
+			continue
+		}
+		cc, err := cons.Consume(func(m jetstream.Msg) { watch.Reported(m) },
+			jetstream.ConsumeErrHandler(func(_ jetstream.ConsumeContext, err error) { logger.Printf("hearing the bus: %v", err) }))
+		if err != nil {
+			return err
+		}
+		defer cc.Stop()
+	}
+	errs := make(chan error, 8)
+	// The watchman's presence: a node coming back online asks again a check whose forge was not heard (UnheardWords), and
+	// the assigner's own presence says whether a composition is being made (compositionWatch, ADR 0537 §4). A check is no
+	// longer held for a node: its asks wait in the build seats' streams, which redeliver a lost node's ask (ADR 0525 §6,
+	// issue 1912), so the node-engine's have is not watched here.
+	switch kv, err := js.KeyValue(ctx, delivery.PresenceBucket); {
+	case errors.Is(err, jetstream.ErrBucketNotFound):
+		logger.Printf("the bucket %s does not exist yet: no node counts as online until the checker starts again", delivery.PresenceBucket)
+	case err != nil:
+		return fmt.Errorf("the bucket %s: %w", delivery.PresenceBucket, err)
+	default:
+		pw, err := settle(ctx, kv, func(e jetstream.KeyValueEntry) { presence.Put(e.Key(), e.Value(), !opOf(e)) })
+		if err != nil {
+			return err
+		}
+		go func() {
+			errs <- follow(ctx, pw, func(e jetstream.KeyValueEntry) {
+				if presence.Put(e.Key(), e.Value(), !opOf(e)) {
+					ch.NodesChanged(ctx) // a node came online or went: a check whose forge was not heard may now be heard
+				}
+			})
+		}()
+	}
+	// The gate's source says the trunk head of each repository, which a pull request is merged onto. Where it is not there
+	// yet no trunk is known, so nothing is checked.
+	switch kv, err := js.KeyValue(ctx, delivery.SourceBucket); {
+	case errors.Is(err, jetstream.ErrBucketNotFound):
+		logger.Printf("the bucket %s does not exist yet: no trunk is known until the checker starts again", delivery.SourceBucket)
+	case err != nil:
+		return fmt.Errorf("the bucket %s: %w", delivery.SourceBucket, err)
+	default:
+		sw, err := settle(ctx, kv, func(e jetstream.KeyValueEntry) {
+			if e.Key() == delivery.SourceMainKey {
+				trunks.Put(e.Value(), !opOf(e))
+			}
+		})
+		if err != nil {
+			return err
+		}
+		go func() {
+			errs <- follow(ctx, sw, func(e jetstream.KeyValueEntry) {
+				if e.Key() == delivery.SourceMainKey && trunks.Put(e.Value(), !opOf(e)) {
+					ch.TrunkMoved(ctx) // the trunk moved: its statuses go pending, and a verdict for the old trunk is judged again
+				}
+			})
+		}()
+	}
+	// The modules say which repository holds a TypeScript module, so the Node build module judges it too.
+	mw, err := settle(ctx, buckets[delivery.ModulesBucket], func(e jetstream.KeyValueEntry) { repos.Put(ctx, e.Key(), e.Value(), !opOf(e)) })
+	if err != nil {
+		return err
+	}
+	go func() {
+		errs <- follow(ctx, mw, func(e jetstream.KeyValueEntry) { repos.Put(ctx, e.Key(), e.Value(), !opOf(e)) })
+	}()
+	each := func(e jetstream.KeyValueEntry) {
+		if opOf(e) {
+			ch.Candidate(ctx, e.Key(), e.Value())
+		} else {
+			ch.Forget(e.Key())
+		}
+	}
+	w, err := settle(ctx, buckets[delivery.CandidatesBucket], each)
+	if err != nil {
+		return err
+	}
+	// A key left running for heads no candidate holds is closed; the candidates are all known now.
+	if err := ch.Sweep(ctx); err != nil {
+		return err
+	}
+	// The tries: a queued one starts, one left running is taken over, an ended one past its keeping is removed.
+	tw, err := settle(ctx, buckets[check.TriesBucket], func(jetstream.KeyValueEntry) {})
+	if err != nil {
+		return err
+	}
+	tryer.Reconsider(ctx)
+	go func() {
+		errs <- follow(ctx, tw, func(e jetstream.KeyValueEntry) {
+			if opOf(e) {
+				tryer.Put(ctx, e.Key(), e.Value())
+			}
+		})
+	}()
+	logger.Printf("started on %s", cred.Node)
+	go func() { errs <- follow(ctx, w, each) }()
+	select {
+	case <-ctx.Done():
+		ch.Wait()
+		tryer.Wait()
+		return nil
+	case err := <-errs:
+		return err
+	case err := <-watch.errs:
+		return err
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/nodes_test.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+// 1912: with checks as asks on the build seats' streams, the stream redelivers a lost node's ask (ADR 0525 §6), so the
+// checker program opens no node-engine have to start again a check that failed for want of a node.
+func TestTheCheckerWatchesNoHave(t *testing.T) {
+	raw, err := os.ReadFile("main.go")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, s := range []string{"delivery.HaveBucket", "buildrun.HaveSet"} {
+		if strings.Contains(string(raw), s) {
+			t.Errorf("the checker program still reads %s", s)
+		}
+	}
+}

modules/mesh-delivery-checker/cmd/mesh-delivery-checker/toolchains.go

@@ -0,0 +1,104 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log"
+	"strings"
+	"sync"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+// toolchainStreams are the stream each build module carries its toolchain.reported event on, as the bus names it
+// (declared by the build modules, heard by this module through consumes).
+var toolchainStreams = map[string]string{buildrun.GoBuildModule: "TOOLCHAINS_GO", buildrun.NodeBuildModule: "TOOLCHAINS_NODE"}
+
+// toolchainWatch keeps the build modules' toolchains in a buildrun.ToolchainSet and tells the builder when one changed. A
+// build module's bucket is made when it is assigned, after the builder started, and the builder holds no timer (ADR 0437
+// §8): it watches the buckets that exist at start, and a build module says each time it wrote its toolchains key
+// (toolchain.reported, handled by Reported); a bucket not watched yet is then watched.
+type toolchainWatch struct {
+	ctx     context.Context
+	js      bucketOpener
+	set     *buildrun.ToolchainSet
+	changed func(ctx context.Context) // a language's entries changed: the failed builds are tried again
+	logger  *log.Logger
+	errs    chan error
+	mu      sync.Mutex
+	watched map[string]bool
+}
+
+func newToolchainWatch(ctx context.Context, js bucketOpener, set *buildrun.ToolchainSet, changed func(context.Context), logger *log.Logger) *toolchainWatch {
+	return &toolchainWatch{ctx: ctx, js: js, set: set, changed: changed, logger: logger, errs: make(chan error, len(buildrun.LanguageOf)), watched: map[string]bool{}}
+}
+
+// start watches the buckets that exist now; a missing one is said and waits for its build module's event.
+func (w *toolchainWatch) start() error {
+	for module := range buildrun.LanguageOf {
+		if err := w.ensure(module); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (w *toolchainWatch) ensure(module string) error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if w.watched[module] {
+		return nil
+	}
+	name := delivery.ToolchainsBucket(module)
+	kv, err := w.js.KeyValue(w.ctx, name)
+	switch {
+	case errors.Is(err, jetstream.ErrBucketNotFound):
+		w.logger.Printf("the bucket %s does not exist yet: it is watched when %s reports a toolchain", name, module)
+		return nil
+	case err != nil:
+		return fmt.Errorf("the bucket %s: %w", name, err)
+	}
+	watcher, err := settle(w.ctx, kv, func(e jetstream.KeyValueEntry) { w.set.Put(module, e.Key(), e.Value(), !opOf(e)) })
+	if err != nil {
+		return err
+	}
+	w.watched[module] = true
+	go func() {
+		w.errs <- follow(w.ctx, watcher, func(e jetstream.KeyValueEntry) {
+			if w.set.Put(module, e.Key(), e.Value(), !opOf(e)) {
+				w.changed(w.ctx)
+			}
+		})
+	}()
+	w.changed(w.ctx) // what the settle read is new to the builder
+	return nil
+}
+
+// delivered is the part of a JetStream message the watch uses.
+type delivered interface {
+	Subject() string
+	Ack() error
+	Term() error
+}
+
+// Reported takes one toolchain.reported event of a build module in: the module is read off the subject,
+// mesh.stream.<module>.event.toolchain.reported, and its bucket is watched if it is not. A subject of no build module is
+// terminated; a failure stays unacknowledged, and the server delivers it again.
+func (w *toolchainWatch) Reported(m delivered) {
+	module, _, _ := strings.Cut(strings.TrimPrefix(m.Subject(), "mesh.stream."), ".event.")
+	if _, known := buildrun.LanguageOf[module]; !known || !strings.HasPrefix(m.Subject(), "mesh.stream.") {
+		w.logger.Printf("%s: not a build module's event, dropped", m.Subject())
+		_ = m.Term()
+		return
+	}
+	if err := w.ensure(module); err != nil {
+		w.logger.Printf("%s: left for redelivery: %v", m.Subject(), err)
+		return
+	}
+	_ = m.Ack()
+}

modules/mesh-delivery-checker/go.mod

@@ -0,0 +1,22 @@
+module mesh-delivery-checker
+
+go 1.26.0
+
+require (
+	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261023213200-403a5d72ab93
+	github.com/nats-io/nats-server/v2 v2.11.17
+	github.com/nats-io/nats.go v1.54.0
+)
+
+require (
+	github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op // indirect
+	github.com/google/go-tpm v0.9.8 // indirect
+	github.com/klauspost/compress v1.20.0 // indirect
+	github.com/minio/highwayhash v1.0.4 // indirect
+	github.com/nats-io/jwt/v2 v2.8.1 // indirect
+	github.com/nats-io/nkeys v0.4.16 // indirect
+	github.com/nats-io/nuid v1.0.1 // indirect
+	golang.org/x/crypto v0.57.0 // indirect
+	golang.org/x/sys v0.48.0 // indirect
+	golang.org/x/time v0.15.0 // indirect
+)

modules/mesh-delivery-checker/go.sum

@@ -0,0 +1,27 @@
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261023213200-403a5d72ab93 h1:FAiFY2KBKEoZSH49OZTt7/zRBIQxyl5g/KhYrpggbN4=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261023213200-403a5d72ab93/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op h1:Z/MZK75wC/NSrkgqeNIa7jexam9uWzhLmFTSCPI/kn0=
+github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op/go.mod h1:FQyySiasQQM8735Ddel3MRojmy4dA1IqCeyJ5jmPMbI=
+github.com/google/go-tpm v0.9.8 h1:slArAR9Ft+1ybZu0lBwpSmpwhRXaa85hWtMinMyRAWo=
+github.com/google/go-tpm v0.9.8/go.mod h1:h9jEsEECg7gtLis0upRBQU+GhYVH6jMjrFxI8u6bVUY=
+github.com/klauspost/compress v1.20.0 h1:a3C1ke2ohxFymNlb2HWAHjDeKCI90scRskErZkR0ezA=
+github.com/klauspost/compress v1.20.0/go.mod h1:LUdAzn7YLVvxLpc7y3V1m40wESHTgc1422pwwBSKYuI=
+github.com/minio/highwayhash v1.0.4 h1:asJizugGgchQod2ja9NJlGOWq4s7KsAWr5XUc9Clgl4=
+github.com/minio/highwayhash v1.0.4/go.mod h1:GGYsuwP/fPD6Y9hMiXuapVvlIUEhFhMTh0rxU3ik1LQ=
+github.com/nats-io/jwt/v2 v2.8.1 h1:V0xpGuD/N8Mi+fQNDynXohVvp7ZztevW5io8CUWlPmU=
+github.com/nats-io/jwt/v2 v2.8.1/go.mod h1:nWnOEEiVMiKHQpnAy4eXlizVEtSfzacZ1Q43LIRavZg=
+github.com/nats-io/nats-server/v2 v2.11.17 h1:GKEghcFK6A+aFx11Yf1LjgLC3txAwvyhnYzhBIQZA8I=
+github.com/nats-io/nats-server/v2 v2.11.17/go.mod h1:B1sFVz4StNosQ903ak4N1G01Fl/9f8e06mXpFIE2K24=
+github.com/nats-io/nats.go v1.54.0 h1:vsXoOxjHp/GmPUN+EcI7uOf/uB+iAP+kEsAFNQN0yzA=
+github.com/nats-io/nats.go v1.54.0/go.mod h1:y+DZoD1oBOYfZTU681eTUiUjI0vbqYGixNVFHcjHJ0k=
+github.com/nats-io/nkeys v0.4.16 h1:rd5oAuLOb8mnAycB0xleuEBNS1pVVnN0fv/FF34Eypg=
+github.com/nats-io/nkeys v0.4.16/go.mod h1:llLgWoI0o4z/Q57q2R1kHfmocyhGV6VG/U18Glg1Afs=
+github.com/nats-io/nuid v1.0.1 h1:5iA8DT8V7q8WK2EScv2padNa/rTESc1KdnPw4TC2paw=
+github.com/nats-io/nuid v1.0.1/go.mod h1:19wcPz3Ph3q0Jbyiqsd0kePYG7A95tJPxeL+1OSON2c=
+golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
+golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
+golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
+golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
+golang.org/x/time v0.15.0 h1:bbrp8t3bGUeFOx08pvsMYRTCVSMk89u4tKbNOZbp88U=
+golang.org/x/time v0.15.0/go.mod h1:Y4YMaQmXwGQZoFaVFk4YpCt4FLQMYKZe9oeV/f4MSno=

modules/mesh-delivery-checker/internal/check/awaiting.go

@@ -0,0 +1,141 @@
+package check
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// ErrAssignerNotRunning is what a wait for a composition answers when no instance of the assigner is online: nobody is
+// making it, so the check does not wait for it (issue 1297). The verdict says the composition is not judged, and when the
+// assigner starts and writes it, the checker takes it in then (Checker.Composed).
+var ErrAssignerNotRunning = errors.New(delivery.AssignerNotRunning)
+
+// PresenceEvent is a change of the watchman's presence bucket, or Settled once what stands was handed.
+type PresenceEvent struct {
+	Key     string
+	Online  bool
+	Settled bool
+}
+
+// CompositionEvent is a change of the composition's key (its value, nil for a delete), or Settled once what stands was
+// handed.
+type CompositionEvent struct {
+	Value   []byte
+	Settled bool
+}
+
+// AwaitComposition answers the assigner's composition once one is written that does not wait, while an instance of the
+// assigner is online by the watchman's presence (`part.mesh-delivery-assigner.<instance>`). Once both watches handed
+// what stands, no instance online is ErrAssignerNotRunning at once, and so is the last instance going offline during the
+// wait. No timer: every answer follows an event; ctx ending is ctx's error.
+func AwaitComposition(ctx context.Context, presence <-chan PresenceEvent, comps <-chan CompositionEvent) (delivery.CompositionVerdict, error) {
+	online := map[string]bool{}
+	presenceSettled, compSettled := false, false
+	for {
+		select {
+		case <-ctx.Done():
+			return delivery.CompositionVerdict{}, ctx.Err()
+		case e, ok := <-presence:
+			if !ok {
+				return delivery.CompositionVerdict{}, errors.New("the watch of the assigner's presence ended")
+			}
+			if e.Settled {
+				presenceSettled = true
+				break
+			}
+			if _, part, instance, err := delivery.ParsePresenceKey(e.Key); err == nil && part == delivery.AssignerModule {
+				if e.Online {
+					online[instance] = true
+				} else {
+					delete(online, instance)
+				}
+			}
+		case e, ok := <-comps:
+			if !ok {
+				return delivery.CompositionVerdict{}, errors.New("the watch of the composition ended")
+			}
+			if e.Settled {
+				compSettled = true
+				break
+			}
+			if e.Value == nil {
+				break
+			}
+			v, err := delivery.DecodeCompositionVerdict(e.Value)
+			if err != nil {
+				return delivery.CompositionVerdict{}, fmt.Errorf("the composition cannot be read: %w", err)
+			}
+			if v.State != delivery.CompositionWaits {
+				return v, nil
+			}
+		}
+		if presenceSettled && compSettled && len(online) == 0 {
+			return delivery.CompositionVerdict{}, ErrAssignerNotRunning
+		}
+	}
+}
+
+// withComposition is v with the assigner's composition taken in: a failed one fails the check, naming its machine.
+func withComposition(v *delivery.Verdict, comp delivery.CompositionVerdict) {
+	v.Composition = comp.Composition()
+	v.Took.Composition = comp.Took
+	if comp.State == delivery.CompositionFail {
+		machine := comp.Machine
+		if machine == "" {
+			machine = "the composition"
+		}
+		v.State, v.Failed = delivery.VerdictFail, delivery.FailedFirst{Machine: machine, Words: comp.Words}
+	}
+}
+
+// notJudged says whether a verdict's composition was not judged because the assigner was not running.
+func notJudged(v delivery.Verdict) bool {
+	return v.Composition != nil && v.Composition.State == delivery.CompositionNotRun && v.Composition.Words == delivery.AssignerNotRunning
+}
+
+// Composed takes in a composition the assigner wrote after the check's verdict said it was not judged because the
+// assigner was not running (the assigner started since): the verdict and its status are written again with it. A
+// composition of heads no candidate holds now, or of a verdict that judged its composition, is left.
+func (ch *Checker) Composed(ctx context.Context, comp delivery.CompositionVerdict) {
+	ch.init()
+	if comp.State == delivery.CompositionWaits {
+		return
+	}
+	ckey, err := delivery.CandidatesKey(comp.Group)
+	if err != nil {
+		return
+	}
+	ch.mu.Lock()
+	c, ok := ch.known[ckey]
+	ch.mu.Unlock()
+	if !ok {
+		return
+	}
+	cs := CaseOf(c, ch.heads())
+	if cs == nil || cs.HeadsHash != comp.Heads {
+		return
+	}
+	cur, rev, found, err := ch.Verdicts.Get(ctx, cs.Key)
+	if err != nil || !found {
+		return
+	}
+	v, err := delivery.DecodeVerdict(cur)
+	if err != nil || v.State != delivery.VerdictPass || !notJudged(v) {
+		return
+	}
+	withComposition(&v, comp)
+	data, err := delivery.EncodeVerdict(v)
+	if err != nil {
+		ch.logf("%s: the verdict with its composition cannot be written: %v", cs.Key, err)
+		return
+	}
+	if _, err := ch.Verdicts.Update(ctx, cs.Key, data, rev); err != nil {
+		ch.logf("%s: the verdict with its composition could not be written: %v", cs.Key, err)
+		return
+	}
+	ch.writeOwed(ctx, cs, v, Outcome{Verdict: v})
+	ch.logf("%s: the composition came after the verdict: %s", cs.Key, comp.State)
+}

modules/mesh-delivery-checker/internal/check/awaiting_test.go

@@ -0,0 +1,149 @@
+package check
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+func assignerOn(instance string, online bool) PresenceEvent {
+	key, _ := delivery.PresencePartKey(delivery.AssignerModule, instance)
+	return PresenceEvent{Key: key, Online: online}
+}
+
+func compEvent(t *testing.T, v delivery.CompositionVerdict) CompositionEvent {
+	t.Helper()
+	data, err := delivery.EncodeCompositionVerdict(v)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return CompositionEvent{Value: data}
+}
+
+var passed = delivery.CompositionVerdict{Group: "feat/x", Heads: "0123456789ab", State: delivery.CompositionPass, SDK: "x", Machines: []string{"g14"}}
+
+// 1297/B3d: with no assigner online, the wait answers ErrAssignerNotRunning as soon as both watches handed what stands.
+func TestNoAssignerAnswersAtOnce(t *testing.T) {
+	presence, comps := make(chan PresenceEvent, 4), make(chan CompositionEvent, 4)
+	presence <- assignerOn("novox", false)
+	presence <- PresenceEvent{Settled: true}
+	comps <- CompositionEvent{Settled: true}
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	if _, err := AwaitComposition(ctx, presence, comps); !errors.Is(err, ErrAssignerNotRunning) {
+		t.Fatalf("answered %v, want the assigner not running", err)
+	}
+}
+
+// 1297/B3d: with the assigner online it waits for the key, past a composition that waits, and answers the verdict.
+func TestAnOnlineAssignerIsWaitedFor(t *testing.T) {
+	presence, comps := make(chan PresenceEvent, 4), make(chan CompositionEvent, 4)
+	presence <- assignerOn("novox", true)
+	presence <- PresenceEvent{Settled: true}
+	comps <- CompositionEvent{Settled: true}
+	done := make(chan error, 1)
+	var got delivery.CompositionVerdict
+	go func() {
+		var err error
+		got, err = AwaitComposition(context.Background(), presence, comps)
+		done <- err
+	}()
+	comps <- compEvent(t, delivery.CompositionVerdict{Group: "feat/x", Heads: "0123456789ab", State: delivery.CompositionWaits, Words: "w"})
+	select {
+	case err := <-done:
+		t.Fatalf("answered before the composition was written: %v", err)
+	case <-time.After(50 * time.Millisecond):
+	}
+	comps <- compEvent(t, passed)
+	if err := <-done; err != nil || got.State != delivery.CompositionPass {
+		t.Fatalf("answered %+v, %v", got, err)
+	}
+	// And the last instance going offline during a wait ends it as not running.
+	presence2, comps2 := make(chan PresenceEvent, 4), make(chan CompositionEvent, 4)
+	presence2 <- assignerOn("novox", true)
+	presence2 <- PresenceEvent{Settled: true}
+	comps2 <- CompositionEvent{Settled: true}
+	presence2 <- assignerOn("novox", false)
+	if _, err := AwaitComposition(context.Background(), presence2, comps2); !errors.Is(err, ErrAssignerNotRunning) {
+		t.Errorf("the assigner going offline answered %v", err)
+	}
+}
+
+// 1297/B3d: a passing check with no assigner says at once, loud, that its composition is not judged; never a pass of it.
+func TestAPassingCheckWithNoAssignerSaysTheCompositionIsNotJudged(t *testing.T) {
+	b := newBench(t)
+	b.ex.Compositions = &fakeCompositions{err: ErrAssignerNotRunning}
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.Composition == nil || v.Composition.State != delivery.CompositionNotRun || v.Composition.Words != delivery.AssignerNotRunning {
+		t.Fatalf("composition = %+v", v.Composition)
+	}
+	if words := compositionWords(v.Composition, 0); words != "composition not judged: the assigner is not running" {
+		t.Errorf("the line says %q", words)
+	}
+}
+
+// 1297/B3d: the assigner starting writes the composition later, and the checker takes it into the verdict that said it
+// was not judged, writing the status again; a failed one fails the check.
+func TestTheAssignerStartingBringsTheComposition(t *testing.T) {
+	for _, comp := range []delivery.CompositionVerdict{passed,
+		{Group: "feat/x", Heads: "", State: delivery.CompositionFail, SDK: "x", Machine: "g14", Words: "g14 runs web, which the change removes"}} {
+		ch, cs := checkerWithNotJudged(t)
+		comp.Heads = cs.HeadsHash
+		ch.Composed(context.Background(), comp)
+		raw, _, _, _ := ch.Verdicts.Get(context.Background(), cs.Key)
+		v, err := delivery.DecodeVerdict(raw)
+		if err != nil || v.Composition == nil || v.Composition.State != comp.State {
+			t.Fatalf("after the composition came, the verdict is %+v, %v", v, err)
+		}
+		if comp.State == delivery.CompositionFail && (v.State != delivery.VerdictFail || v.Failed.Machine != "g14") {
+			t.Errorf("a failed composition left the verdict %+v", v)
+		}
+		owed := ch.Owed.(*memKV)
+		keys, _ := owed.Keys(context.Background())
+		if len(keys) == 0 {
+			t.Fatal("no status was written again")
+		}
+		data, _, _, _ := owed.Get(context.Background(), keys[0])
+		o, _ := delivery.DecodeCheckerOwed(data)
+		if !strings.Contains(o.Text, "composition passed") && !strings.Contains(o.Text, "g14 runs web") {
+			t.Errorf("the status's line says %q", o.Text)
+		}
+	}
+}
+
+// checkerWithNotJudged is a checker holding a candidate whose passing verdict said its composition was not judged.
+func checkerWithNotJudged(t *testing.T) (*Checker, *Case) {
+	t.Helper()
+	cs := caseOf(t, pullOf(repoA, 7, head1))
+	raw := candidateOf(t, cs.Group, pullOf(repoA, 7, head1))
+	ch := &Checker{Verdicts: newMemKV(), Owed: newMemKV(), Trunks: fixedTrunks{cs.Trunk}}
+	ckey, _ := delivery.CandidatesKey(cs.Group)
+	ch.init()
+	c, err := delivery.DecodeCandidate(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ch.known[ckey] = c
+	if got := CaseOf(c, ch.heads()); got == nil || got.Key != cs.Key {
+		t.Fatalf("the case is %+v, want %s", got, cs.Key)
+	}
+	v := delivery.Verdict{Group: cs.Group, Heads: cs.Heads, State: delivery.VerdictPass,
+		Levels:      map[string]delivery.LevelResult{delivery.LevelUnit: {Run: 1}, delivery.LevelIntegration: {Run: 1}},
+		Composition: &delivery.Composition{State: delivery.CompositionNotRun, Words: delivery.AssignerNotRunning}}
+	data, err := delivery.EncodeVerdict(v)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := ch.Verdicts.Create(context.Background(), cs.Key, data); err != nil {
+		t.Fatal(err)
+	}
+	return ch, cs
+}
+
+type fixedTrunks struct{ heads map[string]string }
+
+func (f fixedTrunks) Heads() map[string]string { return f.heads }

modules/mesh-delivery-checker/internal/check/beside.go

@@ -0,0 +1,106 @@
+package check
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+)
+
+// BesideRef is a sibling repository a repository's tests read, placed beside the fetched tree as a plain directory (ADR
+// 0484 clause 4). Ref names the pull request's head when the commit is only there.
+type BesideRef struct {
+	Repository string `json:"repository"`
+	Commit     string `json:"commit"`
+	Ref        string `json:"ref,omitempty"`
+}
+
+const (
+	catalogueRepository = "novox/mesh-catalog"
+	nodeEngineRepo      = "novox/mesh-host"
+	nodeEngineModule    = "mesh-host"
+	controllerRepo      = "novox/mesh-controller"
+)
+
+// besideRules are the repositories each core repository's tests read, as the tests state it (mesh-sdk go/internal/beside
+// beside.go): the catalogue, the node-engine, the SDK, and the delivery's pinned forge dependencies (mesh-catalog
+// checks/deps). Which commit of each is besideCommit's rule.
+var besideRules = map[string][]string{
+	controllerRepo:        {catalogueRepository, nodeEngineRepo, SDKRepository},
+	nodeEngineRepo:        {catalogueRepository, SDKRepository, controllerRepo},
+	SDKRepository:         {catalogueRepository, nodeEngineRepo},
+	catalogueRepository:   {SDKRepository, controllerRepo},
+	"novox/mesh-delivery": {SDKRepository, catalogueRepository},
+}
+
+// besideFor are the siblings a pull request's tests read (ADR 0484 clause 4): the catalogue at its trunk, always, even in a
+// group holding a catalogue pull request; the node-engine at the commit the mesh runs (the commit of the indexer's module
+// mesh-host, its trunk head when none is known); mesh-sdk, for the controller's tests, at the commit the controller's go.mod
+// pins; any other sibling at the head of the group's pull request for it when the group holds one, else at its trunk. And
+// first, the change's own repository at the trunk it is merged onto, so a test comparing a shrink-only list with the
+// trunk's copy reads it at $MESH_CHECK_BESIDE/<name> (issue 1887 A12, ADR 0529 §2).
+func (j *Examiner) besideFor(ctx context.Context, c *Case, p Pull) ([]BesideRef, error) {
+	var heads map[string]string
+	if j.Trunks != nil {
+		heads = j.Trunks.Heads()
+	}
+	var out []BesideRef
+	if p.Trunk != "" {
+		out = append(out, BesideRef{Repository: p.Repository, Commit: p.Trunk})
+	}
+	for _, repo := range besideRules[p.Repository] {
+		switch {
+		case repo == catalogueRepository:
+			if head := heads[repo]; head != "" {
+				out = append(out, BesideRef{Repository: repo, Commit: head})
+			}
+		case repo == nodeEngineRepo:
+			commit := ""
+			if j.Runs != nil {
+				commit = j.Runs.CommitOf(nodeEngineModule)
+			}
+			if commit == "" {
+				commit = heads[repo]
+			}
+			if commit != "" {
+				out = append(out, BesideRef{Repository: repo, Commit: commit})
+			}
+		case repo == SDKRepository && p.Repository == controllerRepo && j.Forge != nil:
+			text, err := j.Forge.File(ctx, p.Repository, "go.mod", p.Head)
+			if err != nil {
+				return nil, fmt.Errorf("go.mod of %s#%d cannot be read to place the mesh-sdk its tests read: %w", p.Repository, p.Number, err)
+			}
+			pin, ok := SDKPin(text)
+			if !ok {
+				return nil, fmt.Errorf("go.mod of %s#%d names no mesh-sdk commit, so the mesh-sdk its tests read cannot be placed", p.Repository, p.Number)
+			}
+			full, err := j.Forge.FullSHA(ctx, SDKRepository, pin)
+			if err != nil {
+				return nil, fmt.Errorf("mesh-sdk %s, which %s#%d pins, cannot be found: %w", pin, p.Repository, p.Number, err)
+			}
+			out = append(out, BesideRef{Repository: repo, Commit: full})
+		default:
+			if member := c.member(repo); member != nil {
+				out = append(out, BesideRef{Repository: repo, Commit: member.Head, Ref: refOf(member.Number)})
+			} else if head := heads[repo]; head != "" {
+				out = append(out, BesideRef{Repository: repo, Commit: head})
+			}
+		}
+	}
+	return out, nil
+}
+
+func (c *Case) member(repository string) *Pull {
+	for i := range c.Pulls {
+		if c.Pulls[i].Repository == repository {
+			return &c.Pulls[i]
+		}
+	}
+	return nil
+}
+
+func refOf(number int) string {
+	if number <= 0 {
+		return ""
+	}
+	return "refs/pull/" + strconv.Itoa(number) + "/head"
+}

modules/mesh-delivery-checker/internal/check/builds.go

@@ -0,0 +1,66 @@
+package check
+
+import (
+	"context"
+	"sort"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// The states of a build the status line says (ADR 0484 clause 7).
+const (
+	BuildBuilt   = "built"
+	BuildFailed  = "failed"
+	BuildWaiting = "waiting"
+)
+
+// BuildStates reads the builder's build of a module at a fingerprint of the new form (builds.<module>.<fingerprint>): the
+// value and whether the key exists.
+type BuildStates interface {
+	Build(ctx context.Context, module, fp2 string) (delivery.BuilderBuild, bool, error)
+}
+
+// NoteOf is the state of a build as the line says it: done is built, failed is failed, and one queued, building or not
+// begun is waiting.
+func NoteOf(b delivery.BuilderBuild, found bool) string {
+	switch {
+	case !found:
+		return BuildWaiting
+	case b.State == delivery.BuildDone:
+		return BuildBuilt
+	case b.State == delivery.BuildFailed:
+		return BuildFailed
+	}
+	return BuildWaiting
+}
+
+// buildNotes are the state of each build the case's modules carry a fingerprint of, by module, sorted. A module two pull
+// requests give is said once.
+func (j *Examiner) buildNotes(ctx context.Context, c *Case) []BuildNote {
+	if j.Builds == nil {
+		return nil
+	}
+	fps := map[string]string{}
+	for _, p := range c.Pulls {
+		for module, cm := range p.Fps {
+			if cm.FP2 != "" {
+				fps[module] = cm.FP2
+			}
+		}
+	}
+	modules := make([]string, 0, len(fps))
+	for m := range fps {
+		modules = append(modules, m)
+	}
+	sort.Strings(modules)
+	var notes []BuildNote
+	for _, m := range modules {
+		b, found, err := j.Builds.Build(ctx, m, fps[m])
+		if err != nil {
+			j.logf("the build of %s at %s cannot be read: %v", m, fps[m], err)
+			found = false
+		}
+		notes = append(notes, BuildNote{Module: m, State: NoteOf(b, found)})
+	}
+	return notes
+}

modules/mesh-delivery-checker/internal/check/case.go

@@ -0,0 +1,150 @@
+package check
+
+import (
+	"fmt"
+	"maps"
+	"sort"
+	"strings"
+	"sync"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// Pull is one pull request the checker judges: its head, the trunk head of its repository it is merged onto and the
+// modules the indexer says it touches, with the fingerprints the indexer wrote for them.
+type Pull struct {
+	Repository string
+	Number     int
+	Head       string
+	Trunk      string
+	Modules    []string
+	Fps        map[string]delivery.CandidateModule
+}
+
+// Case is one check: a candidate's pull requests that are judged (those of a repository whose trunk is not known are left
+// out; hq is judged as any repository since R4g, its checks Go tests: ADR 0527), the trunk head of each repository and the key of the verdict.
+type Case struct {
+	// Key is the verdict key, `<group>.<heads hash>`.
+	Key       string
+	Group     string
+	HeadsHash string
+	// Heads is the heads hash the gate matches an Approve's members by (GateHeads): a verdict carries it.
+	Heads string
+	Pulls []Pull
+	// Trunk is the trunk head of each repository of Pulls.
+	Trunk map[string]string
+	// Left says why pull requests of the candidate are not judged (a repository with no known trunk); empty when all are.
+	Left []string
+	// Queued is when the checker took the case up, for the time of its queue.
+	Queued time.Time
+	// Try narrows a try's check (its level, its tests); nil for a pull request's.
+	Try *TryOptions
+	// Progress says what the check is doing, so a check that ran past its bound names the step it was stuck at.
+	Progress *Progress
+	// Kind is what asked the check (KindNew, KindNodes, KindTrunk): a re-judge after a trunk move is asked on the build
+	// seats' recheck stream, every other check on check (ADR 0536 §4).
+	Kind string
+}
+
+// Progress is the step a check is at, written by the check and read when its bound passes.
+type Progress struct {
+	mu          sync.Mutex
+	stage, node string
+}
+
+// Set records the step now running and the node it runs on, empty for none.
+func (p *Progress) Set(stage, node string) {
+	p.mu.Lock()
+	p.stage, p.node = stage, node
+	p.mu.Unlock()
+}
+
+// Now is the step recorded last and its node.
+func (p *Progress) Now() (stage, node string) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return p.stage, p.node
+}
+
+// CaseOf is the check of a candidate against the trunk heads (the gate's source.main): the pull requests that are judged.
+// The checker judges pull requests into main only (ADR 0484 clause 11): the pull message carries no base, a merge into
+// another branch is a closed message, so every candidate is into the trunk; a repository whose trunk head is not known has
+// none to merge onto. It answers nil when no pull request is left to judge.
+func CaseOf(c delivery.Candidate, trunk map[string]string) *Case {
+	key, err := delivery.CheckerVerdictKey(c.Group, c.HeadsHash)
+	if err != nil {
+		return nil
+	}
+	cs := &Case{Key: key, Group: c.Group, HeadsHash: c.HeadsHash, Heads: GateHeads(c), Trunk: map[string]string{}, Progress: &Progress{}}
+	for _, p := range c.Pulls {
+		switch head, known := trunk[p.Repository]; {
+		case !known || head == "":
+			cs.Left = append(cs.Left, fmt.Sprintf("%s#%d: the trunk head of %s is not known", p.Repository, p.Number, p.Repository))
+		default:
+			cs.Pulls = append(cs.Pulls, Pull{Repository: p.Repository, Number: p.Number, Head: p.Head.Head, Trunk: head, Modules: p.Modules, Fps: p.Fps})
+			cs.Trunk[p.Repository] = head
+		}
+	}
+	if len(cs.Pulls) == 0 {
+		return nil
+	}
+	sort.SliceStable(cs.Pulls, func(i, j int) bool {
+		if cs.Pulls[i].Repository != cs.Pulls[j].Repository {
+			return cs.Pulls[i].Repository < cs.Pulls[j].Repository
+		}
+		return cs.Pulls[i].Number < cs.Pulls[j].Number
+	})
+	return cs
+}
+
+// GateHeads is the hash the gate matches the members an Approve covers by (mesh-catalog mesh-delivery-gate onestatus.go
+// headsOf): delivery.HeadsHash over every pull request of the candidate, hq's included, as
+// `<owner/name lowercase>#<number>=<full head sha lowercase>`. A lone pull request is a group of one. Empty for a candidate
+// with no pull request.
+func GateHeads(c delivery.Candidate) string {
+	heads := make([]delivery.Head, 0, len(c.Pulls))
+	for _, p := range c.Pulls {
+		heads = append(heads, delivery.Head{Repository: strings.ToLower(p.Repository), Number: p.Number, Head: strings.ToLower(p.Head.Head)})
+	}
+	hash, err := delivery.HeadsHash(heads)
+	if err != nil {
+		return ""
+	}
+	return hash
+}
+
+// sameTrunk says whether two verdicts' trunk heads are the same.
+func sameTrunk(a, b map[string]string) bool { return maps.Equal(a, b) }
+
+// Trunks holds the trunk head of each repository, as the gate's source.main says (a watch puts it in).
+type Trunks struct {
+	mu    sync.Mutex
+	heads map[string]string
+}
+
+// Put takes a source.main value in and answers whether the heads changed.
+func (t *Trunks) Put(value []byte, deleted bool) bool {
+	var heads map[string]string
+	if !deleted {
+		s, err := delivery.DecodeSource(value)
+		if err != nil {
+			return false
+		}
+		heads = s.Heads
+	}
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if maps.Equal(t.heads, heads) {
+		return false
+	}
+	t.heads = maps.Clone(heads)
+	return true
+}
+
+// Heads are the trunk heads now (a copy).
+func (t *Trunks) Heads() map[string]string {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return maps.Clone(t.heads)
+}

modules/mesh-delivery-checker/internal/check/checker.go

@@ -0,0 +1,522 @@
+package check
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// DefaultBound is how long a check may run before it is ended failed naming the step it was stuck at (ADR 0484, issue 1678):
+// none since R4g. A check's asks wait in the build seats' streams as long as the backlog is (ADR 0525 §9), and each ask's
+// step is bounded from its start on the node that took it (buildrun.Asker.Bound, DefaultStepBound); a bound set by
+// MESH_CHECKER_BOUND still ends a check that ran past it.
+const DefaultBound time.Duration = 0
+
+// UnheardWords end the Words of a failure because a part of the mesh the check reads was not heard (the forge, issue 1624):
+// like a failure of the nodes, it is not the change's, and is judged again when the nodes change.
+const UnheardWords = "not heard; judged again when the nodes change"
+
+// The events the checker says on its stream checks (module.json): a preview or a status was written, so a part that reads
+// the bucket, which is made when the checker is assigned and may not exist when that part starts, finds it (ADR 0437 §8: no
+// timer). The body is {"key": ...}.
+const (
+	EventPreviewWritten = "preview.written"
+	EventOwedWritten    = "owed.written"
+)
+
+// Announcer says an event of the checker's stream, with the key written.
+type Announcer func(ctx context.Context, event, key string)
+
+// Outcome is what judging a case gives: the verdict (state, failure, levels, times, composition; the checker adds the
+// group, the heads and the trunk) and, for the line, what the check knows of the builds of the modules it touches.
+type Outcome struct {
+	Verdict delivery.Verdict
+	Builds  []BuildNote
+	// Slowest names the slowest tests of a level that went over its bound ("unit pkg.Test 1.2s").
+	Slowest []string
+	// Judged says, by pull request (pullKey), which program judged a change to a build module (ADR 0535 §5); a pull request
+	// that changes none is not named.
+	Judged map[string]string
+}
+
+// BuildNote is the state of a candidate's module build, by module: built, failed or waiting (ADR 0484 clause 7).
+type BuildNote struct {
+	Module string
+	State  string
+}
+
+// Judge runs the check of a case: the merge, the levels. It writes what it is doing to c.Progress. It answers an error
+// only when it could not judge at all; a failure of the change is a Verdict.
+type Judge interface {
+	Judge(ctx context.Context, c *Case) (Outcome, error)
+}
+
+// Checker judges the candidates the indexer writes, dark (ADR 0453 clause 4, ADR 0484): for each candidate it claims a
+// verdict key, runs the check through its Judge, writes the verdict and, for each pull request judged, the owed status
+// `mesh/check` the forge bridge performs. It holds no timer; a check starts from a candidate or from a change of the
+// nodes, the trunk or the controller's plan, and ends when its judge does or its bound passes.
+type Checker struct {
+	Verdicts KV
+	Owed     KV
+	Judge    Judge
+	Trunks   interface{ Heads() map[string]string }
+	// Bound is how long one check may run; none when 0 (DefaultBound).
+	Bound time.Duration
+	// Link is the base of the address a status points at; the verdict key follows.
+	Link string
+	// Announce says a status was written (EventOwedWritten); nil says nothing.
+	Announce Announcer
+	Now      func() time.Time
+	Logf     func(format string, args ...any)
+
+	once      sync.Once
+	wg        sync.WaitGroup
+	mu        sync.Mutex
+	known     map[string]delivery.Candidate // by candidates key
+	inflight  map[string]bool               // by verdict key
+	again     map[string]bool               // by verdict key: asked again while it ran
+	tried     map[string]bool               // by verdict key: looked at since this process started
+	epoch     uint64                        // changes of the nodes seen since this process started
+	nodesFail map[string]uint64             // by verdict key: the epoch a failure of the nodes was written at
+}
+
+func (ch *Checker) init() {
+	ch.once.Do(func() {
+		ch.known, ch.inflight, ch.again, ch.tried = map[string]delivery.Candidate{}, map[string]bool{}, map[string]bool{}, map[string]bool{}
+		ch.nodesFail = map[string]uint64{}
+	})
+}
+
+func (ch *Checker) logf(format string, args ...any) {
+	if ch.Logf != nil {
+		ch.Logf(format, args...)
+	}
+}
+
+func (ch *Checker) now() time.Time {
+	if ch.Now != nil {
+		return ch.Now()
+	}
+	return time.Now()
+}
+
+func (ch *Checker) bound() time.Duration {
+	if ch.Bound > 0 {
+		return ch.Bound
+	}
+	return DefaultBound
+}
+
+// Wait returns when every check started so far has ended.
+func (ch *Checker) Wait() { ch.wg.Wait() }
+
+// Candidate takes one value of the indexer's candidates bucket in (the key is the group) and checks it if it is to be
+// checked. A value that is not a candidate is said and left.
+func (ch *Checker) Candidate(ctx context.Context, key string, value []byte) {
+	ch.init()
+	c, err := delivery.DecodeCandidate(value)
+	if err != nil {
+		ch.logf("candidates.%s holds what is not a candidate, left: %v", key, err)
+		return
+	}
+	ch.mu.Lock()
+	ch.known[key] = c
+	ch.mu.Unlock()
+	ch.consider(ctx, key, c)
+}
+
+// Forget takes a candidate out (its key was deleted).
+func (ch *Checker) Forget(key string) {
+	ch.init()
+	ch.mu.Lock()
+	delete(ch.known, key)
+	ch.mu.Unlock()
+}
+
+// NodesChanged is Reconsider after a change of the nodes: one came online or went, a build module became healthy or
+// stopped being, or a toolchain moved. A check that failed because no node qualified is run again only after such a change.
+func (ch *Checker) NodesChanged(ctx context.Context) {
+	ch.init()
+	ch.mu.Lock()
+	ch.epoch++
+	ch.mu.Unlock()
+	ch.Reconsider(ctx)
+}
+
+// Reconsider looks at every candidate again: the trunk moved, the nodes changed or a delivery ended. A candidate whose
+// verdict stands for the trunk it was judged against is left.
+func (ch *Checker) Reconsider(ctx context.Context) {
+	ch.init()
+	ch.mu.Lock()
+	known := make(map[string]delivery.Candidate, len(ch.known))
+	for k, c := range ch.known {
+		known[k] = c
+	}
+	ch.mu.Unlock()
+	for k, c := range known {
+		ch.consider(ctx, k, c)
+	}
+}
+
+func (ch *Checker) heads() map[string]string {
+	if ch.Trunks == nil {
+		return nil
+	}
+	return ch.Trunks.Heads()
+}
+
+func (ch *Checker) consider(ctx context.Context, key string, c delivery.Candidate) {
+	cs := CaseOf(c, ch.heads())
+	if cs == nil {
+		return // nothing to judge: no trunk known
+	}
+	cs.Queued = ch.now()
+	ch.mu.Lock()
+	if ch.inflight[cs.Key] {
+		ch.again[cs.Key] = true // looked at once more when the check ends, so a change of the trunk is never lost
+		ch.mu.Unlock()
+		return
+	}
+	ch.inflight[cs.Key] = true
+	ch.mu.Unlock()
+	ch.wg.Add(1)
+	go func() {
+		defer ch.wg.Done()
+		for {
+			// Every check is asked at once: the build seats' streams hold the backlog, a new head's check and a check after a
+			// failure of the nodes on check, a re-judge after a trunk move on recheck, pulled after them (ADR 0525 §4, §9;
+			// ADR 0536 §4). The checker holds no place and no capacity of its own.
+			cs.Kind = ch.kindOf(ctx, cs)
+			ch.try(ctx, key, cs)
+			ch.mu.Lock()
+			more := ch.again[cs.Key]
+			delete(ch.again, cs.Key)
+			if !more || ctx.Err() != nil {
+				delete(ch.inflight, cs.Key)
+				ch.mu.Unlock()
+				return
+			}
+			ch.mu.Unlock()
+			if next := CaseOf(ch.candidate(key, c), ch.heads()); next != nil {
+				cs = next
+			}
+			cs.Queued = ch.now()
+		}
+	}()
+}
+
+// The kinds of a check (ADR 0536 §4): a head never judged and a head asked again after a failure of the nodes are asked on
+// the build seats' check stream, a head asked again only because its trunk moved on the recheck stream, pulled after.
+const (
+	KindNew   = "new"
+	KindNodes = "nodes"
+	KindTrunk = "trunk"
+)
+
+// kindOf is the kind of a case's check, read from its verdict key: none (or one left running) is a head never judged; a
+// failure of the nodes is asked again after the nodes changed; a verdict on other trunk heads is a re-judge after a trunk
+// move. A verdict that stands is ranked with the re-judges: its claim finds nothing to do.
+func (ch *Checker) kindOf(ctx context.Context, cs *Case) string {
+	value, _, found, err := ch.Verdicts.Get(ctx, cs.Key)
+	if err != nil || !found {
+		return KindNew
+	}
+	v, err := delivery.DecodeVerdict(value)
+	switch {
+	case err != nil || v.State == delivery.VerdictRunning:
+		return KindNew
+	case IsNodesFailure(v):
+		return KindNodes
+	}
+	return KindTrunk
+}
+
+func (ch *Checker) candidate(key string, fallback delivery.Candidate) delivery.Candidate {
+	ch.mu.Lock()
+	defer ch.mu.Unlock()
+	if c, ok := ch.known[key]; ok {
+		return c
+	}
+	return fallback
+}
+
+// claimed is a verdict key the checker holds: the revision the next write is made at.
+type claimed struct{ rev uint64 }
+
+// claim takes the check of the case, or answers nil when it is not this checker's to run now:
+//   - no key: it is created running; a create that finds the key made meanwhile gets nothing;
+//   - a key left running is taken over as it stands when this process looks at it for the first time (it was left by the
+//     checker that stopped; there is one instance, as there is one builder per node, ADR 0478 clause 6), and left otherwise;
+//   - a pass or a failure for the trunk heads the case has stands; one for other trunk heads (the trunk moved) is taken
+//     again by compare-and-set on the same key, and so is a failure of the nodes after the nodes changed.
+func (ch *Checker) claim(ctx context.Context, cs *Case, first bool, epoch uint64) (*claimed, error) {
+	running := delivery.Verdict{Group: cs.Group, Heads: cs.Heads, Trunk: cs.Trunk, State: delivery.VerdictRunning}
+	data, err := delivery.EncodeVerdict(running)
+	if err != nil {
+		return nil, err
+	}
+	value, rev, found, err := ch.Verdicts.Get(ctx, cs.Key)
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", cs.Key, err)
+	}
+	if !found {
+		rev, err := ch.Verdicts.Create(ctx, cs.Key, data)
+		if errors.Is(err, ErrConflict) {
+			return nil, nil // another checker made it first
+		}
+		if err != nil {
+			return nil, fmt.Errorf("%s: %w", cs.Key, err)
+		}
+		return &claimed{rev}, nil
+	}
+	cur, err := delivery.DecodeVerdict(value)
+	if err != nil {
+		return nil, fmt.Errorf("%s holds what is not a verdict: %w", cs.Key, err)
+	}
+	retake := false
+	switch {
+	case cur.State == delivery.VerdictRunning:
+		if first {
+			return &claimed{rev}, nil
+		}
+		return nil, nil
+	case !sameTrunk(cur.Trunk, cs.Trunk):
+		retake = true
+	case cur.State == delivery.VerdictFail && IsNodesFailure(cur):
+		ch.mu.Lock()
+		at, ok := ch.nodesFail[cs.Key]
+		ch.mu.Unlock()
+		retake = !ok || epoch > at
+	}
+	if !retake {
+		return nil, nil
+	}
+	rev, err = ch.Verdicts.Update(ctx, cs.Key, data, rev)
+	if errors.Is(err, ErrConflict) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", cs.Key, err)
+	}
+	return &claimed{rev}, nil
+}
+
+// IsNodesFailure says whether a verdict failed because a part of the mesh the check reads was not heard (UnheardWords):
+// it is judged again when the nodes change. No check fails for want of a build node any more: its asks wait in the build
+// seats' streams (ADR 0525 §6, issue 1912).
+func IsNodesFailure(v delivery.Verdict) bool {
+	return v.State == delivery.VerdictFail && strings.Contains(v.Failed.Words, UnheardWords)
+}
+
+// try claims the check, judges it within its bound and writes the verdict and the owed statuses. A check that ends
+// because ctx did is left running: the checker takes it again when it starts.
+func (ch *Checker) try(ctx context.Context, key string, cs *Case) {
+	ch.mu.Lock()
+	first := !ch.tried[cs.Key]
+	ch.tried[cs.Key] = true
+	epoch := ch.epoch
+	ch.mu.Unlock()
+	cl, err := ch.claim(ctx, cs, first, epoch)
+	if err != nil {
+		ch.logf("%s: %v", cs.Key, err)
+		return
+	}
+	if cl == nil {
+		return
+	}
+	began := ch.now()
+	ch.writeOwed(ctx, cs, delivery.Verdict{State: delivery.VerdictRunning}, Outcome{})
+	out := ch.judge(ctx, cs)
+	if ctx.Err() != nil {
+		return
+	}
+	v := out.Verdict
+	v.Group, v.Heads, v.Trunk = cs.Group, cs.Heads, cs.Trunk
+	if v.Took.Queue == 0 && !cs.Queued.IsZero() && began.After(cs.Queued) {
+		v.Took.Queue = began.Sub(cs.Queued).Milliseconds()
+	}
+	data, err := delivery.EncodeVerdict(v)
+	if err != nil {
+		ch.logf("%s: the verdict cannot be written: %v", cs.Key, err)
+		v = delivery.Verdict{Group: cs.Group, Heads: cs.Heads, Trunk: cs.Trunk, State: delivery.VerdictFail,
+			Failed: delivery.FailedFirst{Machine: "checker", Words: "the verdict could not be written: " + err.Error()}}
+		if data, err = delivery.EncodeVerdict(v); err != nil {
+			return
+		}
+	}
+	if _, err := ch.Verdicts.Update(ctx, cs.Key, data, cl.rev); err != nil {
+		ch.logf("%s: the verdict could not be written: %v", cs.Key, err)
+		return
+	}
+	if IsNodesFailure(v) {
+		ch.mu.Lock()
+		ch.nodesFail[cs.Key] = epoch
+		ch.mu.Unlock()
+	}
+	if ch.movedSince(cs) {
+		// Judged on a trunk that moved while it ran: the verdict is kept as judged, and the status stays pending until the
+		// check of the new trunk, which Reconsider starts, ends.
+		ch.writeOwed(ctx, cs, delivery.Verdict{State: delivery.VerdictRunning}, Outcome{})
+		ch.logf("%s: %s on a trunk that moved while it ran; the status stays pending", cs.Key, v.State)
+		return
+	}
+	ch.writeOwed(ctx, cs, v, out)
+	ch.logf("%s: %s", cs.Key, v.State)
+}
+
+// judge runs the case within the bound. A judge that fails to judge, and a check that ran past its bound, are verdicts of
+// failure naming the machine and the step.
+func (ch *Checker) judge(ctx context.Context, cs *Case) Outcome {
+	out, _ := judgeWithin(ctx, ch.Judge, cs, ch.bound())
+	return out
+}
+
+var errBound = errors.New("the check ran past its bound")
+
+func failure(machine, words string) delivery.Verdict {
+	return delivery.Verdict{State: delivery.VerdictFail, Failed: delivery.FailedFirst{Machine: machine, Words: words}}
+}
+
+// writeOwed writes, for each pull request judged, the status the forge bridge performs: pending while the check runs, success
+// or failure at its end (ADR 0484 clause 2). A key already holding the same value is not written again, so the bridge
+// performs one act for each change; an older head's key is never touched.
+func (ch *Checker) writeOwed(ctx context.Context, cs *Case, v delivery.Verdict, out Outcome) {
+	for _, p := range cs.Pulls {
+		key, err := delivery.CheckerOwedKey(p.Repository, p.Number, p.Head)
+		if err != nil {
+			ch.logf("%s: %v", cs.Key, err)
+			continue
+		}
+		state := map[string]string{delivery.VerdictRunning: "pending", delivery.VerdictPass: "success", delivery.VerdictFail: "failure"}[v.State]
+		o := delivery.Owed{Act: delivery.OwedStatus, Context: delivery.StatusContextCheck, State: state,
+			Target: strings.TrimSuffix(ch.Link, "/") + "/" + cs.Key, Text: Line(v, cs, p, out.Builds, out.Slowest, out.Judged)}
+		data, err := delivery.EncodeCheckerOwed(o)
+		if err != nil {
+			ch.logf("%s: the status of %s cannot be written: %v", cs.Key, key, err)
+			continue
+		}
+		wrote, err := putOnce(ctx, ch.Owed, key, data, func(cur []byte) bool {
+			held, err := delivery.DecodeCheckerOwed(cur)
+			o.V = delivery.Version
+			return err == nil && delivery.SameOwed(held, o)
+		})
+		if err != nil {
+			ch.logf("%s: the status of %s cannot be written: %v", cs.Key, key, err)
+		} else if wrote && ch.Announce != nil {
+			ch.Announce(ctx, EventOwedWritten, key)
+		}
+	}
+}
+
+// putOnce writes data under key by create, or by compare-and-set when the key exists, and writes nothing when same says the
+// key holds the value already.
+func putOnce(ctx context.Context, kv KV, key string, data []byte, same func(cur []byte) bool) (bool, error) {
+	for try := 0; try < 4; try++ {
+		cur, rev, found, err := kv.Get(ctx, key)
+		if err != nil {
+			return false, err
+		}
+		if found && same(cur) {
+			return false, nil
+		}
+		if !found {
+			_, err = kv.Create(ctx, key, data)
+		} else {
+			_, err = kv.Update(ctx, key, data, rev)
+		}
+		if errors.Is(err, ErrConflict) {
+			continue
+		}
+		return err == nil, err
+	}
+	return false, fmt.Errorf("%s changed under every one of 4 tries", key)
+}
+
+// Sweep closes, at start, every verdict left running for a candidate that no longer holds those heads: nothing will check
+// them again, and the key would stay running for ever (the builder's Sweep, issue 1660). Call it once the candidates have been
+// read. A key of heads a candidate holds now is not touched: the check takes it over.
+func (ch *Checker) Sweep(ctx context.Context) error {
+	ch.init()
+	keys, err := ch.Verdicts.Keys(ctx)
+	if err != nil {
+		return err
+	}
+	ch.mu.Lock()
+	current := map[string]bool{}
+	for _, c := range ch.known {
+		if k, err := delivery.CheckerVerdictKey(c.Group, c.HeadsHash); err == nil {
+			current[k] = true
+		}
+	}
+	ch.mu.Unlock()
+	for _, key := range keys {
+		if current[key] {
+			continue
+		}
+		value, rev, found, err := ch.Verdicts.Get(ctx, key)
+		if err != nil || !found {
+			continue
+		}
+		cur, err := delivery.DecodeVerdict(value)
+		if err != nil || cur.State != delivery.VerdictRunning {
+			continue
+		}
+		cur.State = delivery.VerdictFail
+		cur.Failed = delivery.FailedFirst{Machine: "checker", Words: "closed at start: left running, and no candidate holds these heads any more, so nothing will check them"}
+		data, err := delivery.EncodeVerdict(cur)
+		if err != nil {
+			return err
+		}
+		if _, err := ch.Verdicts.Update(ctx, key, data, rev); err != nil && !errors.Is(err, ErrConflict) {
+			return fmt.Errorf("%s: %w", key, err)
+		}
+		ch.logf("%s: closed, left running for heads no candidate holds", key)
+	}
+	return nil
+}
+
+// TrunkMoved is Reconsider after a move of a trunk, which first owes mesh/check pending on every open pull request of a
+// candidate whose verdict was judged on other trunk heads, every member's for a group (the lead's decision L4, the checker's
+// part of issue 1302): the forge's success of the old trunk never stands while the check waits for a place or for a delivery
+// that holds it, so the gate never reads it as the head's.
+func (ch *Checker) TrunkMoved(ctx context.Context) {
+	ch.init()
+	ch.mu.Lock()
+	known := make(map[string]delivery.Candidate, len(ch.known))
+	for k, c := range ch.known {
+		known[k] = c
+	}
+	ch.mu.Unlock()
+	heads := ch.heads()
+	for _, c := range known {
+		cs := CaseOf(c, heads)
+		if cs == nil {
+			continue
+		}
+		value, _, found, err := ch.Verdicts.Get(ctx, cs.Key)
+		if err != nil || !found {
+			continue // never judged: no status to put out of date
+		}
+		if v, err := delivery.DecodeVerdict(value); err == nil && sameTrunk(v.Trunk, cs.Trunk) {
+			continue
+		}
+		ch.writeOwed(ctx, cs, delivery.Verdict{State: delivery.VerdictRunning}, Outcome{})
+	}
+	ch.Reconsider(ctx)
+}
+
+// movedSince says whether a trunk the case was judged on is no longer the trunk's head.
+func (ch *Checker) movedSince(cs *Case) bool {
+	now := ch.heads()
+	for repo, head := range cs.Trunk {
+		if now[repo] != head {
+			return true
+		}
+	}
+	return false
+}

modules/mesh-delivery-checker/internal/check/checker_test.go

@@ -0,0 +1,380 @@
+package check
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+const hqRepo = "novox/hq"
+
+const (
+	repoA   = "novox/mesh-delivery"
+	repoSDK = "novox/mesh-sdk"
+	head1   = "1111111111111111111111111111111111111111"
+	head2   = "2222222222222222222222222222222222222222"
+	trunkA  = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+	trunkA2 = "abababababababababababababababababababab"
+	trunkS  = "5555555555555555555555555555555555555555"
+	trunkS2 = "5656565656565656565656565656565656565656"
+)
+
+// candidateOf is a candidate of a group with the given pull requests, as the indexer writes one.
+func candidateOf(t testing.TB, group string, pulls ...delivery.CandidatePull) []byte {
+	t.Helper()
+	heads := make([]delivery.Head, len(pulls))
+	for i, p := range pulls {
+		heads[i] = p.Head
+	}
+	hash, err := delivery.HeadsHash(heads)
+	if err != nil {
+		t.Fatal(err)
+	}
+	c := delivery.Candidate{V: delivery.Version, Group: group, HeadsHash: hash, Pulls: pulls, FPSet: delivery.FingerprintSet(pulls)}
+	data, err := delivery.EncodeCandidate(c)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return data
+}
+
+func pullOf(repo string, number int, head string) delivery.CandidatePull {
+	return delivery.CandidatePull{Head: delivery.Head{Repository: repo, Number: number, Head: head}, Modules: []string{}}
+}
+
+// judgeFunc is a Judge written as a function; it counts its calls.
+type judgeFunc struct {
+	mu    sync.Mutex
+	calls int
+	f     func(ctx context.Context, c *Case, call int) (Outcome, error)
+}
+
+func (j *judgeFunc) Judge(ctx context.Context, c *Case) (Outcome, error) {
+	j.mu.Lock()
+	j.calls++
+	n := j.calls
+	j.mu.Unlock()
+	return j.f(ctx, c, n)
+}
+
+func (j *judgeFunc) count() int { j.mu.Lock(); defer j.mu.Unlock(); return j.calls }
+
+func passing() delivery.Verdict {
+	return delivery.Verdict{State: delivery.VerdictPass, Levels: map[string]delivery.LevelResult{
+		delivery.LevelUnit: {Run: 2, Kept: 3}, delivery.LevelIntegration: {Run: 1}}}
+}
+
+func passJudge() *judgeFunc {
+	return &judgeFunc{f: func(context.Context, *Case, int) (Outcome, error) { return Outcome{Verdict: passing()}, nil }}
+}
+
+type rig struct {
+	ch       *Checker
+	verdicts *memKV
+	owed     *memKV
+	trunks   *Trunks
+}
+
+func newRig(t testing.TB, j Judge) *rig {
+	t.Helper()
+	r := &rig{verdicts: newMemKV(), owed: newMemKV(), trunks: &Trunks{}}
+	r.setTrunks(t, map[string]string{repoA: trunkA, repoSDK: trunkS})
+	r.ch = &Checker{Verdicts: r.verdicts, Owed: r.owed, Judge: j, Trunks: r.trunks, Link: "https://view.invalid/checks", Now: time.Now}
+	return r
+}
+
+func (r *rig) setTrunks(t testing.TB, heads map[string]string) bool {
+	t.Helper()
+	data, err := delivery.EncodeSource(delivery.Source{Group: "g", Heads: heads})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return r.trunks.Put(data, false)
+}
+
+func (r *rig) verdict(t testing.TB, key string) delivery.Verdict {
+	t.Helper()
+	raw, _, found, _ := r.verdicts.Get(context.Background(), key)
+	if !found {
+		t.Fatalf("no verdict %s; the bucket holds %v", key, r.verdicts.vals)
+	}
+	v, err := delivery.DecodeVerdict(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return v
+}
+
+func keyOf(t testing.TB, group string, value []byte) string {
+	t.Helper()
+	c, err := delivery.DecodeCandidate(value)
+	if err != nil {
+		t.Fatal(err)
+	}
+	k, err := delivery.CheckerVerdictKey(group, c.HeadsHash)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return k
+}
+
+func TestACandidateNotYetCheckedGetsItsVerdictKeyCreatedOnceAndIsJudged(t *testing.T) { // N6/AC1, 1678
+	ctx, j := context.Background(), passJudge()
+	r := newRig(t, j)
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1))
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	key := keyOf(t, "feat/x", cand)
+	if v := r.verdict(t, key); v.State != delivery.VerdictPass || v.Group != "feat/x" || v.Trunk[repoA] != trunkA {
+		t.Fatalf("verdict = %+v", v)
+	}
+	if r.verdicts.creates[key] != 1 || j.count() != 1 {
+		t.Errorf("creates = %d, judged = %d, want one each", r.verdicts.creates[key], j.count())
+	}
+	// The same candidate heard again, with nothing changed, is not judged again.
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	if j.count() != 1 {
+		t.Errorf("judged %d times after the same candidate again, want once", j.count())
+	}
+}
+
+// racyKV lets another instance create the key just before this one's create.
+type racyKV struct {
+	*memKV
+	other []byte
+}
+
+func (r racyKV) Create(ctx context.Context, key string, value []byte) (uint64, error) {
+	if r.other != nil {
+		_, _ = r.memKV.Create(ctx, key, r.other)
+	}
+	return r.memKV.Create(ctx, key, value)
+}
+
+func TestASecondInstancesCreateIsRefusedAndItDoesNothing(t *testing.T) { // N6/AC1
+	ctx, j := context.Background(), passJudge()
+	r := newRig(t, j)
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1))
+	key := keyOf(t, "feat/x", cand)
+	other, _ := delivery.EncodeVerdict(delivery.Verdict{Group: "feat/x", Heads: strings.SplitN(key, ".", 2)[1], State: delivery.VerdictRunning})
+	r.ch.Verdicts = racyKV{r.verdicts, other}
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	if j.count() != 0 {
+		t.Errorf("the instance that lost the create judged %d times, want none", j.count())
+	}
+	if v := r.verdict(t, key); v.State != delivery.VerdictRunning {
+		t.Errorf("the other instance's key was changed: %+v", v)
+	}
+}
+
+func TestARestartWithARunningKeyJudgesItAgain(t *testing.T) { // N6/AC2
+	ctx, j := context.Background(), passJudge()
+	r := newRig(t, j)
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1))
+	key := keyOf(t, "feat/x", cand)
+	left, _ := delivery.EncodeVerdict(delivery.Verdict{Group: "feat/x", Heads: strings.SplitN(key, ".", 2)[1], Trunk: map[string]string{repoA: trunkA}, State: delivery.VerdictRunning})
+	if _, err := r.verdicts.Create(ctx, key, left); err != nil {
+		t.Fatal(err)
+	}
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	if j.count() != 1 || r.verdict(t, key).State != delivery.VerdictPass {
+		t.Fatalf("judged %d times, verdict %+v, want the left check judged once and passed", j.count(), r.verdict(t, key))
+	}
+}
+
+func TestACheckPastItsBoundFailsNamingTheStuckStep(t *testing.T) { // N6/AC3
+	ctx := context.Background()
+	j := &judgeFunc{f: func(ctx context.Context, c *Case, _ int) (Outcome, error) {
+		c.Progress.Set("test the unit level of mesh-delivery", "shanks")
+		<-ctx.Done()
+		return Outcome{}, ctx.Err()
+	}}
+	r := newRig(t, j)
+	r.ch.Bound = 30 * time.Millisecond
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1))
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	v := r.verdict(t, keyOf(t, "feat/x", cand))
+	if v.State != delivery.VerdictFail || v.Failed.Machine != "shanks" || !strings.Contains(v.Failed.Words, "stuck at: test the unit level of mesh-delivery") {
+		t.Fatalf("verdict = %+v, want a failure naming shanks and the stuck step", v)
+	}
+}
+
+// A check whose forge was not heard is judged again when the nodes change (issue 1912: no check fails for want of a build
+// node any more; its asks wait in the streams).
+func TestAnUnheardForgeFailsWithTheReasonAndIsJudgedAgainWhenTheNodesChange(t *testing.T) { // N6/AC4
+	ctx := context.Background()
+	j := &judgeFunc{f: func(_ context.Context, _ *Case, n int) (Outcome, error) {
+		if n == 1 {
+			return Outcome{Verdict: failure("the forge", "novox/mesh-delivery#7: go.mod cannot be read: no responders (the forge was "+UnheardWords+")")}, nil
+		}
+		return Outcome{Verdict: passing()}, nil
+	}}
+	r := newRig(t, j)
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1))
+	key := keyOf(t, "feat/x", cand)
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	if v := r.verdict(t, key); !IsNodesFailure(v) {
+		t.Fatalf("verdict = %+v, want a failure of the nodes", v)
+	}
+	r.ch.Reconsider(ctx) // nothing changed: not judged again
+	r.ch.Wait()
+	if j.count() != 1 {
+		t.Fatalf("judged %d times with the nodes unchanged, want once", j.count())
+	}
+	r.ch.NodesChanged(ctx)
+	r.ch.Wait()
+	if j.count() != 2 || r.verdict(t, key).State != delivery.VerdictPass {
+		t.Fatalf("after the nodes changed: judged %d times, verdict %+v", j.count(), r.verdict(t, key))
+	}
+}
+
+func TestARepositoryWithNoTrunkGetsNoVerdict(t *testing.T) { // N6/AC6, ADR 0484 clause 11
+	ctx, j := context.Background(), passJudge()
+	r := newRig(t, j)
+	r.ch.Candidate(ctx, "feat/y", candidateOf(t, "feat/y", pullOf("novox/unknown", 4, head1)))
+	r.ch.Wait()
+	if j.count() != 0 || len(r.verdicts.vals) != 0 || len(r.owed.vals) != 0 {
+		t.Errorf("judged %d times, %d verdicts, %d statuses, want none", j.count(), len(r.verdicts.vals), len(r.owed.vals))
+	}
+}
+
+// 1887/A10, ADR 0527 §2: hq is judged as any repository, its checks Go tests, and its pull request gets a verdict and a
+// mesh/check; in a group, hq's member is judged with the others.
+func TestAnHqPullRequestGetsAVerdictAndAStatus(t *testing.T) {
+	ctx, j := context.Background(), passJudge()
+	r := newRig(t, j)
+	r.setTrunks(t, map[string]string{repoA: trunkA, repoSDK: trunkS, hqRepo: trunkA2})
+	r.ch.Candidate(ctx, "feat/hq", candidateOf(t, "feat/hq", pullOf(hqRepo, 3, head1)))
+	r.ch.Wait()
+	if j.count() != 1 || len(r.verdicts.vals) != 1 {
+		t.Fatalf("judged %d times, %d verdicts, want one", j.count(), len(r.verdicts.vals))
+	}
+	if s := owedState(t, r, hqRepo, 3, head1); s != "success" {
+		t.Errorf("hq#3 owes %q, want success", s)
+	}
+	r.ch.Candidate(ctx, "feat/x", candidateOf(t, "feat/x", pullOf(hqRepo, 4, head2), pullOf(repoA, 7, head2)))
+	r.ch.Wait()
+	if s := owedState(t, r, hqRepo, 4, head2); s != "success" {
+		t.Errorf("hq#4 in a group owes %q, want success", s)
+	}
+}
+
+func TestATrunkMoveRewritesTheSameVerdictKeyAndTheHeadsStatus(t *testing.T) { // 1300/AC7
+	ctx, j := context.Background(), passJudge()
+	r := newRig(t, j)
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1))
+	key := keyOf(t, "feat/x", cand)
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	_, rev1, _, _ := r.verdicts.Get(ctx, key)
+	owedKey, _ := delivery.CheckerOwedKey(repoA, 7, head1)
+	_, orev1, _, _ := r.owed.Get(ctx, owedKey)
+	if !r.setTrunks(t, map[string]string{repoA: trunkA2, repoSDK: trunkS}) {
+		t.Fatal("the trunks did not change")
+	}
+	r.ch.Reconsider(ctx)
+	r.ch.Wait()
+	_, rev2, _, _ := r.verdicts.Get(ctx, key)
+	if j.count() != 2 || rev2 <= rev1 || r.verdict(t, key).Trunk[repoA] != trunkA2 {
+		t.Fatalf("judged %d times, revisions %d then %d, trunk %v", j.count(), rev1, rev2, r.verdict(t, key).Trunk)
+	}
+	if r.verdicts.creates[key] != 1 {
+		t.Errorf("the key was created %d times, want the same key rewritten", r.verdicts.creates[key])
+	}
+	if _, orev2, _, _ := r.owed.Get(ctx, owedKey); orev2 <= orev1 {
+		// the line is the same when nothing differs; the status is rewritten when the words change, here the trunk is in them
+		t.Logf("the status keeps revision %d (its words did not change)", orev2)
+	}
+	// A new head is another key, and the older head's status is not touched.
+	older, _, _, _ := r.owed.Get(ctx, owedKey)
+	cand2 := candidateOf(t, "feat/x", pullOf(repoA, 7, head2))
+	r.ch.Candidate(ctx, "feat%2Fx", cand2)
+	r.ch.Wait()
+	if again, _, _, _ := r.owed.Get(ctx, owedKey); string(again) != string(older) {
+		t.Errorf("the older head's status was rewritten")
+	}
+	if n := len(r.owed.vals); n != 2 {
+		t.Errorf("%d statuses, want one for each head", n)
+	}
+}
+
+func TestTheStatusIsPendingWhileTheCheckRunsAndEndsSuccessOrFailure(t *testing.T) { // 1300/AC5 (unit part)
+	ctx := context.Background()
+	var seen []string
+	var r *rig
+	j := &judgeFunc{f: func(ctx context.Context, c *Case, _ int) (Outcome, error) {
+		key, _ := delivery.CheckerOwedKey(repoA, 7, head1)
+		raw, _, _, _ := r.owed.Get(ctx, key)
+		o, _ := delivery.DecodeCheckerOwed(raw)
+		seen = append(seen, o.State)
+		return Outcome{Verdict: delivery.Verdict{State: delivery.VerdictFail, Failed: delivery.FailedFirst{Test: "m/a.TestX"}}}, nil
+	}}
+	r = newRig(t, j)
+	r.ch.Candidate(ctx, "feat/x", candidateOf(t, "feat/x", pullOf(repoA, 7, head1)))
+	r.ch.Wait()
+	key, _ := delivery.CheckerOwedKey(repoA, 7, head1)
+	raw, _, _, _ := r.owed.Get(ctx, key)
+	o, err := delivery.DecodeCheckerOwed(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(seen) != 1 || seen[0] != "pending" || o.State != "failure" || o.Context != delivery.StatusContextCheck || !strings.HasPrefix(o.Target, "https://view.invalid/checks/") {
+		t.Errorf("while running %v, at the end %+v", seen, o)
+	}
+}
+
+func TestSweepClosesARunningKeyNoCandidateHoldsAndLeavesOneItDoes(t *testing.T) {
+	ctx, j := context.Background(), passJudge()
+	r := newRig(t, j)
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1))
+	live := keyOf(t, "feat/x", cand)
+	dead, _ := delivery.CheckerVerdictKey("feat/gone", "0123456789ab")
+	for _, k := range []string{live, dead} {
+		group, heads, _ := delivery.ParseCheckerVerdictKey(k)
+		raw, _ := delivery.EncodeVerdict(delivery.Verdict{Group: group, Heads: heads, State: delivery.VerdictRunning})
+		_, _ = r.verdicts.Create(ctx, k, raw)
+	}
+	r.ch.init()
+	var c delivery.Candidate
+	_ = json.Unmarshal(cand, &c)
+	r.ch.known["feat%2Fx"] = c
+	if err := r.ch.Sweep(ctx); err != nil {
+		t.Fatal(err)
+	}
+	if v := r.verdict(t, dead); v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "closed at start") {
+		t.Errorf("the dead key = %+v", v)
+	}
+	if v := r.verdict(t, live); v.State != delivery.VerdictRunning {
+		t.Errorf("the live key = %+v, want it left for the check to take over", v)
+	}
+}
+
+func TestTheForgeBridgeIsToldOnceForEachChangeOfAStatus(t *testing.T) { // 1683 (the checker's half of AC5)
+	ctx, j := context.Background(), passJudge()
+	r := newRig(t, j)
+	var told []string
+	r.ch.Announce = func(_ context.Context, event, key string) { told = append(told, event+" "+key) }
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1))
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	key, _ := delivery.CheckerOwedKey(repoA, 7, head1)
+	want := []string{EventOwedWritten + " " + key, EventOwedWritten + " " + key} // pending, then success
+	if len(told) != 2 || told[0] != want[0] || told[1] != want[1] {
+		t.Fatalf("told %v, want the status said when pending and when success", told)
+	}
+	r.ch.Candidate(ctx, "feat%2Fx", cand) // nothing changed: nothing written, nothing said
+	r.ch.Wait()
+	if len(told) != 2 {
+		t.Errorf("told %v after a check that changed nothing", told)
+	}
+}

modules/mesh-delivery-checker/internal/check/composition_test.go

@@ -0,0 +1,80 @@
+package check
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// fakeCompositions answers the assigner's composition of a check from memory, recording the keys asked.
+type fakeCompositions struct {
+	v     delivery.CompositionVerdict
+	err   error
+	asked []string
+}
+
+func (f *fakeCompositions) Await(_ context.Context, key string) (delivery.CompositionVerdict, error) {
+	f.asked = append(f.asked, key)
+	return f.v, f.err
+}
+
+// 1297/AC3 (its unit half): a check whose tests pass takes the assigner's composition of it, by the check's own key,
+// into its verdict: a pass says it passed with the mesh-sdk and machines it composed, and is no longer "not run".
+func TestAPassingCheckTakesTheAssignersComposition(t *testing.T) {
+	b := newBench(t)
+	f := &fakeCompositions{v: delivery.CompositionVerdict{Group: "feat/x", Heads: "0123456789ab", State: delivery.CompositionPass, SDK: "v0.1.14-x", Machines: []string{"g14"}, Took: 40}}
+	b.ex.Compositions = f
+	cs := caseOf(t, pullOf(repoA, 7, head1))
+	v := b.judge(t, cs).Verdict
+	if v.State != delivery.VerdictPass || v.Composition == nil || v.Composition.State != delivery.CompositionPass || v.Composition.SDK != "v0.1.14-x" || v.Took.Composition != 40 {
+		t.Fatalf("verdict = %+v, composition %+v", v, v.Composition)
+	}
+	if len(f.asked) != 1 || f.asked[0] != cs.Key {
+		t.Errorf("asked %v, want the check's key %s", f.asked, cs.Key)
+	}
+	if !compositionMentions(v, "passed") {
+		t.Errorf("the line says %q", compositionWords(v.Composition, v.Took.Composition))
+	}
+}
+
+func compositionMentions(v delivery.Verdict, word string) bool {
+	return strings.Contains(compositionWords(v.Composition, v.Took.Composition), word)
+}
+
+// 1297/AC2 at the checker: a failed composition fails the check, naming the machine it failed at and its words.
+func TestAFailedCompositionFailsTheCheck(t *testing.T) {
+	b := newBench(t)
+	b.ex.Compositions = &fakeCompositions{v: delivery.CompositionVerdict{Group: "feat/x", Heads: "0123456789ab", State: delivery.CompositionFail, SDK: "x",
+		Machine: "g14", Words: "g14 runs web, which the change removes from its source"}}
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.State != delivery.VerdictFail || v.Failed.Machine != "g14" || v.Composition == nil || v.Composition.State != delivery.CompositionFail {
+		t.Fatalf("verdict = %+v", v)
+	}
+	v.Group, v.Heads = "feat/x", "0123456789ab" // the checker names them when it writes the verdict
+	if _, err := delivery.EncodeVerdict(v); err != nil {
+		t.Errorf("the verdict cannot be written: %v", err)
+	}
+}
+
+// 1297/B3d: a composition that cannot be read leaves it not run; a try is not composed.
+func TestACompositionNotHadIsNotRun(t *testing.T) {
+	b := newBench(t)
+	f := &fakeCompositions{err: errors.New("the check's bound passed")}
+	b.ex.Compositions = f
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.State != delivery.VerdictPass || v.Composition == nil || v.Composition.State != delivery.CompositionNotRun {
+		t.Fatalf("verdict = %+v", v)
+	}
+	b2 := newBench(t)
+	f2 := &fakeCompositions{v: delivery.CompositionVerdict{State: delivery.CompositionFail, Words: "w", SDK: "x"}}
+	b2.ex.Compositions = f2
+	cs := caseOf(t, pullOf(repoA, 7, head1))
+	cs.Try = &TryOptions{}
+	b2.judge(t, cs)
+	if len(f2.asked) != 0 {
+		t.Errorf("a try asked for a composition: %v", f2.asked)
+	}
+}

modules/mesh-delivery-checker/internal/check/digestform_test.go

@@ -0,0 +1,83 @@
+package check
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// 1930/AC3: given a check ask whose stored end keeps the digest's packages as a list of {package, digest} (issue 1930),
+// or one stored before it with the packages a map keyed by package path, when the same heads are checked a second time,
+// then the kept verdicts the first check wrote are read from it: every package it passed is kept, none run again.
+func TestKeptVerdictsAreReadFromTheDigestsListForm(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		old  bool
+	}{{"the list form", false}, {"a map stored before issue 1930", true}} {
+		t.Run(tc.name, func(t *testing.T) {
+			b := newBench(t)
+			var stored []string
+			b.asks.Answer = func(a delivery.StepAsk) delivery.Step {
+				s := b.answer(a)
+				if tc.old && s.State == delivery.StepPassed {
+					s.Result = oldDigestForm(t, s.Result)
+				}
+				stored = append(stored, string(s.Result))
+				return s
+			}
+			first := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+			u := first.Levels[delivery.LevelUnit]
+			if first.State != delivery.VerdictPass || u.Run == 0 || u.Kept != 0 {
+				t.Fatalf("the first check = %+v", first)
+			}
+			if len(stored) == 0 {
+				t.Fatal("no ask's end was stored")
+			}
+			list := strings.Contains(stored[0], `"packages":[{"package":"fixture/slow"`)
+			if list == tc.old || strings.Contains(stored[0], `"fixture/slow":"`) != tc.old {
+				t.Fatalf("the stored end is not in the form under test: %s", stored[0])
+			}
+			b.steps.calls = nil
+			second := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+			if s := second.Levels[delivery.LevelUnit]; second.State != delivery.VerdictPass || s.Kept != u.Run || s.Run != 0 {
+				t.Fatalf("the second check's unit level = %+v, want %d kept and none run", s, u.Run)
+			}
+			if n := len(b.steps.tool("test")); n != 0 {
+				t.Errorf("%d test steps ran on the second check", n)
+			}
+		})
+	}
+}
+
+// oldDigestForm rewrites a check answer's level digests to the form stored before issue 1930: packages as a map keyed by
+// package path.
+func oldDigestForm(t *testing.T, result json.RawMessage) json.RawMessage {
+	t.Helper()
+	var a struct {
+		Fetch  json.RawMessage  `json:"fetch"`
+		Levels []map[string]any `json:"levels"`
+	}
+	if err := json.Unmarshal(result, &a); err != nil {
+		t.Fatal(err)
+	}
+	for _, l := range a.Levels {
+		d, ok := l["digest"].(map[string]any)
+		if !ok {
+			continue
+		}
+		m := map[string]any{}
+		list, _ := d["packages"].([]any)
+		for _, p := range list {
+			pd := p.(map[string]any)
+			m[pd["package"].(string)] = pd["digest"]
+		}
+		d["packages"] = m
+	}
+	raw, err := json.Marshal(a)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return raw
+}

modules/mesh-delivery-checker/internal/check/doc.go

@@ -0,0 +1,6 @@
+// Package check is the checker's logic (novox/hq ADR 0484, ADR 0453 clause 4, ADR 0447, ADR 0444), apart from the bus: the
+// claim of a verdict key, the judging of a pull request's head merged onto its trunk through the build modules' fetch,
+// digest and test steps, the kept verdicts, the line of the status and the act the forge bridge performs. The bus is
+// reached through the small interfaces here, so each part is tested with fakes. The checker runs dark: nothing reads its
+// answers to merge or deliver (ADR 0453 clause 4).
+package check

modules/mesh-delivery-checker/internal/check/examiner_test.go

@@ -0,0 +1,845 @@
+package check
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"reflect"
+	"sort"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+// captured reads a result the build module's own code marshalled (testdata/captured/README).
+func captured[T any](t testing.TB, name string) T {
+	t.Helper()
+	raw, err := os.ReadFile(filepath.Join("testdata", "captured", name+".json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var v T
+	if err := json.Unmarshal(raw, &v); err != nil {
+		t.Fatal(err)
+	}
+	return v
+}
+
+type stepCall struct {
+	module, node, tool string
+	args               map[string]any
+}
+
+// fakeSteps stands for the build modules: a handler for each tool answers what the module's code answers.
+type fakeSteps struct {
+	mu       sync.Mutex
+	calls    []stepCall
+	handlers map[string]func(c stepCall) (any, error)
+}
+
+func (f *fakeSteps) Run(_ context.Context, module, node, tool string, args map[string]any) (json.RawMessage, error) {
+	c := stepCall{module, node, tool, args}
+	f.mu.Lock()
+	f.calls = append(f.calls, c)
+	h := f.handlers[tool]
+	f.mu.Unlock()
+	if h == nil {
+		return nil, fmt.Errorf("the fake build module has no tool %s", tool)
+	}
+	v, err := h(c)
+	if err != nil {
+		return nil, err
+	}
+	return json.Marshal(v)
+}
+
+func (f *fakeSteps) tool(name string) []stepCall {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	var out []stepCall
+	for _, c := range f.calls {
+		if strings.HasSuffix(c.tool, "_"+name) {
+			out = append(out, c)
+		}
+	}
+	return out
+}
+
+type entries []delivery.NodeToolchain
+
+func (e entries) Entries(language string) []delivery.NodeToolchain {
+	var out []delivery.NodeToolchain
+	for _, x := range e {
+		if x.Language == language {
+			out = append(out, x)
+		}
+	}
+	return out
+}
+
+type langs map[string][]string
+
+func (l langs) BuildModules(repository string) []string {
+	if m, ok := l[repository]; ok {
+		return m
+	}
+	return []string{buildrun.GoBuildModule}
+}
+
+func goEntries(nodes ...string) entries {
+	var e entries
+	for _, n := range nodes {
+		e = append(e, delivery.NodeToolchain{Node: n, Toolchain: delivery.Toolchain{Language: "go", Version: "go1.27.1", Recipe: "7"}})
+		e = append(e, delivery.NodeToolchain{Node: n, Toolchain: delivery.Toolchain{Language: "typescript", Version: "node24", Recipe: "3"}})
+	}
+	return e
+}
+
+const digC = "cc33cc33cc33cc33cc33cc33cc33cc33cc33cc33cc33cc33cc33cc33cc33cc33"
+const digD = "dd44dd44dd44dd44dd44dd44dd44dd44dd44dd44dd44dd44dd44dd44dd44dd44"
+
+type bench struct {
+	ex     *Examiner
+	asks   *buildrun.FakeAsks
+	steps  *fakeSteps
+	kept   *memKV
+	prev   *memKV
+	fetch  Fetched
+	digest map[string]Digested // by level
+	test   func(c stepCall) (any, error)
+}
+
+// refsOf reads the siblings of a fetch's arguments, as they arrive in an ask (JSON) or as the checker gave them.
+func refsOf(v any) []BesideRef {
+	raw, _ := json.Marshal(v)
+	var refs []BesideRef
+	_ = json.Unmarshal(raw, &refs)
+	return refs
+}
+
+// toolPrefix is the start of each build module's tool names, as the fake build modules answer them.
+var toolPrefix = map[string]string{buildrun.GoBuildModule: "build_go_", buildrun.NodeBuildModule: "build_node_"}
+
+// answer runs a check ask as the build module that pulls it does (buildstep.RunAsk), with the fake tools on shanks and the
+// bench's kept verdicts, and answers the step it writes.
+func (b *bench) answer(a delivery.StepAsk) delivery.Step {
+	module, _ := delivery.BuildModuleOf(a.Language)
+	const node = "shanks"
+	tool := func(name string) buildstep.StepFunc {
+		return func(ctx context.Context, args map[string]any) (any, error) {
+			raw, err := b.steps.Run(ctx, module, node, toolPrefix[module]+name, args)
+			if err != nil {
+				return nil, err
+			}
+			return raw, nil
+		}
+	}
+	steps := buildstep.AskSteps{Fetch: tool("fetch"), Test: tool("test"),
+		Kept: func(ctx context.Context, level, digest string) (int, bool, error) {
+			k, found, err := (Kept{Store: b.kept}).Lookup(ctx, level, digest)
+			return k.Tests, found, err
+		}}
+	if module == buildrun.GoBuildModule {
+		steps.Digest = tool("digest")
+	}
+	out, err := buildstep.RunAsk(context.Background(), steps, a)
+	began := time.Date(2026, 10, 21, 19, 0, 0, 0, time.UTC)
+	step := delivery.Step{ID: a.ID, Tool: a.Kind + " ask", Node: node, State: delivery.StepPassed, Started: began, Ended: began.Add(2 * time.Second)}
+	if err != nil {
+		step.State, step.Reason = delivery.StepFailed, err.Error()
+		return step
+	}
+	step.Result, _ = json.Marshal(out)
+	return step
+}
+
+// newBench is an examiner over fake build modules that merge cleanly, digest the captured fixture's packages and pass
+// the captured slow fixture's result at both levels, on shanks.
+func newBench(t testing.TB) *bench {
+	b := &bench{steps: &fakeSteps{}, kept: newMemKV(), prev: newMemKV()}
+	b.fetch = captured[Fetched](t, "go-fetch-clean")
+	b.fetch.Modules, b.fetch.Changed, b.fetch.Trees = []string{"."}, []string{"README.md"}, nil
+	one := captured[Digested](t, "go-digest")
+	b.digest = map[string]Digested{
+		delivery.LevelUnit:        {Level: "unit", Packages: map[string]string{"fixture/slow": digA}},
+		delivery.LevelIntegration: {Level: "integration", Packages: map[string]string{"fixture/slow": digB}},
+	}
+	_ = one
+	slow := captured[Tested](t, "go-test-slow")
+	b.test = func(c stepCall) (any, error) {
+		r := slow
+		r.Level, _ = c.args["level"].(string)
+		return r, nil
+	}
+	b.steps.handlers = map[string]func(stepCall) (any, error){
+		"build_go_fetch":   func(stepCall) (any, error) { return b.fetch, nil },
+		"build_node_fetch": func(stepCall) (any, error) { return b.fetch, nil },
+		"build_go_digest":  func(c stepCall) (any, error) { return echoBeside(b, b.digest[c.args["level"].(string)]), nil },
+		"build_go_test":    func(c stepCall) (any, error) { return b.test(c) },
+		"build_node_test":  func(c stepCall) (any, error) { return b.test(c) },
+	}
+	now := time.Date(2026, 10, 21, 19, 0, 0, 0, time.UTC)
+	b.asks = &buildrun.FakeAsks{Answer: b.answer}
+	b.ex = &Examiner{Asks: buildrun.Asker{Publisher: b.asks, Waiter: b.asks, Bound: 5 * time.Second}, Toolchains: goEntries("shanks"), Kept: Kept{Store: b.kept}, Previews: b.prev,
+		Modules: langs{}, Trunks: &Trunks{}, Now: func() time.Time { now = now.Add(50 * time.Millisecond); return now }}
+	return b
+}
+
+func caseOf(t testing.TB, pulls ...delivery.CandidatePull) *Case {
+	t.Helper()
+	raw := candidateOf(t, "feat/x", pulls...)
+	c, err := delivery.DecodeCandidate(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	cs := CaseOf(c, map[string]string{repoA: trunkA, repoSDK: trunkS, "novox/mesh-controller": trunkA, "novox/mesh-catalog": trunkA})
+	if cs == nil {
+		t.Fatal("no case")
+	}
+	return cs
+}
+
+func (b *bench) judge(t testing.TB, cs *Case) Outcome {
+	t.Helper()
+	out, err := b.ex.Judge(context.Background(), cs)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return out
+}
+
+func testedWith(t testing.TB, name string, edit func(*Tested)) Tested {
+	r := captured[Tested](t, name)
+	if edit != nil {
+		edit(&r)
+	}
+	return r
+}
+
+func packagesOf(c stepCall) []string {
+	var out []string
+	if l, ok := c.args["packages"].([]string); ok {
+		out = l
+	}
+	return out
+}
+
+func TestACleanMergeIsFetchedAtItsTrunkAndBothLevelsPass(t *testing.T) { // 1679/AC1
+	b := newBench(t)
+	cs := caseOf(t, pullOf(repoA, 7, head1))
+	out := b.judge(t, cs)
+	v := out.Verdict
+	if v.State != delivery.VerdictPass || v.Levels[delivery.LevelUnit].Run != 2 || v.Levels[delivery.LevelIntegration].Run != 2 {
+		t.Fatalf("verdict = %+v", v)
+	}
+	if v.Composition == nil || v.Composition.State != delivery.CompositionNotRun {
+		t.Errorf("composition = %+v, want not run", v.Composition)
+	}
+	if len(v.Machines) != 1 || v.Machines[0] != "shanks" {
+		t.Errorf("machines = %v", v.Machines)
+	}
+	fetch := b.steps.tool("fetch")
+	if len(fetch) != 1 || fetch[0].args["repository"] != repoA || fetch[0].args["commit"] != head1 || fetch[0].args["base"] != trunkA || fetch[0].args["ref"] != "refs/pull/7/head" {
+		t.Fatalf("fetch calls = %+v", fetch)
+	}
+	if v.Took.Clone <= 0 || v.Took.Unit <= 0 {
+		t.Errorf("took = %+v, want the clone and the unit level timed", v.Took)
+	}
+	// What passed is kept under each level's digest.
+	for _, k := range []string{"unit." + digA, "integration." + digB} {
+		if _, _, found, _ := b.kept.Get(context.Background(), k); !found {
+			t.Errorf("%s was not kept", k)
+		}
+	}
+}
+
+func TestOnlyThePackageWithoutAKeptVerdictRuns(t *testing.T) { // 1288/AC1
+	b := newBench(t)
+	b.digest[delivery.LevelUnit] = Digested{Level: "unit", Packages: map[string]string{"fixture/slow": digA, "fixture/other": digC}}
+	if _, err := (Kept{Store: b.kept}).Keep(context.Background(), "unit", digC, keptValue("fixture/other", 40)); err != nil {
+		t.Fatal(err)
+	}
+	out := b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	tests := b.steps.tool("test")
+	if len(tests) != 2 || strings.Join(packagesOf(tests[0]), ",") != "fixture/slow" || tests[0].args["level"] != "unit" {
+		t.Fatalf("test calls = %+v, want the unit level of fixture/slow alone, then the integration level", tests)
+	}
+	if u := out.Verdict.Levels[delivery.LevelUnit]; u.Run != 2 || u.Kept != 40 {
+		t.Errorf("unit = %+v, want 2 run and 40 kept", u)
+	}
+}
+
+func TestAReAskRunsOnlyWhatFailedAndWhatChanged(t *testing.T) { // 1288/AC2, AC3
+	b := newBench(t)
+	failing := captured[Tested](t, "go-test-failing")
+	b.digest[delivery.LevelUnit] = Digested{Level: "unit", Packages: map[string]string{"fixture/failing/bad": digA, "fixture/failing/good": digB}}
+	b.test = func(c stepCall) (any, error) {
+		if c.args["level"] == "unit" {
+			return failing, nil
+		}
+		return captured[Tested](t, "go-test-slow"), nil
+	}
+	cs := caseOf(t, pullOf(repoA, 7, head1))
+	first := b.judge(t, cs).Verdict
+	if first.State != delivery.VerdictFail || first.Failed.Test != "unit: fixture/failing/bad.TestThreeIsFour" {
+		t.Fatalf("first = %+v", first)
+	}
+	if _, _, found, _ := b.kept.Get(context.Background(), "unit."+digB); !found {
+		t.Fatal("the package that passed in the failing run was not kept")
+	}
+	if _, _, found, _ := b.kept.Get(context.Background(), "unit."+digA); found {
+		t.Fatal("the package that failed was kept")
+	}
+	// Asked again with nothing changed: only the failed package runs; the good one is taken.
+	b.steps.calls = nil
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	tests := b.steps.tool("test")
+	if len(tests) == 0 || strings.Join(packagesOf(tests[0]), ",") != "fixture/failing/bad" {
+		t.Fatalf("the re-ask ran %+v, want only fixture/failing/bad", tests)
+	}
+	// The trunk moved and one digest changed: that package runs, the unchanged one is taken.
+	b.digest[delivery.LevelUnit] = Digested{Level: "unit", Packages: map[string]string{"fixture/failing/bad": digA, "fixture/failing/good": digD}}
+	b.steps.calls = nil
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	tests = b.steps.tool("test")
+	if got := strings.Join(packagesOf(tests[0]), ","); got != "fixture/failing/bad,fixture/failing/good" && got != "fixture/failing/good,fixture/failing/bad" {
+		t.Errorf("after a digest changed the run was %q, want the failed package and the changed one", got)
+	}
+}
+
+func TestANodePackageIsNeverKeptAndRunsEveryCheck(t *testing.T) { // 1288/AC4, 1292/AC1
+	b := newBench(t)
+	b.ex.Modules = langs{repoA: {buildrun.NodeBuildModule}}
+	b.fetch = captured[Fetched](t, "node-fetch-clean")
+	b.test = func(c stepCall) (any, error) {
+		return Tested{Level: c.args["level"].(string), Module: "modules/m", Passed: true, Elapsed: 0.4, Bound: 5}, nil
+	}
+	cs := caseOf(t, pullOf(repoA, 7, head1))
+	for i := 0; i < 2; i++ {
+		v := b.judge(t, cs).Verdict
+		if v.State != delivery.VerdictPass || v.Levels[delivery.LevelUnit].Kept != 0 || v.Levels[delivery.LevelUnit].Run != 1 {
+			t.Fatalf("round %d: verdict = %+v", i, v)
+		}
+	}
+	if n := len(b.steps.tool("test")); n != 4 {
+		t.Errorf("%d node test calls in two checks, want 4 (both levels each time)", n)
+	}
+	if n := len(b.steps.tool("digest")); n != 0 {
+		t.Errorf("the node build module was asked for a digest %d times", n)
+	}
+	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 0 {
+		t.Errorf("kept %v for a node package", keys)
+	}
+}
+
+func TestTheChangesOwnFailingTestRunsFirstAndNothingElseRuns(t *testing.T) { // 1289/AC1, AC2
+	b := newBench(t)
+	b.fetch.Changed = []string{"modules/m/internal/b/b_test.go"}
+	b.digest[delivery.LevelUnit] = Digested{Level: "unit", Packages: map[string]string{"m/internal/a": digA, "m/internal/b": digB}}
+	failing := captured[Tested](t, "go-test-failing")
+	b.test = func(c stepCall) (any, error) {
+		if got := packagesOf(c); len(got) == 1 && got[0] == "m/internal/b" {
+			return failing, nil
+		}
+		return captured[Tested](t, "go-test-slow"), nil
+	}
+	out := b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if out.Verdict.State != delivery.VerdictFail || !strings.Contains(out.Verdict.Failed.Test, "TestThreeIsFour") {
+		t.Fatalf("verdict = %+v", out.Verdict)
+	}
+	tests := b.steps.tool("test")
+	if len(tests) != 1 || strings.Join(packagesOf(tests[0]), ",") != "m/internal/b" {
+		t.Fatalf("test calls = %+v, want only m/internal/b, once", tests)
+	}
+	if n := len(b.steps.tool("digest")); n != 1 {
+		t.Errorf("%d digest calls, want the unit level's alone (the check stopped)", n)
+	}
+	if out.Verdict.Composition == nil || out.Verdict.Composition.State != delivery.CompositionNotRun {
+		t.Errorf("composition = %+v", out.Verdict.Composition)
+	}
+}
+
+func TestTheChangesOwnPassingTestRunsFirstAndTheRestFollow(t *testing.T) { // 1289/AC3
+	b := newBench(t)
+	b.fetch.Changed = []string{"modules/m/internal/b/b_test.go", "modules/m/internal/a/a.go"}
+	b.digest[delivery.LevelUnit] = Digested{Level: "unit", Packages: map[string]string{"m/internal/a": digA, "m/internal/b": digB}}
+	out := b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if out.Verdict.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", out.Verdict)
+	}
+	var unit []string
+	for _, c := range b.steps.tool("test") {
+		if c.args["level"] == "unit" {
+			unit = append(unit, strings.Join(packagesOf(c), ","))
+		}
+	}
+	if strings.Join(unit, " | ") != "m/internal/b | m/internal/a" {
+		t.Errorf("the unit level ran %v, want the changed test's package first, then the rest", unit)
+	}
+}
+
+func TestAHeadThatDoesNotMergeEndsFailedNamingTheFilesAndRunsNoTest(t *testing.T) { // 1289/AC4
+	b := newBench(t)
+	b.fetch = captured[Fetched](t, "go-fetch-conflict")
+	out := b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	f := out.Verdict.Failed
+	if out.Verdict.State != delivery.VerdictFail || f.Machine != "shanks" || !strings.Contains(f.Words, "files in conflict: a.go, sub/b.go") {
+		t.Fatalf("verdict = %+v", out.Verdict)
+	}
+	if n := len(b.steps.tool("digest")) + len(b.steps.tool("test")); n != 0 {
+		t.Errorf("%d digest and test steps ran after a conflict", n)
+	}
+}
+
+func TestALevelWhoseDigestIsNotNamedRunsWholeAndKeepsNothing(t *testing.T) { // 1287/AC4
+	b := newBench(t)
+	b.steps.handlers["build_go_digest"] = func(stepCall) (any, error) { return nil, fmt.Errorf("go list failed") }
+	out := b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if out.Verdict.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", out.Verdict)
+	}
+	tests := b.steps.tool("test")
+	if len(tests) != 2 || tests[0].args["packages"] != nil {
+		t.Errorf("test calls = %+v, want each level once, whole", tests)
+	}
+	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 0 {
+		t.Errorf("kept %v with no digest", keys)
+	}
+}
+
+func TestALevelOverItsBoundIsNamedWithItsSlowestTestsAndKeepsItsVerdict(t *testing.T) { // 1300/AC3
+	b := newBench(t)
+	b.test = func(c stepCall) (any, error) {
+		return testedWith(t, "go-test-slow", func(r *Tested) {
+			r.Level = c.args["level"].(string)
+			r.OverBound = true
+			r.OverWhich = "run"
+			r.Elapsed = 7
+		}), nil
+	}
+	out := b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	v := out.Verdict
+	if v.State != delivery.VerdictPass || strings.Join(v.OverBound, ",") != "unit,integration" {
+		t.Fatalf("verdict = %+v", v)
+	}
+	if len(out.Slowest) == 0 || !strings.Contains(out.Slowest[0], "TestTakesAWhile") {
+		t.Errorf("slowest = %v", out.Slowest)
+	}
+}
+
+func TestSkippedTestsAreCountedPerLevel(t *testing.T) { // 1300/AC6, 1251
+	b := newBench(t)
+	b.test = func(c stepCall) (any, error) {
+		return testedWith(t, "go-test-slow", func(r *Tested) { r.Level = c.args["level"].(string); r.Skipped = 3 }), nil
+	}
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.Levels[delivery.LevelUnit].Skipped != 3 || v.Levels[delivery.LevelIntegration].Skipped != 3 {
+		t.Errorf("levels = %+v", v.Levels)
+	}
+}
+
+func TestAGroupIsOneVerdictAndEachMembersTestsReadTheOthersAtTheirHeads(t *testing.T) { // 1624/AC1
+	b := newBench(t)
+	cs := caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2))
+	v := b.judge(t, cs).Verdict
+	if v.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", v)
+	}
+	fetch := b.steps.tool("fetch")
+	if len(fetch) != 2 {
+		t.Fatalf("%d fetches, want one for each member", len(fetch))
+	}
+	var forA []BesideRef
+	for _, f := range fetch {
+		if f.args["repository"] == repoA {
+			forA, _ = refsOf(f.args["beside"]), true
+		}
+	}
+	found := false
+	for _, r := range forA {
+		if r.Repository == repoSDK && r.Commit == head2 && r.Ref == "refs/pull/12/head" {
+			found = true
+		}
+	}
+	if !found {
+		t.Errorf("mesh-delivery's tests were not given the SDK member at its head: %+v", forA)
+	}
+}
+
+func TestAnExaminerIsAJudgeOfTheChecker(t *testing.T) {
+	var _ Judge = (*Examiner)(nil)
+}
+
+const (
+	manA = "0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a0a"
+)
+
+func TestACleanMergeWritesItsPreviewWithTheTreesManifestsAndLocks(t *testing.T) { // 1445/AC1
+	b := newBench(t)
+	b.fetch.Trees = map[string]MergeTree{
+		"modules/avahi": {Tree: "7777777777777777777777777777777777777777", Manifest: manA, Locks: map[string]string{"go.sum": "ff00"}},
+		"modules/bare":  {Tree: "8888888888888888888888888888888888888888"}, // no manifest digest: left out
+	}
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	key, _ := delivery.PreviewKey(repoA, head1, trunkA)
+	raw, _, found, _ := b.prev.Get(context.Background(), key)
+	if !found {
+		t.Fatalf("no preview %s; the bucket holds %v", key, b.prev.vals)
+	}
+	pv, err := delivery.DecodePreview(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	m := pv.Modules["modules/avahi"]
+	if pv.Merge != b.fetch.Merge || pv.Trunk != trunkA || pv.Head != head1 || len(pv.Modules) != 1 || m.Tree != "7777777777777777777777777777777777777777" || m.Manifest != manA || m.Locks["go.sum"] != "ff00" {
+		t.Errorf("preview = %+v", pv)
+	}
+}
+
+func TestAHeadThatDoesNotMergeWritesAPreviewOfItsConflictsAlone(t *testing.T) { // 1445/AC5
+	b := newBench(t)
+	b.fetch = captured[Fetched](t, "go-fetch-conflict")
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	key, _ := delivery.PreviewKey(repoA, head1, trunkA)
+	raw, _, found, _ := b.prev.Get(context.Background(), key)
+	if !found {
+		t.Fatalf("no preview for a head that does not merge; the bucket holds %v", b.prev.vals)
+	}
+	pv, err := delivery.DecodePreview(raw)
+	if err != nil || strings.Join(pv.Conflicts, ",") != "a.go,sub/b.go" || pv.Merge != "" || len(pv.Modules) != 0 {
+		t.Errorf("preview = %+v, %v, want the files in conflict and no merge", pv, err)
+	}
+}
+
+func TestAPreviewIsWrittenOnceAndAnExistingKeyStands(t *testing.T) {
+	b := newBench(t)
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	b.fetch.Merge = "5656565656565656565656565656565656565656"
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	key, _ := delivery.PreviewKey(repoA, head1, trunkA)
+	if b.prev.creates[key] != 1 {
+		t.Errorf("the preview was created %d times, want once", b.prev.creates[key])
+	}
+	raw, _, _, _ := b.prev.Get(context.Background(), key)
+	if pv, _ := delivery.DecodePreview(raw); pv.Merge == b.fetch.Merge {
+		t.Error("the second merge commit replaced the first")
+	}
+}
+
+func TestTheIndexerIsToldOfAPreviewOnceWhenItIsCreated(t *testing.T) { // 1445/AC4 (the checker's half)
+	b := newBench(t)
+	var told []string
+	b.ex.Announce = func(_ context.Context, event, key string) { told = append(told, event+" "+key) }
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	key, _ := delivery.PreviewKey(repoA, head1, trunkA)
+	if len(told) != 1 || told[0] != EventPreviewWritten+" "+key {
+		t.Errorf("told %v, want once of %s", told, key)
+	}
+}
+
+type fakeBuilds map[string]delivery.BuilderBuild
+
+func (f fakeBuilds) Build(_ context.Context, module, fp2 string) (delivery.BuilderBuild, bool, error) {
+	b, ok := f[module+" "+fp2]
+	return b, ok, nil
+}
+
+func TestTheOutcomeSaysIfEachCandidatesModuleIsBuiltFailedOrWaiting(t *testing.T) { // N7/AC1 (the checker reads the builder's keys)
+	b := newBench(t)
+	fpA := "src2:" + strings.Repeat("a", 64)
+	fpB := "src2:" + strings.Repeat("b", 64)
+	fpC := "src2:" + strings.Repeat("c", 64)
+	b.ex.Builds = fakeBuilds{
+		"avahi " + fpA:      {State: delivery.BuildDone},
+		"mesh-tools " + fpB: {State: delivery.BuildFailed, Error: "boom"},
+		// netcheck has no key yet
+	}
+	p := pullOf(repoA, 7, head1)
+	p.Modules = []string{"avahi", "mesh-tools", "netcheck", "nofp"}
+	p.Fps = map[string]delivery.CandidateModule{"avahi": {FP2: fpA}, "mesh-tools": {FP2: fpB}, "netcheck": {FP2: fpC}, "nofp": {None2: "toolchain not yet reported"}}
+	out := b.judge(t, caseOf(t, p))
+	var got []string
+	for _, n := range out.Builds {
+		got = append(got, n.Module+" "+n.State)
+	}
+	if strings.Join(got, ", ") != "avahi built, mesh-tools failed, netcheck waiting" {
+		t.Errorf("builds = %v, want one note for each module that has a fingerprint, sorted", got)
+	}
+}
+
+// trunksOf are trunk heads of every repository, as the gate's source names them.
+func trunksOf(t *testing.T, heads map[string]string) *Trunks {
+	t.Helper()
+	data, err := delivery.EncodeSource(delivery.Source{Group: "g", Heads: heads})
+	if err != nil {
+		t.Fatal(err)
+	}
+	tr := &Trunks{}
+	tr.Put(data, false)
+	return tr
+}
+
+func TestNothingIsKeptForAWorkspaceGivenSiblingsWhenTheDigestDoesNotSayItCoversThem(t *testing.T) { // review D1, ADR 0444, issue 1287
+	b := newBench(t)
+	// A build module whose digest does not echo the siblings (before DigestVersion 3).
+	b.steps.handlers["build_go_digest"] = func(c stepCall) (any, error) { return b.digest[c.args["level"].(string)], nil }
+	b.ex.Trunks = trunksOf(t, map[string]string{repoSDK: trunkS, "novox/mesh-catalog": trunkA})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if got := len(b.steps.tool("fetch")); got != 1 || b.steps.tool("fetch")[0].args["beside"] == nil {
+		t.Fatalf("the fetch was not given siblings: %+v", b.steps.tool("fetch"))
+	}
+	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 0 {
+		t.Errorf("kept %v for a package whose digest does not say it covers the siblings", keys)
+	}
+	// And a kept verdict of the same digest from elsewhere is not taken for it: everything runs.
+	if _, err := (Kept{Store: b.kept}).Keep(context.Background(), "unit", digA, keptValue("fixture/slow", 2)); err != nil {
+		t.Fatal(err)
+	}
+	b.steps.calls = nil
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if n := len(b.steps.tool("test")); n != 2 {
+		t.Errorf("%d test steps, want both levels run whole", n)
+	}
+}
+
+// besideDigest stands for the Go build module's digest over a workspace with siblings (DigestVersion 3, lead decision L5):
+// each package's digest folds the siblings' commits in, and the answer echoes the lines it folded.
+// echoBeside is d with the siblings the fetches placed, as the Go build module's digest echoes them (its DigestResult's
+// Beside): every check now places the change's own repository at its trunk (issue 1887 A12).
+func echoBeside(b *bench, d Digested) Digested {
+	var lines []string
+	for _, f := range b.steps.tool("fetch") {
+		refs, _ := refsOf(f.args["beside"]), true
+		for _, r := range refs {
+			lines = append(lines, r.Repository+" "+r.Commit)
+		}
+	}
+	sort.Strings(lines)
+	d.Beside = lines
+	return d
+}
+
+func besideDigest(b *bench) func(c stepCall) (any, error) {
+	return func(c stepCall) (any, error) {
+		level := c.args["level"].(string)
+		var lines []string
+		for _, f := range b.steps.tool("fetch") {
+			refs, _ := refsOf(f.args["beside"]), true
+			for _, r := range refs {
+				lines = append(lines, r.Repository+" "+r.Commit)
+			}
+		}
+		sort.Strings(lines)
+		sum := sha256.Sum256([]byte(level + "\n" + strings.Join(lines, "\n")))
+		return Digested{Level: level, Packages: map[string]string{"fixture/slow": hex.EncodeToString(sum[:])}, Beside: lines}, nil
+	}
+}
+
+func TestACoreRepositorysPassingPackageIsKeptUnderADigestCoveringItsSiblings(t *testing.T) { // 1287 AC1-AC3, AC7 with L5
+	b := newBench(t)
+	b.steps.handlers["build_go_digest"] = besideDigest(b)
+	b.ex.Trunks = trunksOf(t, map[string]string{repoSDK: trunkS, "novox/mesh-catalog": trunkA})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	keys, _ := b.kept.Keys(context.Background())
+	if len(keys) != 2 {
+		t.Fatalf("kept %v, want the passing package at both levels", keys)
+	}
+	// The same siblings again: everything is taken, nothing runs.
+	b.steps.calls = nil
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if n := len(b.steps.tool("test")); n != 0 || v.Levels[delivery.LevelUnit].Run != 0 || v.Levels[delivery.LevelUnit].Kept == 0 {
+		t.Fatalf("%d test steps, unit %+v, want none run and the kept verdict taken", n, v.Levels[delivery.LevelUnit])
+	}
+	// A sibling's commit moves: a new digest, so the package runs again and is kept under it.
+	b.ex.Trunks = trunksOf(t, map[string]string{repoSDK: trunkS2, "novox/mesh-catalog": trunkA})
+	b.steps.calls = nil
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if n := len(b.steps.tool("test")); n != 2 {
+		t.Errorf("%d test steps after a sibling moved, want both levels run", n)
+	}
+	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 4 {
+		t.Errorf("kept %v, want a second key per level under the new digest", keys)
+	}
+}
+
+func TestADigestThatEchoesOtherSiblingsKeepsNothing(t *testing.T) { // 1287 with L5: an echo that differs is not trusted
+	b := newBench(t)
+	inner := besideDigest(b)
+	b.steps.handlers["build_go_digest"] = func(c stepCall) (any, error) {
+		v, err := inner(c)
+		d := v.(Digested)
+		d.Beside = d.Beside[:len(d.Beside)-1]
+		return d, err
+	}
+	b.ex.Trunks = trunksOf(t, map[string]string{repoSDK: trunkS, "novox/mesh-catalog": trunkA})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 0 {
+		t.Errorf("kept %v under a digest that does not cover every sibling", keys)
+	}
+}
+
+type pkgPaths map[string][]string
+
+func (p pkgPaths) PackagePaths(repository string) []string { return p[repository] }
+
+// groupPackageBench is a group of a TypeScript member (mesh-delivery) and the mesh-sdk member, whose merge changes sdkChanged.
+func groupPackageBench(t *testing.T, sdkChanged []string) *bench {
+	b := newBench(t)
+	b.ex.Modules = langs{repoA: {buildrun.GoBuildModule, buildrun.NodeBuildModule}, repoSDK: {buildrun.GoBuildModule, buildrun.NodeBuildModule}}
+	b.ex.Packages = pkgPaths{repoSDK: {"src", "test", "package.json", "package-lock.json", "tsconfig.json"}}
+	fetch := func(c stepCall) (any, error) {
+		f := b.fetch
+		if c.args["repository"] == repoSDK {
+			f.Changed = sdkChanged
+		}
+		return f, nil
+	}
+	b.steps.handlers["build_go_fetch"], b.steps.handlers["build_node_fetch"] = fetch, fetch
+	return b
+}
+
+func nodeFetchOf(b *bench, repo string) stepCall {
+	for _, c := range b.steps.tool("fetch") {
+		if c.module == buildrun.NodeBuildModule && c.args["repository"] == repo {
+			return c
+		}
+	}
+	return stepCall{}
+}
+
+func TestATypeScriptMemberTakesTheGroupsPackageWhenTheSDKMemberChangesItsPaths(t *testing.T) { // ADR 0500 §5, C11b
+	b := groupPackageBench(t, []string{"go/delivery/x.go", "src/state.ts"})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2)))
+	want := map[string]any{"repository": repoSDK, "commit": head2, "ref": "refs/pull/12/head"}
+	if got := nodeFetchOf(b, repoA).args["package"]; !reflect.DeepEqual(got, want) {
+		t.Errorf("mesh-delivery's Node fetch was given the package %v, want %v", got, want)
+	}
+	if got := nodeFetchOf(b, repoSDK).args["package"]; got != nil {
+		t.Errorf("the mesh-sdk member's own fetch was given %v: it builds its package itself", got)
+	}
+}
+
+func TestATypeScriptMemberResolvesTheRegistryWhenTheSDKMemberLeavesItsPaths(t *testing.T) { // ADR 0500 §5: the manifest alone, or Go alone
+	for _, changed := range [][]string{{"go/delivery/x.go"}, {"module.json"}, {"srcx/a.ts"}} {
+		b := groupPackageBench(t, changed)
+		b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2)))
+		if got := nodeFetchOf(b, repoA).args["package"]; got != nil {
+			t.Errorf("%v: the Node fetch was given %v, want the registry", changed, got)
+		}
+	}
+	// A lone TypeScript pull request: no group package either.
+	b := groupPackageBench(t, []string{"src/state.ts"})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if got := nodeFetchOf(b, repoA).args["package"]; got != nil {
+		t.Errorf("a lone pull request's Node fetch was given %v", got)
+	}
+}
+
+func TestNoStepOfACheckCarriesPublish(t *testing.T) { // ADR 0500 §4, 1309 (the checker's half): only the builder's trunk build publishes
+	b := groupPackageBench(t, []string{"src/state.ts"})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2)))
+	if len(b.steps.calls) == 0 {
+		t.Fatal("no step ran")
+	}
+	for _, c := range b.steps.calls {
+		if _, ok := c.args["publish"]; ok {
+			t.Errorf("%s was given publish: %v", c.tool, c.args)
+		}
+		if strings.HasSuffix(c.tool, "_build") || strings.HasSuffix(c.tool, "_pack") {
+			t.Errorf("the checker asked %s: a check builds no artifact of its own", c.tool)
+		}
+	}
+}
+
+// 1890/AC1, 1887/A5a: an ask whose step never ends (the build node stopped with it running, and nothing redelivered it in
+// time) ends the check loudly at the asker's bound; the checker holds no place to free.
+func TestAnAskWhoseStepNeverEndsEndsTheCheckLoudly(t *testing.T) {
+	b := newBench(t)
+	// A node took the ask and its step stays running: the bound runs from its start (review round 2 item 1).
+	b.asks.Answer = func(a delivery.StepAsk) delivery.Step {
+		return delivery.Step{ID: a.ID, Tool: "check ask", Node: "shanks", State: delivery.StepRunning, Started: time.Now()}
+	}
+	b.ex.Asks = buildrun.Asker{Publisher: b.asks, Waiter: b.asks, Bound: 20 * time.Millisecond}
+	out := b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if f := out.Verdict.Failed; out.Verdict.State != delivery.VerdictFail || !strings.Contains(f.Words, "on shanks did not end within") {
+		t.Fatalf("verdict = %+v", out.Verdict)
+	}
+	if n := len(b.asks.Asks()); n != 1 || b.asks.Asks()[0].Kind != delivery.AskCheck || b.asks.Asks()[0].Check == nil {
+		t.Fatalf("asks = %+v, want one check ask", b.asks.Asks())
+	}
+}
+
+// 1887/A5a, ADR 0536 §4: a check is one ask per pull request and build module on the check stream, a re-judge after a
+// trunk move one on the recheck stream, each carrying both levels with the kept verdicts taken by the build module.
+func TestACheckIsOneAskAndAReJudgeGoesOnTheRecheckStream(t *testing.T) {
+	b := newBench(t)
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	asks := b.asks.Asks()
+	if len(asks) != 1 || asks[0].Kind != delivery.AskCheck || asks[0].Language != delivery.AskGo || asks[0].Asker != delivery.CheckerModule {
+		t.Fatalf("asks = %+v, want one Go check ask", asks)
+	}
+	if j := asks[0].Check; j == nil || !j.Kept || strings.Join(j.Levels, ",") != "unit,integration" || j.Fetch["repository"] != repoA {
+		t.Fatalf("the job = %+v", asks[0].Check)
+	}
+	cs := caseOf(t, pullOf(repoA, 7, head1))
+	cs.Kind = KindTrunk
+	b.judge(t, cs)
+	if asks := b.asks.Asks(); len(asks) != 2 || asks[1].Kind != delivery.AskRecheck {
+		t.Fatalf("asks = %+v, want the re-judge on recheck", asks)
+	}
+}
+
+// Review round 2 item 1: a check ask that waits in its stream longer than the step bound (no node has a free slot during a
+// large rebuild) is not failed: the check goes on when a node takes it, and no second ask is put.
+func TestACheckAskWaitingInItsStreamIsNotBounded(t *testing.T) {
+	b := newBench(t)
+	answer := b.asks.Answer
+	b.asks.Answer = nil
+	b.ex.Asks = buildrun.Asker{Publisher: b.asks, Waiter: b.asks, Bound: 20 * time.Millisecond}
+	done := make(chan Outcome, 1)
+	go func() { done <- b.judge(t, caseOf(t, pullOf(repoA, 7, head1))) }()
+	for deadline := time.Now().Add(2 * time.Second); len(b.asks.Asks()) == 0; time.Sleep(time.Millisecond) {
+		if time.Now().After(deadline) {
+			t.Fatal("no ask was put")
+		}
+	}
+	time.Sleep(100 * time.Millisecond) // five bounds in the stream
+	select {
+	case out := <-done:
+		t.Fatalf("the check ended while its ask waited: %+v", out.Verdict)
+	default:
+	}
+	b.asks.End(answer(b.asks.Asks()[0])) // a node took it and ran it
+	if out := <-done; out.Verdict.State != delivery.VerdictPass || len(b.asks.Asks()) != 1 {
+		t.Fatalf("verdict %+v after %d asks, want a pass from the one ask", out.Verdict, len(b.asks.Asks()))
+	}
+}
+
+// 1917: the digest is taken inside the check ask, as the build module's own digest step answers it (no step key is asked
+// of it), so a second check of the same heads keeps every package the first one passed: "N kept", nothing run again.
+func TestASecondCheckOfTheSameHeadsKeepsWhatTheFirstPassed(t *testing.T) {
+	b := newBench(t)
+	first := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	u := first.Levels[delivery.LevelUnit]
+	if first.State != delivery.VerdictPass || u.Run == 0 || u.Kept != 0 {
+		t.Fatalf("the first check = %+v", first)
+	}
+	b.steps.calls = nil
+	second := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if s := second.Levels[delivery.LevelUnit]; second.State != delivery.VerdictPass || s.Kept != u.Run || s.Run != 0 {
+		t.Fatalf("the second check's unit level = %+v, want %d kept and none run", s, u.Run)
+	}
+	if n := len(b.steps.tool("test")); n != 0 {
+		t.Errorf("%d test steps ran on the second check", n)
+	}
+}

modules/mesh-delivery-checker/internal/check/failure_words_test.go

@@ -0,0 +1,73 @@
+package check
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// The failure the build module reported for group r4g on 2026-10-23: the test logged a line, then failed with a multi-line
+// t.Fatalf. Its output is what the build module now sends (its last lines, with the error line as Cause).
+func fatalAfterLog() Failure {
+	return Failure{
+		Package: "github.com/novox/mesh-controller/internal/broker", Test: "TestTheCataloguesDerivedSubjectsMeet",
+		Cause: "3 subscription(s) derive to a subject no emitter owns:",
+		Output: "    agreement_catalogue_test.go:130: judged against /var/lib/mesh-build-go-work/id/beside/mesh-catalog as cloned\n" +
+			"    agreement_catalogue_test.go:186: 3 subscription(s) derive to a subject no emitter owns:\n" +
+			"          a.b.c\n          d.e.f\n          g.h.i\n--- FAIL: TestTheCataloguesDerivedSubjectsMeet (0.00s)",
+	}
+}
+
+func TestAFailedTestsVerdictKeepsItsWholeFailureMessage(t *testing.T) { // 1901/AC1
+	v := levelFailure(&target{}, "unit", Tested{Failed: []Failure{fatalAfterLog()}})
+	for _, want := range []string{"3 subscription(s) derive to a subject no emitter owns:", "a.b.c", "d.e.f", "g.h.i"} {
+		if !strings.Contains(v.Failed.Words, want) {
+			t.Errorf("words lack %q: %q", want, v.Failed.Words)
+		}
+	}
+	if len(v.Failed.Words) > MaxWords+200 {
+		t.Errorf("words are %d bytes, bound %d", len(v.Failed.Words), MaxWords)
+	}
+}
+
+func TestTheStatusLineNamesTheFailureNotTheFirstLoggedLine(t *testing.T) { // 1901/AC2
+	v := levelFailure(&target{}, "unit", Tested{Failed: []Failure{fatalAfterLog()}})
+	got := firstFailed(*v)
+	if !strings.Contains(got, "3 subscription(s) derive to a subject no emitter owns:") || strings.Contains(got, "judged against") || strings.Contains(got, "\n") {
+		t.Errorf("firstFailed = %q", got)
+	}
+	// With no cause told apart (an older build module), the words still start at the first line, as before.
+	f := fatalAfterLog()
+	f.Cause = ""
+	v = levelFailure(&target{}, "unit", Tested{Failed: []Failure{f}})
+	if !strings.HasPrefix(v.Failed.Words, "agreement_catalogue_test.go:130") {
+		t.Errorf("words = %q", v.Failed.Words)
+	}
+}
+
+func TestWordsLongerThanTheBoundKeepTheirLastLines(t *testing.T) { // 1901/AC1
+	f := Failure{Output: strings.Repeat("log line of some length\n", 500) + "the cause is here"}
+	v := levelFailure(&target{}, "unit", Tested{Failed: []Failure{f}})
+	if !strings.HasSuffix(v.Failed.Words, "the cause is here") || len(v.Failed.Words) > MaxWords+200 {
+		t.Errorf("%d bytes, ends %q", len(v.Failed.Words), v.Failed.Words[len(v.Failed.Words)-30:])
+	}
+	_ = delivery.VerdictFail
+}
+
+// An older build module sends no "cause": its answer is still accepted and the verdict's words are its output, as before.
+func TestAnOlderBuildModulesFailureIsAcceptedWithItsWholeOutput(t *testing.T) { // 1901/AC3
+	old := `{"package":"p","test":"TestX","output":"x_test.go:1: logged\nx_test.go:2: the old kept lines"}`
+	var f Failure
+	if err := json.Unmarshal([]byte(old), &f); err != nil || f.Cause != "" {
+		t.Fatalf("1901/AC3: err = %v, cause = %q", err, f.Cause)
+	}
+	v := levelFailure(&target{}, "unit", Tested{Failed: []Failure{f}})
+	if v.Failed.Words != "x_test.go:1: logged\nx_test.go:2: the old kept lines" {
+		t.Errorf("1901/AC3: words = %q", v.Failed.Words)
+	}
+	if got := firstFailed(*v); !strings.Contains(got, "logged") || strings.Contains(got, "\n") {
+		t.Errorf("1901/AC3: status = %q", got)
+	}
+}

modules/mesh-delivery-checker/internal/check/fakes_test.go

@@ -0,0 +1,62 @@
+package check
+
+import (
+	"context"
+	"sort"
+	"sync"
+)
+
+// memKV is a bucket in memory with the revisions a real one gives.
+type memKV struct {
+	mu   sync.Mutex
+	vals map[string][]byte
+	revs map[string]uint64
+	next uint64
+	// creates counts the creates that succeeded, by key.
+	creates map[string]int
+}
+
+func newMemKV() *memKV {
+	return &memKV{vals: map[string][]byte{}, revs: map[string]uint64{}, creates: map[string]int{}}
+}
+
+func (m *memKV) Get(_ context.Context, key string) ([]byte, uint64, bool, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	v, ok := m.vals[key]
+	return v, m.revs[key], ok, nil
+}
+
+func (m *memKV) Create(_ context.Context, key string, value []byte) (uint64, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if _, ok := m.vals[key]; ok {
+		return 0, ErrConflict
+	}
+	m.next++
+	m.vals[key], m.revs[key] = append([]byte(nil), value...), m.next
+	m.creates[key]++
+	return m.next, nil
+}
+
+func (m *memKV) Update(_ context.Context, key string, value []byte, revision uint64) (uint64, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if _, ok := m.vals[key]; !ok || m.revs[key] != revision {
+		return 0, ErrConflict
+	}
+	m.next++
+	m.vals[key], m.revs[key] = append([]byte(nil), value...), m.next
+	return m.next, nil
+}
+
+func (m *memKV) Keys(context.Context) ([]string, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	keys := make([]string, 0, len(m.vals))
+	for k := range m.vals {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys, nil
+}

modules/mesh-delivery-checker/internal/check/gate_test.go

@@ -0,0 +1,116 @@
+package check
+
+import (
+	"context"
+	"strings"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// What the gate reads of the checker (R4e, lead's interface with dev-r4e-gate): the verdict's heads are the gate's hash over
+// `<owner/name lowercase>#<number>=<full head sha>`, a lone pull request is a group of one, and a move of a trunk marks
+// mesh/check pending on every open pull request into it, every member's for a group, before any check starts.
+
+func owedState(t testing.TB, r *rig, repo string, number int, head string) string {
+	t.Helper()
+	key, err := delivery.CheckerOwedKey(repo, number, head)
+	if err != nil {
+		t.Fatal(err)
+	}
+	raw, _, found, _ := r.owed.Get(context.Background(), key)
+	if !found {
+		return ""
+	}
+	o, err := delivery.DecodeCheckerOwed(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return o.State
+}
+
+func TestTheVerdictsHeadsAreTheGatesHashOverLowercaseHeads(t *testing.T) { // gate (b), (c)
+	ctx := context.Background()
+	r := newRig(t, passJudge())
+	upper := strings.ToUpper(head1[:20]) + head1[20:]
+	r.setTrunks(t, map[string]string{"Novox/Mesh-Delivery": trunkA, repoA: trunkA, repoSDK: trunkS})
+	cand := candidateOf(t, "feat/x", pullOf("Novox/Mesh-Delivery", 7, upper))
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	want, _ := delivery.HeadsHash([]delivery.Head{{Repository: repoA, Number: 7, Head: head1}})
+	if v := r.verdict(t, keyOf(t, "feat/x", cand)); v.Heads != want {
+		t.Errorf("heads = %q, want the gate's hash of the lone pull request, a group of one, %q", v.Heads, want)
+	}
+}
+
+func TestAGroupsVerdictHeadsCoverEveryMember(t *testing.T) { // gate (b): hq's member too, as the gate's ask covers it
+	ctx := context.Background()
+	r := newRig(t, passJudge())
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2), pullOf(hqRepo, 3, head2))
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	want, _ := delivery.HeadsHash([]delivery.Head{{Repository: repoA, Number: 7, Head: head1}, {Repository: repoSDK, Number: 12, Head: head2},
+		{Repository: hqRepo, Number: 3, Head: head2}})
+	if v := r.verdict(t, keyOf(t, "feat/x", cand)); v.Heads != want {
+		t.Errorf("heads = %q, want %q", v.Heads, want)
+	}
+}
+
+func TestATrunkMoveMarksEveryOpenPullRequestIntoItPendingAtOnce(t *testing.T) { // gate (a), lead decision L4 (1302's checker part)
+	ctx := context.Background()
+	r := newRig(t, passJudge())
+	r.ch.Candidate(ctx, "feat%2Fg", candidateOf(t, "feat/g", pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2)))
+	r.ch.Candidate(ctx, "feat%2Fs", candidateOf(t, "feat/s", pullOf(repoSDK, 13, head1)))
+	r.ch.Wait()
+	for _, p := range []struct {
+		repo string
+		n    int
+		head string
+	}{{repoA, 7, head1}, {repoSDK, 12, head2}, {repoSDK, 13, head1}} {
+		if s := owedState(t, r, p.repo, p.n, p.head); s != "success" {
+			t.Fatalf("%s#%d is %q before the move", p.repo, p.n, s)
+		}
+	}
+	// mesh-delivery's trunk moves; the re-judges it asks are held in their judge (in the stream, since R4g) meanwhile.
+	release := make(chan struct{})
+	r.ch.Judge = &judgeFunc{f: func(context.Context, *Case, int) (Outcome, error) { <-release; return Outcome{Verdict: passing()}, nil }}
+	defer func() { close(release); r.ch.Wait() }()
+	r.setTrunks(t, map[string]string{repoA: trunkA2, repoSDK: trunkS})
+	r.ch.TrunkMoved(ctx)
+	if s := owedState(t, r, repoA, 7, head1); s != "pending" {
+		t.Errorf("mesh-delivery#7, into the moved trunk, is %q, want pending", s)
+	}
+	if s := owedState(t, r, repoSDK, 12, head2); s != "pending" {
+		t.Errorf("mesh-sdk#12, a member of the same group, is %q, want pending", s)
+	}
+	if s := owedState(t, r, repoSDK, 13, head1); s != "success" {
+		t.Errorf("mesh-sdk#13, alone into a trunk that did not move, is %q, want its success to stand", s)
+	}
+}
+
+func TestACheckThatEndsAfterItsTrunkMovedOwesPendingNotItsVerdict(t *testing.T) { // gate (a): a pass on an old trunk is never shown
+	ctx := context.Background()
+	var r *rig
+	release, judged := make(chan struct{}), make(chan struct{})
+	j := &judgeFunc{f: func(ctx context.Context, c *Case, call int) (Outcome, error) {
+		if call == 1 {
+			r.setTrunks(t, map[string]string{repoA: trunkA2, repoSDK: trunkS}) // the trunk moves while it runs
+			defer close(judged)
+		} else {
+			<-release // the check asked again for the new trunk waits in the stream meanwhile
+		}
+		return Outcome{Verdict: passing()}, nil
+	}}
+	r = newRig(t, j)
+	r.ch.Candidate(ctx, "feat%2Fx", candidateOf(t, "feat/x", pullOf(repoA, 7, head1)))
+	<-judged
+	for deadline := time.Now().Add(2 * time.Second); owedState(t, r, repoA, 7, head1) == "" && time.Now().Before(deadline); time.Sleep(time.Millisecond) {
+	}
+	time.Sleep(20 * time.Millisecond)
+	if s := owedState(t, r, repoA, 7, head1); s != "pending" {
+		t.Errorf("the status is %q, want pending: the pass was judged on a trunk that moved", s)
+	}
+	close(release)
+	r.ch.Wait()
+}

modules/mesh-delivery-checker/internal/check/heard.go

@@ -0,0 +1,21 @@
+package check
+
+import (
+	"errors"
+
+	"github.com/nats-io/nats.go"
+)
+
+// Unheard is the error of a call that reached nobody: the bus had no responder for it, or none answered within the call's
+// bound. The program wraps the errors of its forge calls in it where the bus gives a timeout; a no-responders error is
+// known as it is. A build step is no call since R4g: an ask whose node stops is delivered again by its stream (ADR 0525 §6).
+type Unheard struct{ Err error }
+
+func (u *Unheard) Error() string { return u.Err.Error() }
+func (u *Unheard) Unwrap() error { return u.Err }
+
+// isUnheard says whether err is a call that reached nobody. A step that began and failed, or ended failed, is not.
+func isUnheard(err error) bool {
+	var u *Unheard
+	return errors.As(err, &u) || errors.Is(err, nats.ErrNoResponders)
+}

modules/mesh-delivery-checker/internal/check/heard_test.go

@@ -0,0 +1,21 @@
+package check
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/nats-io/nats.go"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// Issue 1820 AC5: a read of the forge that nobody answers is the forge's failure, not a build node's. (AC1-AC4 moved a
+// step to another node; since R4g an ask whose node stops is delivered again by its stream: ADR 0525 §6.)
+func TestAPinReadThatNobodyAnswersIsTheForgesFailureNotABuildNodes(t *testing.T) { // 1820/AC5
+	b := groupBench(t, "cb54756c3865")
+	b.ex.Forge.(*fakeForge).err = fmt.Errorf("gitea.gitea_get_file: %w", nats.ErrNoResponders)
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2))).Verdict
+	if v.State != delivery.VerdictFail || v.Failed.Machine != "forge" {
+		t.Errorf("verdict = %+v, want a failure at the forge: no build node was to blame", v)
+	}
+}

modules/mesh-delivery-checker/internal/check/judge.go

@@ -0,0 +1,580 @@
+package check
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"path"
+	"slices"
+	"sort"
+	"strings"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+// goModule is the build module the Go repositories are judged by.
+const goModule = buildrun.GoBuildModule
+
+// RunnerWorkspace is the runner the Go build module's digest and test steps are asked with when the merge changes the build
+// module itself: the installed module compiles the candidate's program from the merged tree and runs the step as it, shut
+// off (ADR 0535 §1).
+const RunnerWorkspace = "workspace"
+
+// buildGoDir is the Go build module's directory in the catalogue: a merge changing a path under it is judged by its
+// candidate (ADR 0535 §1). mesh-build-node's own directory is judged by the installed module until its part of issue 1898.
+const buildGoDir = "modules/mesh-build-go/"
+
+// changesBuildGo says whether a merge of the repository with these changed paths changes the Go build module.
+func changesBuildGo(repository string, changed []string) bool {
+	if repository != catalogueRepository {
+		return false
+	}
+	for _, p := range changed {
+		if strings.HasPrefix(p, buildGoDir) {
+			return true
+		}
+	}
+	return false
+}
+
+// The words of the line on the program that judged a change to the Go build module (ADR 0535 §2, §5).
+const (
+	judgedByOldInstalled = "judged by the installed mesh-build-go: it does not run a candidate yet"
+	judgedByInstalled    = "judged by the installed mesh-build-go"
+	judgedByCandidate    = "judged by the candidate's mesh-build-go at "
+)
+
+// verdictPtr is a verdict of failure a step of the check ends with.
+type verdictPtr = *delivery.Verdict
+
+func failed(machine, words string) verdictPtr { return fail(machine, words) }
+
+// Asks puts a check's ask on its build seat's stream and waits for its step (buildrun.Asker; ADR 0525 §1, §6): the
+// checker chooses no node, starts no step and holds none; whichever build node pulls the ask runs the check.
+type Asks interface {
+	Put(ctx context.Context, a delivery.StepAsk) error
+	Wait(ctx context.Context, a delivery.StepAsk) (delivery.Step, error)
+}
+
+// ToolchainEntries are the nodes' toolchain entries of a language (buildrun.ToolchainSet).
+type ToolchainEntries interface {
+	Entries(language string) []delivery.NodeToolchain
+}
+
+// BuildModules says which build modules judge a repository: the Go one always, the Node one when the repository holds a
+// TypeScript module.
+type BuildModules interface {
+	BuildModules(repository string) []string
+}
+
+// askLanguage is the build seat language of each build module the checker asks.
+var askLanguage = map[string]string{buildrun.GoBuildModule: delivery.AskGo, buildrun.NodeBuildModule: delivery.AskNode}
+
+// Examiner judges a case through the build seats (ADR 0484 clauses 3, 4, 10, 13; ADR 0525 §1, §3): for each pull request
+// and build module it puts one check ask whose job fetches the head merged onto its trunk head, then runs the unit level
+// and the integration level, taking the kept verdicts of unchanged packages, running the change's own tests first and
+// stopping at the first failure; it judges the step's answer as it judged the tools' answers.
+type Examiner struct {
+	Asks Asks
+	// Toolchains are the nodes' toolchains: a kept verdict names the toolchain the nodes agree on.
+	Toolchains ToolchainEntries
+	Kept       Kept
+	// Previews is the previews bucket; nil writes none.
+	Previews KV
+	Modules  BuildModules
+	// Runs says which commit the mesh runs of a module (the indexer's modules); nil knows none.
+	Runs interface{ CommitOf(module string) string }
+	// Forge reads the go.mod files of the Go members and says whether a mesh-sdk commit is on its trunk (ADR 0484 clause 9);
+	// nil checks no pin.
+	Forge Forge
+	// Builds says how the build of a fingerprint the candidate carries stands (the builder's builds bucket); nil says nothing
+	// of the builds.
+	Builds BuildStates
+	// Announce says a preview was written under the key (EventPreviewWritten); nil says nothing.
+	Announce Announcer
+	// Packages names, of a repository, the paths (repository-relative) its TypeScript package artifacts are built from, from
+	// the indexer's modules (delivery.Module.ArtifactPaths, lead decision L8); nil serves no group package.
+	Packages interface {
+		PackagePaths(repository string) []string
+	}
+	// Trunks are the trunk heads of every repository, for the siblings a repository's tests read.
+	Trunks interface{ Heads() map[string]string }
+	// Compositions answers the assigner's composition check of a check by the check's key (delivery.CompositionKey),
+	// waiting until the assigner wrote a verdict that does not wait, or ctx ends (ADR 0528 clause 5, issue 1297); nil
+	// leaves the composition not run.
+	Compositions CompositionReader
+	Now          func() time.Time
+	Logf         func(format string, args ...any)
+}
+
+// CompositionReader answers the assigner's composition of a check by the check's key, waiting until the assigner wrote
+// a verdict that does not wait, or ctx ends.
+type CompositionReader interface {
+	Await(ctx context.Context, key string) (delivery.CompositionVerdict, error)
+}
+
+func (j *Examiner) now() time.Time {
+	if j.Now != nil {
+		return j.Now()
+	}
+	return time.Now()
+}
+
+func (j *Examiner) logf(format string, args ...any) {
+	if j.Logf != nil {
+		j.Logf(format, args...)
+	}
+}
+
+// besideLines are the siblings as the digest step echoes them: `<owner/repo> <commit>`, sorted.
+func besideLines(refs []BesideRef) []string {
+	out := make([]string, 0, len(refs))
+	for _, r := range refs {
+		out = append(out, r.Repository+" "+r.Commit)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// target is a pull request on one build module: the node that pulled its ask, the workspace its fetch made and what it
+// said.
+type target struct {
+	pull      Pull
+	module    string
+	node      string
+	toolchain string
+	fetched   Fetched
+	// fetchArgs are the arguments of the fetch its check ask runs.
+	fetchArgs map[string]any
+	// priority are the Go packages (import paths) or the Node module directories whose test files the merge changes.
+	changed []string
+	// beside are the lines `<owner/repo> <commit>` of the siblings the workspace was given, sorted: its tests may read them,
+	// so a verdict is kept or taken only under a digest that says it folded exactly these in (lead decision L5).
+	beside []string
+	// runner is RunnerWorkspace when the target's ask runs the candidate's own build module (ADR 0535 §1), empty otherwise.
+	runner string
+	// judged is what the line says of the program that judged a change to the build module; empty for any other change.
+	judged string
+}
+
+// judgedBy takes what a step under runner workspace answered of the program that ran it (judged_by): the candidate, or the
+// installed module (a module that does not take the runner says nothing, and is asked without it from now on: ADR 0535 §2).
+// It says whether the candidate ran.
+func (t *target) judgedBy(answer string) bool {
+	switch {
+	case strings.HasPrefix(answer, "candidate "):
+		t.judged = judgedByCandidate + short12(strings.TrimPrefix(answer, "candidate "))
+		return true
+	case answer == "":
+		t.judged, t.runner = judgedByOldInstalled, ""
+	default:
+		t.judged, t.runner = judgedByInstalled, ""
+	}
+	return false
+}
+
+// stepArgs are a step's arguments with the target's runner.
+func (t *target) stepArgs(args map[string]any) map[string]any {
+	if t.runner != "" {
+		args["runner"] = t.runner
+	}
+	return args
+}
+
+// acc collects a level's counts across targets.
+type acc struct {
+	run, kept, skipped int
+	elapsed, setup     float64
+	lint               float64
+	over               bool
+	slowest            []TestTime
+}
+
+// state is one judging.
+type state struct {
+	j       *Examiner
+	c       *Case
+	targets []*target
+	levels  map[string]*acc
+	nodes   map[string]bool
+	clone   time.Duration
+	slow    []string
+}
+
+// Judge runs the case (it is the Judge of a Checker). A failure of the change, of a merge or of a step is a verdict; an error is only a case that cannot
+// be judged at all.
+func (j *Examiner) Judge(ctx context.Context, c *Case) (Outcome, error) {
+	st := &state{j: j, c: c, levels: map[string]*acc{delivery.LevelUnit: {}, delivery.LevelIntegration: {}}, nodes: map[string]bool{}}
+	if v := st.judgeAll(ctx); v != nil {
+		return st.finish(ctx, *v), nil
+	}
+	return st.finish(ctx, delivery.Verdict{State: delivery.VerdictPass}), nil
+}
+
+// finish is the outcome of the verdict with the state of the builds the candidate's modules carry, and, for a check
+// whose tests passed, the assigner's composition of it.
+func (st *state) finish(ctx context.Context, v delivery.Verdict) Outcome {
+	out := st.outcome(v)
+	if out.Verdict.State == delivery.VerdictPass {
+		st.composed(ctx, &out.Verdict)
+	}
+	out.Builds = st.j.buildNotes(ctx, st.c)
+	return out
+}
+
+// composed reads the assigner's composition of the check into its verdict (ADR 0528 clause 5): a failed composition
+// fails the check, naming the machine it failed at. A try is not composed (it has no candidate); a composition that
+// cannot be had leaves it not run, said; with no assigner running it is not judged, said at once.
+func (st *state) composed(ctx context.Context, v *delivery.Verdict) {
+	if st.j.Compositions == nil || st.c.Try != nil {
+		return
+	}
+	comp, err := st.j.Compositions.Await(ctx, st.c.Key)
+	switch {
+	case errors.Is(err, ErrAssignerNotRunning):
+		v.Composition = &delivery.Composition{State: delivery.CompositionNotRun, Words: delivery.AssignerNotRunning}
+		return
+	case err != nil:
+		st.j.logf("%s: the composition could not be read, so it is said as not run: %v", st.c.Key, err)
+		return
+	}
+	withComposition(v, comp)
+}
+
+// outcome fills the verdict's levels, times, machines and composition from what ran.
+func (st *state) outcome(v delivery.Verdict) Outcome {
+	if v.State == delivery.VerdictPass || len(v.Levels) == 0 {
+		v.Levels = map[string]delivery.LevelResult{}
+		for level, a := range st.levels {
+			v.Levels[level] = delivery.LevelResult{Run: a.run, Kept: a.kept, Skipped: a.skipped}
+		}
+	}
+	ms := func(s float64) int64 { return int64(s * 1000) }
+	u, i := st.levels[delivery.LevelUnit], st.levels[delivery.LevelIntegration]
+	v.Took = delivery.Took{Clone: st.clone.Milliseconds(), Unit: ms(u.elapsed), Lint: ms(u.lint), IntegrationSetup: ms(i.setup), IntegrationRun: ms(i.elapsed)}
+	for node := range st.nodes {
+		v.Machines = append(v.Machines, node)
+	}
+	sort.Strings(v.Machines)
+	for _, level := range []string{delivery.LevelUnit, delivery.LevelIntegration} {
+		if st.levels[level].over {
+			v.OverBound = append(v.OverBound, level)
+		}
+	}
+	// The composition is the assigner's check (issue 1297): until it delivers a verdict says it was not run (ADR 0484 clause 6).
+	v.Composition = &delivery.Composition{State: delivery.CompositionNotRun}
+	var slow []string
+	for _, level := range []string{delivery.LevelUnit, delivery.LevelIntegration} {
+		a := st.levels[level]
+		if !a.over {
+			continue
+		}
+		sort.SliceStable(a.slowest, func(x, y int) bool { return a.slowest[x].Elapsed > a.slowest[y].Elapsed })
+		for n, s := range a.slowest {
+			if n == 3 {
+				break
+			}
+			slow = append(slow, fmt.Sprintf("%s %s %.1fs", level, path.Base(s.Package)+"."+s.Test, s.Elapsed))
+		}
+	}
+	out := Outcome{Verdict: v, Slowest: slow}
+	for _, t := range st.targets {
+		if t.judged != "" {
+			if out.Judged == nil {
+				out.Judged = map[string]string{}
+			}
+			out.Judged[pullKey(Pull{Repository: t.pull.Repository, Number: t.pull.Number})] = t.judged
+		}
+	}
+	return out
+}
+
+// fail is a verdict of failure at a machine.
+func fail(machine, words string) *delivery.Verdict {
+	v := failure(machine, words)
+	return &v
+}
+
+// levels are the levels a case's asks run: both, or the one a try names.
+func (st *state) levelsOf() []string {
+	if st.c.Try != nil && st.c.Try.Level != "" {
+		return []string{st.c.Try.Level} // a try of one level runs that level alone
+	}
+	return []string{delivery.LevelUnit, delivery.LevelIntegration}
+}
+
+// judgeAll puts one check ask per pull request and build module the repository needs, the mesh-sdk member first, and
+// judges each answer. A head that does not merge, a pin that is not allowed or a level that fails ends the check at once
+// (ADR 0484 clause 13).
+func (st *state) judgeAll(ctx context.Context) *delivery.Verdict {
+	// The mesh-sdk member first: whether its merge changes the TypeScript package's paths decides whether the other members'
+	// Node fetches take the group's package (ADR 0500 §5).
+	pulls := slices.Clone(st.c.Pulls)
+	slices.SortStableFunc(pulls, func(a, b Pull) int {
+		if (a.Repository == SDKRepository) != (b.Repository == SDKRepository) {
+			if a.Repository == SDKRepository {
+				return -1
+			}
+			return 1
+		}
+		return 0
+	})
+	var groupPackage map[string]any
+	for _, p := range pulls {
+		var merged []Fetched
+		for _, bm := range st.j.Modules.BuildModules(p.Repository) {
+			t := &target{pull: p, module: bm}
+			if tc, none := delivery.AgreedToolchain(st.j.Toolchains.Entries(buildrun.LanguageOf[bm])); none == "" {
+				t.toolchain = tc.Version
+			}
+			args := map[string]any{"repository": p.Repository, "commit": p.Head, "ref": refOf(p.Number), "base": p.Trunk}
+			if bm == buildrun.NodeBuildModule && groupPackage != nil && p.Repository != SDKRepository {
+				args["package"] = groupPackage
+			}
+			if bm == buildrun.GoBuildModule {
+				beside, err := st.j.besideFor(ctx, st.c, p)
+				if err != nil {
+					return fail(forgeMachine(err, bm), err.Error()+unheardWords(err))
+				}
+				if len(beside) > 0 {
+					args["beside"] = beside
+					t.beside = besideLines(beside)
+				}
+				if p.Repository == catalogueRepository {
+					t.runner = RunnerWorkspace // used by the build module when the merge changes it (ADR 0535 §1)
+				}
+			}
+			t.fetchArgs = args
+			st.targets = append(st.targets, t)
+			if v := st.ask(ctx, t, &merged); v != nil {
+				return v
+			}
+		}
+		if st.c.Try == nil { // a try owes the indexer no preview: no pull request holds its head
+			st.j.writePreview(ctx, p, merged)
+		}
+		if p.Repository == SDKRepository && len(st.c.Pulls) > 1 && st.j.changesPackage(p, merged) {
+			groupPackage = map[string]any{"repository": p.Repository, "commit": p.Head, "ref": refOf(p.Number)}
+		}
+	}
+	return nil
+}
+
+// ask puts the target's check ask, waits for the step of the node that pulled it and judges its answer: the fetch, the
+// pins of its go.mod files, then each level's digest, kept verdicts and tests.
+func (st *state) ask(ctx context.Context, t *target, merged *[]Fetched) *delivery.Verdict {
+	p := t.pull
+	job := &delivery.CheckJob{Fetch: t.fetchArgs, Levels: st.levelsOf(), Kept: true}
+	if t.runner != "" {
+		job.Runner, job.RunnerWhen = t.runner, buildGoDir
+	}
+	if st.c.Try != nil && st.c.Try.Run != "" {
+		job.Run, job.Kept = st.c.Try.Run, false // a try of some tests runs them alone: a partial run proves no package
+	}
+	kind := delivery.AskCheck
+	if st.c.Kind == KindTrunk {
+		kind = delivery.AskRecheck // a re-judge after a trunk move goes after every new head's check (ADR 0536 §4)
+	}
+	a := delivery.StepAsk{ID: buildstep.NewID(), Kind: kind, Language: askLanguage[t.module], Asker: delivery.CheckerModule,
+		At: st.j.now().UTC(), Check: job}
+	st.c.Progress.Set(fmt.Sprintf("the %s ask %s of %s#%d", kind, a.ID, p.Repository, p.Number), "")
+	if err := st.j.Asks.Put(ctx, a); err != nil {
+		return fail(t.module, fmt.Sprintf("the check of %s#%d could not be asked: %v", p.Repository, p.Number, err))
+	}
+	step, err := st.j.Asks.Wait(ctx, a)
+	if err != nil {
+		if ctx.Err() != nil {
+			return fail(t.module, ctx.Err().Error())
+		}
+		return fail(t.module, fmt.Sprintf("the check of %s#%d: %v", p.Repository, p.Number, err))
+	}
+	// The fetch and the digests are what of the ask's time its levels' running did not take (Took.Clone).
+	took := time.Duration(0)
+	if !step.Started.IsZero() && step.Ended.After(step.Started) {
+		took = step.Ended.Sub(step.Started)
+	}
+	t.node = step.Node
+	st.nodes[step.Node] = true
+	st.c.Progress.Set(fmt.Sprintf("judge the check of %s#%d", p.Repository, p.Number), step.Node)
+	if step.State != delivery.StepPassed {
+		return fail(step.Node, fmt.Sprintf("the check of %s#%d %s: %s%s", p.Repository, p.Number, step.State, step.Reason, pinHint(st.c, step.Reason)))
+	}
+	var answer delivery.CheckAnswer
+	if err := json.Unmarshal(step.Result, &answer); err != nil {
+		return fail(step.Node, fmt.Sprintf("the check of %s#%d answered what is not a check: %s", p.Repository, p.Number, step.Result))
+	}
+	if err := json.Unmarshal(answer.Fetch, &t.fetched); err != nil || t.fetched.Workspace == "" {
+		return fail(step.Node, fmt.Sprintf("the fetch of %s#%d answered no workspace: %s", p.Repository, p.Number, answer.Fetch))
+	}
+	if len(t.fetched.Conflicts) > 0 {
+		if st.c.Try == nil {
+			st.j.writePreview(ctx, p, append(*merged, t.fetched))
+		}
+		return fail(step.Node, fmt.Sprintf("%s#%d does not merge into the trunk: files in conflict: %s", p.Repository, p.Number, strings.Join(t.fetched.Conflicts, ", ")))
+	}
+	t.changed = t.fetched.Changed
+	if !changesBuildGo(p.Repository, t.changed) {
+		t.runner = "" // the build module used no runner: the merge does not change it
+	}
+	*merged = append(*merged, t.fetched)
+	if v := st.checkPinsOf(ctx, t); v != nil {
+		return v
+	}
+	ran := 0.0
+	for _, la := range answer.Levels {
+		v, elapsed := st.level(ctx, t, la)
+		ran += elapsed
+		if v != nil {
+			st.clone += max(0, took-time.Duration(ran*float64(time.Second)))
+			return v
+		}
+	}
+	st.clone += max(0, took-time.Duration(ran*float64(time.Second)))
+	return nil
+}
+
+// level judges one level of a check ask's answer as the tools' answers were judged: the digest keys the kept verdicts
+// of the packages that passed, the kept ones taken are counted, and the first test result that did not pass is the
+// verdict. It answers the level's running time (its tests' and setup's).
+func (st *state) level(ctx context.Context, t *target, la delivery.LevelAnswer) (*delivery.Verdict, float64) {
+	level := la.Level
+	a := st.levels[level]
+	if a == nil {
+		return fail(t.node, fmt.Sprintf("the check of %s#%d answered the level %q, which is no level", t.pull.Repository, t.pull.Number, level)), 0
+	}
+	var digests map[string]string
+	if t.module == buildrun.GoBuildModule && la.Digest != nil {
+		// The packages come as a list, never keyed by a package path (issue 1930); an answer stored before reads too.
+		digests = la.Digest.Map()
+		if t.runner != "" {
+			t.judgedBy(la.Digest.JudgedBy) // the installed module judged it: the runner is not used again
+		}
+	}
+	if t.runner != "" && la.Judged != "" {
+		t.judgedBy(la.Judged) // the candidate judged the level: nothing is kept (ADR 0535 §4)
+	}
+	for _, k := range la.Kept {
+		a.kept += k.Tests
+	}
+	elapsed := 0.0
+	for _, raw := range la.Tests {
+		var res Tested
+		if err := json.Unmarshal(raw, &res); err != nil {
+			return fail(t.node, fmt.Sprintf("the %s level of %s#%d answered what is not a result: %v", level, t.pull.Repository, t.pull.Number, err)), elapsed
+		}
+		if t.runner != "" {
+			t.judgedBy(res.JudgedBy)
+		}
+		elapsed += res.Elapsed + res.Setup + res.Lint
+		if t.module == buildrun.NodeBuildModule {
+			if !res.NoTests {
+				a.run++ // a Node package is counted whole: its build module counts no tests (ADR 0484 clause 10)
+			}
+		} else {
+			a.run += res.Tests
+			a.skipped += res.Skipped
+			a.slowest = append(a.slowest, res.Slowest...)
+		}
+		a.elapsed += res.Elapsed
+		a.setup += res.Setup
+		a.lint += res.Lint
+		a.over = a.over || res.OverBound
+		if len(digests) > 0 {
+			if _, err := st.j.Kept.KeepPasses(ctx, t.pull.Repository, level, t.toolchain, res, digests, st.j.now()); err != nil {
+				st.j.logf("%s#%d: a passing package could not be kept: %v", t.pull.Repository, t.pull.Number, err)
+			}
+		}
+		if !res.Passed {
+			return levelFailure(t, level, res), elapsed
+		}
+	}
+	return nil, elapsed
+}
+
+// changesPackage says whether the merge of a pull request changes a file inside the named paths of one of its repository's
+// TypeScript packages: a change of the manifest alone, or of files outside those paths, does not (ADR 0500 §5).
+func (j *Examiner) changesPackage(p Pull, merged []Fetched) bool {
+	if j.Packages == nil {
+		return false
+	}
+	paths := j.Packages.PackagePaths(p.Repository)
+	for _, f := range merged {
+		for _, changed := range f.Changed {
+			for _, named := range paths {
+				named = strings.TrimSuffix(strings.TrimPrefix(named, "./"), "/")
+				if changed == named || strings.HasPrefix(changed, named+"/") {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+// failedName names a failure: its package and test.
+func failedName(f Failure) string {
+	if f.Test == "" {
+		return f.Package
+	}
+	return f.Package + "." + f.Test
+}
+
+// MaxWords is the most a failed test's words in a verdict hold (issue 1901). **The words keep the failure's last lines**,
+// where a test says why it failed: the first line is often something it logged before (the group r4g verdict kept a
+// "judged against" line and lost the t.Fatalf after it), and the 120 characters kept before cut a docker command's echo
+// before docker's own error. Four kilobytes holds a long message and is small beside a verdict's other parts.
+const MaxWords = 4096
+
+// failureWords is a failure's words: its output's last lines up to MaxWords, with the line the build module told apart as
+// the test's error first when the output does not start with it, so the first line of the words is the cause and the
+// status line, which is cut short, names it.
+func failureWords(f Failure) string {
+	out := strings.TrimSpace(f.Output)
+	if len(out) > MaxWords {
+		out = out[len(out)-MaxWords:]
+		// Start on a whole line, and a whole character.
+		if i := strings.IndexByte(out, '\n'); i >= 0 {
+			out = "... " + strings.TrimLeft(out[i:], "\n")
+		}
+		out = strings.ToValidUTF8(out, "")
+	}
+	if c := strings.TrimSpace(f.Cause); c != "" && !strings.HasPrefix(firstLine(out), c) {
+		out = c + "\n" + out
+	}
+	return out
+}
+
+// firstLine is the first non-empty line of a failure's words.
+func firstLine(s string) string {
+	for _, l := range strings.Split(s, "\n") {
+		if l = strings.TrimSpace(l); l != "" {
+			return l
+		}
+	}
+	return ""
+}
+
+// failure turns a level that did not pass into a verdict naming what failed first.
+func levelFailure(t *target, level string, res Tested) *delivery.Verdict {
+	v := delivery.Verdict{State: delivery.VerdictFail}
+	switch {
+	case len(res.Failed) > 0:
+		f := res.Failed[0]
+		name := failedName(f)
+		if t.module == buildrun.NodeBuildModule && f.Package == "" {
+			name = res.Module
+		}
+		v.Failed = delivery.FailedFirst{Test: level + ": " + name, Words: failureWords(f)}
+	default:
+		why := res.Why
+		if why == "" {
+			why = "the " + level + " level did not pass"
+		}
+		v.Failed = delivery.FailedFirst{Test: level + ": " + t.pull.Repository, Words: why}
+	}
+	return &v
+}

modules/mesh-delivery-checker/internal/check/judged_test.go

@@ -0,0 +1,207 @@
+package check
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// The judged_by answer of mesh-build-go's digest and test steps (ADR 0535 §5; the milestone file's interface for issue
+// 1898): "installed" for a step its installed program ran, "candidate <merge commit>" for one the candidate's program ran
+// under runner workspace; an installed module older than the runner names nothing (it ignores the unknown argument: the
+// SDK's tool server checks no argument against the input schema).
+
+const buildGoFile = "modules/mesh-build-go/cmd/mesh-build-go/digest.go"
+
+// candidateBench is a bench whose fetch changes the Go build module's directory, and whose build module runs the candidate
+// when asked to (a module with the runner) or ignores the runner (one without).
+func candidateBench(t *testing.T, takesRunner bool) *bench {
+	b := newBench(t)
+	b.fetch.Changed = []string{"README.md", buildGoFile}
+	judged := func(c stepCall) string {
+		if !takesRunner {
+			return ""
+		}
+		if c.args["runner"] == RunnerWorkspace {
+			return "candidate " + b.fetch.Merge
+		}
+		return "installed"
+	}
+	b.steps.handlers["build_go_digest"] = func(c stepCall) (any, error) {
+		d := echoBeside(b, b.digest[c.args["level"].(string)])
+		d.JudgedBy = judged(c)
+		return d, nil
+	}
+	b.test = func(c stepCall) (any, error) {
+		r := captured[Tested](t, "go-test-slow")
+		r.Level, _ = c.args["level"].(string)
+		r.JudgedBy = judged(c)
+		return r, nil
+	}
+	return b
+}
+
+func TestAMergeChangingTheGoBuildModuleIsAskedWithTheCandidateRunner(t *testing.T) { // 1898/AC1
+	b := candidateBench(t, true)
+	b.judge(t, caseOf(t, pullOf(catalogueRepository, 9, head1)))
+	asked := append(b.steps.tool("digest"), b.steps.tool("test")...)
+	if len(asked) < 3 {
+		t.Fatalf("asked %+v, want the digest and both levels", asked)
+	}
+	for _, c := range asked {
+		if c.args["runner"] != RunnerWorkspace {
+			t.Errorf("%s %v was asked with runner %v, want %s", c.tool, c.args["level"], c.args["runner"], RunnerWorkspace)
+		}
+	}
+}
+
+func TestAMergeNotChangingTheGoBuildModuleIsAskedWithoutARunner(t *testing.T) { // 1898/AC1
+	for _, tc := range []struct {
+		name, repo, path string
+	}{
+		{"another module of the catalogue", catalogueRepository, "modules/mesh-build-node/cmd/mesh-build-node/main.go"},
+		{"a look-alike path in another repository", repoA, buildGoFile},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			b := candidateBench(t, true)
+			b.fetch.Changed = []string{tc.path}
+			out := b.judge(t, caseOf(t, pullOf(tc.repo, 9, head1)))
+			for _, c := range append(b.steps.tool("digest"), b.steps.tool("test")...) {
+				if _, ok := c.args["runner"]; ok {
+					t.Errorf("%s was asked with runner %v", c.tool, c.args["runner"])
+				}
+			}
+			if len(out.Judged) != 0 {
+				t.Errorf("judged = %v, want nothing said of the program", out.Judged)
+			}
+		})
+	}
+}
+
+func TestAnInstalledModuleWithoutTheRunnerJudgesAsTodayAndTheLineSaysSo(t *testing.T) { // 1898/AC2
+	b := candidateBench(t, false)
+	cs := caseOf(t, pullOf(catalogueRepository, 9, head1))
+	out := b.judge(t, cs)
+	if out.Verdict.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", out.Verdict)
+	}
+	// As today: the digests key kept verdicts, and the levels are asked without the runner the module ignored.
+	for _, c := range b.steps.tool("test") {
+		if _, ok := c.args["runner"]; ok {
+			t.Errorf("the %v level was asked again with the runner the module does not take", c.args["level"])
+		}
+	}
+	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 2 {
+		t.Errorf("kept %v, want the passing package at both levels, as today", keys)
+	}
+	p := cs.Pulls[0]
+	want := "judged by the installed mesh-build-go: it does not run a candidate yet"
+	if got := out.Judged[pullKey(p)]; got != want {
+		t.Fatalf("judged = %q, want %q", got, want)
+	}
+	if l := Line(out.Verdict, cs, p, out.Builds, out.Slowest, out.Judged); !strings.Contains(l, want) {
+		t.Errorf("line %q does not say %q", l, want)
+	}
+}
+
+func TestACandidateJudgedCheckTakesNoKeptVerdictAndWritesNone(t *testing.T) { // 1898/AC3
+	b := candidateBench(t, true)
+	if _, err := (Kept{Store: b.kept}).Keep(context.Background(), "unit", digA, keptValue("fixture/slow", 2)); err != nil {
+		t.Fatal(err)
+	}
+	out := b.judge(t, caseOf(t, pullOf(catalogueRepository, 9, head1)))
+	if out.Verdict.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", out.Verdict)
+	}
+	tests := b.steps.tool("test")
+	if len(tests) != 2 {
+		t.Fatalf("test calls = %+v, want both levels", tests)
+	}
+	for _, c := range tests {
+		if _, ok := c.args["packages"]; ok {
+			t.Errorf("the %v level was asked for %v, want it whole", c.args["level"], c.args["packages"])
+		}
+	}
+	if u := out.Verdict.Levels[delivery.LevelUnit]; u.Kept != 0 {
+		t.Errorf("unit = %+v, want nothing taken", u)
+	}
+	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 1 || keys[0] != "unit."+digA {
+		t.Errorf("kept keys = %v, want only the one kept before", keys)
+	}
+}
+
+func TestTheLineNamesTheCandidateThatJudged(t *testing.T) { // 1898/AC6
+	b := candidateBench(t, true)
+	cs := caseOf(t, pullOf(catalogueRepository, 9, head1))
+	out := b.judge(t, cs)
+	p := cs.Pulls[0]
+	want := "judged by the candidate's mesh-build-go at " + b.fetch.Merge[:12]
+	for name, l := range map[string]string{
+		"line":   Line(out.Verdict, cs, p, out.Builds, out.Slowest, out.Judged),
+		"report": Report(out.Verdict, cs, p, out.Builds, out.Slowest, out.Judged),
+	} {
+		if !strings.Contains(l, want) {
+			t.Errorf("the %s %q does not say %q", name, l, want)
+		}
+	}
+	// A long failing line keeps the program it was judged by; only the lesser parts go.
+	v := out.Verdict
+	v.State = delivery.VerdictFail
+	v.Failed = delivery.FailedFirst{Test: "unit: git.novox.be/novox/mesh-catalog/modules/mesh-build-go/cmd/mesh-build-go.TestADigestFoldsTheSiblings", Words: strings.Repeat("x", 60)}
+	if l := Line(v, cs, p, out.Builds, out.Slowest, out.Judged); !strings.Contains(l, "judged by the candidate's") {
+		t.Errorf("the long line %q dropped the program", l)
+	}
+}
+
+func TestInAGroupOnlyTheBuildModulesPullRequestNamesItsProgram(t *testing.T) { // 1898/AC6
+	b := candidateBench(t, true)
+	cs := caseOf(t, pullOf(catalogueRepository, 9, head1), pullOf(repoA, 7, head1))
+	out := b.judge(t, cs)
+	for _, p := range cs.Pulls {
+		l := Report(out.Verdict, cs, p, out.Builds, out.Slowest, out.Judged)
+		says := strings.Contains(l, "judged by")
+		if says != (p.Repository == catalogueRepository) {
+			t.Errorf("%s#%d: %q", p.Repository, p.Number, l)
+		}
+	}
+}
+
+func TestACandidateThatDoesNotCompileFailsTheCheckWithTheCompilersWords(t *testing.T) { // ADR 0535 §3, checker side
+	b := candidateBench(t, true)
+	refusal := "the candidate's mesh-build-go does not compile: modules/mesh-build-go/cmd/mesh-build-go/digest.go:12:2: undefined: x"
+	b.steps.handlers["build_go_digest"] = func(stepCall) (any, error) { return nil, errorString(refusal) }
+	b.test = func(stepCall) (any, error) { return nil, errorString(refusal) }
+	out := b.judge(t, caseOf(t, pullOf(catalogueRepository, 9, head1)))
+	if out.Verdict.State != delivery.VerdictFail || !strings.Contains(out.Verdict.Failed.Words, "undefined: x") {
+		t.Fatalf("verdict = %+v, want a failure naming the compile error", out.Verdict)
+	}
+	if n := len(b.steps.tool("test")); n != 1 {
+		t.Errorf("%d test steps, want the first one's failure to end the check", n)
+	}
+}
+
+type errorString string
+
+func (e errorString) Error() string { return string(e) }
+
+func TestTheStatusTheForgeShowsNamesTheProgramThatJudged(t *testing.T) { // 1898/AC6, the forge's line
+	ctx := context.Background()
+	words := judgedByCandidate + "fedcba987654"
+	j := &judgeFunc{f: func(context.Context, *Case, int) (Outcome, error) {
+		return Outcome{Verdict: passing(), Judged: map[string]string{repoA + "#7": words}}, nil
+	}}
+	r := newRig(t, j)
+	r.ch.Candidate(ctx, "feat/x", candidateOf(t, "feat/x", pullOf(repoA, 7, head1)))
+	r.ch.Wait()
+	key, _ := delivery.CheckerOwedKey(repoA, 7, head1)
+	raw, _, _, _ := r.owed.Get(ctx, key)
+	o, err := delivery.DecodeCheckerOwed(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if o.State != "success" || !strings.Contains(o.Text, words) {
+		t.Errorf("status %+v, want success saying %q", o, words)
+	}
+}

modules/mesh-delivery-checker/internal/check/kept.go

@@ -0,0 +1,90 @@
+package check
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"sort"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// Kept is the checker's bucket of kept verdicts (ADR 0444, ADR 0484 clause 13): a passing verdict per package and level,
+// under the digest the language's build module named for it. A key is written once, by a create that fails when it
+// exists, from the result the checker read from the test step and never from anything the code under test wrote; nothing
+// changes it afterwards.
+type Kept struct{ Store KV }
+
+// Lookup is the kept verdict of a level under a digest, or none.
+func (k Kept) Lookup(ctx context.Context, level, digest string) (delivery.Kept, bool, error) {
+	key, err := delivery.KeptKey(level, digest)
+	if err != nil {
+		return delivery.Kept{}, false, err
+	}
+	value, _, found, err := k.Store.Get(ctx, key)
+	if err != nil || !found {
+		return delivery.Kept{}, false, err
+	}
+	v, err := delivery.DecodeKept(value)
+	if err != nil {
+		return delivery.Kept{}, false, fmt.Errorf("%s holds what is not a kept verdict: %w", key, err)
+	}
+	return v, true, nil
+}
+
+// Keep writes v under level and digest by a create. It answers false, and writes nothing, when the key exists: the first
+// value stands.
+func (k Kept) Keep(ctx context.Context, level, digest string, v delivery.Kept) (bool, error) {
+	key, err := delivery.KeptKey(level, digest)
+	if err != nil {
+		return false, err
+	}
+	v.Level = level
+	data, err := delivery.EncodeKept(v)
+	if err != nil {
+		return false, err
+	}
+	if _, err := k.Store.Create(ctx, key, data); err != nil {
+		if errors.Is(err, ErrConflict) {
+			return false, nil
+		}
+		return false, fmt.Errorf("%s: %w", key, err)
+	}
+	return true, nil
+}
+
+// KeepPasses keeps, for the packages of a test result that passed with tests, a verdict under the digest the build module
+// named for the package at the level. A package that failed, has no tests or has no digest is never kept (ADR 0444 clause
+// 1): it runs every check. It answers the packages it kept now.
+func (k Kept) KeepPasses(ctx context.Context, repository, level, toolchain string, res Tested, digests map[string]string, at time.Time) ([]string, error) {
+	var kept []string
+	for _, p := range res.Packages {
+		digest, ok := digests[p.Package]
+		if !ok || !p.Passed || p.NoTests || p.Tests == 0 {
+			continue
+		}
+		if failedIn(res, p.Package) {
+			continue
+		}
+		made, err := k.Keep(ctx, level, digest, delivery.Kept{State: delivery.VerdictPass, Repository: repository, Package: p.Package,
+			Level: level, Tests: p.Tests, Took: int64(p.Elapsed * 1000), Toolchain: toolchain, At: at})
+		if err != nil {
+			return kept, err
+		}
+		if made {
+			kept = append(kept, p.Package)
+		}
+	}
+	sort.Strings(kept)
+	return kept, nil
+}
+
+func failedIn(res Tested, pkg string) bool {
+	for _, f := range res.Failed {
+		if f.Package == pkg {
+			return true
+		}
+	}
+	return false
+}

modules/mesh-delivery-checker/internal/check/kept_test.go

@@ -0,0 +1,102 @@
+package check
+
+import (
+	"context"
+	"strings"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+var at0 = time.Date(2026, 10, 21, 19, 0, 0, 0, time.UTC)
+
+const (
+	digA = "aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11aa11"
+	digB = "bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22bb22"
+)
+
+func keptValue(pkg string, tests int) delivery.Kept {
+	return delivery.Kept{State: delivery.VerdictPass, Repository: "novox/mesh-delivery", Package: pkg, Tests: tests, Took: 120, Toolchain: "go1.26.0", At: at0}
+}
+
+func TestAPassIsKeptByACreateUnderItsLevelAndDigest(t *testing.T) { // 1287/AC1
+	ctx, st := context.Background(), newMemKV()
+	k := Kept{Store: st}
+	made, err := k.Keep(ctx, delivery.LevelUnit, digA, keptValue("m/a", 3))
+	if err != nil || !made {
+		t.Fatalf("Keep = %v, %v, want made", made, err)
+	}
+	key, _ := delivery.KeptKey(delivery.LevelUnit, digA)
+	if st.creates[key] != 1 {
+		t.Fatalf("the key %s was created %d times, want once", key, st.creates[key])
+	}
+	got, found, err := k.Lookup(ctx, delivery.LevelUnit, digA)
+	if err != nil || !found || got.Package != "m/a" || got.Tests != 3 || got.Level != delivery.LevelUnit || got.Toolchain != "go1.26.0" {
+		t.Fatalf("Lookup = %+v, %v, %v", got, found, err)
+	}
+}
+
+func TestASecondKeepUnderTheSameDigestIsRefusedAndTheFirstStands(t *testing.T) { // 1287/AC2
+	ctx, st := context.Background(), newMemKV()
+	k := Kept{Store: st}
+	if made, err := k.Keep(ctx, delivery.LevelUnit, digA, keptValue("m/a", 3)); err != nil || !made {
+		t.Fatal(made, err)
+	}
+	made, err := k.Keep(ctx, delivery.LevelUnit, digA, keptValue("m/other", 9))
+	if err != nil || made {
+		t.Fatalf("the second Keep = %v, %v, want refused without an error", made, err)
+	}
+	got, _, _ := k.Lookup(ctx, delivery.LevelUnit, digA)
+	if got.Package != "m/a" || got.Tests != 3 {
+		t.Errorf("the first value did not stand: %+v", got)
+	}
+}
+
+func TestOnlyPassingPackagesWithADigestAreKept(t *testing.T) { // 1287/AC3, AC4
+	ctx, st := context.Background(), newMemKV()
+	k := Kept{Store: st}
+	res := Tested{Level: "unit", Passed: false, Packages: []GoPackage{
+		{Package: "m/a", Passed: true, Tests: 4, Elapsed: 0.2},
+		{Package: "m/b", Passed: false, Tests: 2},
+		{Package: "m/c", Passed: true, Tests: 1},      // no digest named
+		{Package: "m/d", Passed: true, NoTests: true}, // no tests
+	}, Failed: []Failure{{Package: "m/b", Test: "TestB"}}}
+	kept, err := k.KeepPasses(ctx, "novox/mesh-delivery", "unit", "go1.26.0", res, map[string]string{"m/a": digA, "m/b": digB, "m/d": digB}, at0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.Join(kept, ",") != "m/a" {
+		t.Fatalf("kept %v, want only m/a", kept)
+	}
+	if keys, _ := st.Keys(ctx); len(keys) != 1 {
+		t.Errorf("the bucket holds %v, want one key", keys)
+	}
+}
+
+func TestAKeptValueOfAnotherDigestIsNotRead(t *testing.T) { // 1287/AC7
+	ctx, st := context.Background(), newMemKV()
+	k := Kept{Store: st}
+	if _, err := k.Keep(ctx, delivery.LevelUnit, digA, keptValue("m/a", 3)); err != nil {
+		t.Fatal(err)
+	}
+	// A toolchain change changes the digest, so the new digest finds nothing and the old key is not deleted.
+	if _, found, _ := k.Lookup(ctx, delivery.LevelUnit, digB); found {
+		t.Error("a digest that was not kept was found")
+	}
+	if _, found, _ := k.Lookup(ctx, delivery.LevelIntegration, digA); found {
+		t.Error("a kept unit verdict was found at the integration level")
+	}
+	if keys, _ := st.Keys(ctx); len(keys) != 1 {
+		t.Errorf("the old key was removed: %v", keys)
+	}
+}
+
+func TestAKeptVerdictThatIsNotAPassIsRefused(t *testing.T) {
+	k := Kept{Store: newMemKV()}
+	v := keptValue("m/a", 1)
+	v.State = delivery.VerdictFail
+	if _, err := k.Keep(context.Background(), delivery.LevelUnit, digA, v); err == nil {
+		t.Error("a failure was kept")
+	}
+}

modules/mesh-delivery-checker/internal/check/line.go

@@ -0,0 +1,277 @@
+package check
+
+import (
+	"fmt"
+	"slices"
+	"strings"
+	"unicode/utf8"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// MaxLine is the most characters a status's line has: the forge shows a status's description in a short space, and the full
+// report is linked (ADR 0447 clause 3, ADR 0484 clause 7). A line that would be longer drops its lesser parts in a fixed
+// order, and is cut last.
+const MaxLine = 140
+
+// seconds is a time in milliseconds in the unit a person reads: 350ms, 4.1s, 72s.
+func seconds(ms int64) string {
+	switch {
+	case ms < 1000:
+		return fmt.Sprintf("%dms", ms)
+	case ms < 10000:
+		return fmt.Sprintf("%.1fs", float64(ms)/1000)
+	}
+	return fmt.Sprintf("%ds", (ms+500)/1000)
+}
+
+func short12(s string) string {
+	if len(s) > 12 {
+		return s[:12]
+	}
+	return s
+}
+
+// firstFailed is what failed first, in words: a conflict, a refused step or a test, named before anything else.
+func firstFailed(v delivery.Verdict) string {
+	f := v.Failed
+	switch {
+	case f.Test != "":
+		if w := firstWordsLine(f.Words); w != "" {
+			return f.Test + ": " + w
+		}
+		return f.Test
+	case f.Machine != "" && firstWordsLine(f.Words) != "":
+		return f.Machine + ": " + firstWordsLine(f.Words)
+	case f.Machine != "":
+		return f.Machine
+	}
+	return firstWordsLine(f.Words)
+}
+
+// firstWordsLine is the first line of a failure's words: the words are several lines (issue 1901) and the status line one.
+func firstWordsLine(w string) string { return firstLine(w) }
+
+// pieces are the parts of a line, from the most to the least needed.
+type pieces struct {
+	head, commits, counts, shortCounts, times, shortTimes, over, builds, composition, shortComposition, group string
+	// judged names the program that judged a change to a build module (ADR 0535 §5); never dropped.
+	judged string
+}
+
+// pullKey names a pull request of a case: `<owner/repo>#<number>`.
+func pullKey(p Pull) string { return fmt.Sprintf("%s#%d", p.Repository, p.Number) }
+
+func (p pieces) join(drop int) string {
+	parts := []string{p.head, p.commits, p.counts, p.judged}
+	switch {
+	case drop < 3 && p.times != "":
+		parts = append(parts, p.times)
+	case drop == 3 && p.shortTimes != "":
+		parts = []string{p.head, p.commits, p.shortCounts, p.judged, p.shortTimes}
+	}
+	if p.over != "" {
+		parts = append(parts, p.over)
+	}
+	if drop < 1 && p.builds != "" {
+		parts = append(parts, p.builds)
+	}
+	if drop < 2 && p.group != "" {
+		parts = append(parts, p.group)
+	}
+	switch {
+	case drop >= 3 && p.shortComposition != "":
+		parts = append(parts, p.shortComposition)
+	case p.composition != "":
+		parts = append(parts, p.composition)
+	}
+	return joinSet(parts...)
+}
+
+func levelWords(name string, r delivery.LevelResult) string {
+	s := fmt.Sprintf("%s %d run, %d kept", name, r.Run, r.Kept)
+	if r.Skipped > 0 {
+		s += fmt.Sprintf(", %d skipped", r.Skipped)
+	}
+	return s
+}
+
+// compositionWords says the composition: not yet run, or once the assigner's check reports it (issue 1297) passed or
+// failed, with the time it took and the machines it composed (issue 1300).
+func compositionWords(c *delivery.Composition, took int64) string { return composition(c, took, false) }
+
+// composition is compositionWords; short counts the machines and leaves the SDK commit to the report.
+func composition(c *delivery.Composition, took int64, short bool) string {
+	if c != nil && c.State == delivery.CompositionNotRun && c.Words != "" {
+		return "composition not judged: " + c.Words
+	}
+	if c == nil || c.State == delivery.CompositionNotRun {
+		return "composition not yet run"
+	}
+	in := ""
+	if took > 0 {
+		in = " in " + seconds(took)
+	}
+	on := ""
+	if len(c.Machines) > 0 {
+		machines := slices.Sorted(slices.Values(c.Machines))
+		on = " on " + strings.Join(machines, ", ")
+		switch {
+		case len(machines) > 1 && short:
+			on = fmt.Sprintf(" on %d machines", len(machines))
+		case len(machines) > 1:
+			on = fmt.Sprintf(" on %d machines: %s", len(machines), strings.Join(machines, ", "))
+		}
+	}
+	switch {
+	case c.State == delivery.CompositionPass && short:
+		return "composition passed" + in + on // the SDK it composed with is in the report
+	case c.State == delivery.CompositionPass:
+		return "composition passed" + in + " with " + short12(c.SDK) + on
+	}
+	return "composition failed" + in + on + ": " + c.Words
+}
+
+func buildWords(builds []BuildNote) string {
+	if len(builds) == 0 {
+		return ""
+	}
+	parts := make([]string, len(builds))
+	for i, b := range builds {
+		parts[i] = b.Module + " " + b.State
+	}
+	return "builds: " + strings.Join(parts, ", ")
+}
+
+// parts makes the pieces of the line of a pull request of a case.
+func parts(v delivery.Verdict, cs *Case, p Pull, builds []BuildNote, slowest []string, judged map[string]string) pieces {
+	var pc pieces
+	pc.judged = judged[pullKey(p)]
+	commits := short12(p.Head) + " on " + short12(p.Trunk)
+	switch v.State {
+	case delivery.VerdictRunning:
+		pc.head = "checking " + commits
+	case delivery.VerdictPass:
+		pc.head = "pass " + commits
+	default:
+		pc.head = "failed: " + firstFailed(v)
+		pc.commits = commits
+	}
+	var counts []string
+	for _, level := range []string{delivery.LevelUnit, delivery.LevelIntegration} {
+		if r, ok := v.Levels[level]; ok {
+			counts = append(counts, levelWords(level, r))
+		}
+	}
+	pc.counts = strings.Join(counts, " | ")
+	var short []string
+	for _, level := range []string{delivery.LevelUnit, delivery.LevelIntegration} {
+		if r, ok := v.Levels[level]; ok {
+			name := map[string]string{delivery.LevelUnit: "unit", delivery.LevelIntegration: "int"}[level]
+			w := fmt.Sprintf("%s %d run %d kept", name, r.Run, r.Kept)
+			if r.Skipped > 0 {
+				w += fmt.Sprintf(" %d skipped", r.Skipped)
+			}
+			short = append(short, w)
+		}
+	}
+	pc.shortCounts = strings.Join(short, " | ")
+	if v.State != delivery.VerdictRunning {
+		t := v.Took
+		var times []string
+		for _, x := range []struct {
+			name string
+			ms   int64
+		}{{"queue", t.Queue}, {"clone", t.Clone}, {"lint", t.Lint}, {"unit", t.Unit}, {"int setup", t.IntegrationSetup}, {"int run", t.IntegrationRun}} {
+			if x.ms > 0 {
+				times = append(times, x.name+" "+seconds(x.ms))
+			}
+		}
+		if len(times) > 0 {
+			pc.times = strings.Join(times, ", ")
+		}
+		// The compact form for a line that is too long: the parts that dominate, the integration level's setup and run as one.
+		short = short[:0:0]
+		if t.Clone > 0 {
+			short = append(short, "clone "+seconds(t.Clone))
+		}
+		if t.Lint > 0 {
+			short = append(short, "lint "+seconds(t.Lint))
+		}
+		if t.Unit > 0 {
+			short = append(short, "unit "+seconds(t.Unit))
+		}
+		switch {
+		case t.IntegrationSetup > 0 && t.IntegrationRun > 0:
+			short = append(short, "int "+seconds(t.IntegrationSetup)+"+"+seconds(t.IntegrationRun))
+		case t.IntegrationRun > 0:
+			short = append(short, "int "+seconds(t.IntegrationRun))
+		}
+		pc.shortTimes = strings.Join(short, " ")
+	}
+	if len(v.OverBound) > 0 {
+		pc.over = "over bound: " + strings.Join(v.OverBound, ", ")
+		if len(slowest) > 0 {
+			pc.over += " (slowest " + strings.Join(slowest, ", ") + ")"
+		}
+	}
+	pc.builds = buildWords(builds)
+	if v.State != delivery.VerdictRunning {
+		pc.composition = compositionWords(v.Composition, v.Took.Composition)
+		pc.shortComposition = composition(v.Composition, v.Took.Composition, true)
+	}
+	if cs != nil && len(cs.Pulls) > 1 {
+		pc.group = fmt.Sprintf("group %s of %d pull requests", cs.Group, len(cs.Pulls))
+		if v.State != delivery.VerdictPass {
+			pc.group = fmt.Sprintf("%s#%d in group %s", p.Repository, p.Number, cs.Group)
+		}
+	}
+	return pc
+}
+
+// Report is the full line of a pull request's status, with no limit: what the read tools and the full report say.
+func Report(v delivery.Verdict, cs *Case, p Pull, builds []BuildNote, slowest []string, judged map[string]string) string {
+	return parts(v, cs, p, builds, slowest, judged).join(0)
+}
+
+// Line is the words of a status for one pull request of a case (ADR 0447 clause 3, ADR 0484 clause 7): the verdict first (a
+// failure names the conflict, the refused step or the test before anything), the head and the trunk commit as twelve
+// characters each, the tests run, kept and skipped per level, the time of each part, a level over its bound with its slowest
+// tests, the builds of the touched modules, and that the composition was not yet run; for a change to a build module, the
+// program that judged it (judged, by pullKey; ADR 0535 §5). It is at most MaxLine characters: the
+// builds, then the group drop first, then the times are given in their compact form, then dropped, and the line is cut at last.
+// The program that judged is never dropped: a line naming it gives the counts in their compact form, then drops them and
+// what follows, and is cut in its first part rather than lose it.
+func Line(v delivery.Verdict, cs *Case, p Pull, builds []BuildNote, slowest []string, judged map[string]string) string {
+	pc := parts(v, cs, p, builds, slowest, judged)
+	for drop := 0; drop <= 4; drop++ {
+		if s := pc.join(drop); utf8.RuneCountInString(s) <= MaxLine {
+			return s
+		}
+	}
+	if pc.judged != "" {
+		for _, counts := range []string{pc.shortCounts, ""} {
+			if s := joinSet(pc.head, pc.commits, counts, pc.judged); utf8.RuneCountInString(s) <= MaxLine {
+				return s
+			}
+		}
+		rest := " | " + joinSet(pc.commits, pc.judged)
+		room := MaxLine - utf8.RuneCountInString(rest) - 1
+		if head := []rune(pc.head); room > 0 && len(head) > room {
+			return string(head[:room]) + "…" + rest
+		}
+	}
+	runes := []rune(pc.join(4))
+	return string(runes[:MaxLine-1]) + "…"
+}
+
+// joinSet joins the parts that are not empty.
+func joinSet(parts ...string) string {
+	out := make([]string, 0, len(parts))
+	for _, s := range parts {
+		if s != "" {
+			out = append(out, s)
+		}
+	}
+	return strings.Join(out, " | ")
+}

modules/mesh-delivery-checker/internal/check/line_test.go

@@ -0,0 +1,179 @@
+package check
+
+import (
+	"strings"
+	"testing"
+	"unicode/utf8"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+func lineCase(t testing.TB, pulls ...delivery.CandidatePull) (*Case, Pull) {
+	cs := caseOf(t, pulls...)
+	return cs, cs.Pulls[0]
+}
+
+func passVerdict() delivery.Verdict {
+	return delivery.Verdict{State: delivery.VerdictPass,
+		Levels:      map[string]delivery.LevelResult{delivery.LevelUnit: {Run: 12, Kept: 301}, delivery.LevelIntegration: {Run: 3, Kept: 40}},
+		Took:        delivery.Took{Queue: 800, Clone: 4100, Unit: 400, IntegrationSetup: 3200, IntegrationRun: 12000},
+		Composition: &delivery.Composition{State: delivery.CompositionNotRun}}
+}
+
+func TestAPassOpensWithTheVerdictAndSaysTheCommitsTheCountsTheTimesAndThatTheCompositionWasNotRun(t *testing.T) { // 1300/AC1
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	full := Report(passVerdict(), cs, p, nil, nil, nil)
+	for _, want := range []string{"pass 111111111111 on aaaaaaaaaaaa", "unit 12 run, 301 kept", "integration 3 run, 40 kept", "queue 800ms", "clone 4.1s", "unit 400ms", "int setup 3.2s", "int run 12s", "composition not yet run"} {
+		if !strings.Contains(full, want) {
+			t.Errorf("the report %q lacks %q", full, want)
+		}
+	}
+	if !strings.HasPrefix(full, "pass ") || strings.Contains(full, "composition passed") {
+		t.Errorf("report = %q", full)
+	}
+	line := Line(passVerdict(), cs, p, nil, nil, nil)
+	if n := utf8.RuneCountInString(line); n > MaxLine {
+		t.Errorf("the line is %d characters, want at most %d: %q", n, MaxLine, line)
+	}
+	if !strings.HasPrefix(line, "pass 111111111111 on aaaaaaaaaaaa") || !strings.Contains(line, "composition not yet run") || !strings.Contains(line, "unit 12 run 301 kept") ||
+		!strings.Contains(line, "clone 4.1s") || !strings.Contains(line, "int 3.2s+12s") {
+		t.Errorf("line = %q", line)
+	}
+}
+
+func TestAFailureNamesTheTestTheConflictOrTheRefusedStepFirst(t *testing.T) { // 1300/AC2
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	for name, c := range map[string]struct {
+		v    delivery.Verdict
+		want string
+	}{
+		"test":     {delivery.Verdict{State: delivery.VerdictFail, Failed: delivery.FailedFirst{Test: "unit: m/a.TestX", Words: "want 4"}}, "failed: unit: m/a.TestX: want 4"},
+		"conflict": {delivery.Verdict{State: delivery.VerdictFail, Failed: delivery.FailedFirst{Machine: "shanks", Words: "novox/mesh-delivery#7 does not merge into the trunk: files in conflict: go.mod"}}, "failed: shanks: novox/mesh-delivery#7 does not merge into the trunk: files in conflict: go.mod"},
+		"refused":  {delivery.Verdict{State: delivery.VerdictFail, Failed: delivery.FailedFirst{Machine: "mesh-build-go", Words: "no go build node qualifies: builders disagree"}}, "failed: mesh-build-go: no go build node qualifies"},
+	} {
+		line := Line(c.v, cs, p, nil, nil, nil)
+		if !strings.HasPrefix(line, c.want) || !strings.Contains(line, "111111111111 on aaaaaaaaaaaa") {
+			t.Errorf("%s: line = %q, want it to open with %q and name the commits", name, line, c.want)
+		}
+	}
+}
+
+func TestALevelOverItsBoundIsNamedWithItsSlowestTestsAndTheVerdictIsNotChanged(t *testing.T) { // 1300/AC3
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	v := passVerdict()
+	v.OverBound = []string{"unit"}
+	line := Line(v, cs, p, nil, []string{"unit pkg.TestSlow 7.0s"}, nil)
+	if !strings.HasPrefix(line, "pass ") || !strings.Contains(Report(v, cs, p, nil, []string{"unit pkg.TestSlow 7.0s"}, nil), "over bound: unit (slowest unit pkg.TestSlow 7.0s)") {
+		t.Errorf("line = %q", line)
+	}
+}
+
+func TestSkippedTestsAreSaidAndNeverAFlatPass(t *testing.T) { // 1300/AC6
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	v := passVerdict()
+	v.Levels[delivery.LevelUnit] = delivery.LevelResult{Run: 12, Kept: 301, Skipped: 2}
+	if line := Line(v, cs, p, nil, nil, nil); !strings.Contains(line, "unit 12 run, 301 kept, 2 skipped") {
+		t.Errorf("line = %q", line)
+	}
+}
+
+func TestAGroupsMembersEachCarryTheSameVerdict(t *testing.T) { // 1300/AC4
+	cs := caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2))
+	a := Line(passVerdict(), cs, cs.Pulls[0], nil, nil, nil)
+	b := Line(passVerdict(), cs, cs.Pulls[1], nil, nil, nil)
+	if !strings.HasPrefix(a, "pass ") || !strings.HasPrefix(b, "pass ") || !strings.Contains(Report(passVerdict(), cs, cs.Pulls[0], nil, nil, nil), "group feat/x of 2 pull requests") {
+		t.Errorf("lines %q and %q", a, b)
+	}
+	if !strings.Contains(a, "111111111111") || !strings.Contains(b, "222222222222") {
+		t.Errorf("each member's line names its own head: %q and %q", a, b)
+	}
+}
+
+func TestTheBuildsOfTheTouchedModulesAreSaidAndDroppedFirstWhenTheLineIsTooLong(t *testing.T) { // ADR 0484 clause 7
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	builds := []BuildNote{{"avahi", "built"}, {"mesh-tools", "waiting"}}
+	if r := Report(passVerdict(), cs, p, builds, nil, nil); !strings.Contains(r, "builds: avahi built, mesh-tools waiting") {
+		t.Errorf("report = %q", r)
+	}
+	line := Line(passVerdict(), cs, p, builds, nil, nil)
+	if utf8.RuneCountInString(line) > MaxLine {
+		t.Errorf("line %q is too long", line)
+	}
+	short := passVerdict()
+	short.Took = delivery.Took{}
+	if l := Line(short, cs, p, builds[:1], nil, nil); !strings.Contains(l, "builds: avahi built") {
+		t.Errorf("a short line keeps its builds: %q", l)
+	}
+}
+
+func TestALineIsNeverLongerThanTheLimit(t *testing.T) { // 1300/AC1
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	v := delivery.Verdict{State: delivery.VerdictFail, Failed: delivery.FailedFirst{Test: "integration: " + strings.Repeat("pkg/", 50) + ".TestSomething", Words: strings.Repeat("because ", 40)}}
+	if line := Line(v, cs, p, nil, nil, nil); utf8.RuneCountInString(line) > MaxLine || !strings.HasPrefix(line, "failed: integration: ") {
+		t.Errorf("line = %q (%d)", line, utf8.RuneCountInString(line))
+	}
+}
+
+func TestARunningCheckIsPending(t *testing.T) {
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	if line := Line(delivery.Verdict{State: delivery.VerdictRunning}, cs, p, nil, nil, nil); line != "checking 111111111111 on aaaaaaaaaaaa" {
+		t.Errorf("line = %q", line)
+	}
+}
+
+func TestThePassedCompositionIsSaidOnlyWhenItWasRun(t *testing.T) { // ADR 0484 clause 6
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	v := passVerdict()
+	v.Composition = &delivery.Composition{State: delivery.CompositionPass, SDK: "afbe371003a570f088be4a394d83aa7a9458f7ab"}
+	if r := Report(v, cs, p, nil, nil, nil); !strings.Contains(r, "composition passed with afbe371003a5") {
+		t.Errorf("report = %q", r)
+	}
+	v.Composition = nil
+	if r := Report(v, cs, p, nil, nil, nil); !strings.Contains(r, "composition not yet run") || strings.Contains(r, "composition passed") {
+		t.Errorf("a verdict with no composition: %q", r)
+	}
+}
+
+func TestTheCompositionsTimeAndMachinesAreSaidOnceTheAssignerReportsThem(t *testing.T) { // 1300 (C10), the assigner's verdict (issue 1297)
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	v := passVerdict()
+	v.Took.Composition = 2400
+	v.Composition = &delivery.Composition{State: delivery.CompositionPass, SDK: "afbe371003a570f088be4a394d83aa7a9458f7ab", Machines: []string{"g14", "ace", "novox", "shanks"}}
+	r := Report(v, cs, p, nil, nil, nil)
+	for _, want := range []string{"composition passed in 2.4s with afbe371003a5 on 4 machines: ace, g14, novox, shanks"} {
+		if !strings.Contains(r, want) {
+			t.Errorf("report %q lacks %q", r, want)
+		}
+	}
+	if l := Line(v, cs, p, nil, nil, nil); !strings.Contains(l, "composition passed in 2.4s") || !strings.Contains(l, "on 4 machines") || utf8.RuneCountInString(l) > MaxLine {
+		t.Errorf("line = %q", l)
+	}
+	v.State, v.Failed = delivery.VerdictFail, delivery.FailedFirst{Machine: "novox", Words: "composition refused"}
+	v.Composition = &delivery.Composition{State: delivery.CompositionFail, Words: "novox: two seats claim dns", Machines: []string{"novox"}}
+	if r := Report(v, cs, p, nil, nil, nil); !strings.Contains(r, "composition failed in 2.4s on novox: novox: two seats claim dns") {
+		t.Errorf("failed composition report = %q", r)
+	}
+}
+
+// 1887/D7-go, review round 2 item 5: the line says the unit level's gofmt and go vet time beside its tests'.
+func TestTheLineSaysTheLintTime(t *testing.T) {
+	b := newBench(t)
+	test := b.test
+	b.test = func(c stepCall) (any, error) {
+		r, err := test(c)
+		if res, ok := r.(Tested); ok && res.Level == delivery.LevelUnit {
+			res.Lint = 1.5
+			return res, err
+		}
+		return r, err
+	}
+	out := b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if out.Verdict.Took.Lint != 1500 {
+		t.Fatalf("took = %+v, want the lint's 1.5 s", out.Verdict.Took)
+	}
+	cs := caseOf(t, pullOf(repoA, 7, head1))
+	pc := parts(out.Verdict, cs, cs.Pulls[0], out.Builds, out.Slowest, out.Judged)
+	if !strings.Contains(pc.times, "lint 1.5s") || !strings.Contains(pc.shortTimes, "lint 1.5s") {
+		t.Errorf("times = %q, short %q, want the lint's time in both forms of the line", pc.times, pc.shortTimes)
+	}
+}

modules/mesh-delivery-checker/internal/check/pins.go

@@ -0,0 +1,133 @@
+package check
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"path"
+	"regexp"
+	"strings"
+)
+
+// The pin of mesh-sdk in a Go member's go.mod (novox/hq ADR 0484 clause 9, ADR 0482 clause 2, issue 1624): a delivery group
+// has one verdict, and the mesh-sdk its Go members are built and tested with is the group's: a pin to the head of the group's
+// mesh-sdk pull request, or to a commit already on mesh-sdk's trunk. Any other commit is a stale or a foreign pin, and the
+// group fails naming the member and the commit.
+
+// SDKRepository is the repository of mesh-sdk, and SDKModulePath its Go module.
+const (
+	SDKRepository = "novox/mesh-sdk"
+	SDKModulePath = "git.novox.be/novox/mesh-sdk/go"
+)
+
+// Issue1148 is why a pin that only a head carries fails the check.
+const Issue1148 = "issue 1148"
+
+// ErrNotFound is what Forge.File wraps when the ref holds no such file (the forge answered 404): a file the ref does not hold,
+// told from a forge that could not be read (issue 1845).
+var ErrNotFound = errors.New("the ref holds no such file")
+
+// Forge reads a file of a repository at a ref, and says whether a commit is on a repository's trunk.
+type Forge interface {
+	// File is the text of a file at a ref (a branch, a tag or a commit).
+	File(ctx context.Context, repository, path, ref string) (string, error)
+	// OnTrunk says whether commit (a full or a 12-digit sha) is already merged into the trunk of the repository: it holds no
+	// commit the trunk does not.
+	OnTrunk(ctx context.Context, repository, commit string) (bool, error)
+	// FullSHA is the 40-digit sha of a commit named by its first 12 digits.
+	FullSHA(ctx context.Context, repository, commit string) (string, error)
+}
+
+var pseudoVersion = regexp.MustCompile(`-([0-9a-f]{12})$`)
+
+// SDKPin is the commit (12 hex digits) a go.mod names for mesh-sdk by a pseudo-version, or none for a go.mod that does not
+// require mesh-sdk or requires a version that is no pseudo-version (a tag is a release the SDK itself names).
+func SDKPin(goMod string) (commit string, ok bool) {
+	for _, line := range strings.Split(goMod, "\n") {
+		f := strings.Fields(strings.TrimSpace(strings.TrimPrefix(strings.TrimSpace(line), "require")))
+		if len(f) >= 2 && f[0] == SDKModulePath {
+			if m := pseudoVersion.FindStringSubmatch(f[1]); m != nil {
+				return m[1], true
+			}
+			return "", false
+		}
+	}
+	return "", false
+}
+
+// checkPinsOf refuses a Go member whose go.mod names a mesh-sdk commit that is neither on mesh-sdk's trunk nor the head of the
+// group's mesh-sdk pull request. It reads each go.mod the fetch named from the forge: the one the check builds, which is the
+// head's when the head holds the file and the trunk's when it does not, since a module added on the trunk after the branch was
+// cut is in the merge and not at the head (issue 1845). It answers nil when every pin is the group's.
+func (st *state) checkPinsOf(ctx context.Context, t *target) verdictPtr {
+	if st.j.Forge == nil {
+		return nil
+	}
+	sdk := st.c.member(SDKRepository)
+	if t.module != goModule || t.pull.Repository == SDKRepository {
+		return nil
+	}
+	{
+		for _, dir := range t.fetched.Modules {
+			file := path.Join(dir, "go.mod")
+			st.c.Progress.Set(fmt.Sprintf("read %s of %s#%d", file, t.pull.Repository, t.pull.Number), t.node)
+			text, err := st.j.Forge.File(ctx, t.pull.Repository, file, t.pull.Head)
+			if errors.Is(err, ErrNotFound) && t.pull.Trunk != "" {
+				// Only a file the head does not hold is read at the trunk; any other failure fails the check as it did.
+				text, err = st.j.Forge.File(ctx, t.pull.Repository, file, t.pull.Trunk)
+			}
+			if err != nil {
+				return failed(forgeMachine(err, t.node), fmt.Sprintf("%s#%d: %s cannot be read to check its mesh-sdk pin: %v%s", t.pull.Repository, t.pull.Number, file, err, unheardWords(err)))
+			}
+			pin, ok := SDKPin(text)
+			if !ok {
+				continue
+			}
+			if sdk != nil && strings.HasPrefix(sdk.Head, pin) {
+				continue // the group's own head
+			}
+			onTrunk, err := st.j.Forge.OnTrunk(ctx, SDKRepository, pin)
+			if err != nil {
+				return failed(forgeMachine(err, t.node), fmt.Sprintf("%s#%d: whether mesh-sdk %s is on its trunk cannot be told: %v%s", t.pull.Repository, t.pull.Number, pin, err, unheardWords(err)))
+			}
+			if onTrunk {
+				continue
+			}
+			nor := "the group has no mesh-sdk pull request"
+			if sdk != nil {
+				nor = "the head of the group's mesh-sdk pull request is " + short12(sdk.Head)
+			}
+			return failed(t.node, fmt.Sprintf("%s#%d: %s names mesh-sdk %s, which is neither on mesh-sdk's trunk nor the group's head (%s)", t.pull.Repository, t.pull.Number, file, pin, nor))
+		}
+	}
+	return nil
+}
+
+// failureVerdict is a verdict of failure the check ends with.
+
+// pinHint is added to the failure of a Go member's fetch that names mesh-sdk while the group holds a mesh-sdk pull request:
+// a pin to that pull request's head names a commit only the head carries, which go mod download cannot resolve before the
+// pull request is merged (issue 1148), so such a check fails and never passes.
+func pinHint(c *Case, fetchError string) string {
+	if c.member(SDKRepository) == nil || !strings.Contains(fetchError, "mesh-sdk") {
+		return ""
+	}
+	return " (a pin to the head of the group's mesh-sdk pull request names a commit only that head carries, which go mod download cannot resolve; " + Issue1148 + ")"
+}
+
+// unheardWords ends the words of a failed read of the forge that reached nobody: the forge was not heard (UnheardWords).
+func unheardWords(err error) string {
+	if isUnheard(err) {
+		return " (the forge was " + UnheardWords + ")"
+	}
+	return ""
+}
+
+// forgeMachine is the machine a failed read of the forge is put at: the forge when nobody answered it (no build node is to
+// blame, issue 1820), the build node whose workspace was read otherwise.
+func forgeMachine(err error, node string) string {
+	if isUnheard(err) {
+		return "forge"
+	}
+	return node
+}

modules/mesh-delivery-checker/internal/check/pins_test.go

@@ -0,0 +1,348 @@
+package check
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// fakeForge answers the forge's two reads from files and commits it is given.
+type fakeForge struct {
+	goMods  map[string]string // `<repository> <path> <ref>` -> text
+	onTrunk map[string]bool   // by commit prefix
+	err     error
+	errAt   map[string]error // by ref: a read at that ref fails with it
+}
+
+func (f *fakeForge) File(_ context.Context, repository, path, ref string) (string, error) {
+	if f.err != nil {
+		return "", f.err
+	}
+	if e := f.errAt[ref]; e != nil {
+		return "", e
+	}
+	if s, ok := f.goMods[repository+" "+path+" "+ref]; ok {
+		return s, nil
+	}
+	return "", fmt.Errorf("no file %s of %s at %s: %w", path, repository, ref, ErrNotFound)
+}
+
+func (f *fakeForge) FullSHA(_ context.Context, _ string, commit string) (string, error) {
+	if f.err != nil {
+		return "", f.err
+	}
+	return commit + strings.Repeat("0", 40-len(commit)), nil
+}
+
+func (f *fakeForge) OnTrunk(_ context.Context, _ string, commit string) (bool, error) {
+	if f.err != nil {
+		return false, f.err
+	}
+	return f.onTrunk[commit[:12]], nil
+}
+
+// capturedGoMod is the go.mod the forge answered (testdata/captured/forge-get-file-go-mod.json), pinned to the commit given.
+func capturedGoMod(t *testing.T, pin string) string {
+	t.Helper()
+	raw, err := os.ReadFile(filepath.Join("testdata", "captured", "forge-get-file-go-mod.json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var a struct{ File struct{ Content string } }
+	if err := json.Unmarshal(raw, &a); err != nil {
+		t.Fatal(err)
+	}
+	return strings.Replace(a.File.Content, "cb54756c3865", pin, 1)
+}
+
+func TestTheSDKPinIsTheCommitOfAPseudoVersion(t *testing.T) { // 1624
+	if c, ok := SDKPin(capturedGoMod(t, "cb54756c3865")); !ok || c != "cb54756c3865" {
+		t.Errorf("pin = %q, %v", c, ok)
+	}
+	if _, ok := SDKPin("module x\n\nrequire git.novox.be/novox/mesh-sdk/go v0.2.0\n"); ok {
+		t.Error("a tagged version is no commit")
+	}
+	if c, ok := SDKPin("module x\n\nrequire git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261021100209-cb54756c3865\n"); !ok || c != "cb54756c3865" {
+		t.Errorf("a one-line require: %q, %v", c, ok)
+	}
+	if _, ok := SDKPin("module x\n\ngo 1.26\n"); ok {
+		t.Error("a go.mod that does not require mesh-sdk has a pin")
+	}
+}
+
+// groupBench is a group of mesh-delivery#7 and the SDK's pull request 12, mesh-delivery's go.mod at its head naming pin.
+func groupBench(t *testing.T, pin string, trunk ...string) *bench {
+	b := newBench(t)
+	b.fetch.Modules = []string{"modules/m"}
+	forge := &fakeForge{goMods: map[string]string{repoA + " modules/m/go.mod " + head1: capturedGoMod(t, pin)}, onTrunk: map[string]bool{}}
+	for _, c := range trunk {
+		forge.onTrunk[c] = true
+	}
+	b.ex.Forge = forge
+	return b
+}
+
+func TestAMemberPinnedToTheSDKMembersHeadPassesAndIsBuiltAgainstIt(t *testing.T) { // 1624/AC2, AC4
+	b := groupBench(t, head2[:12])
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2))).Verdict
+	if v.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", v)
+	}
+	var besideSDK bool
+	for _, f := range b.steps.tool("fetch") {
+		if f.args["repository"] == repoA {
+			refs, _ := refsOf(f.args["beside"]), true
+			for _, r := range refs {
+				besideSDK = besideSDK || (r.Repository == repoSDK && r.Commit == head2)
+			}
+		}
+	}
+	if !besideSDK {
+		t.Error("mesh-delivery's tests were not given the SDK member at its head")
+	}
+}
+
+func TestAMemberPinnedToAnOlderHeadOfTheSDKMemberFailsNamingTheMemberAndTheCommit(t *testing.T) { // 1624/AC2, AC4
+	b := groupBench(t, "9aaa5c80ac5c") // a commit of the SDK branch, not its head, not on the trunk
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2))).Verdict
+	f := v.Failed
+	if v.State != delivery.VerdictFail || f.Machine != "shanks" || !strings.Contains(f.Words, repoA+"#7") || !strings.Contains(f.Words, "9aaa5c80ac5c") ||
+		!strings.Contains(f.Words, "neither on mesh-sdk's trunk nor the group's head") || !strings.Contains(f.Words, short12(head2)) {
+		t.Fatalf("verdict = %+v", v)
+	}
+	// Since R4g the levels run in the member's one check ask before its go.mod pins are judged (ADR 0525 §3); the verdict is
+	// still the pin's, whatever the levels said.
+}
+
+func TestAMemberPinnedToACommitOnTheTrunkPasses(t *testing.T) { // 1624/AC2, AC4
+	b := groupBench(t, "cb54756c3865", "cb54756c3865")
+	if v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2))).Verdict; v.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", v)
+	}
+	// A lone pull request of a Go member is held to the trunk alone.
+	b = groupBench(t, "9aaa5c80ac5c")
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "the group has no mesh-sdk pull request") {
+		t.Errorf("a foreign pin with no SDK member: %+v", v)
+	}
+}
+
+func TestAPinOnlyTheSDKHeadCarriesThatDownloadCannotResolveFailsNamingIssue1148(t *testing.T) { // 1624/AC5, ADR 0453 clause 12
+	b := groupBench(t, head2[:12])
+	b.steps.handlers["build_go_fetch"] = func(c stepCall) (any, error) {
+		if c.args["repository"] == repoA {
+			return nil, fmt.Errorf("go mod download: git.novox.be/novox/mesh-sdk/go@v0.1.14-0.20261021100209-%s: invalid version: unknown revision", head2[:12])
+		}
+		return b.fetch, nil
+	}
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2))).Verdict
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "issue 1148") || !strings.Contains(v.Failed.Words, head2[:12]) {
+		t.Errorf("verdict = %+v, want a failure naming issue 1148 and the commit", v)
+	}
+}
+
+func TestAPinThatCannotBeCheckedFailsAndNeverPasses(t *testing.T) { // ADR 0453 clause 12
+	b := groupBench(t, "cb54756c3865")
+	b.ex.Forge.(*fakeForge).err = fmt.Errorf("the forge is down")
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2))).Verdict
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "the forge is down") {
+		t.Errorf("verdict = %+v", v)
+	}
+}
+
+// trunkOnlyBench is a group of mesh-delivery#7 whose fetch holds two Go modules: modules/m, which the head holds, and
+// modules/new, which only the trunk holds (added on the trunk after the branch was cut). The SDK pin of each go.mod is given.
+func trunkOnlyBench(t *testing.T, headPin, trunkPin string) *bench {
+	b := newBench(t)
+	b.fetch.Modules = []string{"modules/m", "modules/new"}
+	forge := &fakeForge{goMods: map[string]string{
+		repoA + " modules/m/go.mod " + head1:    capturedGoMod(t, headPin),
+		repoA + " modules/m/go.mod " + trunkA:   capturedGoMod(t, headPin),
+		repoA + " modules/new/go.mod " + trunkA: capturedGoMod(t, trunkPin),
+	}, onTrunk: map[string]bool{"cb54756c3865": true}}
+	b.ex.Forge = forge
+	return b
+}
+
+func TestAModuleOnlyTheTrunkHoldsIsReadAtTheTrunkAndPasses(t *testing.T) { // 1845/AC1
+	b := trunkOnlyBench(t, "cb54756c3865", "cb54756c3865")
+	if v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict; v.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", v)
+	}
+}
+
+func TestAStalePinOfAModuleOnlyTheTrunkHoldsStillFailsNamingTheFileAndTheCommit(t *testing.T) { // 1845/AC2
+	b := trunkOnlyBench(t, "cb54756c3865", "9aaa5c80ac5c")
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, repoA+"#7") || !strings.Contains(v.Failed.Words, "modules/new/go.mod") || !strings.Contains(v.Failed.Words, "9aaa5c80ac5c") {
+		t.Fatalf("verdict = %+v", v)
+	}
+}
+
+func TestAModuleTheHeadHoldsIsJudgedByTheHeadsPin(t *testing.T) { // 1845/AC3
+	b := trunkOnlyBench(t, "9aaa5c80ac5c", "cb54756c3865") // the head's pin is stale, the trunk's go.mod of the same module is fine
+	b.ex.Forge.(*fakeForge).goMods[repoA+" modules/m/go.mod "+trunkA] = capturedGoMod(t, "cb54756c3865")
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "modules/m/go.mod") || !strings.Contains(v.Failed.Words, "9aaa5c80ac5c") {
+		t.Fatalf("verdict = %+v", v)
+	}
+}
+
+func TestAReadThatFailsForAnotherReasonStillFailsAndIsNotTriedAtTheTrunk(t *testing.T) { // 1845/AC4
+	b := trunkOnlyBench(t, "cb54756c3865", "cb54756c3865")
+	b.ex.Forge.(*fakeForge).errAt = map[string]error{head1: fmt.Errorf("the forge answered 500")}
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "modules/m/go.mod") || !strings.Contains(v.Failed.Words, "the forge answered 500") {
+		t.Fatalf("verdict = %+v", v)
+	}
+}
+
+type runsAt map[string]string
+
+func (r runsAt) CommitOf(module string) string { return r[module] }
+
+func besideOf(t *testing.T, b *bench, repository string) map[string]BesideRef {
+	t.Helper()
+	out := map[string]BesideRef{}
+	for _, f := range b.steps.tool("fetch") {
+		if f.args["repository"] == repository {
+			refs, _ := refsOf(f.args["beside"]), true
+			for _, r := range refs {
+				out[r.Repository] = r
+			}
+		}
+	}
+	return out
+}
+
+func TestTheSiblingsAreWhereTheTestsStateThem(t *testing.T) { // review D2, ADR 0484 clause 4
+	const controller, catalogue, host = "novox/mesh-controller", "novox/mesh-catalog", "novox/mesh-host"
+	hostRuns := strings.Repeat("7", 40)
+	b := newBench(t)
+	b.ex.Trunks = trunksOf(t, map[string]string{controller: trunkA, catalogue: trunkS, host: trunkA2, SDKRepository: "9999999999999999999999999999999999999999"})
+	b.ex.Runs = runsAt{"mesh-host": hostRuns}
+	forge := &fakeForge{goMods: map[string]string{controller + " go.mod " + head1: capturedGoMod(t, "cb54756c3865"),
+		catalogue + " go.mod " + head2: "module git.novox.be/novox/mesh-catalog\n"}, onTrunk: map[string]bool{"cb54756c3865": true}}
+	b.ex.Forge = forge
+	// A group of the controller and the catalogue: the controller's tests read the catalogue's trunk, not the group's head.
+	b.judge(t, caseOf(t, pullOf(controller, 7, head1), pullOf(catalogue, 12, head2)))
+	got := besideOf(t, b, controller)
+	if c := got[catalogue]; c.Commit != trunkS || c.Ref != "" {
+		t.Errorf("the catalogue beside the controller = %+v, want its trunk %s", c, trunkS)
+	}
+	if h := got[host]; h.Commit != hostRuns {
+		t.Errorf("the node-engine beside the controller = %+v, want the commit the mesh runs %s", h, hostRuns)
+	}
+	if s := got[SDKRepository]; s.Commit != "cb54756c3865"+strings.Repeat("0", 28) {
+		t.Errorf("mesh-sdk beside the controller = %+v, want the commit its go.mod pins, whole", s)
+	}
+}
+
+// 1295/R4g: the node-engine's tests read the controller's manifest, so a mesh-host pull request has mesh-controller beside it:
+// at the group member's head when the group holds one, else at its trunk.
+func hostCase(t *testing.T, pulls ...delivery.CandidatePull) *Case {
+	t.Helper()
+	c, err := delivery.DecodeCandidate(candidateOf(t, "feat/x", pulls...))
+	if err != nil {
+		t.Fatal(err)
+	}
+	cs := CaseOf(c, map[string]string{"novox/mesh-host": trunkA, controllerRepo: trunkA2})
+	if cs == nil {
+		t.Fatal("no case")
+	}
+	return cs
+}
+
+func TestTheNodeEnginesTestsHaveTheControllerBesideThem(t *testing.T) {
+	const host = "novox/mesh-host"
+	b := newBench(t)
+	b.ex.Trunks = trunksOf(t, map[string]string{host: trunkA, controllerRepo: trunkA2, catalogueRepository: trunkS, SDKRepository: trunkS})
+	b.judge(t, hostCase(t, pullOf(host, 5, head1)))
+	if c := besideOf(t, b, host)[controllerRepo]; c.Commit != trunkA2 || c.Ref != "" {
+		t.Errorf("the controller beside the node-engine alone = %+v, want its trunk %s", c, trunkA2)
+	}
+	b = newBench(t)
+	b.ex.Trunks = trunksOf(t, map[string]string{host: trunkA, controllerRepo: trunkA2, catalogueRepository: trunkS, SDKRepository: trunkS})
+	b.ex.Forge = &fakeForge{goMods: map[string]string{controllerRepo + " go.mod " + head2: capturedGoMod(t, "cb54756c3865")},
+		onTrunk: map[string]bool{"cb54756c3865": true}}
+	b.judge(t, hostCase(t, pullOf(host, 5, head1), pullOf(controllerRepo, 9, head2)))
+	if c := besideOf(t, b, host)[controllerRepo]; c.Commit != head2 || c.Ref != "refs/pull/9/head" {
+		t.Errorf("the controller beside the node-engine in a group = %+v, want the member's head %s", c, head2)
+	}
+}
+
+func TestThePinOfTheControllerThatCannotBeReadFailsTheCheck(t *testing.T) { // review D2
+	b := newBench(t)
+	b.ex.Trunks = trunksOf(t, map[string]string{"novox/mesh-controller": trunkA})
+	b.ex.Forge = &fakeForge{goMods: map[string]string{}, onTrunk: map[string]bool{}}
+	v := b.judge(t, caseOf(t, pullOf("novox/mesh-controller", 7, head1))).Verdict
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "go.mod") {
+		t.Errorf("verdict = %+v", v)
+	}
+}
+
+func TestAForgeThatIsNotHeardFailsAtTheForgeAndIsJudgedAgainWhenTheNodesChange(t *testing.T) { // 1624 C7
+	b := newBench(t)
+	b.ex.Forge = &fakeForge{err: &Unheard{Err: fmt.Errorf("nats: no responders available for request")}}
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.State != delivery.VerdictFail || v.Failed.Machine != "forge" {
+		t.Fatalf("verdict = %+v, want failed at the forge", v)
+	}
+	if !IsNodesFailure(v) {
+		t.Errorf("a forge that was not heard is not the change's failure: %+v is not judged again when the nodes change", v.Failed)
+	}
+}
+
+// 1887/A12: the change's own repository is placed beside it at the trunk it is merged onto, for every repository, so a
+// shrink-only list test reads the trunk's copy at $MESH_CHECK_BESIDE/<name>.
+func TestTheChangesOwnRepositoryIsBesideItAtItsTrunk(t *testing.T) {
+	b := newBench(t)
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	got := besideOf(t, b, repoA)
+	if own := got[repoA]; own.Commit != trunkA || own.Ref != "" {
+		t.Fatalf("the repository beside its own change = %+v, want its trunk %s", own, trunkA)
+	}
+}
+
+// 1887/A12: a catalogue change's siblings hold the catalogue itself at the trunk it is merged onto, beside mesh-sdk and
+// mesh-controller, so the catalogue's shrink-only list tests read $MESH_CHECK_BESIDE/mesh-catalog.
+func TestACatalogueChangeHasTheCatalogueBesideItAtItsTrunk(t *testing.T) {
+	b := newBench(t)
+	b.ex.Trunks = trunksOf(t, map[string]string{catalogueRepository: trunkA, SDKRepository: trunkS, controllerRepo: trunkA2})
+	b.judge(t, caseOf(t, pullOf(catalogueRepository, 12, head1)))
+	got := besideOf(t, b, catalogueRepository)
+	if c := got[catalogueRepository]; c.Commit != trunkA || c.Ref != "" {
+		t.Fatalf("the catalogue beside its own change = %+v, want its trunk %s", c, trunkA)
+	}
+	if _, ok := got[SDKRepository]; !ok {
+		t.Errorf("mesh-sdk is no longer beside a catalogue change: %v", got)
+	}
+}
+
+// 1887/A12: a mesh-lab head gets a check: with its trunk known it is judged like any repository, its Go fetch finding
+// the nested modules itself.
+func TestAMeshLabHeadGetsACheck(t *testing.T) {
+	const lab = "novox/mesh-lab"
+	raw := candidateOf(t, "fix/x", pullOf(lab, 3, head1))
+	c, err := delivery.DecodeCandidate(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	cs := CaseOf(c, map[string]string{lab: trunkA})
+	if cs == nil || len(cs.Pulls) != 1 || cs.Pulls[0].Repository != lab || len(cs.Left) != 0 {
+		t.Fatalf("the case = %+v, want mesh-lab#3 judged", cs)
+	}
+	b := newBench(t)
+	if v := b.judge(t, cs).Verdict; v.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", v)
+	}
+	if fetched := b.steps.tool("fetch"); len(fetched) == 0 || fetched[0].args["repository"] != lab {
+		t.Fatalf("mesh-lab was not fetched: %+v", fetched)
+	}
+}

modules/mesh-delivery-checker/internal/check/preview.go

@@ -0,0 +1,86 @@
+package check
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"regexp"
+	"slices"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+var digest64 = regexp.MustCompile(`^[0-9a-f]{64}$`)
+
+// PreviewOf is what the fetch steps said of a pull request's head merged onto its trunk head, as the value of a previews
+// key (ADR 0484 clause 3): the merge commit and, for each module directory the fetches named with a manifest, its tree, the
+// digest of its manifest, the hashes of its lock files and its named paths' objects (ADR 0499 clause 2). The fetches of the repository's build modules merge the same
+// trees; the first one's merge commit is kept. A module directory with no tree or no manifest digest is left out, so the
+// indexer gives its module no fingerprint and says why. A head that does not merge has a preview of the files in conflict
+// alone, so the indexer says the candidate's modules have no fingerprint because it does not merge (issue 1445). It
+// answers false when no fetch was made.
+func PreviewOf(p Pull, fetched []Fetched) (delivery.Preview, bool) {
+	var merge string
+	var conflicts []string
+	mods := map[string]delivery.PreviewModule{}
+	for _, f := range fetched {
+		if len(f.Conflicts) > 0 {
+			conflicts = append(conflicts, f.Conflicts...)
+		}
+	}
+	if len(conflicts) > 0 {
+		slices.Sort(conflicts)
+		return delivery.Preview{Repository: p.Repository, Head: p.Head, Trunk: p.Trunk, Conflicts: slices.Compact(conflicts)}, true
+	}
+	for _, f := range fetched {
+		if f.Merge == "" {
+			continue
+		}
+		if merge == "" {
+			merge = f.Merge
+		}
+		for dir, t := range f.Trees {
+			if t.Tree == "" || !digest64.MatchString(t.Manifest) {
+				continue
+			}
+			mods[dir] = delivery.PreviewModule{Tree: t.Tree, Manifest: t.Manifest, Locks: t.Locks, Paths: t.Paths}
+		}
+	}
+	if merge == "" {
+		return delivery.Preview{}, false
+	}
+	pv := delivery.Preview{Repository: p.Repository, Head: p.Head, Trunk: p.Trunk, Merge: merge}
+	if len(mods) > 0 {
+		pv.Modules = mods
+	}
+	return pv, true
+}
+
+// writePreview writes the preview of a pull request by a create: one writer per key, and the same head on the same trunk
+// head merges to the same trees, so a key that exists stands. A head that did not merge has no preview. A failure is said
+// and does not fail the check: the preview is for the indexer's fingerprints, not for the verdict.
+func (j *Examiner) writePreview(ctx context.Context, p Pull, fetched []Fetched) {
+	if j.Previews == nil {
+		return
+	}
+	pv, ok := PreviewOf(p, fetched)
+	if !ok {
+		return
+	}
+	key, err := delivery.PreviewKey(p.Repository, p.Head, p.Trunk)
+	if err == nil {
+		var data []byte
+		if data, err = delivery.EncodePreview(pv); err == nil {
+			_, err = j.Previews.Create(ctx, key, data)
+			if errors.Is(err, ErrConflict) {
+				return
+			}
+			if err == nil && j.Announce != nil {
+				j.Announce(ctx, EventPreviewWritten, key)
+			}
+		}
+	}
+	if err != nil {
+		j.logf("%s#%d: the preview cannot be written: %v", p.Repository, p.Number, fmt.Errorf("%w", err))
+	}
+}