Merge pull request 'buscompose: the controller's bus composer in the SDK, byte-equal to the controller's, with the mesh-grants grant (ADR 0547)' (#85) from fix/1945-memberships into main

Reviewed-on: #85

.gitignore

@@ -1,2 +1,3 @@
 node_modules/
 dist/
+vendor/

go/README.md

@@ -17,3 +17,5 @@ at the same version as the TypeScript package.
 What it holds, under ADR 0039's test: the stdio loop and the tool type, and `cli`, the local protocol
 `mesh-cli` speaks to the node-engine on its machine (novox/hq ADR 0272): the socket's path and one request and one
 answer; and `seal`, the mesh's sealed box (novox/hq ADR 0206: X25519, HKDF-SHA256, AES-256-GCM, `{v, eph, iv, tag, ct}`), byte for byte the box the licence manager made before it lived here and the TypeScript `@novox/mesh-sdk/seal` makes. Nothing else — no bus, no client, nothing of any module's. `go build ./example` and pipe a `tools/list` request into it.
+
+From release 4a of design 47 (novox/hq ADR 0453 clause 3, ADR 0446 clause 4) it also holds the composition of a machine's declaration, over a plain input and with nothing behind it: `declaration` and `validate`, the node-engine's parser and its validator, copied from mesh-host; `catalogue`, the manifests, their resolution and rendering, and `overlay`, the private network's generator, copied from mesh-controller; `compose`, the controller's planFor, renderingFor and declarationWith as functions of an `Input` (the composition never allocates, makes, keeps or writes: what a send would do it names as foreseen or returns); `sdkversion`, which mesh-sdk version a program was built with; and, in `delivery`, the layouts of the keys the builder, the checker and the indexer write (the source fingerprint's new form, the builds, the verdicts and kept verdicts, the manifests by digest). None of them holds a bus, a store or a vault client, which `go list -deps` of `compose` shows.

go/announce/announce.go

@@ -0,0 +1,126 @@
+// Package announce is how a module says on the bus which states it keeps and which of them others may read (novox/hq
+// ADR 0495 clauses 2 and 3; issue 1790): the subject it says it on, the value it says, and where the controller keeps
+// the last one said by each module. What a module announced is the truth of what it keeps; a reader is granted a read
+// from it, never from a list or from the owner's manifest.
+//
+// A module announces from its code (process.Conn.Keeps, stdio.Keeps, the TypeScript SDK's keeps), never from its
+// manifest, which only the core reads (clause 1). A module that keeps no state on the bus announces nothing.
+package announce
+
+import (
+	"encoding/json"
+	"fmt"
+	"regexp"
+	"sort"
+)
+
+// Version is the version of the value this package writes.
+const Version = 1
+
+// Event is the event type of an announcement, under the module's own namespace.
+const Event = "states"
+
+// Subject is where module announces what it keeps: its own event subject, mesh.mod.<module>.event.states, which its
+// account may already publish to and the events stream keeps.
+func Subject(module string) string { return "mesh.mod." + module + ".event." + Event }
+
+// SubjectAll is every module's announcement, what the controller consumes.
+const SubjectAll = "mesh.mod.*.event." + Event
+
+// KeptBucket is the controller's bucket of the last announcement of each module, by Key.
+const KeptBucket = "mesh-controller_states-announced"
+
+var name = regexp.MustCompile(`^[a-z0-9][a-z0-9-]*$`)
+
+// Key is module's key in KeptBucket: the module itself, which must be one plain name, since a module's name is part of
+// its buckets' names (catalogue.StateProblems).
+func Key(module string) (string, error) {
+	if !name.MatchString(module) {
+		return "", fmt.Errorf("announce: %q is not a module that keeps state: lower-case letters, digits and hyphens", module)
+	}
+	return module, nil
+}
+
+// State is one state a module keeps, by its local name, and whether others may read it. Others never write it: a
+// state another module writes is the owner's own code's business.
+type State struct {
+	Name     string `json:"name"`
+	Readable bool   `json:"readable,omitempty"`
+}
+
+// States is an announcement: the module, the machine whose instance said it, and every state the module keeps, sorted
+// by name. An empty list says the module keeps nothing.
+type States struct {
+	V      int     `json:"v"`
+	Module string  `json:"module"`
+	Node   string  `json:"node,omitempty"`
+	States []State `json:"states"`
+}
+
+// Keeps says whether the module announced keeping the state.
+func (s States) Keeps(state string) bool {
+	for _, k := range s.States {
+		if k.Name == state {
+			return true
+		}
+	}
+	return false
+}
+
+// Readable says whether the module announced the state readable by others.
+func (s States) Readable(state string) bool {
+	for _, k := range s.States {
+		if k.Name == state {
+			return k.Readable
+		}
+	}
+	return false
+}
+
+func (s *States) check() error {
+	if s.Module == "" {
+		return fmt.Errorf("announce: an announcement names no module")
+	}
+	if _, err := Key(s.Module); err != nil {
+		return err
+	}
+	seen := map[string]bool{}
+	for _, k := range s.States {
+		if !name.MatchString(k.Name) {
+			return fmt.Errorf("announce: %s announces the state %q, and a state is named locally: lower-case letters, digits and hyphens", s.Module, k.Name)
+		}
+		if seen[k.Name] {
+			return fmt.Errorf("announce: %s announces the state %q twice", s.Module, k.Name)
+		}
+		seen[k.Name] = true
+	}
+	return nil
+}
+
+// Encode is s as JSON at Version, its states sorted; it refuses a module or a state no bucket could be named by and a
+// state announced twice, naming it.
+func Encode(s States) ([]byte, error) {
+	if err := s.check(); err != nil {
+		return nil, err
+	}
+	s.V = Version
+	s.States = append([]State{}, s.States...)
+	sort.Slice(s.States, func(i, j int) bool { return s.States[i].Name < s.States[j].Name })
+	return json.Marshal(s)
+}
+
+// Decode reads an announcement; it refuses another version and what Encode refuses.
+func Decode(data []byte) (States, error) {
+	var s States
+	if err := json.Unmarshal(data, &s); err != nil {
+		return States{}, fmt.Errorf("announce: the announcement is not JSON: %w", err)
+	}
+	if s.V != Version {
+		return States{}, fmt.Errorf("announce: the announcement is version %d, and this reads version %d", s.V, Version)
+	}
+	if err := s.check(); err != nil {
+		return States{}, err
+	}
+	sort.Slice(s.States, func(i, j int) bool { return s.States[i].Name < s.States[j].Name })
+	return s, nil
+}

go/announce/announce_test.go

@@ -0,0 +1,71 @@
+package announce
+
+import (
+	"strings"
+	"testing"
+)
+
+// A module says on the bus which states it keeps and which of them others may read (novox/hq ADR 0495 clause 2), on its
+// own event subject, in a versioned value the controller keeps by module.
+func TestAnAnnouncementRoundTripsSortedAndSaysWhatIsReadable(t *testing.T) {
+	data, err := Encode(States{Module: "mesh-controller", Node: "novox", States: []State{
+		{Name: "plans-building", Readable: true}, {Name: "assignments", Readable: true}, {Name: "own"}}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	back, err := Decode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if back.V != Version || back.Module != "mesh-controller" || back.Node != "novox" {
+		t.Fatalf("decoded %+v", back)
+	}
+	var names []string
+	for _, s := range back.States {
+		names = append(names, s.Name)
+	}
+	if strings.Join(names, ",") != "assignments,own,plans-building" {
+		t.Fatalf("the states are not sorted: %v", names)
+	}
+	if !back.Readable("plans-building") || back.Readable("own") || back.Readable("absent") {
+		t.Fatal("Readable does not say what was announced readable")
+	}
+	if !back.Keeps("own") || back.Keeps("absent") {
+		t.Fatal("Keeps does not say what was announced")
+	}
+	if Subject("mesh-controller") != "mesh.mod.mesh-controller.event.states" || SubjectAll != "mesh.mod.*.event.states" {
+		t.Fatalf("the subjects are %q and %q", Subject("mesh-controller"), SubjectAll)
+	}
+	if KeptBucket != "mesh-controller_states-announced" {
+		t.Fatalf("the kept bucket is %q", KeptBucket)
+	}
+	if k, err := Key("mesh-delivery-builder"); err != nil || k != "mesh-delivery-builder" {
+		t.Fatalf("Key = %q, %v", k, err)
+	}
+	if nothing, err := Encode(States{Module: "quiet"}); err != nil || !strings.Contains(string(nothing), `"states":[]`) {
+		t.Fatalf("a module keeping nothing: %s, %v", nothing, err)
+	}
+}
+
+func TestAnAnnouncementRefusesWhatNoBucketCouldBe(t *testing.T) {
+	for _, c := range []struct {
+		s    States
+		says string
+	}{
+		{States{Module: ""}, "no module"},
+		{States{Module: "a.b"}, `"a.b"`},
+		{States{Module: "a", States: []State{{Name: "x_y"}}}, `"x_y"`},
+		{States{Module: "a", States: []State{{Name: ""}}}, `""`},
+		{States{Module: "a", States: []State{{Name: "x"}, {Name: "x", Readable: true}}}, "twice"},
+	} {
+		if _, err := Encode(c.s); err == nil || !strings.Contains(err.Error(), c.says) {
+			t.Errorf("%+v: %v, wanted a refusal saying %s", c.s, err, c.says)
+		}
+	}
+	if _, err := Decode([]byte(`{"v":2,"module":"a","states":[]}`)); err == nil {
+		t.Error("an unknown version was read")
+	}
+	if _, err := Key("a.b"); err == nil {
+		t.Error("a module with a dot became a key")
+	}
+}

go/announcetest/announcetest.go

@@ -0,0 +1,91 @@
+// Package announcetest is the test each module runs with its own checks to hold that it announces on the bus every
+// state it keeps (novox/hq ADR 0495 clause 5; issue 1790): it starts the module against a bus of the test's own and
+// compares what the module announced with what its code declares. With the bind guard of process.Conn.Keeps,
+// stdio.Keeps and the TypeScript keeps, which refuses a state the code did not announce, announcement and code agree.
+//
+// It replaces the merge gate's check of one module's reads against another's manifest (clause 5); a test using it
+// carries `//go:build integration`, since it starts a bus.
+package announcetest
+
+import (
+	"context"
+	"fmt"
+	"reflect"
+	"sort"
+	"testing"
+	"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/testbus"
+)
+
+// Wait is how long Check waits for the module's announcement once it started it.
+var Wait = 10 * time.Second
+
+// Check starts a bus of the test's own, with a stream taking module's events, calls start with its address (start
+// runs the module, or its part that connects, against it, and answers how to stop it), waits for the module's
+// announcement and fails the test unless it is module's and names exactly want (in any order), readable as want says.
+// It answers the announcement.
+func Check(t testing.TB, module string, want []announce.State, start func(url string) (stop func())) announce.States {
+	t.Helper()
+	url := testbus.URL(t)
+	nc, err := nats.Connect(url)
+	if err != nil {
+		t.Fatalf("announcetest: connecting to the test bus: %v", err)
+	}
+	defer nc.Close()
+	js, err := jetstream.New(nc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), Wait)
+	defer cancel()
+	stream, err := js.CreateStream(ctx, jetstream.StreamConfig{Name: "ANNOUNCETEST", Subjects: []string{"mesh.mod." + module + ".event.>"}})
+	if err != nil {
+		t.Fatalf("announcetest: making the events stream: %v", err)
+	}
+	stop := start(url)
+	if stop != nil {
+		defer stop()
+	}
+	got, err := waitFor(ctx, stream, module)
+	if err != nil {
+		t.Fatalf("announcetest: %v", err)
+	}
+	if problem := differs(got, module, want); problem != "" {
+		t.Fatalf("announcetest: %s", problem)
+	}
+	return got
+}
+
+// waitFor reads the stream until module's announcement is in it.
+func waitFor(ctx context.Context, stream jetstream.Stream, module string) (announce.States, error) {
+	for {
+		msg, err := stream.GetLastMsgForSubject(ctx, announce.Subject(module))
+		if err == nil {
+			return announce.Decode(msg.Data)
+		}
+		select {
+		case <-ctx.Done():
+			return announce.States{}, fmt.Errorf("%s announced nothing on %s within %s", module, announce.Subject(module), Wait)
+		case <-time.After(50 * time.Millisecond):
+		}
+	}
+}
+
+// differs says how got is not module's announcement of want, or "".
+func differs(got announce.States, module string, want []announce.State) string {
+	if got.Module != module {
+		return fmt.Sprintf("the announcement names the module %q, not %q", got.Module, module)
+	}
+	w := append([]announce.State{}, want...)
+	sort.Slice(w, func(i, j int) bool { return w[i].Name < w[j].Name })
+	g := append([]announce.State{}, got.States...)
+	if !reflect.DeepEqual(g, w) && !(len(g) == 0 && len(w) == 0) {
+		return fmt.Sprintf("%s announced %v, and its code declares %v", module, g, w)
+	}
+	return ""
+}

go/announcetest/announcetest_integration_test.go

@@ -0,0 +1,29 @@
+//go:build integration
+
+package announcetest
+
+import (
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/announce"
+	"git.novox.be/novox/mesh-sdk/go/process"
+)
+
+// 1790/S11: a module started against the test bus announces through process.Conn.Keeps, and Check reads that
+// announcement back against what the code declares.
+func TestCheckReadsTheModulesAnnouncementOffARealBus(t *testing.T) {
+	declared := []announce.State{{Name: "accounts", Readable: true}, {Name: "drafts"}}
+	got := Check(t, "mesh-mail", declared, func(url string) func() {
+		conn, err := process.Connect(process.Account{URL: url, Module: "mesh-mail", Node: "novox", User: "u", Password: "p"})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := conn.Keeps(declared...); err != nil {
+			t.Fatal(err)
+		}
+		return conn.Close
+	})
+	if got.Node != "novox" {
+		t.Fatalf("announced from %q", got.Node)
+	}
+}

go/announcetest/announcetest_test.go

@@ -0,0 +1,32 @@
+package announcetest
+
+import (
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/announce"
+)
+
+// The comparison is exact up to order: a state missing, one extra, a readability that differs or another module's
+// announcement each fail, naming what differs.
+func TestAnAnnouncementDiffersFromTheCodeByNameAndReadability(t *testing.T) {
+	got := announce.States{Module: "m", States: []announce.State{{Name: "a", Readable: true}, {Name: "b"}}}
+	if p := differs(got, "m", []announce.State{{Name: "b"}, {Name: "a", Readable: true}}); p != "" {
+		t.Fatalf("an equal announcement differs: %s", p)
+	}
+	for _, want := range [][]announce.State{
+		{{Name: "a", Readable: true}},
+		{{Name: "a", Readable: true}, {Name: "b"}, {Name: "c"}},
+		{{Name: "a"}, {Name: "b"}},
+	} {
+		if p := differs(got, "m", want); p == "" || !strings.Contains(p, "declares") {
+			t.Errorf("want %v: %q", want, p)
+		}
+	}
+	if p := differs(got, "other", nil); !strings.Contains(p, `"other"`) {
+		t.Errorf("another module's announcement: %q", p)
+	}
+	if p := differs(announce.States{Module: "m"}, "m", nil); p != "" {
+		t.Errorf("a module keeping nothing: %q", p)
+	}
+}

go/asks/condition.go

@@ -0,0 +1,149 @@
+package asks
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+// ConditionSubject is where a module says a condition to the operator: a by-caller accept of the operator-channel
+// seat, `mesh.seat.operator-channel.accept.condition.<publisher>` (novox/hq ADR 0437 §9). The router reads the
+// verb at the fifth part and the caller at the sixth, so the publisher is one token, the module's own name; it is
+// refused when empty or when it holds a dot, a wildcard or whitespace.
+func ConditionSubject(publisher string) (string, error) {
+	if publisher == "" {
+		return "", errors.New("asks: the condition's publisher is empty")
+	}
+	if strings.ContainsAny(publisher, ".*> \t\r\n") || strings.ContainsFunc(publisher, func(r rune) bool { return r <= ' ' }) {
+		return "", fmt.Errorf("asks: the condition's publisher %q is not one token: it holds a dot, a wildcard or whitespace", publisher)
+	}
+	return "mesh.seat." + Seat + ".accept.condition." + publisher, nil
+}
+
+// ConditionVersion is the version of the condition value this package writes and the only one it reads.
+const ConditionVersion = 1
+
+// ErrUnknownConditionVersion is what DecodeCondition returns for a value whose version is missing or not
+// ConditionVersion. Test it with errors.Is.
+var ErrUnknownConditionVersion = errors.New("asks: unknown condition version")
+
+// The words a condition's explanation opens with (novox/hq ADR 0253 §1).
+const (
+	NothingToDo = "Nothing for you to do."
+	NeedsYou    = "Needs you: "
+)
+
+// The severities and states of a condition.
+const (
+	SeverityUrgent  = "urgent"
+	SeverityWarning = "warning"
+	StateRaised     = "raised"
+	StateCleared    = "cleared"
+)
+
+// Scope is what a condition is about, under the controller's names.
+type Scope struct {
+	Scope   string `json:"scope"`
+	ID      string `json:"id"`
+	Machine string `json:"machine,omitempty"`
+}
+
+// Action is one answer a notification offers, under the controller's names.
+type Action struct {
+	Label     string            `json:"label"`
+	Verb      string            `json:"verb"`
+	Machine   string            `json:"machine,omitempty"`
+	Arguments map[string]string `json:"arguments,omitempty"`
+	Level     Level             `json:"level,omitempty"`
+}
+
+// Condition is a condition a module says to the operator, under the names of the controller's conditions: its key,
+// severity, subject, state (raised or cleared), summary and the plain words of ADR 0253. A cleared condition needs
+// only its key, subject and state. The router alone chooses the channels.
+type Condition struct {
+	V           int      `json:"v"`
+	Key         string   `json:"key"`
+	Severity    string   `json:"severity,omitempty"`
+	Subject     Scope    `json:"subject"`
+	State       string   `json:"state"`
+	Summary     string   `json:"summary,omitempty"`
+	Headline    string   `json:"headline,omitempty"`
+	Needs       string   `json:"needs,omitempty"`
+	Explanation string   `json:"explanation,omitempty"`
+	Resolved    string   `json:"resolved,omitempty"`
+	Actions     []Action `json:"actions,omitempty"`
+}
+
+func (c Condition) check() error {
+	if c.Key == "" {
+		return errors.New("asks: a condition has no key")
+	}
+	if c.Subject.Scope == "" || c.Subject.ID == "" {
+		return errors.New("asks: a condition's subject needs its scope and id")
+	}
+	switch c.State {
+	case StateCleared:
+		return nil
+	case StateRaised:
+	default:
+		return fmt.Errorf("asks: the condition's state %q is not raised or cleared", c.State)
+	}
+	switch c.Severity {
+	case SeverityUrgent, SeverityWarning:
+	default:
+		return fmt.Errorf("asks: the condition's severity %q is not urgent or warning", c.Severity)
+	}
+	if c.Headline == "" {
+		return errors.New("asks: a raised condition has no headline")
+	}
+	if n := len([]rune(c.Headline)); n > HeadlineLength {
+		return fmt.Errorf("asks: the condition's headline is %d characters, more than %d", n, HeadlineLength)
+	}
+	verdict := NothingToDo
+	if c.Needs != "" {
+		verdict = NeedsYou + c.Needs
+	}
+	if !strings.HasPrefix(c.Explanation, verdict) {
+		return fmt.Errorf("asks: the condition's explanation must open with %q", verdict)
+	}
+	return nil
+}
+
+// EncodeCondition is c as JSON at ConditionVersion; it refuses what ADR 0253 and ADR 0437 §9 refuse.
+func EncodeCondition(c Condition) ([]byte, error) {
+	if err := c.check(); err != nil {
+		return nil, err
+	}
+	c.V = ConditionVersion
+	return json.Marshal(c)
+}
+
+// DecodeCondition reads a condition; it refuses an unknown version (ErrUnknownConditionVersion) and what
+// EncodeCondition refuses.
+func DecodeCondition(data []byte) (Condition, error) {
+	var probe struct {
+		V *int `json:"v"`
+	}
+	if err := json.Unmarshal(data, &probe); err != nil {
+		return Condition{}, fmt.Errorf("asks: the condition is not JSON: %w", err)
+	}
+	if probe.V == nil {
+		return Condition{}, fmt.Errorf("%w: no version in the value, this reader reads %d", ErrUnknownConditionVersion, ConditionVersion)
+	}
+	if *probe.V != ConditionVersion {
+		return Condition{}, fmt.Errorf("%w: the value is version %d, this reader reads %d", ErrUnknownConditionVersion, *probe.V, ConditionVersion)
+	}
+	var c Condition
+	if err := json.Unmarshal(data, &c); err != nil {
+		return Condition{}, fmt.Errorf("asks: the condition does not fit its shape: %w", err)
+	}
+	if err := c.check(); err != nil {
+		return Condition{}, err
+	}
+	return c, nil
+}
+
+// SameCondition says whether two conditions are the same value.
+func SameCondition(a, b Condition) bool { return reflect.DeepEqual(a, b) }

go/asks/condition_test.go

@@ -0,0 +1,143 @@
+package asks
+
+import (
+	"encoding/json"
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestConditionSubject(t *testing.T) { // 1202/AC1
+	s, err := ConditionSubject("mesh-delivery-teller")
+	if err != nil || s != "mesh.seat.operator-channel.accept.condition.mesh-delivery-teller" {
+		t.Fatalf("subject = %q, %v", s, err)
+	}
+	// The router splits an accept subject in six parts and reads the verb at 4 and the caller at 5.
+	parts := strings.Split(s, ".")
+	if len(parts) != 6 || parts[4] != "condition" || parts[5] != "mesh-delivery-teller" {
+		t.Errorf("subject %q does not keep the router's shape: %v", s, parts)
+	}
+	for _, bad := range []string{"", "a.b", "a*", "a>", "a b", "a\tb", "a\nb"} {
+		if _, err := ConditionSubject(bad); err == nil {
+			t.Errorf("publisher %q accepted", bad)
+		}
+	}
+}
+
+func raisedCondition() Condition {
+	return Condition{
+		Key: "delivery.stuck.mesh-mail", Severity: "warning",
+		Subject: Scope{Scope: "module", ID: "mesh-mail", Machine: "ace"}, State: "raised",
+		Summary: "plan 12 stopped", Headline: "Delivery of mesh-mail is stuck",
+		Needs: "approve the merge.", Explanation: "Needs you: approve the merge. The plan waits.",
+		Resolved: "The delivery of mesh-mail moved on.",
+		Actions: []Action{{Label: "Approve", Verb: "mesh-controller.assign", Machine: "ace",
+			Arguments: map[string]string{"why": ""}, Level: Approve}},
+	}
+}
+
+func clearedCondition() Condition {
+	return Condition{Key: "delivery.stuck.mesh-mail", Subject: Scope{Scope: "module", ID: "mesh-mail"}, State: "cleared"}
+}
+
+func TestConditionRoundTrip(t *testing.T) { // 1202/AC2
+	for _, c := range []Condition{raisedCondition(), clearedCondition()} {
+		data, err := EncodeCondition(c)
+		if err != nil {
+			t.Fatalf("%s: %v", c.State, err)
+		}
+		var probe map[string]any
+		if err := json.Unmarshal(data, &probe); err != nil || probe["v"] != float64(1) {
+			t.Fatalf("%s: %s does not carry v:1", c.State, data)
+		}
+		c.V = ConditionVersion
+		got, err := DecodeCondition(data)
+		if err != nil || !SameCondition(got, c) {
+			t.Errorf("%s round trip: %+v %v", c.State, got, err)
+		}
+	}
+	data, _ := EncodeCondition(raisedCondition())
+	var probe map[string]any
+	_ = json.Unmarshal(data, &probe)
+	for _, name := range []string{"key", "severity", "subject", "summary", "headline", "needs", "explanation", "resolved", "actions", "state"} {
+		if _, ok := probe[name]; !ok {
+			t.Errorf("the JSON has no %q: %s", name, data)
+		}
+	}
+	subject := probe["subject"].(map[string]any)
+	for _, name := range []string{"scope", "id", "machine"} {
+		if _, ok := subject[name]; !ok {
+			t.Errorf("the subject has no %q: %s", name, data)
+		}
+	}
+	action := probe["actions"].([]any)[0].(map[string]any)
+	for _, name := range []string{"label", "verb", "machine", "arguments", "level"} {
+		if _, ok := action[name]; !ok {
+			t.Errorf("the action has no %q: %s", name, data)
+		}
+	}
+	for _, in := range []string{`{"key":"k"}`, `{"v":2,"key":"k"}`} {
+		if _, err := DecodeCondition([]byte(in)); !errors.Is(err, ErrUnknownConditionVersion) {
+			t.Errorf("decode of %s = %v, want ErrUnknownConditionVersion", in, err)
+		}
+	}
+}
+
+func TestConditionVerdict(t *testing.T) { // 1202/AC3
+	c := raisedCondition()
+	c.Needs, c.Explanation = "", "The plan waits."
+	_, err := EncodeCondition(c)
+	if err == nil || !strings.Contains(err.Error(), "Nothing for you to do.") {
+		t.Errorf("empty needs without its verdict: %v", err)
+	}
+	c.Explanation = "Nothing for you to do. The plan waits."
+	if _, err := EncodeCondition(c); err != nil {
+		t.Errorf("empty needs with its verdict refused: %v", err)
+	}
+	c = raisedCondition()
+	c.Explanation = "Nothing for you to do. The plan waits."
+	_, err = EncodeCondition(c)
+	if err == nil || !strings.Contains(err.Error(), "Needs you: approve the merge.") {
+		t.Errorf("needs set with the wrong verdict: %v", err)
+	}
+	c.Explanation = "Needs you: something else. The plan waits."
+	if _, err = EncodeCondition(c); err == nil {
+		t.Error("needs set with other needs in the verdict accepted")
+	}
+}
+
+func TestConditionRefused(t *testing.T) { // 1202/AC4
+	mutate := func(f func(*Condition)) error {
+		c := raisedCondition()
+		f(&c)
+		_, err := EncodeCondition(c)
+		return err
+	}
+	for name, f := range map[string]func(*Condition){
+		"severity":      func(c *Condition) { c.Severity = "critical" },
+		"state":         func(c *Condition) { c.State = "open" },
+		"key":           func(c *Condition) { c.Key = "" },
+		"headline":      func(c *Condition) { c.Headline = "" },
+		"long headline": func(c *Condition) { c.Headline = strings.Repeat("h", HeadlineLength+1) },
+	} {
+		if err := mutate(f); err == nil {
+			t.Errorf("a condition with a bad %s accepted", name)
+		}
+	}
+	if err := mutate(func(c *Condition) { c.Headline = strings.Repeat("h", HeadlineLength) }); err != nil {
+		t.Errorf("a headline of the greatest length refused: %v", err)
+	}
+	if _, err := EncodeCondition(clearedCondition()); err != nil {
+		t.Errorf("a cleared condition with only key, subject and state refused: %v", err)
+	}
+	c := clearedCondition()
+	c.Key = ""
+	if _, err := EncodeCondition(c); err == nil {
+		t.Error("a cleared condition without its key accepted")
+	}
+	c = clearedCondition()
+	c.State = "gone"
+	if _, err := EncodeCondition(c); err == nil {
+		t.Error("a condition with an unknown state accepted")
+	}
+}

go/buildstep/askrun.go

@@ -0,0 +1,401 @@
+package buildstep
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"path"
+	"slices"
+	"sort"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// **One ask, one whole job** (novox/hq ADR 0525 §3). A build module runs a pulled ask with its own step tools' bodies,
+// the same ones its request and reply tools run (ADR 0525 §8), in the order the job names: a build ask fetches, then
+// builds or copies each artifact; a check ask fetches, digests the level, takes the kept verdicts and tests the rest,
+// the packages whose tests the change touches first. The answers are the tools' own, whole, so the asker judges them as
+// it judged the tools' answers.
+
+// StepFunc is one step tool's body: its arguments in, its answer out.
+type StepFunc func(ctx context.Context, args map[string]any) (any, error)
+
+// AskSteps are the step tools a build module runs an ask with. Copy is the image module's alone; Digest the Go module's.
+type AskSteps struct {
+	Fetch, Build, Copy, Digest, Test StepFunc
+	// Toolchain is the toolchain the module builds with now; a build ask naming another is refused. Nil checks nothing
+	// (an image or an archive names none).
+	Toolchain func(ctx context.Context) (delivery.ToolchainUsed, error)
+	// Kept looks up a kept verdict by level and digest (the checker's kept bucket, delivery.KeptKey): whether one is
+	// kept and how many tests it counted. Nil takes none.
+	Kept func(ctx context.Context, level, digest string) (tests int, found bool, err error)
+	// Release removes a workspace once the ask's steps on it ended (the module's release tool's body); nil leaves it to
+	// the module's sweep.
+	Release func(workspace string) error
+	Logf    func(format string, args ...any)
+}
+
+// RunAsk runs ask's job with steps and answers a delivery.BuildAnswer or a delivery.CheckAnswer.
+func RunAsk(ctx context.Context, steps AskSteps, ask delivery.StepAsk) (any, error) {
+	if ask.Build != nil {
+		return steps.build(ctx, *ask.Build)
+	}
+	if ask.Check != nil {
+		return steps.check(ctx, *ask.Check)
+	}
+	return nil, Refuse("the ask %s holds no job", ask.ID)
+}
+
+func raw(v any) (json.RawMessage, error) {
+	if r, ok := v.(json.RawMessage); ok {
+		return r, nil
+	}
+	return json.Marshal(v)
+}
+
+// fetched is what an ask reads of a fetch's answer.
+type fetched struct {
+	Workspace string   `json:"workspace"`
+	Merge     string   `json:"merge"`
+	Conflicts []string `json:"conflicts"`
+	Changed   []string `json:"changed"`
+	Modules   []string `json:"modules"`
+}
+
+func (s AskSteps) fetch(ctx context.Context, args map[string]any) (json.RawMessage, fetched, error) {
+	if s.Fetch == nil {
+		return nil, fetched{}, Refuse("this build module fetches nothing")
+	}
+	out, err := s.Fetch(ctx, args)
+	if err != nil {
+		return nil, fetched{}, err
+	}
+	r, err := raw(out)
+	if err != nil {
+		return nil, fetched{}, err
+	}
+	var f fetched
+	if err := json.Unmarshal(r, &f); err != nil || f.Workspace == "" {
+		return r, f, fmt.Errorf("the fetch answered no workspace: %s", r)
+	}
+	return r, f, nil
+}
+
+func (s AskSteps) build(ctx context.Context, job delivery.BuildJob) (any, error) {
+	answer := delivery.BuildAnswer{}
+	if job.Toolchain != nil && s.Toolchain != nil {
+		tc, err := s.Toolchain(ctx)
+		if err != nil {
+			return nil, err
+		}
+		if tc.Version != job.Toolchain.Version || tc.Recipe != job.Toolchain.Recipe {
+			return nil, Refuse("the ask is for %s (recipe %s) and this node builds with %s (recipe %s)",
+				job.Toolchain.Version, job.Toolchain.Recipe, tc.Version, tc.Recipe)
+		}
+		answer.Toolchain = &tc
+	}
+	var f fetched
+	defer func() { s.release(f.Workspace) }()
+	for _, a := range job.Artifacts {
+		if a.From == "" && f.Workspace == "" {
+			r, got, err := s.fetch(ctx, job.Fetch)
+			if err != nil {
+				return nil, err
+			}
+			if _, candidate := job.Fetch["base"]; candidate {
+				// A candidate is built from its head merged onto the trunk; a head that does not merge leaves the tree at the
+				// trunk, and building that would store the trunk's build under the candidate's fingerprint.
+				if len(got.Conflicts) > 0 {
+					return nil, fmt.Errorf("the head does not merge into the trunk: files in conflict: %s", strings.Join(got.Conflicts, ", "))
+				}
+				if got.Merge == "" {
+					return nil, fmt.Errorf("the fetch with a base answered no merge: %s", r)
+				}
+			}
+			f = got
+		}
+		var (
+			out any
+			err error
+		)
+		if a.From != "" {
+			if s.Copy == nil {
+				return nil, Refuse("this build module copies no artifact (%s)", a.Artifact)
+			}
+			out, err = s.Copy(ctx, map[string]any{"module": job.Module, "artifact": a.Artifact, "from": a.From})
+		} else {
+			if s.Build == nil {
+				return nil, Refuse("this build module builds no artifact (%s)", a.Artifact)
+			}
+			args := map[string]any{"workspace": f.Workspace, "module": job.Path, "artifact": a.Artifact}
+			if job.Publish {
+				args["publish"] = true
+			}
+			out, err = s.Build(ctx, args)
+		}
+		if err != nil {
+			return nil, fmt.Errorf("%s: %w", a.Artifact, err)
+		}
+		r, err := raw(out)
+		if err != nil {
+			return nil, err
+		}
+		var built struct {
+			Digest    string `json:"digest"`
+			Reference string `json:"reference"`
+		}
+		if err := json.Unmarshal(r, &built); err != nil || built.Digest == "" {
+			return nil, fmt.Errorf("the build of %s answered no digest: %s", a.Artifact, r)
+		}
+		answer.Artifacts = append(answer.Artifacts, delivery.AskBuilt{Artifact: a.Artifact, Digest: built.Digest, Reference: built.Reference})
+	}
+	return answer, nil
+}
+
+func (s AskSteps) check(ctx context.Context, job delivery.CheckJob) (any, error) {
+	r, f, err := s.fetch(ctx, job.Fetch)
+	if err != nil {
+		return nil, err
+	}
+	defer s.release(f.Workspace)
+	answer := delivery.CheckAnswer{Fetch: r}
+	if len(f.Conflicts) > 0 {
+		return answer, nil // the asker reads the conflict from the fetch's answer: a verdict, not an error
+	}
+	if s.Test == nil {
+		return nil, Refuse("this build module tests nothing")
+	}
+	runner := ""
+	if job.Runner != "" && (job.RunnerWhen == "" || changesUnder(f.Changed, job.RunnerWhen)) {
+		runner = job.Runner
+	}
+	for _, level := range job.Levels {
+		la := delivery.LevelAnswer{Level: level}
+		passed, err := s.level(ctx, job, level, f, runner, &la)
+		answer.Levels = append(answer.Levels, la)
+		if err != nil {
+			return nil, err
+		}
+		if !passed {
+			return answer, nil // the first level that did not pass ends the check (ADR 0484 clause 13)
+		}
+	}
+	return answer, nil
+}
+
+// level runs one level of a check ask and says whether it passed.
+func (s AskSteps) level(ctx context.Context, job delivery.CheckJob, level string, f fetched, runner string, la *delivery.LevelAnswer) (bool, error) {
+	withRunner := func(args map[string]any) map[string]any {
+		if runner != "" {
+			args["runner"] = runner
+		}
+		return args
+	}
+	test := func(args map[string]any) (bool, error) {
+		out, err := s.Test(ctx, args)
+		if err != nil {
+			return false, err
+		}
+		r, err := raw(out)
+		if err != nil {
+			return false, err
+		}
+		la.Tests = append(la.Tests, r)
+		var t struct {
+			Passed bool `json:"passed"`
+		}
+		_ = json.Unmarshal(r, &t)
+		return t.Passed, nil
+	}
+	if s.Digest == nil {
+		// A module with no digest (Node) tests each module directory of the tree, those whose tests changed first.
+		for _, priority := range []bool{true, false} {
+			for _, dir := range f.Modules {
+				if changesTestIn(f.Changed, dir) != priority {
+					continue
+				}
+				passed, err := test(withRunner(map[string]any{"workspace": f.Workspace, "module": dir, "level": level}))
+				if err != nil {
+					return false, fmt.Errorf("the %s level of %s: %w", level, dir, err)
+				}
+				if !passed {
+					return false, nil
+				}
+			}
+		}
+		return true, nil
+	}
+	todo, all, keepRunner := s.plan(ctx, job, level, f, runner, withRunner, la)
+	if !keepRunner {
+		runner = "" // an installed module that ignores the runner judges the level as it judges any other (ADR 0535 §2)
+	}
+	for _, priority := range []bool{true, false} {
+		args := withRunner(map[string]any{"workspace": f.Workspace, "level": level})
+		if job.Run != "" {
+			args["run"] = job.Run
+		}
+		if all {
+			if priority {
+				continue // nothing to put first: the level runs whole after
+			}
+		} else {
+			var run []string
+			for _, p := range todo {
+				if changesTestOf(f.Changed, p) == priority {
+					run = append(run, p)
+				}
+			}
+			if len(run) == 0 {
+				continue
+			}
+			args["packages"] = run
+		}
+		passed, err := test(args)
+		if err != nil {
+			return false, fmt.Errorf("the %s level: %w", level, err)
+		}
+		if !passed {
+			return false, nil
+		}
+	}
+	return true, nil
+}
+
+// release removes an ask's workspace, saying a failure: the module's sweep removes it later.
+func (s AskSteps) release(workspace string) {
+	if workspace == "" || s.Release == nil {
+		return
+	}
+	if err := s.Release(workspace); err != nil && s.Logf != nil {
+		s.Logf("the workspace %s is left to the sweep: %v", workspace, err)
+	}
+}
+
+// plan digests the level and takes the kept verdicts: the packages left to test, or all when the level runs whole, and
+// whether the runner stays. A try of some tests runs whole, digesting nothing (a partial run proves no package). Under the
+// candidate's runner the digest is asked as the candidate: when the candidate answers it, every package runs and nothing
+// is digested for keeping (ADR 0535 §4); when the installed module answers it (it does not take the runner), the level is
+// planned as any other and the runner is dropped. The level runs whole and takes nothing when the digest names no package
+// or does not cover the siblings the fetch placed (ADR 0444, L5).
+func (s AskSteps) plan(ctx context.Context, job delivery.CheckJob, level string, f fetched, runner string, withRunner func(map[string]any) map[string]any, la *delivery.LevelAnswer) ([]string, bool, bool) {
+	if job.Run != "" {
+		return nil, true, true
+	}
+	out, err := s.Digest(ctx, withRunner(map[string]any{"workspace": f.Workspace, "level": level}))
+	if err != nil {
+		if s.Logf != nil {
+			s.Logf("no digest of the %s level, so it runs whole: %v", level, err)
+		}
+		return nil, true, true
+	}
+	r, err := raw(out)
+	if err != nil {
+		return nil, true, true
+	}
+	var d delivery.LevelDigest // packages kept as a sorted list, never keyed by a package path (issue 1930)
+	if err := json.Unmarshal(r, &d); err != nil {
+		return nil, true, true
+	}
+	if runner != "" {
+		if strings.HasPrefix(d.JudgedBy, "candidate ") {
+			la.Judged = d.JudgedBy
+			return nil, true, true // the candidate decides which verdicts would be taken: all run, nothing kept
+		}
+		runner = ""
+	}
+	if len(d.Packages) == 0 || !slices.Equal(d.Beside, besideOf(job.Fetch)) {
+		return nil, true, runner != "" // a digest that names nothing or not the siblings keys no verdict: the level runs whole
+	}
+	la.Digest = &d
+	var todo []string
+	for _, pd := range d.Packages {
+		p := pd.Package
+		if job.Kept && s.Kept != nil {
+			tests, found, err := s.Kept(ctx, level, pd.Digest)
+			if err != nil && s.Logf != nil {
+				s.Logf("the kept verdict of %s at %s cannot be read, so it runs: %v", p, level, err)
+			}
+			if err == nil && found {
+				la.Kept = append(la.Kept, delivery.KeptTaken{Package: p, Digest: pd.Digest, Tests: tests})
+				continue
+			}
+		}
+		todo = append(todo, p)
+	}
+	return todo, false, false
+}
+
+// besideOf are the siblings a fetch's arguments place, as a digest echoes them: `<owner/repo> <commit>`, sorted.
+func besideOf(fetch map[string]any) []string {
+	raw, err := json.Marshal(fetch["beside"])
+	if err != nil {
+		return nil
+	}
+	var refs []struct {
+		Repository string `json:"repository"`
+		Commit     string `json:"commit"`
+	}
+	_ = json.Unmarshal(raw, &refs)
+	var out []string
+	for _, r := range refs {
+		out = append(out, r.Repository+" "+r.Commit)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// changesUnder says whether a path the merge changes is under prefix.
+func changesUnder(changed []string, prefix string) bool {
+	for _, p := range changed {
+		if strings.HasPrefix(p, prefix) {
+			return true
+		}
+	}
+	return false
+}
+
+// isTestFile says whether a repository-relative path is a test file: Go's _test.go, and a TypeScript module's .test.
+// and .spec. files and test directories.
+func isTestFile(p string) bool {
+	switch {
+	case strings.HasSuffix(p, "_test.go"):
+		return true
+	case strings.Contains(p, ".test.") || strings.Contains(p, ".spec."):
+		return true
+	}
+	for _, seg := range strings.Split(path.Dir(p), "/") {
+		if seg == "__tests__" || seg == "test" || seg == "tests" {
+			return true
+		}
+	}
+	return false
+}
+
+// changesTestOf says whether the merge changes a test file of the Go package with the import path pkg: the file's
+// directory and the import path agree on their last segments.
+func changesTestOf(changed []string, pkg string) bool {
+	for _, f := range changed {
+		if !strings.HasSuffix(f, "_test.go") {
+			continue
+		}
+		dir := path.Dir(f)
+		if dir == pkg || strings.HasSuffix(pkg, "/"+dir) || strings.HasSuffix(dir, "/"+pkg) {
+			return true
+		}
+	}
+	return false
+}
+
+// changesTestIn says whether the merge changes a test file inside the directory of a Node module.
+func changesTestIn(changed []string, dir string) bool {
+	for _, f := range changed {
+		if !isTestFile(f) || strings.HasSuffix(f, "_test.go") {
+			continue
+		}
+		if dir == "." || dir == "" || strings.HasPrefix(f, strings.TrimSuffix(dir, "/")+"/") {
+			return true
+		}
+	}
+	return false
+}

go/buildstep/askrun_test.go

@@ -0,0 +1,205 @@
+package buildstep
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strings"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+const runCommit = "0123456789abcdef0123456789abcdef01234567"
+
+// recorder is a build module's step tools that record each call.
+type recorder struct {
+	calls   []string
+	fetch   map[string]any
+	tests   map[string]bool // package or module directory -> passed
+	digests map[string]string
+}
+
+func (r *recorder) steps() AskSteps {
+	call := func(name string, answer func(args map[string]any) any) StepFunc {
+		return func(ctx context.Context, args map[string]any) (any, error) {
+			b, _ := json.Marshal(args)
+			r.calls = append(r.calls, name+" "+string(b))
+			return answer(args), nil
+		}
+	}
+	return AskSteps{
+		Fetch: call("fetch", func(map[string]any) any { return r.fetch }),
+		Build: call("build", func(args map[string]any) any {
+			return map[string]any{"digest": "sha256:" + args["artifact"].(string), "reference": "artifact-store://" + args["artifact"].(string)}
+		}),
+		Copy:   call("copy", func(args map[string]any) any { return map[string]any{"digest": "sha256:copied"} }),
+		Digest: call("digest", func(map[string]any) any { return map[string]any{"level": "unit", "packages": r.digests} }),
+		Test: call("test", func(args map[string]any) any {
+			passed := true
+			if pkgs, ok := args["packages"].([]string); ok {
+				for _, p := range pkgs {
+					passed = passed && r.tests[p]
+				}
+			}
+			if dir, ok := args["module"].(string); ok {
+				passed = r.tests[dir]
+			}
+			return map[string]any{"passed": passed, "tests": 1}
+		}),
+		Kept: func(ctx context.Context, level, digest string) (int, bool, error) { return 7, digest == "d-kept", nil },
+	}
+}
+
+func ask(job any) delivery.StepAsk {
+	a := delivery.StepAsk{ID: NewID(), Kind: delivery.AskCheck, Language: delivery.AskGo, Asker: "t", At: time.Now()}
+	switch j := job.(type) {
+	case delivery.BuildJob:
+		a.Build = &j
+	case delivery.CheckJob:
+		a.Check = &j
+	}
+	return a
+}
+
+// 1887/A3: a build ask fetches once, builds each artifact from the workspace with publish, copies a pinned one without a
+// fetch, and answers each artifact's digest and reference.
+func TestRunAskBuilds(t *testing.T) {
+	r := &recorder{fetch: map[string]any{"workspace": "/w/1"}}
+	steps := r.steps()
+	var released []string
+	steps.Release = func(ws string) error { released = append(released, ws); return nil }
+	out, err := RunAsk(context.Background(), steps, ask(delivery.BuildJob{Module: "m", Path: "modules/m", Publish: true,
+		Fetch:     map[string]any{"repository": "novox/x", "commit": runCommit},
+		Artifacts: []delivery.AskArtifact{{Artifact: "base", From: "registry/b@sha256:00"}, {Artifact: "bundle"}, {Artifact: "lib"}}}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := strings.Join(r.calls, "\n")
+	want := `copy {"artifact":"base","from":"registry/b@sha256:00","module":"m"}
+fetch {"commit":"` + runCommit + `","repository":"novox/x"}
+build {"artifact":"bundle","module":"modules/m","publish":true,"workspace":"/w/1"}
+build {"artifact":"lib","module":"modules/m","publish":true,"workspace":"/w/1"}`
+	if got != want {
+		t.Fatalf("calls:\n%s\nwant:\n%s", got, want)
+	}
+	if len(released) != 1 || released[0] != "/w/1" {
+		t.Errorf("released %v, want the one workspace", released)
+	}
+	a := out.(delivery.BuildAnswer)
+	if len(a.Artifacts) != 3 || a.Artifacts[1].Reference != "artifact-store://bundle" {
+		t.Fatalf("answer %+v", a)
+	}
+}
+
+// A build ask for another toolchain is refused, so its step ends refused and the asker reads why.
+func TestRunAskRefusesAnotherToolchain(t *testing.T) {
+	r := &recorder{fetch: map[string]any{"workspace": "/w"}}
+	s := r.steps()
+	s.Toolchain = func(context.Context) (delivery.ToolchainUsed, error) {
+		return delivery.ToolchainUsed{Version: "go1.27", Recipe: "3"}, nil
+	}
+	_, err := RunAsk(context.Background(), s, ask(delivery.BuildJob{Module: "m", Path: ".", Fetch: map[string]any{"repository": "novox/x", "commit": runCommit},
+		Artifacts: []delivery.AskArtifact{{Artifact: "bundle"}}, Toolchain: &delivery.ToolchainUsed{Version: "go1.26", Recipe: "3"}}))
+	var ref *Refusal
+	if !errors.As(err, &ref) || len(r.calls) != 0 {
+		t.Fatalf("err %v, calls %v", err, r.calls)
+	}
+}
+
+// 1887/A3, A5a, issue 1887 design limit 1: a check ask runs the levels of one check after one fetch: it digests the unit
+// level, takes the kept verdicts, tests the packages whose tests changed first, and stops at the first failure, running
+// no later level.
+func TestRunAskChecksTheLevelsOfOneCheck(t *testing.T) {
+	r := &recorder{
+		fetch:   map[string]any{"workspace": "/w", "changed": []string{"pkg/b/b_test.go"}},
+		digests: map[string]string{"x/pkg/a": "d-a", "x/pkg/b": "d-b", "x/pkg/k": "d-kept"},
+		tests:   map[string]bool{"x/pkg/a": true, "x/pkg/b": false},
+	}
+	out, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit, delivery.LevelIntegration}, Kept: true,
+		Runner: "workspace", RunnerWhen: "modules/mesh-build-go/", Fetch: map[string]any{"repository": "novox/x", "commit": runCommit, "base": runCommit}}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := strings.Join(r.calls, "\n")
+	want := `fetch {"base":"` + runCommit + `","commit":"` + runCommit + `","repository":"novox/x"}
+digest {"level":"unit","workspace":"/w"}
+test {"level":"unit","packages":["x/pkg/b"],"workspace":"/w"}`
+	if got != want {
+		t.Fatalf("calls:\n%s\nwant:\n%s", got, want)
+	}
+	a := out.(delivery.CheckAnswer)
+	if len(a.Levels) != 1 {
+		t.Fatalf("levels %+v, want the unit level alone", a.Levels)
+	}
+	u := a.Levels[0]
+	if u.Level != delivery.LevelUnit || len(u.Kept) != 1 || u.Kept[0].Package != "x/pkg/k" || u.Kept[0].Tests != 7 || len(u.Tests) != 1 || u.Digest == nil {
+		t.Fatalf("the unit level %+v", u)
+	}
+}
+
+// ADR 0535 §2, §4: a merge that changes the build module's own code is judged by the candidate's runner: its digest says
+// the candidate ran, and every package runs with nothing kept; an installed module that ignores the runner is planned as
+// any other, the runner dropped. A digest that does not cover the fetch's siblings runs the level whole too.
+func TestRunAskRunsWholeUnderTheRunnerOrWithoutTheSiblings(t *testing.T) {
+	for _, tc := range []struct{ judged, want string }{
+		{"candidate 999", `digest {"level":"unit","runner":"workspace","workspace":"/w"}
+test {"level":"unit","runner":"workspace","workspace":"/w"}`},
+		{"installed", `digest {"level":"unit","runner":"workspace","workspace":"/w"}`},
+	} {
+		r := &recorder{fetch: map[string]any{"workspace": "/w", "changed": []string{"modules/mesh-build-go/x.go"}},
+			digests: map[string]string{"x/pkg/a": "d-kept"}, tests: map[string]bool{}}
+		steps := r.steps()
+		digest := steps.Digest
+		steps.Digest = func(ctx context.Context, args map[string]any) (any, error) {
+			_, _ = digest(ctx, args)
+			return map[string]any{"level": "unit", "packages": r.digests, "judged_by": tc.judged}, nil
+		}
+		out, err := RunAsk(context.Background(), steps, ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit}, Kept: true,
+			Runner: "workspace", RunnerWhen: "modules/mesh-build-go/", Fetch: map[string]any{"repository": "novox/x", "commit": runCommit}}))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got := strings.Join(r.calls[1:], "\n"); got != tc.want {
+			t.Errorf("judged by %s: calls\n%s\nwant\n%s", tc.judged, got, tc.want)
+		}
+		l := out.(delivery.CheckAnswer).Levels[0]
+		if tc.judged == "installed" && (len(l.Kept) != 1 || l.Judged != "") {
+			t.Errorf("an installed module's level %+v, want the kept verdict taken", l)
+		}
+		if tc.judged != "installed" && (len(l.Kept) != 0 || l.Digest != nil || l.Judged != tc.judged) {
+			t.Errorf("the candidate's level %+v, want nothing kept and the program named", l)
+		}
+	}
+	r := &recorder{fetch: map[string]any{"workspace": "/w"}, digests: map[string]string{"x/pkg/a": "d-kept"}, tests: map[string]bool{}}
+	out, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit}, Kept: true,
+		Fetch: map[string]any{"repository": "novox/x", "commit": runCommit, "beside": []any{map[string]any{"repository": "novox/mesh-sdk", "commit": runCommit}}}}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if l := out.(delivery.CheckAnswer).Levels[0]; len(l.Kept) != 0 || l.Digest != nil {
+		t.Fatalf("a digest without the siblings kept %+v", l)
+	}
+}
+
+// A Node check tests each module directory, the one whose tests changed first; a conflict ends the ask with the fetch
+// alone, a verdict for the asker.
+func TestRunAskChecksNodeModulesAndConflicts(t *testing.T) {
+	r := &recorder{fetch: map[string]any{"workspace": "/w", "modules": []string{"a", "b"}, "changed": []string{"b/test/x.test.ts"}},
+		tests: map[string]bool{"a": true, "b": true}}
+	s := r.steps()
+	s.Digest = nil
+	if _, err := RunAsk(context.Background(), s, ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit}, Fetch: map[string]any{"repository": "novox/x", "commit": runCommit}})); err != nil {
+		t.Fatal(err)
+	}
+	if fmt.Sprint(r.calls[1:]) != `[test {"level":"unit","module":"b","workspace":"/w"} test {"level":"unit","module":"a","workspace":"/w"}]` {
+		t.Fatalf("calls %v", r.calls)
+	}
+	r = &recorder{fetch: map[string]any{"workspace": "/w", "conflicts": []string{"go.mod"}}}
+	out, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit}, Fetch: map[string]any{"repository": "novox/x", "commit": runCommit}}))
+	if err != nil || len(r.calls) != 1 || len(out.(delivery.CheckAnswer).Levels) != 0 {
+		t.Fatalf("a conflict: %v %v", err, r.calls)
+	}
+}

go/buildstep/blob.go

@@ -0,0 +1,170 @@
+package buildstep
+
+import (
+	"bytes"
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"syscall"
+	"time"
+)
+
+// RegistryWait is how long a push waits for an artifact store that refuses connections, longer than its nightly
+// collection holds it still (about a minute and a half, issue 457); RegistryFirstPause is the first pause, doubling
+// to RegistryMostPause. Variables so a test shortens them.
+var (
+	RegistryWait       = 5 * time.Minute
+	RegistryFirstPause = time.Second
+	RegistryMostPause  = 10 * time.Second
+)
+
+// BlobReference is where a pushed bundle or archive is, as a done key names it and the controller delivers from
+// (novox/hq ADR 0498 clause 1): artifact-store://<module>/<artifact>/blobs/<digest>, the store's address left out
+// (issue 102).
+func BlobReference(module, artifact, digest string) string {
+	return "artifact-store://" + module + "/" + artifact + "/blobs/" + digest
+}
+
+// PushBlob puts body into the artifact store at registry (host:port) as a blob of repository (<module>/<artifact>) by
+// its digest (`sha256:` and hex), from the build module's own process, after the build step ended (novox/hq ADR 0498
+// clauses 1 and 2): a blob the store already holds is done without an upload; otherwise it is uploaded (POST
+// blobs/uploads/, then PUT with the digest). A store refusing connections is waited out up to RegistryWait; any other
+// refusal fails, naming the store's status and its own words, for the caller's `not stored:` error. Bytes that are not
+// their digest are refused before anything is sent.
+func PushBlob(ctx context.Context, client *http.Client, registry, repository, digest string, body []byte) error {
+	sum := sha256.Sum256(body)
+	if got := "sha256:" + hex.EncodeToString(sum[:]); got != digest {
+		return fmt.Errorf("the blob is %s, not the digest %s it was to be pushed as", got, digest)
+	}
+	if client == nil {
+		client = http.DefaultClient
+	}
+	base := "http://" + registry + "/v2/" + repository + "/blobs/"
+	var present bool
+	if err := waitForStore(ctx, registry, func() error {
+		var err error
+		present, err = blobPresent(ctx, client, base+digest)
+		return err
+	}); err != nil {
+		return err
+	}
+	if present {
+		return nil
+	}
+	var location string
+	if err := waitForStore(ctx, registry, func() error {
+		var err error
+		location, err = startUpload(ctx, client, base+"uploads/")
+		return err
+	}); err != nil {
+		return err
+	}
+	target, err := url.Parse(base)
+	if err != nil {
+		return err
+	}
+	loc, err := target.Parse(location)
+	if err != nil {
+		return fmt.Errorf("the store answered the upload's location %q, which is not a URL: %w", location, err)
+	}
+	q := loc.Query()
+	q.Set("digest", digest)
+	loc.RawQuery = q.Encode()
+	req, err := http.NewRequestWithContext(ctx, http.MethodPut, loc.String(), bytes.NewReader(body))
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Content-Type", "application/octet-stream")
+	resp, err := client.Do(req)
+	if err != nil {
+		return fmt.Errorf("putting %s of %s: %w", digest, repository, err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusCreated {
+		return storeSaid(resp, "putting "+digest+" of "+repository)
+	}
+	return nil
+}
+
+func blobPresent(ctx context.Context, client *http.Client, at string) (bool, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodHead, at, nil)
+	if err != nil {
+		return false, err
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return false, err
+	}
+	resp.Body.Close()
+	switch resp.StatusCode {
+	case http.StatusOK:
+		return true, nil
+	case http.StatusNotFound:
+		return false, nil
+	}
+	return false, fmt.Errorf("asking the store for %s: it answered %s", at, resp.Status)
+}
+
+func startUpload(ctx context.Context, client *http.Client, at string) (string, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, at, nil)
+	if err != nil {
+		return "", err
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusAccepted {
+		return "", storeSaid(resp, "starting an upload at "+at)
+	}
+	location := resp.Header.Get("Location")
+	if location == "" {
+		return "", fmt.Errorf("starting an upload at %s: the store named no location", at)
+	}
+	return location, nil
+}
+
+// storeSaid is the store's refusal: its status and the first of its own words.
+func storeSaid(resp *http.Response, what string) error {
+	words, _ := io.ReadAll(io.LimitReader(resp.Body, 2048))
+	return fmt.Errorf("%s: the store answered %s: %s", what, resp.Status, strings.TrimSpace(string(words)))
+}
+
+// refused is whether an error is a connection refused.
+func refused(err error) bool {
+	return err != nil && (errors.Is(err, syscall.ECONNREFUSED) || strings.Contains(err.Error(), "connection refused"))
+}
+
+// waitForStore runs try, and while it fails because the store refuses connections, tries again with a growing pause
+// until RegistryWait has passed. A refusal is the one error waited for: nothing was sent, so trying again does nothing
+// twice.
+func waitForStore(ctx context.Context, registry string, try func() error) error {
+	err := try()
+	if !refused(err) {
+		return err
+	}
+	started, pause := time.Now(), RegistryFirstPause
+	for {
+		left := RegistryWait - time.Since(started)
+		if left <= 0 {
+			return fmt.Errorf("the artifact store at %s refused every connection for %s, longer than its nightly collection holds it still, so it is down, not paused: %w",
+				registry, time.Since(started).Round(time.Millisecond), err)
+		}
+		select {
+		case <-ctx.Done():
+			return fmt.Errorf("stopped while waiting for the artifact store at %s: %w (last: %v)", registry, ctx.Err(), err)
+		case <-time.After(min(pause, left)):
+		}
+		pause = min(pause*2, RegistryMostPause)
+		if err = try(); !refused(err) {
+			return err
+		}
+	}
+}

go/buildstep/blob_test.go

@@ -0,0 +1,151 @@
+package buildstep
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+func digestOfBytes(b []byte) string {
+	h := sha256.Sum256(b)
+	return "sha256:" + hex.EncodeToString(h[:])
+}
+
+// registry is an artifact store as far as a blob push needs one: HEAD a blob, start an upload, PUT it with its digest.
+type registry struct {
+	mu    sync.Mutex
+	blobs map[string][]byte
+	calls []string
+	put   int // the status a PUT answers, 201 when 0
+}
+
+func (r *registry) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.calls = append(r.calls, req.Method+" "+req.URL.Path)
+	switch {
+	case req.Method == http.MethodHead && strings.Contains(req.URL.Path, "/blobs/sha256:"):
+		if _, ok := r.blobs[req.URL.Path[strings.LastIndex(req.URL.Path, "/")+1:]]; ok {
+			w.WriteHeader(http.StatusOK)
+			return
+		}
+		w.WriteHeader(http.StatusNotFound)
+	case req.Method == http.MethodPost && strings.HasSuffix(req.URL.Path, "/blobs/uploads/"):
+		w.Header().Set("Location", strings.TrimSuffix(req.URL.Path, "/")+"/u1?state=x")
+		w.WriteHeader(http.StatusAccepted)
+	case req.Method == http.MethodPut && strings.Contains(req.URL.Path, "/blobs/uploads/u1"):
+		if r.put != 0 {
+			w.WriteHeader(r.put)
+			_, _ = io.WriteString(w, `{"errors":[{"code":"DIGEST_INVALID","message":"provided digest did not match uploaded content"}]}`)
+			return
+		}
+		body, _ := io.ReadAll(req.Body)
+		d := req.URL.Query().Get("digest")
+		if req.URL.Query().Get("state") != "x" || d != digestOfBytes(body) {
+			w.WriteHeader(http.StatusBadRequest)
+			return
+		}
+		r.blobs[d] = body
+		w.WriteHeader(http.StatusCreated)
+	default:
+		w.WriteHeader(http.StatusMethodNotAllowed)
+	}
+}
+
+// A done build's bundle or archive is pushed to the artifact store by its build module (novox/hq ADR 0498 clauses 1
+// and 2): a blob the store already holds is done with no upload; one it lacks is uploaded by digest; its reference is
+// the artifact-store form the builder's key and the controller check.
+func TestABlobIsPushedOnceByItsDigest(t *testing.T) {
+	reg := &registry{blobs: map[string][]byte{}}
+	srv := httptest.NewServer(reg)
+	defer srv.Close()
+	addr := strings.TrimPrefix(srv.URL, "http://")
+	body := []byte("the packed bundle")
+	d := digestOfBytes(body)
+	if err := PushBlob(context.Background(), srv.Client(), addr, "mail/code", d, body); err != nil {
+		t.Fatal(err)
+	}
+	if string(reg.blobs[d]) != string(body) {
+		t.Fatalf("the store holds %q", reg.blobs[d])
+	}
+	reg.calls = nil
+	if err := PushBlob(context.Background(), srv.Client(), addr, "mail/code", d, body); err != nil {
+		t.Fatal(err)
+	}
+	if len(reg.calls) != 1 || !strings.HasPrefix(reg.calls[0], "HEAD ") {
+		t.Fatalf("a blob the store holds was uploaded again: %v", reg.calls)
+	}
+	ref := BlobReference("mail", "code", d)
+	if ref != "artifact-store://mail/code/blobs/"+d {
+		t.Fatalf("BlobReference = %q", ref)
+	}
+	b := delivery.BuilderBuild{State: delivery.BuildDone, Manifest: strings.Repeat("4", 64),
+		Artifacts: []delivery.BuiltArtifact{{Name: "code", Kind: "bundle", Digest: d, Reference: ref}}}
+	if _, err := delivery.EncodeBuilderBuild(b); err != nil {
+		t.Fatalf("the key refuses the reference BlobReference gives: %v", err)
+	}
+}
+
+// A store that refuses the upload fails the push naming the store's own words; bytes that are not the digest are
+// refused before anything is sent.
+func TestAPushTheStoreRefusesSaysTheStoresWords(t *testing.T) {
+	reg := &registry{blobs: map[string][]byte{}, put: http.StatusBadRequest}
+	srv := httptest.NewServer(reg)
+	defer srv.Close()
+	addr := strings.TrimPrefix(srv.URL, "http://")
+	body := []byte("x")
+	err := PushBlob(context.Background(), srv.Client(), addr, "mail/code", digestOfBytes(body), body)
+	if err == nil || !strings.Contains(err.Error(), "provided digest did not match") || !strings.Contains(err.Error(), "400") {
+		t.Fatalf("a refused upload said %v", err)
+	}
+	reg.calls = nil
+	err = PushBlob(context.Background(), srv.Client(), addr, "mail/code", digestOfBytes([]byte("other")), body)
+	if err == nil || len(reg.calls) != 0 {
+		t.Fatalf("bytes that are not their digest: %v, calls %v", err, reg.calls)
+	}
+}
+
+// A store refusing connections (its nightly collection holds it still) is waited out, up to RegistryWait (issue 457).
+func TestAPushWaitsOutAStoreRefusingConnections(t *testing.T) {
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	addr := l.Addr().String()
+	l.Close() // refusing now
+	reg := &registry{blobs: map[string][]byte{}}
+	go func() {
+		time.Sleep(300 * time.Millisecond)
+		l2, err := net.Listen("tcp", addr)
+		if err != nil {
+			return
+		}
+		_ = http.Serve(l2, reg)
+	}()
+	beforeWait, beforePause := RegistryWait, RegistryFirstPause
+	RegistryWait, RegistryFirstPause = 3*time.Second, 100*time.Millisecond
+	defer func() { RegistryWait, RegistryFirstPause = beforeWait, beforePause }()
+	body := []byte("late")
+	if err := PushBlob(context.Background(), http.DefaultClient, addr, "mail/code", digestOfBytes(body), body); err != nil {
+		t.Fatalf("a store that came back was not waited for: %v", err)
+	}
+
+	l3, _ := net.Listen("tcp", "127.0.0.1:0")
+	gone := l3.Addr().String()
+	l3.Close()
+	RegistryWait = 300 * time.Millisecond
+	err = PushBlob(context.Background(), http.DefaultClient, gone, "mail/code", digestOfBytes(body), body)
+	if err == nil || !strings.Contains(err.Error(), "refused every connection") {
+		t.Fatalf("a store that stayed down said %v", err)
+	}
+}

go/buildstep/capacity.go

@@ -0,0 +1,61 @@
+package buildstep
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
+)
+
+// CapacitySetting is the build modules' setting of each node's build capacity (novox/hq ADR 0525 §5): `<node>=<asks at
+// once>` pairs separated by commas, as the builder's was (ADR 0485 §1). Each build module declares it with
+// DefaultCapacities as its default, and the controller lays it into the module's settings file.
+const CapacitySetting = "capacity"
+
+// DefaultCapacities is the setting's default, the builder's before R4g: the control-node (novox) and the laptop (g14)
+// build nothing.
+const DefaultCapacities = "shanks=3,ace=2,g14=0,novox=0"
+
+// NodeCapacity is node's build capacity, read from the module's settings file at path at every call, so a change takes
+// effect at the next pull; with no path it reads fallback. A node the setting does not name runs one ask at a time (as
+// the builder's did). A file or a setting that cannot be read gives 0 and says why: pulling on a setting nobody can read
+// could build on a node that must not.
+func NodeCapacity(path, fallback, node string, logf func(string, ...any)) func() int {
+	say := func(format string, args ...any) {
+		if logf != nil {
+			logf(format, args...)
+		}
+	}
+	return func() int {
+		setting := fallback
+		if path != "" {
+			raw, err := os.ReadFile(path)
+			if err != nil {
+				say("the build capacity cannot be read, so %s pulls nothing: %v", node, err)
+				return 0
+			}
+			var s map[string]any
+			if err := json.Unmarshal(raw, &s); err != nil {
+				say("the settings file %s is not JSON, so %s pulls nothing: %v", path, node, err)
+				return 0
+			}
+			setting, _ = s[CapacitySetting].(string)
+		}
+		n, err := capacityOf(setting, node)
+		if err != nil {
+			say("%v, so %s pulls nothing", err, node)
+			return 0
+		}
+		return n
+	}
+}
+
+// capacityOf is node's capacity in a setting's `<node>=<asks>` pairs: DefaultCapacity for a node it does not name.
+func capacityOf(setting, node string) (int, error) {
+	caps, err := buildrun.ParseCapacity(setting)
+	if err != nil {
+		return 0, fmt.Errorf("the build capacity: %w", err)
+	}
+	return (&buildrun.Places{Capacity: caps}).CapacityOf(node), nil
+}

go/buildstep/capacity_test.go

@@ -0,0 +1,38 @@
+package buildstep
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// 1887/A7: the node's build capacity is the build module's setting, read at every pull: the control-node at 0 pulls
+// nothing, a change takes effect at the next read, and a setting that cannot be read pulls nothing.
+func TestNodeCapacity(t *testing.T) {
+	if got := NodeCapacity("", DefaultCapacities, "novox", nil)(); got != 0 {
+		t.Errorf("novox = %d by default, want 0", got)
+	}
+	if got := NodeCapacity("", DefaultCapacities, "shanks", nil)(); got != 3 {
+		t.Errorf("shanks = %d by default, want 3", got)
+	}
+	file := filepath.Join(t.TempDir(), "settings.json")
+	os.WriteFile(file, []byte(`{"capacity":"shanks=1,ace=2"}`), 0o600)
+	capacity := NodeCapacity(file, DefaultCapacities, "shanks", nil)
+	if got := capacity(); got != 1 {
+		t.Errorf("shanks = %d from the file, want 1", got)
+	}
+	os.WriteFile(file, []byte(`{"capacity":"shanks=4"}`), 0o600)
+	if got := capacity(); got != 4 {
+		t.Errorf("shanks = %d after the change, want 4", got)
+	}
+	if got := NodeCapacity(file, "", "pi", nil)(); got != 1 {
+		t.Errorf("a node not named = %d, want 1", got)
+	}
+	os.WriteFile(file, []byte(`{"capacity":"shanks=lots"}`), 0o600)
+	if got := capacity(); got != 0 {
+		t.Errorf("an unreadable setting = %d, want 0", got)
+	}
+	if got := NodeCapacity(filepath.Join(t.TempDir(), "none"), DefaultCapacities, "shanks", nil)(); got != 0 {
+		t.Errorf("a missing file = %d, want 0", got)
+	}
+}

go/buildstep/digestshape_test.go

@@ -0,0 +1,234 @@
+package buildstep
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"sort"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// credentialField is the node runtime's rule for a state value (mesh-tools node-tools/internal/bus/state.go, novox/hq
+// ADR 0201), copied whole: the first field anywhere in the value whose name, lower-cased and without - _ and spaces, ends
+// in a credential word, or "". A step's end is refused when it answers a field.
+func credentialField(value json.RawMessage) string {
+	endings := []string{"password", "passwd", "secret", "token", "credential", "credentials",
+		"authorization", "apikey", "privatekey", "accesskey", "cookie"}
+	var v any
+	if json.Unmarshal(value, &v) != nil {
+		return ""
+	}
+	var walk func(any) string
+	walk = func(v any) string {
+		switch t := v.(type) {
+		case map[string]any:
+			keys := make([]string, 0, len(t))
+			for k := range t {
+				keys = append(keys, k)
+			}
+			sort.Strings(keys)
+			for _, k := range keys {
+				norm := strings.NewReplacer("-", "", "_", "", " ", "").Replace(strings.ToLower(k))
+				for _, end := range endings {
+					if strings.HasSuffix(norm, end) {
+						return k
+					}
+				}
+				if found := walk(t[k]); found != "" {
+					return found
+				}
+			}
+		case []any:
+			for _, x := range t {
+				if found := walk(x); found != "" {
+					return found
+				}
+			}
+		}
+		return ""
+	}
+	return walk(v)
+}
+
+// runtimeState is a steps state that refuses a value as the node runtime does, and keeps every value it took.
+type runtimeState struct {
+	mu      sync.Mutex
+	took    map[string][]delivery.Step
+	refused int
+}
+
+func newRuntimeState() *runtimeState { return &runtimeState{took: map[string][]delivery.Step{}} }
+
+func (s *runtimeState) put(key string, value any) (uint64, error) {
+	raw, _ := value.(json.RawMessage)
+	if f := credentialField(raw); f != "" {
+		s.mu.Lock()
+		s.refused++
+		s.mu.Unlock()
+		return 0, fmt.Errorf("steps.%s carries a field %q, which names a credential", key, f)
+	}
+	st, err := delivery.DecodeStep(raw)
+	if err != nil {
+		return 0, err
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.took[key] = append(s.took[key], st)
+	return uint64(len(s.took[key])), nil
+}
+
+func (s *runtimeState) last(key string) (delivery.Step, bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	t := s.took[key]
+	if len(t) == 0 {
+		return delivery.Step{}, false
+	}
+	return t[len(t)-1], true
+}
+
+func fastEnds(t *testing.T) {
+	attempts, retry := EndAttempts, EndRetry
+	EndAttempts, EndRetry = 2, time.Millisecond
+	t.Cleanup(func() { EndAttempts, EndRetry = attempts, retry })
+}
+
+// 1930/AC1: given a check of a repository with the package .../internal/token, when its ask's answer is stored as the
+// step's end, then no field is keyed by a package path: the runtime's credential rule takes the value, and the package
+// and its digest read back from the stored end.
+func TestADigestOfAPackageNamedTokenIsStoredAsAList(t *testing.T) {
+	fastEnds(t)
+	r := &recorder{
+		fetch:   map[string]any{"workspace": "/w"},
+		digests: map[string]string{"x/internal/token": "d-token", "x/pkg/a": "d-a"},
+		tests:   map[string]bool{"x/internal/token": true, "x/pkg/a": true},
+	}
+	out, err := RunAsk(context.Background(), r.steps(), ask(delivery.CheckJob{Levels: []string{delivery.LevelUnit},
+		Fetch: map[string]any{"repository": "novox/x", "commit": runCommit}}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	old, _ := json.Marshal(map[string]any{"levels": []any{map[string]any{"level": "unit", "digest": map[string]any{"packages": r.digests}}}})
+	if credentialField(old) != "x/internal/token" {
+		t.Fatalf("the rule does not refuse the form before issue 1930 (%s): the test proves nothing", old)
+	}
+	st := newRuntimeState()
+	if err := finish(st.put, "shanks.a1", delivery.Step{ID: "a1", Tool: "check ask", Node: "shanks", State: delivery.StepRunning, Started: time.Now()}, out, nil, t.Logf); err != nil {
+		t.Fatal(err)
+	}
+	s, ok := st.last("shanks.a1")
+	if !ok || s.State != delivery.StepPassed || st.refused != 0 {
+		t.Fatalf("the end %+v (written %v, refused %d), want it passed and taken at once", s, ok, st.refused)
+	}
+	var a delivery.CheckAnswer
+	if err := json.Unmarshal(s.Result, &a); err != nil {
+		t.Fatal(err)
+	}
+	if len(a.Levels) != 1 || a.Levels[0].Digest == nil {
+		t.Fatalf("levels %+v, want the unit level with its digest", a.Levels)
+	}
+	want := []delivery.PackageDigest{{Package: "x/internal/token", Digest: "d-token"}, {Package: "x/pkg/a", Digest: "d-a"}}
+	if got := a.Levels[0].Digest.Packages; fmt.Sprint(got) != fmt.Sprint(want) {
+		t.Errorf("packages %v, want %v", got, want)
+	}
+	if !strings.Contains(string(s.Result), `"package":"x/internal/token"`) {
+		t.Errorf("the stored end does not name the package as a value: %s", s.Result)
+	}
+}
+
+// 1930/AC2: given an end the state refuses every time, when finish writes it, then it logs the refusal and writes a small
+// failed end without the result that names the write's error; and when no end can be written at all it answers an error.
+func TestARefusedEndIsSaidAndEndsTheStepFailed(t *testing.T) {
+	fastEnds(t)
+	big := errors.New("the value carries a field \"x/internal/token\", which names a credential")
+	var refused int
+	var stored []delivery.Step
+	put := func(key string, value any) (uint64, error) {
+		st, _ := delivery.DecodeStep(value.(json.RawMessage))
+		if len(st.Result) > 0 {
+			refused++
+			return 0, big
+		}
+		stored = append(stored, st)
+		return 1, nil
+	}
+	var logged []string
+	logf := func(format string, args ...any) { logged = append(logged, fmt.Sprintf(format, args...)) }
+	err := finish(put, "shanks.a2", delivery.Step{ID: "a2", Tool: "check ask", Node: "shanks", State: delivery.StepRunning, Started: time.Now()}, map[string]any{"levels": 1}, nil, logf)
+	if err != nil {
+		t.Fatalf("finish answered %v, want the small end written", err)
+	}
+	if refused != EndAttempts || len(stored) != 1 {
+		t.Fatalf("refused %d, stored %d, want %d refusals and one small end", refused, len(stored), EndAttempts)
+	}
+	s := stored[0]
+	if s.State != delivery.StepFailed || len(s.Result) != 0 || !strings.Contains(s.Reason, "could not be written") ||
+		!strings.Contains(s.Reason, big.Error()) || !strings.Contains(s.Reason, "passed") {
+		t.Errorf("the small end %+v, want failed, no result, naming the write's error and that it passed", s)
+	}
+	if len(logged) == 0 || !strings.Contains(logged[0], big.Error()) {
+		t.Errorf("logged %q, want the refusal said", logged)
+	}
+	none := func(string, any) (uint64, error) { return 0, errors.New("the bus is gone") }
+	if err := finish(none, "shanks.a3", delivery.Step{ID: "a3", Tool: "check ask", Node: "shanks", Started: time.Now()}, nil, nil, logf); err == nil || !strings.Contains(err.Error(), "the bus is gone") {
+		t.Errorf("finish with no write possible answered %v, want the error", err)
+	}
+}
+
+// 1930/AC2: given an ask whose end the state refuses, when it runs, then the ask is acknowledged only once its small
+// failed end is written; when no end can be written at all, it is given back, never acknowledged as done.
+func TestAnAskWhoseEndCannotBeWrittenIsNotAcked(t *testing.T) {
+	fastEnds(t)
+	for _, tc := range []struct {
+		name      string
+		smallOK   bool
+		wantAcked bool
+	}{{"the small end written", true, true}, {"no end written", false, false}} {
+		t.Run(tc.name, func(t *testing.T) {
+			src := NewFakeAsks()
+			a := testAsk(delivery.AskCheck)
+			_ = src.PublishAsk(a)
+			var mu sync.Mutex
+			var ends []delivery.Step
+			put := func(key string, value any) (uint64, error) {
+				st, err := delivery.DecodeStep(value.(json.RawMessage))
+				if err != nil {
+					return 0, err
+				}
+				if st.State != delivery.StepRunning && (len(st.Result) > 0 || !tc.smallOK) {
+					return 0, errors.New("refused")
+				}
+				mu.Lock()
+				ends = append(ends, st)
+				mu.Unlock()
+				return 1, nil
+			}
+			p := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: put, Capacity: func() int { return 1 },
+				PullWait: 10 * time.Millisecond, Logf: t.Logf,
+				Run: func(ctx context.Context, a delivery.StepAsk) (any, error) { return map[string]any{"ran": true}, nil }}
+			ctx, cancel := context.WithCancel(context.Background())
+			defer cancel()
+			go p.Pull(ctx)
+			waitFor(t, "the ask's fate", func() bool { ac, tm, nk := src.Fates(); return len(ac)+len(tm)+len(nk) > 0 })
+			cancel()
+			acked, termed, naked := src.Fates()
+			if tc.wantAcked && (len(acked) != 1 || len(naked) != 0) || !tc.wantAcked && (len(acked) != 0 || len(naked) == 0) || len(termed) != 0 {
+				t.Fatalf("acked %v naked %v termed %v", acked, naked, termed)
+			}
+			mu.Lock()
+			defer mu.Unlock()
+			if tc.smallOK {
+				last := ends[len(ends)-1]
+				if last.State != delivery.StepFailed || !strings.Contains(last.Reason, "refused") {
+					t.Errorf("the end %+v, want the small failed end", last)
+				}
+			}
+		})
+	}
+}

go/buildstep/fetch.go

@@ -0,0 +1,201 @@
+package buildstep
+
+import (
+	"context"
+	"fmt"
+	"net/url"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// Option changes FetchCommit.
+type Option func(*fetchOptions)
+
+type fetchOptions struct {
+	allowFile bool
+	mirror    string
+}
+
+// AllowFileRemote lets FetchCommit take a file:// remote. It is for a test's local repository; production
+// code does not pass it, and FetchCommit then refuses anything but ssh://.
+func AllowFileRemote() Option { return func(o *fetchOptions) { o.allowFile = true } }
+
+// WithMirror makes FetchCommit (and MergeInto) borrow objects from mirror, a bare repository that UpdateMirror keeps
+// in the build module's own cache (novox/hq ADR 0536 §2; issue 890): the workspace's .git/objects/info/alternates
+// names the mirror's objects directory, so git transfers only the objects the mirror lacks. It is a plain file, never
+// a symlink. mirror must be an absolute path of an existing directory; the workspace never writes to it.
+func WithMirror(mirror string) Option { return func(o *fetchOptions) { o.mirror = mirror } }
+
+// useMirror writes the alternates file of the repository in dir, when a mirror is set.
+func useMirror(o fetchOptions, dir string) error {
+	if o.mirror == "" {
+		return nil
+	}
+	info := filepath.Join(dir, ".git", "objects", "info")
+	if err := os.MkdirAll(info, 0o755); err != nil {
+		return fmt.Errorf("buildstep: the mirror cannot be used: %w", err)
+	}
+	line := filepath.Join(o.mirror, "objects") + "\n"
+	if err := os.WriteFile(filepath.Join(info, "alternates"), []byte(line), 0o644); err != nil {
+		return fmt.Errorf("buildstep: the mirror cannot be used: %w", err)
+	}
+	return nil
+}
+
+var (
+	commitOK = regexp.MustCompile(`^[0-9a-f]{40}$`)
+	refOK    = regexp.MustCompile(`^refs/[A-Za-z0-9._/-]+$`)
+)
+
+// FetchCommit fetches one commit of a forge repository into dir, an empty directory, and checks it out detached
+// (novox/hq ADR 0466 §4, §5; issue 1474). remote is ssh://<ssh name>/<owner>/<repo>.git, the ssh name being the
+// one the build module's templates set up (ADR 0409 §1); commit is a full 40-hex sha; ref is optional, and names
+// the pull request's head (refs/pull/<n>/head) when the commit is only there. Every git command runs through run
+// as `git -C dir ...` with GIT_TERMINAL_PROMPT=0 and no credential helper, so nothing is asked for and no
+// credential is used. A remote that is not ssh://, or one with user information, and a commit that is not 40
+// hex digits are refused before anything runs.
+func FetchCommit(ctx context.Context, run forgekey.Runner, dir, remote, commit, ref string, opts ...Option) error {
+	var o fetchOptions
+	for _, opt := range opts {
+		opt(&o)
+	}
+	if err := checkFetch(o, dir, remote, commit, ref); err != nil {
+		return err
+	}
+	env := []string{"GIT_TERMINAL_PROMPT=0"}
+	git := func(args ...string) (string, error) {
+		full := append([]string{"-c", "credential.helper=", "-C", dir}, args...)
+		r := run(ctx, env, "git", full...)
+		if r.Status != 0 || r.Err != "" {
+			return "", fmt.Errorf("git %s: %s", args[0], firstLine(r.Err+" "+r.Stderr))
+		}
+		return r.Stdout, nil
+	}
+	if _, err := git("init", "-q"); err != nil {
+		return err
+	}
+	if err := useMirror(o, dir); err != nil {
+		return err
+	}
+	if _, err := git("remote", "add", "origin", remote); err != nil {
+		return err
+	}
+	if _, err := git("fetch", "--no-tags", "--depth", "1", "origin", commit); err != nil {
+		if ref == "" {
+			return err
+		}
+		if _, rerr := git("fetch", "--no-tags", "origin", ref); rerr != nil {
+			return fmt.Errorf("%v; then the ref %s: %w", err, ref, rerr)
+		}
+		if _, verr := git("cat-file", "-e", commit+"^{commit}"); verr != nil {
+			return fmt.Errorf("the commit %s is not in %s: %w", commit, ref, verr)
+		}
+	}
+	if _, err := git("checkout", "-q", "--detach", commit); err != nil {
+		return err
+	}
+	out, err := git("rev-parse", "HEAD")
+	if err != nil {
+		return err
+	}
+	if head := strings.TrimSpace(out); head != commit {
+		return fmt.Errorf("the checkout is at %s, not at the commit %s", head, commit)
+	}
+	return nil
+}
+
+// UpdateMirror brings the bare repository mirror to commit: it makes the mirror when it is absent (git init --bare,
+// origin set to remote), then fetches the commit, or the ref when only the ref holds it, with the same rules as
+// FetchCommit (no prompt, no credential helper, ssh:// or an allowed file:// remote, a 40-hex commit). The mirror
+// keeps every commit it was brought to, so later fetches through WithMirror transfer only what is new. Callers
+// serialise updates of one mirror.
+func UpdateMirror(ctx context.Context, run forgekey.Runner, mirror, remote, commit, ref string, opts ...Option) error {
+	var o fetchOptions
+	for _, opt := range opts {
+		opt(&o)
+	}
+	if !filepath.IsAbs(mirror) {
+		return fmt.Errorf("buildstep: the mirror %q is not an absolute path", mirror)
+	}
+	if err := checkFetch(o, mirror, remote, commit, ref); err != nil {
+		return err
+	}
+	env := []string{"GIT_TERMINAL_PROMPT=0"}
+	git := func(args ...string) error {
+		r := run(ctx, env, "git", append([]string{"-c", "credential.helper="}, args...)...)
+		if r.Status != 0 || r.Err != "" {
+			return fmt.Errorf("git %s: %s", args[0], firstLine(r.Err+" "+r.Stderr))
+		}
+		return nil
+	}
+	in := func(args ...string) error { return git(append([]string{"-C", mirror}, args...)...) }
+	if _, err := os.Stat(filepath.Join(mirror, "HEAD")); err != nil {
+		if err := git("init", "-q", "--bare", mirror); err != nil {
+			return err
+		}
+		if err := in("remote", "add", "origin", remote); err != nil {
+			return err
+		}
+	} else if err := in("remote", "set-url", "origin", remote); err != nil {
+		return err
+	}
+	if err := in("fetch", "--no-tags", "origin", commit); err != nil {
+		if ref == "" {
+			return err
+		}
+		if rerr := in("fetch", "--no-tags", "origin", ref); rerr != nil {
+			return fmt.Errorf("%v; then the ref %s: %w", err, ref, rerr)
+		}
+	}
+	if err := in("cat-file", "-e", commit+"^{commit}"); err != nil {
+		return fmt.Errorf("the commit %s is not in the mirror: %w", commit, err)
+	}
+	return nil
+}
+
+func checkFetch(o fetchOptions, dir, remote, commit, ref string) error {
+	if dir == "" {
+		return fmt.Errorf("buildstep: no workspace directory")
+	}
+	if o.mirror != "" {
+		if !filepath.IsAbs(o.mirror) {
+			return fmt.Errorf("buildstep: the mirror %q is not an absolute path", o.mirror)
+		}
+		if fi, err := os.Stat(o.mirror); err != nil || !fi.IsDir() {
+			return fmt.Errorf("buildstep: the mirror %q is not an existing directory", o.mirror)
+		}
+	}
+	if !commitOK.MatchString(commit) {
+		return fmt.Errorf("buildstep: %q is not a full commit (40 hex digits)", commit)
+	}
+	if ref != "" && !refOK.MatchString(ref) {
+		return fmt.Errorf("buildstep: %q is not a ref (refs/...)", ref)
+	}
+	u, err := url.Parse(remote)
+	if err != nil {
+		return fmt.Errorf("buildstep: the remote is not a URL: %w", err)
+	}
+	if u.User != nil {
+		return fmt.Errorf("buildstep: the remote carries user information; the key is the credential")
+	}
+	switch {
+	case u.Scheme == "ssh" && u.Host != "":
+	case u.Scheme == "file" && o.allowFile:
+	default:
+		return fmt.Errorf("buildstep: the remote %q is not ssh://", remote)
+	}
+	return nil
+}
+
+func firstLine(s string) string {
+	for _, l := range strings.Split(s, "\n") {
+		if l = strings.TrimSpace(l); l != "" {
+			return l
+		}
+	}
+	return ""
+}

go/buildstep/fetch_integration_test.go

@@ -0,0 +1,59 @@
+//go:build integration
+
+package buildstep
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+func gitIn(t *testing.T, dir string, args ...string) string {
+	t.Helper()
+	cmd := exec.Command("git", append([]string{"-C", dir, "-c", "user.name=t", "-c", "user.email=t@example.invalid"}, args...)...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("git %v: %v\n%s", args, err, out)
+	}
+	return strings.TrimSpace(string(out))
+}
+
+// 1474/AC5: a local bare repository with a commit only under refs/pull/1/head (a file:// remote, allowed by the
+// test-only option): the workspace's HEAD is the commit. The forge itself is proven live after the build
+// modules' delivery (ADR 0466 §5).
+func TestFetchCommitFromAPullRefOnly(t *testing.T) {
+	root := t.TempDir()
+	bare := filepath.Join(root, "r.git")
+	work := filepath.Join(root, "work")
+	for _, d := range []string{bare, work} {
+		if err := os.MkdirAll(d, 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	gitIn(t, bare, "init", "-q", "--bare")
+	gitIn(t, work, "init", "-q")
+	if err := os.WriteFile(filepath.Join(work, "f"), []byte("x"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	gitIn(t, work, "add", "f")
+	gitIn(t, work, "commit", "-q", "-m", "pull request head")
+	commit := gitIn(t, work, "rev-parse", "HEAD")
+	gitIn(t, work, "push", "-q", bare, "HEAD:refs/pull/1/head")
+
+	ws := filepath.Join(root, "ws")
+	if err := os.MkdirAll(ws, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	err := FetchCommit(context.Background(), forgekey.ExecRunner, ws, "file://"+bare, commit, "refs/pull/1/head", AllowFileRemote())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if head := gitIn(t, ws, "rev-parse", "HEAD"); head != commit {
+		t.Errorf("HEAD = %s, want %s", head, commit)
+	}
+}

go/buildstep/fetch_test.go

@@ -0,0 +1,137 @@
+package buildstep
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+const sha = "0123456789abcdef0123456789abcdef01234567"
+
+// fakeGit records every command and answers by a rule.
+type fakeGit struct {
+	calls []string
+	envs  [][]string
+	rule  func(args string) forgekey.Ran
+}
+
+func (f *fakeGit) run(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+	line := name + " " + strings.Join(args, " ")
+	f.calls = append(f.calls, line)
+	f.envs = append(f.envs, env)
+	if f.rule != nil {
+		if r := f.rule(line); r.Status != 0 || r.Stdout != "" || r.Err != "" {
+			return r
+		}
+	}
+	if len(args) > 4 && args[4] == "rev-parse" {
+		return forgekey.Ran{Stdout: sha + "\n"}
+	}
+	return forgekey.Ran{}
+}
+
+const pre = "git -c credential.helper= -C /w "
+
+// 1474/AC1: the git commands are exactly the sequence, none with a credential or an https remote.
+func TestFetchCommitRunsTheSequence(t *testing.T) {
+	f := &fakeGit{}
+	if err := FetchCommit(context.Background(), f.run, "/w", "ssh://mesh-forge/novox/mesh-sdk.git", sha, ""); err != nil {
+		t.Fatal(err)
+	}
+	want := []string{
+		pre + "init -q",
+		pre + "remote add origin ssh://mesh-forge/novox/mesh-sdk.git",
+		pre + "fetch --no-tags --depth 1 origin " + sha,
+		pre + "checkout -q --detach " + sha,
+		pre + "rev-parse HEAD",
+	}
+	if strings.Join(f.calls, "\n") != strings.Join(want, "\n") {
+		t.Errorf("commands:\n%s\nwant:\n%s", strings.Join(f.calls, "\n"), strings.Join(want, "\n"))
+	}
+	for i, c := range f.calls {
+		if strings.Contains(c, "https://") || strings.Contains(c, "@") || !strings.Contains(c, "credential.helper= ") {
+			t.Errorf("command %q carries a credential or https", c)
+		}
+		if len(f.envs[i]) != 1 || f.envs[i][0] != "GIT_TERMINAL_PROMPT=0" {
+			t.Errorf("env %v", f.envs[i])
+		}
+	}
+}
+
+// 1474/AC2: the depth-1 fetch fails and a pull ref is given: the ref is fetched and the commit verified; with no
+// ref, the fetch's failure is the answer.
+func TestFetchCommitFallsBackToThePullRef(t *testing.T) {
+	f := &fakeGit{rule: func(l string) forgekey.Ran {
+		if strings.Contains(l, "--depth 1") {
+			return forgekey.Ran{Status: 128, Stderr: "fatal: couldn't find remote ref " + sha + "\n"}
+		}
+		return forgekey.Ran{}
+	}}
+	if err := FetchCommit(context.Background(), f.run, "/w", "ssh://mesh-forge/o/r.git", sha, "refs/pull/1/head"); err != nil {
+		t.Fatal(err)
+	}
+	want := []string{pre + "fetch --no-tags origin refs/pull/1/head", pre + "cat-file -e " + sha + "^{commit}", pre + "checkout -q --detach " + sha}
+	got := strings.Join(f.calls[3:6], "\n")
+	if got != strings.Join(want, "\n") {
+		t.Errorf("after the failed fetch:\n%s\nwant:\n%s", got, strings.Join(want, "\n"))
+	}
+
+	g := &fakeGit{rule: f.rule}
+	err := FetchCommit(context.Background(), g.run, "/w", "ssh://mesh-forge/o/r.git", sha, "")
+	if err == nil || !strings.Contains(err.Error(), "couldn't find remote ref") || len(g.calls) != 3 {
+		t.Errorf("without a ref: %v after %d commands", err, len(g.calls))
+	}
+
+	h := &fakeGit{rule: func(l string) forgekey.Ran {
+		if strings.Contains(l, "--depth 1") || strings.Contains(l, "cat-file") {
+			return forgekey.Ran{Status: 1, Stderr: "no"}
+		}
+		return forgekey.Ran{}
+	}}
+	if err := FetchCommit(context.Background(), h.run, "/w", "ssh://mesh-forge/o/r.git", sha, "refs/pull/1/head"); err == nil {
+		t.Error("a commit that is not in the ref was accepted")
+	}
+}
+
+// 1474/AC3: HEAD differs from the commit after the checkout: an error naming both.
+func TestFetchCommitAnswersAHeadThatIsNotTheCommit(t *testing.T) {
+	other := strings.Repeat("a", 40)
+	f := &fakeGit{rule: func(l string) forgekey.Ran {
+		if strings.HasSuffix(l, "rev-parse HEAD") {
+			return forgekey.Ran{Stdout: other + "\n"}
+		}
+		return forgekey.Ran{}
+	}}
+	err := FetchCommit(context.Background(), f.run, "/w", "ssh://mesh-forge/o/r.git", sha, "")
+	if err == nil || !strings.Contains(err.Error(), other) || !strings.Contains(err.Error(), sha) {
+		t.Errorf("error = %v, want both shas", err)
+	}
+}
+
+// 1474/AC4: an https remote, user information, a file remote without the option, or a commit that is not 40
+// hex digits is refused before anything runs.
+func TestFetchCommitRefusesBeforeRunningAnything(t *testing.T) {
+	for _, c := range []struct{ remote, commit, ref string }{
+		{"https://forge.example/o/r.git", sha, ""},
+		{"http://forge.example/o/r.git", sha, ""},
+		{"ssh://git@mesh-forge/o/r.git", sha, ""},
+		{"ssh://user:pw@mesh-forge/o/r.git", sha, ""},
+		{"file:///tmp/r.git", sha, ""},
+		{"/tmp/r.git", sha, ""},
+		{"ssh://mesh-forge/o/r.git", "abc123", ""},
+		{"ssh://mesh-forge/o/r.git", strings.ToUpper(sha), ""},
+		{"ssh://mesh-forge/o/r.git", "main", ""},
+		{"ssh://mesh-forge/o/r.git", sha, "--upload-pack=x"},
+	} {
+		f := &fakeGit{}
+		if err := FetchCommit(context.Background(), f.run, "/w", c.remote, c.commit, c.ref); err == nil || len(f.calls) != 0 {
+			t.Errorf("%+v: err %v, %d commands", c, err, len(f.calls))
+		}
+	}
+	f := &fakeGit{}
+	if err := FetchCommit(context.Background(), f.run, "/w", "file:///tmp/r.git", sha, "", AllowFileRemote()); err != nil {
+		t.Errorf("a file remote with the option: %v", err)
+	}
+}

go/buildstep/guard.go

@@ -0,0 +1,52 @@
+package buildstep
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// Guard is a build module's check that the toolchain installed on its node is the one its recipe builds with
+// (novox/hq ADR 0469 §1; issue 1473). The same guard serves ADR 0470 §4's postgres major for the integration
+// level, with its own Probe and Want.
+type Guard struct {
+	// Language is the toolchain's key part: go or typescript (delivery.ToolchainKey).
+	Language string
+	// Want is the toolchain version the recipe builds with, and Recipe the recipe's own version. The indexer
+	// compares both texts as they are written here.
+	Want, Recipe string
+	// Probe reads the installed version (go version, node --version).
+	Probe func(ctx context.Context) (installed string, err error)
+	Node  string
+	// Put is the toolchains state's Put (stdio.State(delivery.ToolchainsState).Put).
+	Put Put
+}
+
+// Check probes the installed version, writes it to <node>.<language> of the toolchains state every time it runs,
+// and answers nil when it is the recipe's. Otherwise it answers a *Refusal naming both versions; the installed
+// version is written even then, so the indexer sees that builders disagree. A probe that fails is a *Refusal
+// naming its failure, and nothing is written. A write that fails is an error that is not a Refusal.
+func (g Guard) Check(ctx context.Context) error {
+	installed, err := g.Probe(ctx)
+	if err != nil {
+		return &Refusal{Text: fmt.Sprintf("the installed %s version could not be read: %v", g.Language, err), Want: g.Want}
+	}
+	key, err := delivery.ToolchainKey(g.Node, g.Language)
+	if err != nil {
+		return err
+	}
+	raw, err := delivery.EncodeToolchain(delivery.Toolchain{Language: g.Language, Version: installed, Recipe: g.Recipe, At: now().UTC()})
+	if err != nil {
+		return err
+	}
+	if _, err := g.Put(key, json.RawMessage(raw)); err != nil {
+		return fmt.Errorf("buildstep: writing the toolchain %s: %w", key, err)
+	}
+	if installed != g.Want {
+		return &Refusal{Text: fmt.Sprintf("%s %s installed, the recipe builds with %s %s", g.Language, installed, g.Language, g.Want),
+			Want: g.Want, Have: installed}
+	}
+	return nil
+}

go/buildstep/guard_test.go

@@ -0,0 +1,79 @@
+package buildstep
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+type toolchainKeys map[string]delivery.Toolchain
+
+func (k toolchainKeys) put(key string, value any) (uint64, error) {
+	tc, err := delivery.DecodeToolchain(value.(json.RawMessage))
+	if err != nil {
+		return 0, err
+	}
+	k[key] = tc
+	return uint64(len(k)), nil
+}
+
+func guardFor(k toolchainKeys, installed string, probeErr error) Guard {
+	return Guard{Language: "go", Want: "1.27.0", Recipe: "r7", Node: "ace", Put: k.put,
+		Probe: func(context.Context) (string, error) { return installed, probeErr }}
+}
+
+// 1473/AC1: the probe answers the recipe's version: nil, and <node>.go holds that version and the recipe's.
+func TestCheckPassesAndWritesTheToolchain(t *testing.T) {
+	k := toolchainKeys{}
+	if err := guardFor(k, "1.27.0", nil).Check(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	tc, ok := k["ace.go"]
+	if !ok || tc.Version != "1.27.0" || tc.Recipe != "r7" || tc.Language != "go" || tc.At.IsZero() {
+		t.Errorf("keys = %+v", k)
+	}
+}
+
+// 1473/AC2: another version: a Refusal naming both, and the key holds the installed version.
+func TestCheckRefusesAnotherVersionAndWritesTheInstalledOne(t *testing.T) {
+	k := toolchainKeys{}
+	err := guardFor(k, "1.27.1", nil).Check(context.Background())
+	var ref *Refusal
+	if !errors.As(err, &ref) {
+		t.Fatalf("Check = %v, want a Refusal", err)
+	}
+	if ref.Text != "go 1.27.1 installed, the recipe builds with go 1.27.0" || ref.Want != "1.27.0" || ref.Have != "1.27.1" {
+		t.Errorf("refusal = %+v", ref)
+	}
+	if k["ace.go"].Version != "1.27.1" {
+		t.Errorf("the key holds %q, want the installed 1.27.1", k["ace.go"].Version)
+	}
+}
+
+// 1473/AC3: a probe that fails: a Refusal naming the failure, and nothing put.
+func TestCheckRefusesAFailedProbeAndPutsNothing(t *testing.T) {
+	k := toolchainKeys{}
+	err := guardFor(k, "", errors.New("go: not found")).Check(context.Background())
+	var ref *Refusal
+	if !errors.As(err, &ref) || !strings.Contains(ref.Text, "go: not found") {
+		t.Fatalf("Check = %v, want a Refusal naming the probe's failure", err)
+	}
+	if len(k) != 0 {
+		t.Errorf("put %v", k)
+	}
+}
+
+// A failed write is an error, not a refusal: the step fails instead of refusing.
+func TestCheckAnswersAFailedWriteAsAnError(t *testing.T) {
+	g := guardFor(toolchainKeys{}, "1.27.0", nil)
+	g.Put = func(string, any) (uint64, error) { return 0, errors.New("no grant") }
+	err := g.Check(context.Background())
+	var ref *Refusal
+	if err == nil || errors.As(err, &ref) {
+		t.Errorf("Check = %v", err)
+	}
+}

go/buildstep/isolate.go

@@ -0,0 +1,175 @@
+package buildstep
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// Bubblewrap is the program a run step runs in (novox/hq ADR 0448): a build module declares its package, which needs
+// unprivileged user namespaces (issue 1308).
+const Bubblewrap = "bwrap"
+
+// Isolation is how a run step's command is shut off (novox/hq ADR 0448; issue 1309, the lead's decision L2 of R4e: one
+// runner in the SDK for every build module). The fetch step holds the forge key and the network and runs none of the
+// change's code; the run step runs the change's build and tests in bubblewrap with:
+//
+//   - no network: its own network namespace, with only a loopback, so a test may start a bus or a store of its own but
+//     resolves no name and reaches no socket of the machine;
+//   - none of the account: not its home, not the forge key, not a bus login, not the runtime directory (/run), since
+//     none of them is bound; HOME is a directory in the step's own /tmp unless Env names one;
+//   - an environment of exactly Env and the runner's env: nothing of the build module's own passes;
+//   - the system's programs and libraries read-only, and of /etc only what a program needs to run (users, libraries,
+//     certificates, time zone), with a hosts file naming only the loopback;
+//   - the Workspace and Writable directories read-write, the ReadOnly ones (the toolchain, the modules the fetch step
+//     downloaded) read-only;
+//   - the shared warm Caches read-only under a throwaway writable layer (S18), or read-write for a trunk build alone
+//     (WriteCaches), so a candidate's code never changes what a later build reads.
+type Isolation struct {
+	Workspace   string
+	Writable    []string
+	ReadOnly    []string
+	Caches      []string
+	WriteCaches bool
+	Env         []string
+	// Hosts is the file bound as /etc/hosts; Isolated writes one naming only the loopback.
+	Hosts string
+}
+
+// etcNeeded is what of /etc a program in the step may read: who the users are, where the libraries are, the
+// certificates, the time zone. Not resolv.conf, not hosts: the step resolves no name.
+var etcNeeded = []string{"/etc/passwd", "/etc/group", "/etc/nsswitch.conf", "/etc/ld.so.cache", "/etc/ld.so.conf",
+	"/etc/ld.so.conf.d", "/etc/ssl", "/etc/ca-certificates", "/etc/pki", "/etc/localtime", "/etc/os-release", "/etc/alternatives"}
+
+// systemArgs binds the system's programs and libraries read-only: /usr, and /bin, /sbin, /lib, /lib64 as the symlinks
+// they are on a merged-usr system, or bound when they are directories. A variable so a unit test fixes it.
+var systemArgs = func() []string {
+	args := []string{"--ro-bind", "/usr", "/usr"}
+	for _, d := range []string{"/bin", "/sbin", "/lib", "/lib64"} {
+		info, err := os.Lstat(d)
+		switch {
+		case err != nil:
+		case info.Mode()&os.ModeSymlink != 0:
+			if target, err := os.Readlink(d); err == nil {
+				args = append(args, "--symlink", target, d)
+			}
+		case info.IsDir():
+			args = append(args, "--ro-bind", d, d)
+		}
+	}
+	for _, e := range etcNeeded {
+		args = append(args, "--ro-bind-try", e, e)
+	}
+	return args
+}
+
+// stepHome is the HOME of a step that is given none: inside its own /tmp, gone with it.
+const stepHome = "/tmp/home"
+
+func checkDir(what, dir string) error {
+	if dir == "" || !strings.HasPrefix(dir, "/") || path.Clean(dir) != dir || dir == "/" {
+		return fmt.Errorf("buildstep: the %s %q is not an absolute, clean directory other than the root", what, dir)
+	}
+	return nil
+}
+
+// Command is the bubblewrap command line that runs name with args shut off as iso says, env added to iso.Env. It
+// refuses a directory that is not absolute and clean, or is the root, and an environment word without "=".
+func (iso Isolation) Command(name string, args ...string) ([]string, error) {
+	return iso.command(nil, name, args...)
+}
+
+func (iso Isolation) command(env []string, name string, args ...string) ([]string, error) {
+	if err := checkDir("workspace", iso.Workspace); err != nil {
+		return nil, err
+	}
+	for _, group := range []struct {
+		what string
+		dirs []string
+	}{{"writable directory", iso.Writable}, {"read-only directory", iso.ReadOnly}, {"cache", iso.Caches}} {
+		for _, d := range group.dirs {
+			if err := checkDir(group.what, d); err != nil {
+				return nil, err
+			}
+		}
+	}
+	words := append(append([]string{}, iso.Env...), env...)
+	home := false
+	for _, w := range words {
+		k, _, ok := strings.Cut(w, "=")
+		if !ok || k == "" {
+			return nil, fmt.Errorf("buildstep: the environment word %q is not NAME=value", w)
+		}
+		home = home || k == "HOME"
+	}
+	argv := []string{"--unshare-all", "--die-with-parent", "--new-session", "--clearenv",
+		"--proc", "/proc", "--dev", "/dev", "--tmpfs", "/tmp", "--dir", stepHome}
+	argv = append(argv, systemArgs()...)
+	for _, d := range iso.ReadOnly {
+		argv = append(argv, "--ro-bind", d, d)
+	}
+	argv = append(argv, cacheArgs(iso.Caches, iso.WriteCaches)...)
+	argv = append(argv, "--bind", iso.Workspace, iso.Workspace)
+	for _, d := range iso.Writable {
+		argv = append(argv, "--bind", d, d)
+	}
+	if iso.Hosts != "" {
+		argv = append(argv, "--ro-bind", iso.Hosts, "/etc/hosts")
+	}
+	for _, w := range words {
+		k, v, _ := strings.Cut(w, "=")
+		argv = append(argv, "--setenv", k, v)
+	}
+	if !home {
+		argv = append(argv, "--setenv", "HOME", stepHome)
+	}
+	argv = append(argv, "--chdir", iso.Workspace, "--", name)
+	return append(argv, args...), nil
+}
+
+// cacheArgs binds the shared warm caches (S18): for a trunk build read-write, so the next build is warm; for any other
+// read-only beneath an overlay whose writes go to a tmpfs of the step's own, so the step writes as a build does and
+// nothing it wrote outlives it (bubblewrap's --tmp-overlay, an overlay mount in the step's user namespace).
+func cacheArgs(caches []string, write bool) []string {
+	var argv []string
+	for _, c := range caches {
+		if write {
+			argv = append(argv, "--bind", c, c)
+			continue
+		}
+		argv = append(argv, "--overlay-src", c, "--tmp-overlay", c)
+	}
+	return argv
+}
+
+// loopbackHosts is the hosts file of a step: the loopback and nothing else.
+const loopbackHosts = "127.0.0.1 localhost\n::1 localhost\n"
+
+// Isolated is run with every command shut off as iso says (Command), run's env going inside the step: the build modules'
+// run steps call their test, build and digest commands through it, never run itself. Each command gets a hosts file of
+// its own, naming only the loopback, removed when it ends.
+func Isolated(run forgekey.Runner, iso Isolation) forgekey.Runner {
+	return func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+		dir, err := os.MkdirTemp("", "step-hosts-")
+		if err != nil {
+			return forgekey.Ran{Status: 1, Err: "the step's hosts file: " + err.Error()}
+		}
+		defer os.RemoveAll(dir)
+		hosts := filepath.Join(dir, "hosts")
+		if err := os.WriteFile(hosts, []byte(loopbackHosts), 0o644); err != nil {
+			return forgekey.Ran{Status: 1, Err: "the step's hosts file: " + err.Error()}
+		}
+		iso := iso
+		iso.Hosts = hosts
+		argv, err := iso.command(env, name, args...)
+		if err != nil {
+			return forgekey.Ran{Status: 1, Err: err.Error()}
+		}
+		return run(ctx, nil, Bubblewrap, argv...)
+	}
+}

go/buildstep/isolate_caches_test.go

@@ -0,0 +1,30 @@
+package buildstep
+
+import "testing"
+
+// The shared warm caches are read under a throwaway writable layer (novox/hq ADR 0448; issue 1309): a candidate's step
+// writes into them as a build does, and nothing it writes outlives it or reaches a later build; only a trunk build
+// writes them.
+func TestACandidatesStepWritesTheCachesOnlyIntoAThrowawayLayer(t *testing.T) {
+	fixedSystem(t)
+	iso := Isolation{Workspace: "/w", Caches: []string{"/var/cache/go-build", "/var/cache/npm"}}
+	argv, err := iso.Command("go", "test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, c := range iso.Caches {
+		if !holds(argv, "--overlay-src", c, "--tmp-overlay", c) {
+			t.Errorf("the cache %s is not under a throwaway layer: %v", c, argv)
+		}
+		if holds(argv, "--bind", c, c) {
+			t.Errorf("a candidate's step writes the cache %s: %v", c, argv)
+		}
+	}
+	iso.WriteCaches = true
+	argv, _ = iso.Command("go", "build")
+	for _, c := range iso.Caches {
+		if !holds(argv, "--bind", c, c) || holds(argv, "--tmp-overlay", c) {
+			t.Errorf("a trunk build does not write the cache %s: %v", c, argv)
+		}
+	}
+}

go/buildstep/isolate_integration_test.go

@@ -0,0 +1,66 @@
+//go:build integration && isolation
+
+package buildstep
+
+import (
+	"context"
+	"net"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// 1309/S19, the issue's proof: a run step, in bubblewrap as Isolated runs it, reads no key and no login, resolves no
+// name, reaches no TCP or unix socket of the machine, finds no home of the account, and leaves the shared cache it
+// wrote unchanged; the workspace it writes keeps what it wrote. It needs bubblewrap and unprivileged user namespaces
+// (issue 1308) on the machine that runs it, and fails naming them when they are not there.
+func TestARunStepReachesNothingAndLeavesTheCachesUnchanged(t *testing.T) {
+	if _, err := exec.LookPath(Bubblewrap); err != nil {
+		t.Fatalf("bubblewrap is not installed here, so the isolation of a run step cannot be proved (issue 1309): %v", err)
+	}
+	root := t.TempDir()
+	account := filepath.Join(root, "account")
+	key, login := filepath.Join(account, ".ssh", "id_ed25519"), filepath.Join(account, "bus-login.json")
+	writeFile(t, filepath.Dir(key), filepath.Base(key), "PRIVATE KEY")
+	writeFile(t, account, "bus-login.json", `{"password":"secret"}`)
+	cacheDir := filepath.Join(root, "cache")
+	writeFile(t, cacheDir, "warm", "warm\n")
+	workspace := filepath.Join(root, "work", "tree")
+	if err := os.MkdirAll(workspace, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	probe := filepath.Join(workspace, "probe")
+	if out, err := exec.Command("go", "build", "-o", probe, "./testdata/isolated-probe").CombinedOutput(); err != nil {
+		t.Fatalf("building the probe: %v\n%s", err, out)
+	}
+	tcp, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer tcp.Close()
+	socket := filepath.Join(account, "bus.sock")
+	unix, err := net.Listen("unix", socket)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer unix.Close()
+
+	run := Isolated(forgekey.ExecRunnerFor(0), Isolation{Workspace: workspace, Caches: []string{cacheDir}})
+	r := run(context.Background(), []string{"PATH=/usr/bin:/bin"}, probe, key, login, tcp.Addr().String(), socket, "localhost.localdomain.invalid", filepath.Join(cacheDir, "warm"))
+	if r.Status != 0 || r.Err != "" || strings.TrimSpace(r.Stdout) != "shut off" {
+		t.Fatalf("the run step was not shut off (status %d, %s):\n%s%s", r.Status, r.Err, r.Stdout, r.Stderr)
+	}
+	if b, _ := os.ReadFile(filepath.Join(cacheDir, "warm")); string(b) != "warm\n" {
+		t.Fatalf("the step changed the shared cache: %q", b)
+	}
+
+	// The workspace is the step's own: what it writes there stays.
+	r = run(context.Background(), nil, "/bin/sh", "-c", "echo built > out")
+	if b, err := os.ReadFile(filepath.Join(workspace, "out")); r.Status != 0 || err != nil || string(b) != "built\n" {
+		t.Fatalf("the step's write to its workspace did not stay (status %d, %s%s): %q %v", r.Status, r.Stderr, r.Err, b, err)
+	}
+}

go/buildstep/isolate_test.go

@@ -0,0 +1,115 @@
+package buildstep
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// pairs says whether argv holds the words of want one after another.
+func holds(argv []string, want ...string) bool {
+	for i := 0; i+len(want) <= len(argv); i++ {
+		match := true
+		for j, w := range want {
+			if argv[i+j] != w {
+				match = false
+				break
+			}
+		}
+		if match {
+			return true
+		}
+	}
+	return false
+}
+
+func fixedSystem(t *testing.T) {
+	t.Helper()
+	before := systemArgs
+	systemArgs = func() []string { return []string{"--ro-bind", "/usr", "/usr", "--symlink", "usr/bin", "/bin"} }
+	t.Cleanup(func() { systemArgs = before })
+}
+
+// A run step's command runs in bubblewrap (novox/hq ADR 0448; issue 1309): no network, no namespace shared, an
+// environment of exactly what the step is given, the workspace the one tree it writes, the toolchain read-only, and
+// nothing else of the machine's: not the account's home, not the forge key or a bus login, not the runtime directory,
+// and no name service.
+func TestARunStepRunsShutOffInBubblewrap(t *testing.T) {
+	fixedSystem(t)
+	iso := Isolation{Workspace: "/work/ab12/tree", ReadOnly: []string{"/usr/lib/go"}, Writable: []string{"/work/ab12/out"},
+		Env: []string{"GOFLAGS=-mod=mod", "PATH=/usr/bin"}, Hosts: "/work/ab12/hosts"}
+	argv, err := iso.Command("go", "test", "./...")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, want := range [][]string{
+		{"--unshare-all"}, {"--die-with-parent"}, {"--new-session"}, {"--clearenv"},
+		{"--proc", "/proc"}, {"--dev", "/dev"}, {"--tmpfs", "/tmp"},
+		{"--ro-bind", "/usr", "/usr"}, {"--symlink", "usr/bin", "/bin"},
+		{"--ro-bind", "/usr/lib/go", "/usr/lib/go"},
+		{"--bind", "/work/ab12/tree", "/work/ab12/tree"}, {"--bind", "/work/ab12/out", "/work/ab12/out"},
+		{"--ro-bind", "/work/ab12/hosts", "/etc/hosts"},
+		{"--setenv", "GOFLAGS", "-mod=mod"}, {"--setenv", "PATH", "/usr/bin"}, {"--setenv", "HOME", "/tmp/home"},
+		{"--chdir", "/work/ab12/tree"},
+		{"--", "go", "test", "./..."},
+	} {
+		if !holds(argv, want...) {
+			t.Errorf("the command has no %v: %v", want, argv)
+		}
+	}
+	if holds(argv, "--share-net") || strings.Contains(strings.Join(argv, " "), "resolv.conf") || strings.Contains(strings.Join(argv, " "), "/run") {
+		t.Errorf("the command reaches the network, the name service or the runtime directory: %v", argv)
+	}
+	// The workspace is mounted after /tmp's tmpfs, so a workspace under /tmp is not hidden by it.
+	if strings.Index(strings.Join(argv, "\x00"), "--tmpfs\x00/tmp") > strings.Index(strings.Join(argv, "\x00"), "--bind\x00/work/ab12/tree") {
+		t.Errorf("the tmpfs of /tmp comes after the workspace: %v", argv)
+	}
+	// A HOME the step is given is its own.
+	iso.Env = append(iso.Env, "HOME=/work/ab12/home")
+	argv, _ = iso.Command("true")
+	if holds(argv, "--setenv", "HOME", "/tmp/home") || !holds(argv, "--setenv", "HOME", "/work/ab12/home") {
+		t.Errorf("the step's own HOME was replaced: %v", argv)
+	}
+}
+
+func TestAnIsolationNamesNoPathItCannotPin(t *testing.T) {
+	for _, iso := range []Isolation{
+		{Workspace: ""},
+		{Workspace: "tree"},
+		{Workspace: "/"},
+		{Workspace: "/w", ReadOnly: []string{"relative"}},
+		{Workspace: "/w", Writable: []string{"/"}},
+		{Workspace: "/w", Caches: []string{"/a/../b"}},
+		{Workspace: "/w", Env: []string{"NOEQUALS"}},
+	} {
+		if _, err := iso.Command("true"); err == nil {
+			t.Errorf("%+v was accepted", iso)
+		}
+	}
+}
+
+// Isolated runs every command through bwrap, with the step's environment inside and a hosts file that names only the
+// loopback, removed after.
+func TestIsolatedRunsEachCommandThroughBubblewrap(t *testing.T) {
+	fixedSystem(t)
+	var ran []string
+	var hosts string
+	inner := func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+		ran = append([]string{name}, args...)
+		for i, a := range args {
+			if a == "/etc/hosts" && i > 0 {
+				hosts = args[i-1]
+			}
+		}
+		return forgekey.Ran{Stdout: "ok"}
+	}
+	r := Isolated(inner, Isolation{Workspace: "/w"})(context.Background(), []string{"A=1"}, "go", "build")
+	if r.Stdout != "ok" || ran[0] != Bubblewrap || !holds(ran, "--setenv", "A", "1") || !holds(ran, "--", "go", "build") {
+		t.Fatalf("ran %v: %+v", ran, r)
+	}
+	if hosts == "" {
+		t.Fatalf("no hosts file was bound: %v", ran)
+	}
+}

go/buildstep/launchers.go

@@ -0,0 +1,24 @@
+package buildstep
+
+import "strings"
+
+// LauncherSuffix is what a TypeScript entrypoint's launcher is called beside it: index.js is started as
+// index.serve.mjs (novox/hq ADR 0193), an ES module by its own extension whatever the bundle's package.json says.
+const LauncherSuffix = ".serve.mjs"
+
+// Launchers are the launchers a bundle's build writes, by entrypoint, relative to the bundle's root: for TypeScript
+// every entrypoint `x.js` is started by `x.serve.mjs` beside it; an entrypoint that is not JavaScript and every other
+// language, whose build is already executable, get none. The one rule mesh-build-node, build-agent and the controller
+// share (R4e), so the name a build writes is the name a reader expects.
+func Launchers(language string, entrypoints []string) map[string]string {
+	out := map[string]string{}
+	if language != "typescript" {
+		return out
+	}
+	for _, entry := range entrypoints {
+		if strings.HasSuffix(entry, ".js") {
+			out[entry] = strings.TrimSuffix(entry, ".js") + LauncherSuffix
+		}
+	}
+	return out
+}

go/buildstep/launchers_test.go

@@ -0,0 +1,22 @@
+package buildstep
+
+import (
+	"reflect"
+	"testing"
+)
+
+// A TypeScript bundle's entrypoint x.js is started as x.serve.mjs beside it (novox/hq ADR 0193), the rule mesh-build-node
+// and build-agent both apply; an entrypoint that is not .js gets none, and another language gets none.
+func TestATypeScriptEntrypointIsStartedByTheLauncherBesideIt(t *testing.T) {
+	got := Launchers("typescript", []string{"index.js", "tools/x.js", "data.json"})
+	want := map[string]string{"index.js": "index.serve.mjs", "tools/x.js": "tools/x.serve.mjs"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("Launchers(typescript) = %v, want %v", got, want)
+	}
+	if got := Launchers("go", []string{"index.js"}); len(got) != 0 {
+		t.Fatalf("a Go bundle got launchers: %v", got)
+	}
+	if got := Launchers("typescript", nil); len(got) != 0 {
+		t.Fatalf("a bundle with no entrypoint got launchers: %v", got)
+	}
+}

go/buildstep/merge.go

@@ -0,0 +1,115 @@
+package buildstep
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// MergeResult is what MergeInto made of a head and a trunk commit: the trunk commit (Base) and the head, whole, and the
+// merge commit and the paths the merge changes against the trunk commit; or, when the head does not merge cleanly, the
+// files in conflict, with Merge and Changed empty.
+type MergeResult struct {
+	Base, Head, Merge string
+	Conflicts         []string
+	Changed           []string
+}
+
+// MergeInto makes, in the workspace dir that FetchCommit left at commit, the merge of commit into the trunk commit
+// base, as the forge's default merge would (a merge commit, never a fast-forward), and leaves the workspace at the merge
+// (novox/hq ADR 0484 clause 3, ADR 0323). It is the one merge the build modules' fetch steps make, with the identity
+// and flags of the controller's check merge (mesh-controller internal/builder/check_merge.go): a name nobody owns, no
+// signature, no hook, nothing of the machine's git configuration that changes a merge. Nothing is pushed.
+//
+// A merge needs both histories, so it makes the fetch whole (the shallow clone FetchCommit made is deepened) and
+// fetches base by its sha. A head that does not merge cleanly is an answer, not an error: the files in conflict, the
+// merge undone and the workspace left at base. A head already in base answers a Merge equal to Base and no changed
+// paths. An error is that the merge could not be tried: a base or commit that is not a full sha, no base, a workspace
+// not at commit, or a fetch or git command that failed. remote and the options are those of FetchCommit; the runner's
+// bound must allow a whole fetch.
+func MergeInto(ctx context.Context, run forgekey.Runner, dir, remote, base, commit string, opts ...Option) (MergeResult, error) {
+	var o fetchOptions
+	for _, opt := range opts {
+		opt(&o)
+	}
+	res := MergeResult{Base: base, Head: commit}
+	if base == "" {
+		return res, fmt.Errorf("buildstep: no base: a merge needs the trunk commit it is made onto")
+	}
+	if err := checkFetch(o, dir, remote, base, ""); err != nil {
+		return res, err
+	}
+	if err := checkFetch(o, dir, remote, commit, ""); err != nil {
+		return res, err
+	}
+	if err := useMirror(o, dir); err != nil {
+		return res, err
+	}
+	env := []string{"GIT_TERMINAL_PROMPT=0"}
+	git := func(args ...string) (string, error) {
+		full := append([]string{"-c", "credential.helper=", "-C", dir}, args...)
+		r := run(ctx, env, "git", full...)
+		if r.Status != 0 || r.Err != "" {
+			return "", fmt.Errorf("git %s: %s", args[0], firstLine(r.Err+" "+r.Stderr))
+		}
+		return r.Stdout, nil
+	}
+	at, err := git("rev-parse", "HEAD")
+	if err != nil {
+		return res, err
+	}
+	if head := strings.TrimSpace(at); head != commit {
+		return res, fmt.Errorf("buildstep: the workspace is at %s, not at the commit %s", head, commit)
+	}
+	shallow, err := git("rev-parse", "--is-shallow-repository")
+	if err != nil {
+		return res, err
+	}
+	fetch := []string{"fetch", "--no-tags", "origin", base}
+	if strings.TrimSpace(shallow) == "true" {
+		fetch = []string{"fetch", "--no-tags", "--unshallow", "origin", base}
+	}
+	if _, err := git(fetch...); err != nil {
+		return res, fmt.Errorf("the trunk commit %s: %w", base, err)
+	}
+	if _, err := git("checkout", "-q", "--detach", base); err != nil {
+		return res, fmt.Errorf("the trunk commit %s cannot be checked out: %w", base, err)
+	}
+	message := fmt.Sprintf("Check the merge of %s into %s (made for a check, never pushed)", short(commit), short(base))
+	args := append(append([]string{}, mergeIdentity...), "merge", "--no-ff", "--no-edit", "--no-verify", "--quiet", "-m", message, commit)
+	if _, err := git(args...); err != nil {
+		out, _ := git("diff", "--name-only", "--diff-filter=U")
+		res.Conflicts = strings.Fields(out)
+		_, _ = git("merge", "--abort")
+		if len(res.Conflicts) == 0 {
+			return res, fmt.Errorf("the head %s could not be merged into the trunk commit %s: %w", short(commit), short(base), err)
+		}
+		return res, nil
+	}
+	merge, err := git("rev-parse", "HEAD")
+	if err != nil {
+		return res, fmt.Errorf("the merge cannot be read: %w", err)
+	}
+	res.Merge = strings.TrimSpace(merge)
+	changed, err := git("diff", "--name-only", "--no-renames", base, res.Merge)
+	if err != nil {
+		return res, fmt.Errorf("the paths the merge changes cannot be read: %w", err)
+	}
+	res.Changed = strings.Fields(changed)
+	return res, nil
+}
+
+// mergeIdentity is who a check's merge is made as: it is never pushed, so it names nobody's account. No hook of the
+// clone's or the build machine's git configuration runs, and no setting there changes the merge (the controller's
+// check merge, internal/builder/check_merge.go).
+var mergeIdentity = []string{"-c", "user.name=mesh merge check", "-c", "user.email=merge-check@mesh.invalid",
+	"-c", "commit.gpgsign=false", "-c", "core.hooksPath=/dev/null", "-c", "merge.verifySignatures=false"}
+
+func short(commit string) string {
+	if len(commit) > 12 {
+		return commit[:12]
+	}
+	return commit
+}

go/buildstep/merge_integration_test.go

@@ -0,0 +1,172 @@
+//go:build integration
+
+package buildstep
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// The merge on real git repositories starts git processes, so it is an integration test (the unit level keeps its bound,
+// issue 895); the unit tests of merge_test.go prove the commands and the refusals with a fake runner.
+
+func realGit(t *testing.T, dir string, args ...string) string {
+	t.Helper()
+	cmd := exec.Command("git", append([]string{"-C", dir, "-c", "user.name=t", "-c", "user.email=t@example.invalid", "-c", "commit.gpgsign=false"}, args...)...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("git %v: %v\n%s", args, err, out)
+	}
+	return strings.TrimSpace(string(out))
+}
+
+func writeFile(t *testing.T, dir, name, content string) {
+	t.Helper()
+	p := filepath.Join(dir, name)
+	if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(p, []byte(content), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// mergeRig is a local bare repository standing in for the forge, a work repository that pushes to it, and an empty
+// workspace: the fetch step's shape (FetchCommit of the head into the workspace, then MergeInto).
+type mergeRig struct {
+	t              *testing.T
+	bare, work, ws string
+	fork, trunk    string // the commit both histories share, and the trunk's head
+	remote         string
+}
+
+func newMergeRig(t *testing.T) *mergeRig {
+	root := t.TempDir()
+	r := &mergeRig{t: t, bare: filepath.Join(root, "r.git"), work: filepath.Join(root, "work"), ws: filepath.Join(root, "ws")}
+	for _, d := range []string{r.bare, r.work, r.ws} {
+		if err := os.MkdirAll(d, 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	r.remote = "file://" + r.bare
+	realGit(t, r.bare, "init", "-q", "--bare")
+	realGit(t, r.work, "init", "-q", "-b", "main")
+	writeFile(t, r.work, "a.txt", "one\ntwo\nthree\n")
+	writeFile(t, r.work, "modules/m/module.json", "{}\n")
+	realGit(t, r.work, "add", ".")
+	realGit(t, r.work, "commit", "-q", "-m", "fork point")
+	r.fork = realGit(t, r.work, "rev-parse", "HEAD")
+	return r
+}
+
+// head makes a commit on a branch off the fork point, pushes it as the pull request's head ref and answers its sha.
+func (r *mergeRig) head(files map[string]string) string {
+	realGit(r.t, r.work, "checkout", "-q", "-B", "pr", r.fork)
+	for n, c := range files {
+		writeFile(r.t, r.work, n, c)
+	}
+	realGit(r.t, r.work, "add", ".")
+	realGit(r.t, r.work, "commit", "-q", "-m", "head")
+	h := realGit(r.t, r.work, "rev-parse", "HEAD")
+	realGit(r.t, r.work, "push", "-q", r.bare, "HEAD:refs/pull/1/head")
+	return h
+}
+
+// advance moves the trunk past the fork point with a commit changing files, pushes it and answers its sha.
+func (r *mergeRig) advance(files map[string]string) string {
+	realGit(r.t, r.work, "checkout", "-q", "-B", "main", r.fork)
+	for n, c := range files {
+		writeFile(r.t, r.work, n, c)
+	}
+	realGit(r.t, r.work, "add", ".")
+	realGit(r.t, r.work, "commit", "-q", "-m", "trunk moves")
+	r.trunk = realGit(r.t, r.work, "rev-parse", "HEAD")
+	realGit(r.t, r.work, "push", "-q", "-f", r.bare, "HEAD:refs/heads/main")
+	return r.trunk
+}
+
+func (r *mergeRig) fetch(head string) {
+	if err := FetchCommit(context.Background(), forgekey.ExecRunner, r.ws, r.remote, head, "refs/pull/1/head", AllowFileRemote()); err != nil {
+		r.t.Fatal(err)
+	}
+}
+
+// 1674/AC1: a clean merge answers the merge commit and the changed files, and leaves the workspace at the merge, which
+// holds both sides' changes.
+func TestMergeIntoACleanMergeAnswersTheMergeCommitAndTheChangedFiles(t *testing.T) {
+	r := newMergeRig(t)
+	head := r.head(map[string]string{"b.txt": "head\n"})
+	base := r.advance(map[string]string{"a.txt": "one\ntwo\nthree\nfour\n"})
+	r.fetch(head)
+	res, err := MergeInto(context.Background(), forgekey.ExecRunner, r.ws, r.remote, base, head, AllowFileRemote())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Base != base || res.Head != head || len(res.Merge) != 40 || res.Merge == base || res.Merge == head || len(res.Conflicts) != 0 {
+		t.Fatalf("result = %+v", res)
+	}
+	if !reflect.DeepEqual(res.Changed, []string{"b.txt"}) {
+		t.Errorf("changed = %v, want only what the head adds to the trunk: b.txt", res.Changed)
+	}
+	if at := realGit(t, r.ws, "rev-parse", "HEAD"); at != res.Merge {
+		t.Errorf("the workspace is at %s, not at the merge %s", at, res.Merge)
+	}
+	for f, want := range map[string]string{"b.txt": "head\n", "a.txt": "one\ntwo\nthree\nfour\n"} {
+		if got, _ := os.ReadFile(filepath.Join(r.ws, f)); string(got) != want {
+			t.Errorf("%s = %q, want %q", f, got, want)
+		}
+	}
+	if parents := strings.Fields(realGit(t, r.ws, "rev-list", "--parents", "-n", "1", res.Merge)); len(parents) != 3 || parents[1] != base || parents[2] != head {
+		t.Errorf("the merge commit's parents = %v, want the trunk commit and the head", parents)
+	}
+	if author := realGit(t, r.ws, "log", "-1", "--format=%an <%ae>", res.Merge); author != "mesh merge check <merge-check@mesh.invalid>" {
+		t.Errorf("the merge is made as %q", author)
+	}
+}
+
+// 1674/AC2: a conflict is an answer: the files in conflict, no merge commit, and the workspace left at the trunk commit.
+func TestMergeIntoAConflictAnswersTheFilesAndLeavesTheTreeAtTheTrunk(t *testing.T) {
+	r := newMergeRig(t)
+	head := r.head(map[string]string{"a.txt": "one\nHEAD\nthree\n", "c.txt": "c\n"})
+	base := r.advance(map[string]string{"a.txt": "one\nTRUNK\nthree\n"})
+	r.fetch(head)
+	res, err := MergeInto(context.Background(), forgekey.ExecRunner, r.ws, r.remote, base, head, AllowFileRemote())
+	if err != nil {
+		t.Fatalf("a conflict is an answer, not an error: %v", err)
+	}
+	if !reflect.DeepEqual(res.Conflicts, []string{"a.txt"}) || res.Merge != "" || len(res.Changed) != 0 || res.Base != base || res.Head != head {
+		t.Fatalf("result = %+v", res)
+	}
+	if at := realGit(t, r.ws, "rev-parse", "HEAD"); at != base {
+		t.Errorf("the workspace is at %s, not at the trunk commit %s", at, base)
+	}
+	if got, _ := os.ReadFile(filepath.Join(r.ws, "a.txt")); string(got) != "one\nTRUNK\nthree\n" {
+		t.Errorf("a.txt = %q, want the trunk's", got)
+	}
+	if st := realGit(t, r.ws, "status", "--porcelain"); st != "" {
+		t.Errorf("the tree is not clean after the aborted merge: %q", st)
+	}
+	if _, err := os.Stat(filepath.Join(r.ws, "c.txt")); err == nil {
+		t.Error("a file of the head is in a tree left at the trunk")
+	}
+}
+
+// A head already in the trunk merges into nothing: the merge is the trunk commit and no path changes.
+func TestMergeIntoAHeadAlreadyInTheTrunkChangesNothing(t *testing.T) {
+	r := newMergeRig(t)
+	head := r.head(map[string]string{"b.txt": "head\n"})
+	r.fork = head // the trunk continues from the head
+	base := r.advance(map[string]string{"a.txt": "one\ntwo\nthree\nfour\n"})
+	r.fetch(head)
+	res, err := MergeInto(context.Background(), forgekey.ExecRunner, r.ws, r.remote, base, head, AllowFileRemote())
+	if err != nil || res.Merge != base || len(res.Changed) != 0 || len(res.Conflicts) != 0 {
+		t.Errorf("result = %+v, %v", res, err)
+	}
+}

go/buildstep/merge_test.go

@@ -0,0 +1,74 @@
+package buildstep
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// 1674/AC3: no base is refused before anything runs; so is a base or a commit that is not a full sha, a workspace that
+// is not at the commit, and a remote that is not ssh://.
+func TestMergeIntoRefusesWhatIsNotAMerge(t *testing.T) {
+	f := &fakeGit{}
+	for name, c := range map[string]struct{ remote, base, commit string }{
+		"no base":          {"ssh://mesh-forge/o/r.git", "", sha},
+		"a short base":     {"ssh://mesh-forge/o/r.git", "abc123", sha},
+		"a branch as base": {"ssh://mesh-forge/o/r.git", "main", sha},
+		"a short commit":   {"ssh://mesh-forge/o/r.git", sha, "abc"},
+		"an https remote":  {"https://forge.example/o/r.git", sha, sha},
+	} {
+		_, err := MergeInto(context.Background(), f.run, "/w", c.remote, c.base, c.commit)
+		if err == nil {
+			t.Errorf("%s accepted", name)
+		}
+	}
+	if len(f.calls) != 0 {
+		t.Errorf("git ran for a refused merge: %v", f.calls)
+	}
+	g := &fakeGit{rule: func(l string) forgekey.Ran {
+		if strings.Contains(l, "rev-parse HEAD") {
+			return forgekey.Ran{Stdout: strings.Repeat("f", 40) + "\n"}
+		}
+		return forgekey.Ran{}
+	}}
+	_, err := MergeInto(context.Background(), g.run, "/w", "ssh://mesh-forge/o/r.git", strings.Repeat("a", 40), sha)
+	if err == nil || !strings.Contains(err.Error(), "not at the commit") || len(g.calls) != 1 {
+		t.Errorf("a workspace at another commit: %v after %d commands", err, len(g.calls))
+	}
+}
+
+// 1674/AC4: the merge is made with the check merge's identity and flags, hooks off, and fetches with no credential.
+func TestMergeIntoRunsTheCheckMergesCommands(t *testing.T) {
+	base := strings.Repeat("b", 40)
+	f := &fakeGit{rule: func(l string) forgekey.Ran {
+		switch {
+		case strings.HasSuffix(l, "rev-parse HEAD"):
+			return forgekey.Ran{Stdout: sha + "\n"}
+		case strings.Contains(l, "--is-shallow-repository"):
+			return forgekey.Ran{Stdout: "true\n"}
+		}
+		return forgekey.Ran{}
+	}}
+	if _, err := MergeInto(context.Background(), f.run, "/w", "ssh://mesh-forge/o/r.git", base, sha); err != nil {
+		t.Fatal(err)
+	}
+	all := strings.Join(f.calls, "\n")
+	for _, want := range []string{
+		pre + "fetch --no-tags --unshallow origin " + base,
+		pre + "checkout -q --detach " + base,
+		"user.name=mesh merge check", "user.email=merge-check@mesh.invalid", "commit.gpgsign=false", "core.hooksPath=/dev/null",
+		"merge --no-ff --no-edit --no-verify --quiet -m",
+		pre + "diff --name-only --no-renames " + base,
+	} {
+		if !strings.Contains(all, want) {
+			t.Errorf("the commands lack %q:\n%s", want, all)
+		}
+	}
+	for _, c := range f.calls {
+		if strings.Contains(c, "https://") || !strings.Contains(c, "credential.helper= ") {
+			t.Errorf("command %q carries a credential or https", c)
+		}
+	}
+}

go/buildstep/mirror_integration_test.go

@@ -0,0 +1,65 @@
+//go:build integration
+
+package buildstep
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// Issue 890 C1 (AC3): a mirror brought to two commits in turn; a fetch through it checks out each commit, the
+// alternates name the mirror, and no symlink is in the workspace.
+func TestMirrorServesTwoCommitsWithoutSymlinks(t *testing.T) {
+	root := t.TempDir()
+	src := filepath.Join(root, "src.git")
+	work := filepath.Join(root, "work")
+	for _, d := range []string{src, work} {
+		if err := os.MkdirAll(d, 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	gitIn(t, src, "init", "-q", "--bare")
+	gitIn(t, work, "init", "-q")
+	var commits []string
+	for _, c := range []string{"one", "two"} {
+		if err := os.WriteFile(filepath.Join(work, "f"), []byte(c), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		gitIn(t, work, "add", "f")
+		gitIn(t, work, "commit", "-q", "-m", c)
+		commits = append(commits, gitIn(t, work, "rev-parse", "HEAD"))
+		gitIn(t, work, "push", "-q", src, "HEAD:refs/heads/main")
+	}
+	remote := "file://" + src
+	mirror := filepath.Join(root, "mirror.git")
+	for i, commit := range commits {
+		if err := UpdateMirror(context.Background(), forgekey.ExecRunner, mirror, remote, commit, "", AllowFileRemote()); err != nil {
+			t.Fatal(err)
+		}
+		ws := filepath.Join(root, "ws"+string(rune('0'+i)))
+		if err := os.MkdirAll(ws, 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := FetchCommit(context.Background(), forgekey.ExecRunner, ws, remote, commit, "", AllowFileRemote(), WithMirror(mirror)); err != nil {
+			t.Fatal(err)
+		}
+		if head := gitIn(t, ws, "rev-parse", "HEAD"); head != commit {
+			t.Errorf("HEAD = %s, want %s", head, commit)
+		}
+		b, _ := os.ReadFile(filepath.Join(ws, ".git", "objects", "info", "alternates"))
+		if !strings.Contains(string(b), filepath.Join(mirror, "objects")) {
+			t.Errorf("alternates %q", b)
+		}
+		_ = filepath.Walk(ws, func(p string, fi os.FileInfo, err error) error {
+			if err == nil && fi.Mode()&os.ModeSymlink != 0 {
+				t.Errorf("symlink %s", p)
+			}
+			return nil
+		})
+	}
+}

go/buildstep/mirror_test.go

@@ -0,0 +1,106 @@
+package buildstep
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// Issue 890 C1 (ADR 0536 §2): a fetch through a bare mirror names the mirror in .git/objects/info/alternates, a
+// plain file, and never links it.
+func TestFetchCommitWithMirrorWritesAlternates(t *testing.T) {
+	mirror := t.TempDir()
+	ws := t.TempDir()
+	f := &fakeGit{}
+	// the fake's init does not create .git; make the objects directory as git init would.
+	if err := os.MkdirAll(filepath.Join(ws, ".git", "objects", "info"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	err := FetchCommit(context.Background(), f.run, ws, "ssh://mesh-forge/novox/mesh-sdk.git", sha, "", WithMirror(mirror))
+	if err != nil {
+		t.Fatal(err)
+	}
+	p := filepath.Join(ws, ".git", "objects", "info", "alternates")
+	b, err := os.ReadFile(p)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := strings.TrimSpace(string(b)), filepath.Join(mirror, "objects"); got != want {
+		t.Errorf("alternates %q, want %q", got, want)
+	}
+	if fi, err := os.Lstat(p); err != nil || !fi.Mode().IsRegular() {
+		t.Errorf("alternates is not a plain file: %v %v", fi, err)
+	}
+	// the alternates exist before the fetch runs
+	if len(f.calls) < 3 || !strings.Contains(f.calls[2], "fetch") {
+		t.Errorf("calls %v", f.calls)
+	}
+}
+
+func TestWithMirrorRefusesARelativeOrMissingMirror(t *testing.T) {
+	for _, m := range []string{"rel/mirror", filepath.Join(t.TempDir(), "absent")} {
+		f := &fakeGit{}
+		err := FetchCommit(context.Background(), f.run, t.TempDir(), "ssh://mesh-forge/novox/x.git", sha, "", WithMirror(m))
+		if err == nil || len(f.calls) != 0 {
+			t.Errorf("mirror %q: err %v, calls %v", m, err, f.calls)
+		}
+	}
+}
+
+func TestUpdateMirrorInitsBareThenFetches(t *testing.T) {
+	mirror := filepath.Join(t.TempDir(), "mirror.git")
+	f := &fakeGit{}
+	if err := UpdateMirror(context.Background(), f.run, mirror, "ssh://mesh-forge/novox/x.git", sha, ""); err != nil {
+		t.Fatal(err)
+	}
+	pm := "git -c credential.helper= -C " + mirror + " "
+	want := []string{
+		"git -c credential.helper= init -q --bare " + mirror,
+		pm + "remote add origin ssh://mesh-forge/novox/x.git",
+		pm + "fetch --no-tags origin " + sha,
+		pm + "cat-file -e " + sha + "^{commit}",
+	}
+	if strings.Join(f.calls, "\n") != strings.Join(want, "\n") {
+		t.Errorf("commands:\n%s\nwant:\n%s", strings.Join(f.calls, "\n"), strings.Join(want, "\n"))
+	}
+}
+
+func TestUpdateMirrorKeepsAnExistingMirrorAndFallsBackToTheRef(t *testing.T) {
+	mirror := t.TempDir() // exists: no init
+	if err := os.WriteFile(filepath.Join(mirror, "HEAD"), []byte("ref: refs/heads/main\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	f := &fakeGit{}
+	f.rule = func(args string) (r forgekey.Ran) {
+		if strings.HasSuffix(args, "origin "+sha) {
+			r.Status = 1
+			r.Stderr = "not our ref"
+		}
+		return
+	}
+	if err := UpdateMirror(context.Background(), f.run, mirror, "ssh://mesh-forge/novox/x.git", sha, "refs/pull/3/head"); err != nil {
+		t.Fatal(err)
+	}
+	all := strings.Join(f.calls, "\n")
+	if strings.Contains(all, "init") || strings.Contains(all, "remote add") || !strings.Contains(all, "fetch --no-tags origin refs/pull/3/head") {
+		t.Errorf("commands:\n%s", all)
+	}
+}
+
+func TestUpdateMirrorRefusesBeforeRunning(t *testing.T) {
+	f := &fakeGit{}
+	for _, c := range []struct{ remote, commit string }{
+		{"https://x/y.git", sha}, {"ssh://u@h/o/r.git", sha}, {"ssh://h/o/r.git", "abc"},
+	} {
+		if err := UpdateMirror(context.Background(), f.run, t.TempDir(), c.remote, c.commit, ""); err == nil {
+			t.Errorf("%v accepted", c)
+		}
+	}
+	if len(f.calls) != 0 {
+		t.Errorf("ran %v", f.calls)
+	}
+}

go/buildstep/narrow.go

@@ -0,0 +1,71 @@
+package buildstep
+
+import (
+	"fmt"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+)
+
+// narrowKept are the files of a module's directory a narrowed build keeps beside its named paths: its manifest and
+// its lock files, each an input of the module's key (ModuleTree's Manifest and Locks). package.json and go.mod are
+// not kept: neither is in the named tree, so a build that needs one names it among its artifact's paths, which puts
+// it in the key (novox/hq ADR 0499 clause 4).
+var narrowKept = append([]string{"module.json"}, lockFiles...)
+
+// Narrow leaves in the fetched tree only what a build of an artifact that names its paths may see (novox/hq ADR 0499
+// clause 4): r.Dir's named paths, its manifest and lock files, and .git; everything else is removed, so a file outside
+// them cannot change what is built without changing its key. A named path absent at the tree is an error naming it,
+// and nothing is removed then. With no paths in r it changes nothing. Both build modules' fetch steps call it.
+func Narrow(tree string, r FetchRequest) error {
+	if len(r.Paths) == 0 {
+		return nil
+	}
+	keep := map[string]bool{".git": true}
+	for _, p := range r.Paths {
+		rel := path.Join(r.Dir, p)
+		if strings.HasPrefix(rel, "../") || rel == ".." || path.IsAbs(p) {
+			return fmt.Errorf("the named path %q leaves the module's directory", p)
+		}
+		if _, err := os.Lstat(filepath.Join(tree, filepath.FromSlash(rel))); err != nil {
+			return fmt.Errorf("the named path %q is not in the fetched tree: %w", p, err)
+		}
+		keep[rel] = true
+	}
+	for _, f := range narrowKept {
+		keep[path.Join(r.Dir, f)] = true
+	}
+	return prune(tree, "", keep)
+}
+
+// prune removes from dir (rel within the tree) every entry that is neither kept nor on the way to one.
+func prune(root, rel string, keep map[string]bool) error {
+	entries, err := os.ReadDir(filepath.Join(root, filepath.FromSlash(rel)))
+	if err != nil {
+		return err
+	}
+	for _, e := range entries {
+		p := path.Join(rel, e.Name())
+		if keep[p] {
+			continue
+		}
+		ancestor := false
+		for k := range keep {
+			if strings.HasPrefix(k, p+"/") {
+				ancestor = true
+				break
+			}
+		}
+		if ancestor && e.IsDir() {
+			if err := prune(root, p, keep); err != nil {
+				return err
+			}
+			continue
+		}
+		if err := os.RemoveAll(filepath.Join(root, filepath.FromSlash(p))); err != nil {
+			return err
+		}
+	}
+	return nil
+}

go/buildstep/narrow_test.go

@@ -0,0 +1,82 @@
+package buildstep
+
+import (
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"testing"
+)
+
+func filesUnder(t *testing.T, root string) []string {
+	t.Helper()
+	var out []string
+	_ = filepath.Walk(root, func(p string, info os.FileInfo, err error) error {
+		if err == nil && !info.IsDir() {
+			rel, _ := filepath.Rel(root, p)
+			out = append(out, filepath.ToSlash(rel))
+		}
+		return nil
+	})
+	sort.Strings(out)
+	return out
+}
+
+// A build of an artifact that names its paths sees only those paths, its manifest and its lock files (novox/hq ADR 0499
+// clause 4): Narrow removes everything else of the fetched tree but .git, package.json and go.mod among it, since
+// neither is in the named tree nor among the lock files; with no paths it changes nothing.
+func TestNarrowLeavesOnlyTheNamedPathsTheManifestAndTheLocks(t *testing.T) {
+	tree := t.TempDir()
+	for _, f := range []string{".git/HEAD", "module.json", "package.json", "package-lock.json", "go.sum", "src/index.ts",
+		"src/deep/a.ts", "test/a.test.ts", "tsconfig.json", "go/delivery/x.go", "README.md", "other/module.json"} {
+		writeTreeFile(t, tree, f, "x")
+	}
+	if err := Narrow(tree, FetchRequest{}); err != nil {
+		t.Fatal(err)
+	}
+	if got := len(filesUnder(t, tree)); got != 12 {
+		t.Fatalf("a request without paths changed the tree: %d files", got)
+	}
+	if err := Narrow(tree, FetchRequest{Dir: ".", Paths: []string{"src", "test", "tsconfig.json"}}); err != nil {
+		t.Fatal(err)
+	}
+	want := ".git/HEAD,go.sum,module.json,package-lock.json,src/deep/a.ts,src/index.ts,test/a.test.ts,tsconfig.json"
+	if got := strings.Join(filesUnder(t, tree), ","); got != want {
+		t.Fatalf("the narrowed tree holds %s\nwant %s", got, want)
+	}
+}
+
+func TestNarrowKeepsAModuleDirectorysPathsAndFailsOnAnAbsentOne(t *testing.T) {
+	tree := t.TempDir()
+	for _, f := range []string{".git/config", "modules/a/module.json", "modules/a/go.mod", "modules/a/src/x.ts",
+		"modules/a/notes.md", "modules/b/module.json", "root.txt"} {
+		writeTreeFile(t, tree, f, "x")
+	}
+	err := Narrow(tree, FetchRequest{Dir: "modules/a", Paths: []string{"src", "gone"}})
+	if err == nil || !strings.Contains(err.Error(), `"gone"`) {
+		t.Fatalf("an absent named path gave %v", err)
+	}
+	if len(filesUnder(t, tree)) != 7 {
+		t.Fatal("a refused narrowing removed files")
+	}
+	if err := Narrow(tree, FetchRequest{Dir: "modules/a", Paths: []string{"src"}}); err != nil {
+		t.Fatal(err)
+	}
+	if got := strings.Join(filesUnder(t, tree), ","); got != ".git/config,modules/a/module.json,modules/a/src/x.ts" {
+		t.Fatalf("the narrowed tree holds %s", got)
+	}
+}
+
+// A build that needs package.json or go.mod names it among its paths, and so keys on it (ADR 0499 clause 4).
+func TestNarrowKeepsAManifestOfTheLanguageOnlyWhenNamed(t *testing.T) {
+	tree := t.TempDir()
+	for _, f := range []string{"module.json", "package.json", "go.mod", "src/a.ts"} {
+		writeTreeFile(t, tree, f, "x")
+	}
+	if err := Narrow(tree, FetchRequest{Dir: ".", Paths: []string{"src", "package.json"}}); err != nil {
+		t.Fatal(err)
+	}
+	if got := strings.Join(filesUnder(t, tree), ","); got != "module.json,package.json,src/a.ts" {
+		t.Fatalf("the narrowed tree holds %s", got)
+	}
+}

go/buildstep/pack.go

@@ -0,0 +1,100 @@
+package buildstep
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+)
+
+// Pack tars and gzips a directory the way the build agent does, byte for byte, and answers the archive and its
+// digest, "sha256:" and the hex of the archive's bytes (issue 1479; novox/hq ADR 0405 §7, ADR 0453 §7). It is a
+// copy of mesh-controller's internal/builder/builder.go pack (origin/main 073ccc29, :1351-1425), which stays
+// where it is until the build agent goes: a build module's digest is compared with the build agent's for one
+// fingerprint, so the bytes must be equal.
+//
+// Deterministically: regular files only (a symlink or a device is refused), sorted relative paths with
+// slashes, each header carrying its name, permission bits and size and nothing else, the gzip default writer.
+func Pack(root string) (archive []byte, digest string, err error) {
+	raw, err := pack(root)
+	if err != nil {
+		return nil, "", err
+	}
+	sum := sha256.Sum256(raw)
+	return raw, "sha256:" + hex.EncodeToString(sum[:]), nil
+}
+
+func pack(root string) ([]byte, error) {
+	info, err := os.Stat(root)
+	if err != nil {
+		return nil, err
+	}
+	if !info.IsDir() {
+		return nil, fmt.Errorf("%s is not a directory", root)
+	}
+
+	var paths []string
+	err = filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if info.IsDir() || !info.Mode().IsRegular() {
+			// Only files. A symlink or a device in an archive is refused by the host that unpacks
+			// it, so putting one in would build something that cannot be applied.
+			if !info.IsDir() && !info.Mode().IsRegular() {
+				return fmt.Errorf("%s is neither a file nor a directory, and an archive carries "+
+					"only those", path)
+			}
+			return nil
+		}
+		paths = append(paths, path)
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	// filepath.Walk walks in lexical order; the sort is kept as the build agent keeps it, since an archive
+	// whose digest changes because the traversal did is a silent failure.
+	sort.Strings(paths)
+
+	var out bytes.Buffer
+	zipped := gzip.NewWriter(&out)
+	writer := tar.NewWriter(zipped)
+	for _, path := range paths {
+		body, err := os.ReadFile(path)
+		if err != nil {
+			return nil, err
+		}
+		relative, err := filepath.Rel(root, path)
+		if err != nil {
+			return nil, err
+		}
+		info, err := os.Stat(path)
+		if err != nil {
+			return nil, err
+		}
+		mode := int64(info.Mode().Perm())
+		if err := writer.WriteHeader(&tar.Header{
+			Name: filepath.ToSlash(relative), Mode: mode, Size: int64(len(body)),
+			Typeflag: tar.TypeReg,
+			// Everything else left at its zero value on purpose: no times, owners or names.
+		}); err != nil {
+			return nil, err
+		}
+		if _, err := writer.Write(body); err != nil {
+			return nil, err
+		}
+	}
+	if err := writer.Close(); err != nil {
+		return nil, err
+	}
+	if err := zipped.Close(); err != nil {
+		return nil, err
+	}
+	return out.Bytes(), nil
+}

go/buildstep/pack_test.go

@@ -0,0 +1,84 @@
+package buildstep
+
+import (
+	"bytes"
+	"compress/gzip"
+	"crypto/sha256"
+	"encoding/hex"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+// fixture writes three files in two directories (modes 0644 and 0755).
+func fixture(t *testing.T) string {
+	t.Helper()
+	root := t.TempDir()
+	for _, f := range []struct {
+		p    string
+		mode os.FileMode
+		body string
+	}{{"a/x.txt", 0o644, "x\n"}, {"a/run.sh", 0o755, "#!/bin/sh\necho hi\n"}, {"b/c/y.txt", 0o644, "why\n"}} {
+		path := filepath.Join(root, f.p)
+		if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(path, []byte(f.body), f.mode); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.Chmod(path, f.mode); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return root
+}
+
+// 1479/AC1: the tar stream inside the archive equals the bytes mesh-controller's pack makes for this tree.
+// testdata/pack-golden.tar is the uncompressed stream, made once by running mesh-controller
+// internal/builder/builder.go pack (origin/main 073ccc29, :1351-1425) on this fixture (above, modes set by chmod)
+// and gunzipping its archive. The gzip layer is not compared byte for byte, since compress/gzip's output differs
+// between Go versions; its header is checked to carry no name, no comment and no time.
+func TestPackEqualsTheBuildAgentsArchive(t *testing.T) {
+	golden, err := os.ReadFile("testdata/pack-golden.tar")
+	if err != nil {
+		t.Fatal(err)
+	}
+	archive, digest, err := Pack(fixture(t))
+	if err != nil {
+		t.Fatal(err)
+	}
+	zr, err := gzip.NewReader(bytes.NewReader(archive))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if zr.Name != "" || zr.Comment != "" || !zr.ModTime.IsZero() {
+		t.Errorf("gzip header = name %q, comment %q, time %v; want none", zr.Name, zr.Comment, zr.ModTime)
+	}
+	tarBytes, err := io.ReadAll(zr)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(tarBytes, golden) {
+		t.Errorf("the tar stream is %d bytes, the build agent's %d, and they differ", len(tarBytes), len(golden))
+	}
+	sum := sha256.Sum256(archive)
+	if digest != "sha256:"+hex.EncodeToString(sum[:]) {
+		t.Errorf("digest = %s, not the sha256 of the archive", digest)
+	}
+}
+
+// 1479/AC2: touching every file's time changes nothing.
+func TestPackDigestIgnoresFileTimes(t *testing.T) {
+	root := fixture(t)
+	_, first, err := Pack(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	later := time.Now().Add(48 * time.Hour)
+	filepath.Walk(root, func(p string, _ os.FileInfo, _ error) error { return os.Chtimes(p, later, later) })
+	if _, second, err := Pack(root); err != nil || second != first {
+		t.Errorf("digests %s and %s (%v)", first, second, err)
+	}
+}

go/buildstep/pack_unix_test.go

@@ -0,0 +1,25 @@
+//go:build unix
+
+package buildstep
+
+import (
+	"path/filepath"
+	"strings"
+	"syscall"
+	"testing"
+)
+
+// 1479/AC3: anything but a file or a directory is refused, naming it. The rule of this repository is that no
+// test makes a symlink, so the non-regular entry is a named pipe: Pack refuses a symlink on the same branch
+// (filepath.Walk reports it by lstat as not regular).
+func TestPackRefusesAnEntryThatIsNotAFile(t *testing.T) {
+	root := fixture(t)
+	pipe := filepath.Join(root, "a", "pipe")
+	if err := syscall.Mkfifo(pipe, 0o644); err != nil {
+		t.Fatal(err)
+	}
+	_, _, err := Pack(root)
+	if err == nil || !strings.Contains(err.Error(), pipe) {
+		t.Errorf("Pack = %v, want a refusal naming %s", err, pipe)
+	}
+}

go/buildstep/pull.go

@@ -0,0 +1,445 @@
+package buildstep
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"sort"
+	"sync"
+	"time"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// **The pull loop the build modules share** (novox/hq ADR 0525 §4-§6, ADR 0536 §4; issue 1887). A build module on a node
+// whose build capacity is above zero pulls the asks of its language's seat: from the delivery worker first, then check,
+// then recheck, holding at most its capacity at once. Each ask runs as a step under the ask's own id, so its end is the
+// key <node>.<ask id> in the module's steps state, which the asker watches; the ask is acknowledged when that end is
+// written, kept alive while it runs by an in-progress signal, and redelivered by the stream to another node if this one
+// stops. No part keeps a timer for an ask: the pull's own wait and the stream's acknowledgement wait are the bus's.
+
+// Pulled is one ask a source handed over, with what decides its fate on the bus.
+type Pulled struct {
+	// Kind is the worker it came from, filled by the puller.
+	Kind string
+	Data []byte
+	// Delivered is how many times the bus has handed it over, this time included.
+	Delivered uint64
+	// Ack ends it: it is never delivered again. InProgress tells the bus it is still being worked, restarting its
+	// acknowledgement wait. Nak hands it back to be delivered again at once (to this node or another). Term drops it.
+	Ack, InProgress, Nak, Term func() error
+}
+
+// AskSource is where a puller takes asks from: the seat's workers on the bus (JetStreamAsks) or a test double
+// (FakeAsks).
+type AskSource interface {
+	// Next takes one ask of kind: with wait 0 only one already waiting, else waiting for one at most wait. It answers
+	// nil and no error when none came.
+	Next(ctx context.Context, kind string, wait time.Duration) (*Pulled, error)
+}
+
+// Defaults of a Puller.
+var (
+	// DefaultPullWait is how long one pull of the delivery worker waits for an ask while every worker is empty: the
+	// pull's own wait (as process.Consume's), after which the check and recheck workers are looked at again.
+	DefaultPullWait = 5 * time.Second
+	// DefaultHeartbeat is how often a running ask tells the bus it is still being worked; under the seat worker's
+	// acknowledgement wait of 60 s (mesh-controller internal/broker HolderConsumerFor).
+	DefaultHeartbeat = 20 * time.Second
+)
+
+// Puller pulls a build seat's asks and runs them.
+type Puller struct {
+	Source   AskSource
+	Language string // the seat's language: delivery.AskGo, AskNode or AskImage
+	Node     string // the node this holder runs on, the first part of its step keys
+	Put      Put    // writes the module's steps state
+	// Capacity is how many asks the node runs at once; read before every pull, so a change takes effect at the next
+	// one. 0 pulls nothing.
+	Capacity func() int
+	// Run runs one ask's job; a *Refusal ends its step refused. Its result is the step's result.
+	Run func(ctx context.Context, ask delivery.StepAsk) (any, error)
+	// PullWait and Heartbeat default to DefaultPullWait and DefaultHeartbeat.
+	PullWait  time.Duration
+	Heartbeat time.Duration
+	Logf      func(format string, args ...any)
+	// Load reads one key of the state the node's pause is kept in (nil and no error when it is absent). When set, Pull
+	// reads the node's pause key (delivery.PauseKey) before it pulls, and Pause and Resume write it with PausePut, so a
+	// pause outlives a restart.
+	Load func(key string) ([]byte, error)
+	// PausePut writes the node's pause key: the module's pauses state (delivery.PausesState), which has no age, so a
+	// pause never ends by itself while the steps state drops its old keys. Put when nil.
+	PausePut Put
+	// WatchConfig, when set, follows the module's config value `capacity` (CapacitySetting) as mesh-config resolves it
+	// for this node, and wakes the puller on each change (watchCapacity): WatchConfigServed in a module, a test's own
+	// double. Until it hands a value the puller judges by Capacity.
+	WatchConfig func(key string, handle func(stdio.ProvisionChange) error) error
+
+	mu      sync.Mutex
+	inHand  int
+	running map[string]RunningAsk
+	paused  bool
+	wake    chan struct{}
+	once    sync.Once
+	// watched is the capacity the config watch handed last, used in place of Capacity once hasWatched.
+	watched    int
+	hasWatched bool
+}
+
+func (p *Puller) init() {
+	p.once.Do(func() { p.wake = make(chan struct{}, 1) })
+}
+
+func (p *Puller) logf(format string, args ...any) {
+	if p.Logf != nil {
+		p.Logf(format, args...)
+	}
+}
+
+// Wake makes a waiting puller look again: after a capacity change, a resume, or a step's end.
+func (p *Puller) Wake() {
+	p.init()
+	select {
+	case p.wake <- struct{}{}:
+	default:
+	}
+}
+
+// Pause stops the puller taking asks; the asks it holds run to their end. by names who paused it. With Load set the
+// pause is written on the node's pause key first, and an error there leaves the puller as it was.
+func (p *Puller) Pause(by string) error { return p.setPaused(true, by) }
+
+// Resume lets the puller take asks again, written as Pause's is.
+func (p *Puller) Resume(by string) error { return p.setPaused(false, by) }
+
+func (p *Puller) setPaused(paused bool, by string) error {
+	if p.Load != nil {
+		key, err := delivery.PauseKey(p.Node)
+		if err != nil {
+			return err
+		}
+		raw, err := delivery.EncodePause(delivery.Pause{Paused: paused, By: by, At: now()})
+		if err != nil {
+			return err
+		}
+		put := p.PausePut
+		if put == nil {
+			put = p.Put
+		}
+		if _, err := put(key, json.RawMessage(raw)); err != nil {
+			return fmt.Errorf("buildstep: writing the pause of %s: %w", p.Node, err)
+		}
+	}
+	p.mu.Lock()
+	p.paused = paused
+	p.mu.Unlock()
+	p.Wake()
+	return nil
+}
+
+// restore reads the node's pause key, when Load is set.
+func (p *Puller) restore() error {
+	if p.Load == nil {
+		return nil
+	}
+	key, err := delivery.PauseKey(p.Node)
+	if err != nil {
+		return err
+	}
+	raw, err := p.Load(key)
+	if err != nil {
+		return fmt.Errorf("buildstep: reading the pause of %s: %w", p.Node, err)
+	}
+	if raw == nil {
+		return nil
+	}
+	v, err := delivery.DecodePause(raw)
+	if err != nil {
+		return fmt.Errorf("buildstep: the pause of %s: %w", p.Node, err)
+	}
+	p.mu.Lock()
+	p.paused = v.Paused
+	p.mu.Unlock()
+	return nil
+}
+
+// Paused says whether the puller takes no asks.
+func (p *Puller) Paused() bool {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return p.paused
+}
+
+// InHand is how many asks run now.
+func (p *Puller) InHand() int {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return p.inHand
+}
+
+// RunningAsk is an ask a puller runs now, as its seat's current verb says it.
+type RunningAsk struct {
+	ID      string    `json:"id"`
+	Kind    string    `json:"kind"`
+	Module  string    `json:"module,omitempty"`
+	Started time.Time `json:"started"`
+}
+
+// Running are the asks the puller runs now, oldest first.
+func (p *Puller) Running() []RunningAsk {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	out := make([]RunningAsk, 0, len(p.running))
+	for _, r := range p.running {
+		out = append(out, r)
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Started.Before(out[j].Started) })
+	return out
+}
+
+// room says whether the puller may take one more ask now.
+func (p *Puller) room() bool {
+	ok, _, _ := p.roomNow()
+	return ok
+}
+
+// roomNow is room, with the capacity and the asks in hand it was judged on.
+func (p *Puller) roomNow() (ok bool, capacity, inHand int) {
+	p.mu.Lock()
+	watched, has := p.watched, p.hasWatched
+	p.mu.Unlock()
+	if has {
+		capacity = watched
+	} else if p.Capacity != nil {
+		capacity = p.Capacity()
+	}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return !p.paused && p.inHand < capacity, capacity, p.inHand
+}
+
+// CapacityNow is the capacity the puller judges by: the config watch's last value, else Capacity.
+func (p *Puller) CapacityNow() int {
+	_, capacity, _ := p.roomNow()
+	return capacity
+}
+
+// Pull takes and runs asks until ctx ends. An ask still running then is neither ended nor acknowledged: the stream
+// delivers it again, to another node or to this one restarted.
+func (p *Puller) Pull(ctx context.Context) error {
+	p.init()
+	if p.Source == nil || p.Put == nil || p.Run == nil {
+		return errors.New("buildstep: a puller needs its source, its steps' put and its run")
+	}
+	if err := p.restore(); err != nil {
+		// An unreadable pause degrades to not paused, said once: a puller that stops silently is the worse failure, and a
+		// node kept from building is held by its capacity (0), not by a pause.
+		p.logf("the pause of %s cannot be read: %v; pulling as not paused", p.Node, err)
+	}
+	go p.watchCapacity() // WatchConfigServed waits for Serve, which a module starts after its pull
+	wait := p.PullWait
+	if wait <= 0 {
+		wait = DefaultPullWait
+	}
+	for {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		if ok, capacity, inHand := p.roomNow(); !ok {
+			// Parked until something wakes it: a capacity change (the config watch), a resume, or a step's end. Every
+			// park logs once, so a puller that sits idle says why (issue 1887).
+			p.logf("the %s puller on %s parks: %d of capacity %d in hand, paused %v", p.Language, p.Node, inHand, capacity, p.Paused())
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			case <-p.wake:
+			}
+			_, capacity, inHand = p.roomNow()
+			p.logf("the %s puller on %s wakes: %d of capacity %d in hand, paused %v", p.Language, p.Node, inHand, capacity, p.Paused())
+			continue
+		}
+		msg, err := p.next(ctx, wait)
+		if err != nil {
+			if ctx.Err() != nil {
+				return ctx.Err()
+			}
+			p.logf("the %s asks cannot be pulled: %v", p.Language, err)
+			select { // the pull's own wait before the next try, as an empty pull's
+			case <-ctx.Done():
+				return ctx.Err()
+			case <-p.wake:
+			case <-time.After(wait):
+			}
+			continue
+		}
+		if msg == nil {
+			continue
+		}
+		p.take(ctx, msg)
+	}
+}
+
+// next is one ask from the workers in their order: one already waiting on delivery, check or recheck, and when none
+// waits, a pull of the delivery worker that waits for one.
+func (p *Puller) next(ctx context.Context, wait time.Duration) (*Pulled, error) {
+	for _, kind := range delivery.AskKinds {
+		msg, err := p.Source.Next(ctx, kind, 0)
+		if err != nil || msg != nil {
+			return withKind(msg, kind), err
+		}
+	}
+	msg, err := p.Source.Next(ctx, delivery.AskDelivery, wait)
+	return withKind(msg, delivery.AskDelivery), err
+}
+
+func withKind(msg *Pulled, kind string) *Pulled {
+	if msg != nil {
+		msg.Kind = kind
+	}
+	return msg
+}
+
+// take starts one ask: it decodes it, refuses one that is not of this seat, and runs it as a step under its own id.
+func (p *Puller) take(ctx context.Context, msg *Pulled) {
+	kind := msg.Kind
+	ask, err := delivery.DecodeStepAsk(msg.Data)
+	if err == nil && (ask.Language != p.Language || (kind != "" && ask.Kind != kind)) {
+		err = fmt.Errorf("the ask %s is a %s ask of %s, pulled from the %s %s worker", ask.ID, ask.Kind, ask.Language, p.Language, kind)
+	}
+	if err != nil {
+		// An ask that is not one runs nowhere: delivering it again would only fail again.
+		p.logf("an ask dropped: %v", err)
+		_ = msg.Term()
+		return
+	}
+	step, key, err := begin(p.Put, p.Node, ask.Kind+" ask", ask.ID)
+	if err != nil {
+		p.logf("the ask %s cannot start on %s: %v", ask.ID, p.Node, err)
+		_ = msg.Nak()
+		return
+	}
+	if msg.Delivered > delivery.AskRuns {
+		// Run AskRuns times and never ended: each run took its node down or died with it. It is run no more, and said
+		// (issue 1907): the asker's key fails with why.
+		why := fmt.Errorf("the ask was taken %d times and no run of it ended: each took its build node down or died with it, so it is run no more (poison)", msg.Delivered-1)
+		p.logf("the ask %s is ended on %s: %v", ask.ID, p.Node, why)
+		_ = finish(p.Put, key, step, nil, why, p.Logf) // run no more either way: the asker's bound says it then
+		_ = msg.Term()
+		return
+	}
+	module := ""
+	if ask.Build != nil {
+		module = ask.Build.Module
+	}
+	p.mu.Lock()
+	p.inHand++
+	if p.running == nil {
+		p.running = map[string]RunningAsk{}
+	}
+	p.running[ask.ID] = RunningAsk{ID: ask.ID, Kind: ask.Kind, Module: module, Started: step.Started}
+	p.mu.Unlock()
+	go p.run(ctx, msg, ask, key, step)
+}
+
+func (p *Puller) run(ctx context.Context, msg *Pulled, ask delivery.StepAsk, key string, step delivery.Step) {
+	defer func() {
+		p.mu.Lock()
+		p.inHand--
+		delete(p.running, ask.ID)
+		p.mu.Unlock()
+		p.Wake()
+	}()
+	beat := p.Heartbeat
+	if beat <= 0 {
+		beat = DefaultHeartbeat
+	}
+	done := make(chan struct{})
+	go func() {
+		t := time.NewTicker(beat)
+		defer t.Stop()
+		for {
+			select {
+			case <-done:
+				return
+			case <-t.C:
+				if msg.InProgress != nil {
+					_ = msg.InProgress()
+				}
+			}
+		}
+	}()
+	result, err := protect(ctx, func(ctx context.Context) (any, error) { return p.Run(ctx, ask) })
+	close(done)
+	if ctx.Err() != nil {
+		// The process stops: the ask is neither ended nor acknowledged here, so the stream gives it to a node that runs.
+		return
+	}
+	if ferr := finish(p.Put, key, step, result, err, p.Logf); ferr != nil {
+		// No end was written: the ask is not acknowledged as done, so the stream gives it again and a run that can
+		// write its end (or the poison rule, issue 1907) ends it where its asker sees it (issue 1930).
+		p.logf("the ask %s ran on %s and no end of it could be written, so it is given back: %v", ask.ID, p.Node, ferr)
+		_ = msg.Nak()
+		return
+	}
+	if aerr := msg.Ack(); aerr != nil {
+		p.logf("the ask %s ended on %s and its acknowledgement failed: %v", ask.ID, p.Node, aerr)
+	}
+}
+
+// watchCapacity follows the module's config value `capacity` when WatchConfig is set (issue 1887, 2026-10-25: g14's
+// puller started at capacity 0 sat parked with capacity 2 set, because nothing woke it to read its settings file
+// again). The value comes as mesh-config resolved it for this node, the event of the change itself: the runtime hands
+// the value now and then each change its machine's provisioner client says moved, so nothing polls, and the puller does
+// not wait for the node-engine to fill its settings file again. Each value handed is kept, used in place of Capacity,
+// and wakes the puller. A watch that cannot start leaves the puller on Capacity, said once.
+func (p *Puller) watchCapacity() {
+	if p.WatchConfig == nil {
+		return
+	}
+	err := p.WatchConfig(CapacitySetting, func(c stdio.ProvisionChange) error {
+		n, why := p.capacityFrom(c)
+		p.mu.Lock()
+		before, had := p.watched, p.hasWatched
+		p.watched, p.hasWatched = n, true
+		p.mu.Unlock()
+		switch {
+		case why != "":
+			p.logf("the %s puller on %s pulls nothing: %s", p.Language, p.Node, why)
+		case !had || before != n:
+			p.logf("the %s build capacity of %s is %d, as mesh-config resolved it", p.Language, p.Node, n)
+		}
+		p.Wake()
+		return nil
+	})
+	if err != nil {
+		p.logf("the %s build capacity of %s cannot be followed on the bus, so it is read from the settings file when the "+
+			"puller wakes: %v", p.Language, p.Node, err)
+	}
+}
+
+// WatchConfigServed is stdio.WatchConfig once Serve has the runtime's channel (stdio.Served): a build module starts its
+// pull before it serves, and a watch asked before that would be refused.
+func WatchConfigServed(key string, handle func(stdio.ProvisionChange) error) error {
+	<-stdio.Served()
+	return stdio.WatchConfig(key, handle)
+}
+
+// capacityFrom is the node's capacity in one value the watch handed, and why it is 0 when it cannot be read.
+func (p *Puller) capacityFrom(c stdio.ProvisionChange) (int, string) {
+	if c.Refused != "" {
+		return 0, "its capacity is no longer answered: " + c.Refused
+	}
+	setting := ""
+	if len(c.Value) > 0 && string(c.Value) != "null" {
+		if err := json.Unmarshal(c.Value, &setting); err != nil {
+			return 0, fmt.Sprintf("its capacity %s is not a string", c.Value)
+		}
+	}
+	n, err := capacityOf(setting, p.Node)
+	if err != nil {
+		return 0, err.Error()
+	}
+	return n, ""
+}

go/buildstep/pull_bus.go

@@ -0,0 +1,102 @@
+package buildstep
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// JetStreamAsks is a build seat's workers on the bus: the shared pull consumer of each kind on the seat's stream
+// (delivery.AskStream, AskWorker), which the broker makes when the seat is declared; a holder only binds them.
+type JetStreamAsks struct {
+	JS       jetstream.JetStream
+	Language string
+
+	mu   sync.Mutex
+	cons map[string]jetstream.Consumer
+}
+
+func (s *JetStreamAsks) consumer(ctx context.Context, kind string) (jetstream.Consumer, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if c, ok := s.cons[kind]; ok {
+		return c, nil
+	}
+	stream, err := delivery.AskStream(s.Language)
+	if err != nil {
+		return nil, err
+	}
+	worker, err := delivery.AskWorker(s.Language, kind)
+	if err != nil {
+		return nil, err
+	}
+	c, err := s.JS.Consumer(ctx, stream, worker)
+	if err != nil {
+		return nil, fmt.Errorf("binding the %s worker %s on %s: %w", kind, worker, stream, err)
+	}
+	if s.cons == nil {
+		s.cons = map[string]jetstream.Consumer{}
+	}
+	s.cons[kind] = c
+	return c, nil
+}
+
+// Next is AskSource's: a fetch of one with no wait when wait is 0, else one that waits at most wait.
+func (s *JetStreamAsks) Next(ctx context.Context, kind string, wait time.Duration) (*Pulled, error) {
+	c, err := s.consumer(ctx, kind)
+	if err != nil {
+		return nil, err
+	}
+	var batch jetstream.MessageBatch
+	if wait <= 0 {
+		batch, err = c.FetchNoWait(1)
+	} else {
+		batch, err = c.Fetch(1, jetstream.FetchMaxWait(wait))
+	}
+	if err != nil {
+		return nil, err
+	}
+	select {
+	case msg, ok := <-batch.Messages():
+		if !ok {
+			return nil, batch.Error()
+		}
+		var delivered uint64 = 1
+		if meta, err := msg.Metadata(); err == nil && meta != nil {
+			delivered = meta.NumDelivered
+		}
+		return &Pulled{Data: append([]byte(nil), msg.Data()...), Delivered: delivered,
+			Ack: msg.Ack, InProgress: msg.InProgress, Nak: msg.Nak, Term: msg.Term}, nil
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	}
+}
+
+// DeclareAskWorkers makes language's seat stream and its three workers on a bus with no broker: a test's (the build
+// modules' integration tests start one). On the mesh the broker declares them from the seat, as it declares every
+// seat's stream (mesh-controller internal/broker SeatStreams); a holder never does.
+func DeclareAskWorkers(ctx context.Context, js jetstream.JetStream, language string, ackWait time.Duration) error {
+	stream, err := delivery.AskStream(language)
+	if err != nil {
+		return err
+	}
+	seat, _ := delivery.BuildSeat(language)
+	if _, err := js.CreateOrUpdateStream(ctx, jetstream.StreamConfig{Name: stream, Subjects: []string{"mesh.seat." + seat + ".accept.>"},
+		Retention: jetstream.WorkQueuePolicy}); err != nil {
+		return fmt.Errorf("the stream %s: %w", stream, err)
+	}
+	for _, kind := range delivery.AskKinds {
+		worker, _ := delivery.AskWorker(language, kind)
+		subject, _ := delivery.AskSubject(language, kind)
+		if _, err := js.CreateOrUpdateConsumer(ctx, stream, jetstream.ConsumerConfig{Durable: worker, FilterSubject: subject,
+			AckPolicy: jetstream.AckExplicitPolicy, AckWait: ackWait, MaxDeliver: 5}); err != nil {
+			return fmt.Errorf("the worker %s: %w", worker, err)
+		}
+	}
+	return nil
+}

go/buildstep/pull_capacity_test.go

@@ -0,0 +1,39 @@
+package buildstep
+
+import (
+	"encoding/json"
+	"sync"
+	"testing"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+)
+
+// configWatch is a double of stdio.WatchConfig: it hands the value now at the start, as the runtime does, and a test
+// hands each change after with set.
+type configWatch struct {
+	mu     sync.Mutex
+	value  string
+	handle func(stdio.ProvisionChange) error
+	asked  string
+}
+
+func (w *configWatch) watch(key string, handle func(stdio.ProvisionChange) error) error {
+	w.mu.Lock()
+	w.asked, w.handle = key, handle
+	value := w.value
+	w.mu.Unlock()
+	return handle(stdio.ProvisionChange{Kind: "config", Key: key, Value: json.RawMessage(`"` + value + `"`)})
+}
+
+func (w *configWatch) set(t *testing.T, value string) {
+	t.Helper()
+	w.mu.Lock()
+	handle, key := w.handle, w.asked
+	w.mu.Unlock()
+	if handle == nil {
+		t.Fatal("the puller watches no config value")
+	}
+	if err := handle(stdio.ProvisionChange{Kind: "config", Key: key, Value: json.RawMessage(`"` + value + `"`)}); err != nil {
+		t.Fatal(err)
+	}
+}

go/buildstep/pull_fake.go

@@ -0,0 +1,113 @@
+package buildstep
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// FakeAsks is a test double of a seat's workers for the build modules' unit tests: Publish puts an ask on a kind's
+// worker, Next hands them out in their order, and the fates the puller gives them are counted. Safe for concurrent use.
+type FakeAsks struct {
+	mu      sync.Mutex
+	waiting map[string][][]byte
+	added   chan struct{}
+	// Acked, Termed and Naked are the asks' ids or data by fate, InProgress how many heartbeats were given.
+	Acked, Termed, Naked []string
+	InProgress           int
+	// Delivered, when set, is the delivery count every ask handed over says (1 when 0): a test of a poisoned ask sets it.
+	Delivered uint64
+}
+
+// NewFakeAsks is an empty double.
+func NewFakeAsks() *FakeAsks {
+	return &FakeAsks{waiting: map[string][][]byte{}, added: make(chan struct{}, 1)}
+}
+
+// Publish puts an encoded ask on kind's worker.
+func (f *FakeAsks) Publish(kind string, data []byte) {
+	f.mu.Lock()
+	f.waiting[kind] = append(f.waiting[kind], data)
+	f.mu.Unlock()
+	select {
+	case f.added <- struct{}{}:
+	default:
+	}
+}
+
+// PublishAsk encodes a and puts it on its kind's worker.
+func (f *FakeAsks) PublishAsk(a delivery.StepAsk) error {
+	raw, err := delivery.EncodeStepAsk(a)
+	if err != nil {
+		return err
+	}
+	f.Publish(a.Kind, raw)
+	return nil
+}
+
+// Waiting is how many asks wait on kind's worker.
+func (f *FakeAsks) Waiting(kind string) int {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return len(f.waiting[kind])
+}
+
+// Fates is a copy of the acked, termed and naked lists.
+func (f *FakeAsks) Fates() (acked, termed, naked []string) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return append([]string(nil), f.Acked...), append([]string(nil), f.Termed...), append([]string(nil), f.Naked...)
+}
+
+// Next is AskSource's.
+func (f *FakeAsks) Next(ctx context.Context, kind string, wait time.Duration) (*Pulled, error) {
+	var deadline <-chan time.Time
+	if wait > 0 {
+		t := time.NewTimer(wait)
+		defer t.Stop()
+		deadline = t.C
+	}
+	for {
+		f.mu.Lock()
+		if q := f.waiting[kind]; len(q) > 0 {
+			data := q[0]
+			f.waiting[kind] = q[1:]
+			f.mu.Unlock()
+			return f.pulled(data), nil
+		}
+		f.mu.Unlock()
+		if wait <= 0 {
+			return nil, nil
+		}
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-deadline:
+			return nil, nil
+		case <-f.added:
+		}
+	}
+}
+
+func (f *FakeAsks) pulled(data []byte) *Pulled {
+	id := string(data)
+	if a, err := delivery.DecodeStepAsk(data); err == nil {
+		id = a.ID
+	}
+	fate := func(list *[]string) func() error {
+		return func() error {
+			f.mu.Lock()
+			*list = append(*list, id)
+			f.mu.Unlock()
+			return nil
+		}
+	}
+	delivered := f.Delivered
+	if delivered == 0 {
+		delivered = 1
+	}
+	return &Pulled{Data: data, Delivered: delivered, Ack: fate(&f.Acked), Nak: fate(&f.Naked), Term: fate(&f.Termed),
+		InProgress: func() error { f.mu.Lock(); f.InProgress++; f.mu.Unlock(); return nil }}
+}

go/buildstep/pull_integration_test.go

@@ -0,0 +1,144 @@
+//go:build integration
+
+package buildstep
+
+import (
+	"context"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/testbus"
+)
+
+func askBus(t *testing.T, ackWait time.Duration) jetstream.JetStream {
+	t.Helper()
+	nc, err := nats.Connect(testbus.URL(t))
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(nc.Close)
+	js, err := jetstream.New(nc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := DeclareAskWorkers(context.Background(), js, delivery.AskGo, ackWait); err != nil {
+		t.Fatal(err)
+	}
+	return js
+}
+
+func publishAsk(t *testing.T, js jetstream.JetStream, a delivery.StepAsk) {
+	t.Helper()
+	raw, err := delivery.EncodeStepAsk(a)
+	if err != nil {
+		t.Fatal(err)
+	}
+	subject, _ := delivery.AskSubject(a.Language, a.Kind)
+	if _, err := js.Publish(context.Background(), subject, raw); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// 1887/A2a, 1887/AC-order, 1887/AC-pull on the real server: a check ask published before a delivery ask runs after it;
+// with capacity 2 and three asks two run, the third waits in the stream and starts when one ends.
+func TestPullOrderAndCapacityOnTheBus(t *testing.T) {
+	js := askBus(t, 30*time.Second)
+	check, first, second := testAsk(delivery.AskCheck), testAsk(delivery.AskDelivery), testAsk(delivery.AskDelivery)
+	publishAsk(t, js, check)
+	publishAsk(t, js, first)
+	publishAsk(t, js, second)
+	release := make(chan struct{})
+	var mu sync.Mutex
+	var order []string
+	st := newSteps()
+	p := &Puller{Source: &JetStreamAsks{JS: js, Language: delivery.AskGo}, Language: delivery.AskGo, Node: "shanks", Put: st.put,
+		Capacity: func() int { return 2 }, PullWait: 200 * time.Millisecond,
+		Run: func(ctx context.Context, a delivery.StepAsk) (any, error) {
+			mu.Lock()
+			order = append(order, a.ID)
+			mu.Unlock()
+			<-release
+			return nil, nil
+		}}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go p.Pull(ctx)
+	waitFor(t, "two in hand", func() bool { return p.InHand() == 2 })
+	time.Sleep(500 * time.Millisecond)
+	mu.Lock()
+	if len(order) != 2 || order[0] != first.ID || order[1] != second.ID {
+		t.Fatalf("ran %v, want the two delivery asks %s %s first", order, first.ID, second.ID)
+	}
+	mu.Unlock()
+	release <- struct{}{}
+	waitFor(t, "the check taken", func() bool { mu.Lock(); defer mu.Unlock(); return len(order) == 3 })
+	close(release)
+	waitFor(t, "every step ended", func() bool {
+		for _, a := range []delivery.StepAsk{check, first, second} {
+			key, _ := delivery.AskStepKey("shanks", a.ID)
+			if s, ok := st.get(key); !ok || s.State != delivery.StepPassed {
+				return false
+			}
+		}
+		return true
+	})
+	info, err := js.Stream(ctx, "SEAT_NODE_BUILD_GO")
+	if err != nil {
+		t.Fatal(err)
+	}
+	waitFor(t, "the stream empty (every ask acknowledged)", func() bool {
+		si, err := info.Info(ctx)
+		return err == nil && si.State.Msgs == 0
+	})
+}
+
+// 1887/A2c, ADR 0525 §6: a killed puller's ask is redelivered by the stream's acknowledgement wait to the other node,
+// whose step key names the reference.
+func TestPullRedeliversAKilledPullersAsk(t *testing.T) {
+	js := askBus(t, 2*time.Second)
+	a := testAsk(delivery.AskDelivery)
+	publishAsk(t, js, a)
+	st := newSteps()
+	taken := make(chan struct{})
+	dying := &Puller{Source: &JetStreamAsks{JS: js, Language: delivery.AskGo}, Language: delivery.AskGo, Node: "ace", Put: st.put,
+		Capacity: func() int { return 1 }, PullWait: 200 * time.Millisecond, Heartbeat: time.Hour,
+		Run: func(ctx context.Context, a delivery.StepAsk) (any, error) {
+			close(taken)
+			<-ctx.Done()
+			return nil, ctx.Err()
+		}}
+	kill, killed := context.WithCancel(context.Background())
+	go dying.Pull(kill)
+	<-taken
+	killed()
+	other := &Puller{Source: &JetStreamAsks{JS: js, Language: delivery.AskGo}, Language: delivery.AskGo, Node: "shanks", Put: st.put,
+		Capacity: func() int { return 1 }, PullWait: 200 * time.Millisecond,
+		Run: func(ctx context.Context, a delivery.StepAsk) (any, error) {
+			return delivery.BuildAnswer{Artifacts: []delivery.AskBuilt{{Artifact: "bundle", Digest: "sha256:00", Reference: "artifact-store://x"}}}, nil
+		}}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go other.Pull(ctx)
+	key, _ := delivery.AskStepKey("shanks", a.ID)
+	deadline := time.Now().Add(10 * time.Second)
+	for {
+		if s, ok := st.get(key); ok && s.State == delivery.StepPassed {
+			if want := `artifact-store://x`; !contains(string(s.Result), want) {
+				t.Fatalf("the step's result %s names no %s", s.Result, want)
+			}
+			return
+		}
+		if time.Now().After(deadline) {
+			t.Fatalf("the killed puller's ask was not taken by shanks within 10 s")
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+}
+
+func contains(s, sub string) bool { return strings.Contains(s, sub) }

go/buildstep/pull_seat.go

@@ -0,0 +1,44 @@
+package buildstep
+
+import (
+	"context"
+	"time"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// SeatAsks is a build seat's workers as a tools bundle reaches them: through its runtime's seat pull and settle
+// (stdio.SeatPull, SeatSettle; issue 1887 A11), one message per pull, only from the workers the module's membership
+// lists.
+type SeatAsks struct {
+	Language string
+	// Pull and Settle are stdio.SeatPull and stdio.SeatSettle when nil; a test gives its own.
+	Pull   func(worker string, wait time.Duration) (*stdio.Pulled, error)
+	Settle func(id, fate string) error
+}
+
+// Next is AskSource's.
+func (s SeatAsks) Next(ctx context.Context, kind string, wait time.Duration) (*Pulled, error) {
+	pull, settle := s.Pull, s.Settle
+	if pull == nil {
+		pull = stdio.SeatPull
+	}
+	if settle == nil {
+		settle = stdio.SeatSettle
+	}
+	worker, err := delivery.AskWorker(s.Language, kind)
+	if err != nil {
+		return nil, err
+	}
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	p, err := pull(worker, wait)
+	if err != nil || p == nil {
+		return nil, err
+	}
+	fate := func(f string) func() error { return func() error { return settle(p.ID, f) } }
+	return &Pulled{Data: p.Body, Delivered: p.Delivered, Ack: fate(stdio.SettleAck), InProgress: fate(stdio.SettleProgress),
+		Nak: fate(stdio.SettleNak), Term: fate(stdio.SettleTerm)}, nil
+}

go/buildstep/pull_seat_test.go

@@ -0,0 +1,40 @@
+package buildstep
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// 1887/A11: a bundle's source pulls the kind's worker by its seat's name and settles each ask by the runtime's id.
+func TestSeatAsksPullsTheKindsWorkerAndSettlesByID(t *testing.T) {
+	var pulled []string
+	var settled []string
+	src := SeatAsks{Language: delivery.AskGo,
+		Pull: func(worker string, wait time.Duration) (*stdio.Pulled, error) {
+			pulled = append(pulled, worker)
+			if worker != "SEAT_NODE_BUILD_GO_CHECK_worker" {
+				return nil, nil
+			}
+			return &stdio.Pulled{ID: "p9", Worker: worker, Body: []byte(`{"v":1}`), Delivered: 2}, nil
+		},
+		Settle: func(id, fate string) error { settled = append(settled, id+" "+fate); return nil }}
+	if p, err := src.Next(context.Background(), delivery.AskDelivery, 0); err != nil || p != nil {
+		t.Fatalf("delivery = %+v, %v", p, err)
+	}
+	p, err := src.Next(context.Background(), delivery.AskCheck, time.Second)
+	if err != nil || p == nil || string(p.Data) != `{"v":1}` || p.Delivered != 2 {
+		t.Fatalf("check = %+v, %v", p, err)
+	}
+	_ = p.InProgress()
+	_ = p.Ack()
+	if len(pulled) != 2 || pulled[0] != "SEAT_NODE_BUILD_GO_DELIVERY_worker" {
+		t.Errorf("pulled %v", pulled)
+	}
+	if len(settled) != 2 || settled[0] != "p9 progress" || settled[1] != "p9 ack" {
+		t.Errorf("settled %v", settled)
+	}
+}

go/buildstep/pull_test.go

@@ -0,0 +1,364 @@
+package buildstep
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// steps records a steps state's puts: the last value of each key.
+type steps struct {
+	mu   sync.Mutex
+	keys map[string]delivery.Step
+}
+
+func newSteps() *steps { return &steps{keys: map[string]delivery.Step{}} }
+
+func (s *steps) put(key string, value any) (uint64, error) {
+	raw, _ := value.(json.RawMessage)
+	st, err := delivery.DecodeStep(raw)
+	if err != nil {
+		return 0, err
+	}
+	s.mu.Lock()
+	s.keys[key] = st
+	s.mu.Unlock()
+	return 1, nil
+}
+
+func (s *steps) get(key string) (delivery.Step, bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	st, ok := s.keys[key]
+	return st, ok
+}
+
+func testAsk(kind string) delivery.StepAsk {
+	id := NewID()
+	a := delivery.StepAsk{ID: id, Kind: kind, Language: delivery.AskGo, Asker: "mesh-delivery-builder", At: time.Now()}
+	fetch := map[string]any{"repository": "novox/x", "commit": "0123456789abcdef0123456789abcdef01234567"}
+	if kind == delivery.AskDelivery {
+		b := buildJobFixture
+		b.Fetch = fetch
+		a.Build = &b
+	} else {
+		a.Check = &delivery.CheckJob{Fetch: fetch, Levels: []string{delivery.LevelUnit}}
+	}
+	return a
+}
+
+var buildJobFixture = delivery.BuildJob{Module: "m", Path: ".", Artifacts: []delivery.AskArtifact{{Artifact: "bundle"}}}
+
+func waitFor(t *testing.T, what string, cond func() bool) {
+	t.Helper()
+	deadline := time.Now().Add(2 * time.Second)
+	for !cond() {
+		if time.Now().After(deadline) {
+			t.Fatalf("waited 2 s for %s", what)
+		}
+		time.Sleep(time.Millisecond)
+	}
+}
+
+// 1887/A2a: given a check ask published before a delivery ask and one slot, the delivery ask runs first.
+func TestPullTakesDeliveryBeforeCheck(t *testing.T) {
+	src, st := NewFakeAsks(), newSteps()
+	check, recheck, deliver := testAsk(delivery.AskCheck), testAsk(delivery.AskRecheck), testAsk(delivery.AskDelivery)
+	for _, a := range []delivery.StepAsk{recheck, check, deliver} {
+		if err := src.PublishAsk(a); err != nil {
+			t.Fatal(err)
+		}
+	}
+	var mu sync.Mutex
+	var order []string
+	p := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: st.put, Capacity: func() int { return 1 },
+		PullWait: 10 * time.Millisecond, Run: func(ctx context.Context, a delivery.StepAsk) (any, error) {
+			mu.Lock()
+			order = append(order, a.Kind)
+			mu.Unlock()
+			return map[string]string{"ran": a.ID}, nil
+		}}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go p.Pull(ctx)
+	waitFor(t, "three asks acked", func() bool { a, _, _ := src.Fates(); return len(a) == 3 })
+	mu.Lock()
+	defer mu.Unlock()
+	if want := []string{delivery.AskDelivery, delivery.AskCheck, delivery.AskRecheck}; len(order) != 3 || order[0] != want[0] || order[1] != want[1] || order[2] != want[2] {
+		t.Fatalf("order = %v, want %v", order, want)
+	}
+	key, _ := delivery.AskStepKey("shanks", deliver.ID)
+	s, ok := st.get(key)
+	if !ok || s.State != delivery.StepPassed || string(s.Result) != `{"ran":"`+deliver.ID+`"}` {
+		t.Fatalf("the step %s = %+v (%v)", key, s, ok)
+	}
+}
+
+// 1887/A2a, 1887/AC-pull: given capacity 2 and three asks waiting, two run and the third waits, and it starts when
+// one ends, with no timer.
+func TestPullHoldsAtMostItsCapacity(t *testing.T) {
+	src, st := NewFakeAsks(), newSteps()
+	for i := 0; i < 3; i++ {
+		_ = src.PublishAsk(testAsk(delivery.AskDelivery))
+	}
+	release := make(chan struct{})
+	var mu sync.Mutex
+	started := 0
+	p := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: st.put, Capacity: func() int { return 2 },
+		PullWait: 10 * time.Millisecond, Run: func(ctx context.Context, a delivery.StepAsk) (any, error) {
+			mu.Lock()
+			started++
+			mu.Unlock()
+			<-release
+			return nil, nil
+		}}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go p.Pull(ctx)
+	waitFor(t, "two in hand", func() bool { return p.InHand() == 2 })
+	time.Sleep(30 * time.Millisecond) // three pull waits: the third must still wait
+	if p.InHand() != 2 || src.Waiting(delivery.AskDelivery) != 1 {
+		t.Fatalf("in hand %d, waiting %d; want 2 and 1", p.InHand(), src.Waiting(delivery.AskDelivery))
+	}
+	release <- struct{}{}
+	waitFor(t, "the third taken", func() bool { return src.Waiting(delivery.AskDelivery) == 0 })
+	// Taken from the source comes a moment before its run starts: wait for the start, not only the take.
+	waitFor(t, "the third started", func() bool { mu.Lock(); defer mu.Unlock(); return started == 3 })
+	close(release)
+	waitFor(t, "all acked", func() bool { a, _, _ := src.Fates(); return len(a) == 3 })
+}
+
+// An ask that is not one, or not this seat's, is dropped and runs nowhere.
+func TestPullDropsWhatIsNoAsk(t *testing.T) {
+	src, st := NewFakeAsks(), newSteps()
+	src.Publish(delivery.AskDelivery, []byte(`{"v":1}`))
+	other := testAsk(delivery.AskDelivery)
+	other.Language = delivery.AskNode
+	_ = src.PublishAsk(other)
+	ran := false
+	p := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: st.put, Capacity: func() int { return 1 },
+		PullWait: 10 * time.Millisecond, Run: func(ctx context.Context, a delivery.StepAsk) (any, error) { ran = true; return nil, nil }}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go p.Pull(ctx)
+	waitFor(t, "two termed", func() bool { _, tm, _ := src.Fates(); return len(tm) == 2 })
+	if ran {
+		t.Fatal("a wrong ask ran")
+	}
+}
+
+// load reads the recorded steps state's raw values: the pause key is not a step, so it is kept apart.
+type kv struct {
+	mu   sync.Mutex
+	vals map[string][]byte
+}
+
+func (k *kv) put(key string, value any) (uint64, error) {
+	raw, _ := value.(json.RawMessage)
+	k.mu.Lock()
+	defer k.mu.Unlock()
+	if k.vals == nil {
+		k.vals = map[string][]byte{}
+	}
+	k.vals[key] = append([]byte(nil), raw...)
+	return 1, nil
+}
+
+func (k *kv) load(key string) ([]byte, error) {
+	k.mu.Lock()
+	defer k.mu.Unlock()
+	return k.vals[key], nil
+}
+
+// 1887/A2b, 1887/AC-zero, 1887/AC-wake: at capacity 0 the puller takes nothing; a capacity raised takes effect at the
+// next pull, or, with the config watch (g14 idle at capacity 2, 2026-10-25), at once when the value moves, with no
+// pause, resume or step end to wake it; a refused value pulls nothing, and a watch that cannot start leaves the
+// settings file's capacity.
+func TestPullAtCapacityZeroTakesNothing(t *testing.T) {
+	t.Run("settings file", func(t *testing.T) {
+		src, st := NewFakeAsks(), &kv{}
+		_ = src.PublishAsk(testAsk(delivery.AskDelivery))
+		var mu sync.Mutex
+		capacity := 0
+		p := &Puller{Source: src, Language: delivery.AskGo, Node: "novox", Put: st.put, PullWait: 10 * time.Millisecond,
+			Capacity: func() int { mu.Lock(); defer mu.Unlock(); return capacity },
+			Run:      func(ctx context.Context, a delivery.StepAsk) (any, error) { return nil, nil }}
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		go p.Pull(ctx)
+		time.Sleep(50 * time.Millisecond)
+		if src.Waiting(delivery.AskDelivery) != 1 {
+			t.Fatal("a node at capacity 0 took an ask")
+		}
+		mu.Lock()
+		capacity = 1
+		mu.Unlock()
+		p.Wake()
+		waitFor(t, "the ask taken at capacity 1", func() bool { a, _, _ := src.Fates(); return len(a) == 1 })
+	})
+	t.Run("config watch wakes", func(t *testing.T) {
+		src, st := NewFakeAsks(), newSteps()
+		_ = src.PublishAsk(testAsk(delivery.AskDelivery))
+		w := &configWatch{value: "shanks=3,g14=0"}
+		p := &Puller{Source: src, Language: delivery.AskGo, Node: "g14", Put: st.put, PullWait: 10 * time.Millisecond,
+			Capacity:    func() int { return 0 }, // the settings file, not refilled yet
+			WatchConfig: w.watch,
+			Run:         func(ctx context.Context, a delivery.StepAsk) (any, error) { return nil, nil }}
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		go p.Pull(ctx)
+		waitFor(t, "the watch of the capacity", func() bool { w.mu.Lock(); defer w.mu.Unlock(); return w.handle != nil })
+		time.Sleep(30 * time.Millisecond)
+		if src.Waiting(delivery.AskDelivery) != 1 {
+			t.Fatal("a node at capacity 0 took an ask")
+		}
+		if w.asked != CapacitySetting {
+			t.Fatalf("the puller watches %q, want %q", w.asked, CapacitySetting)
+		}
+		w.set(t, "shanks=3,g14=2")
+		waitFor(t, "the ask taken once the capacity moved to 2", func() bool { a, _, _ := src.Fates(); return len(a) == 1 })
+	})
+	for _, c := range []struct {
+		name  string
+		watch func(string, func(stdio.ProvisionChange) error) error
+		room  bool
+	}{
+		{"refused value leaves no room", func(key string, handle func(stdio.ProvisionChange) error) error {
+			return handle(stdio.ProvisionChange{Kind: "config", Key: key, Refused: "the module is no longer on g14"})
+		}, false},
+		{"watch that cannot start keeps the settings file", func(string, func(stdio.ProvisionChange) error) error {
+			return errors.New("no runtime")
+		}, true},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			p := &Puller{Source: NewFakeAsks(), Language: delivery.AskGo, Node: "g14", Put: newSteps().put,
+				Capacity: func() int { return 1 }, WatchConfig: c.watch,
+				Run: func(ctx context.Context, a delivery.StepAsk) (any, error) { return nil, nil }}
+			p.watchCapacity()
+			if p.room() != c.room {
+				t.Fatalf("room = %v, want %v", p.room(), c.room)
+			}
+		})
+	}
+}
+
+// 1887/A2b: a paused puller takes nothing, its pause is kept on the pause key, and a puller started again on that state
+// stays paused until resumed.
+func TestPullPauseOutlivesARestart(t *testing.T) {
+	src, st, steps := NewFakeAsks(), &kv{}, &kv{}
+	run := func(ctx context.Context, a delivery.StepAsk) (any, error) { return nil, nil }
+	p := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: steps.put, PausePut: st.put, Load: st.load,
+		PullWait: 10 * time.Millisecond, Capacity: func() int { return 2 }, Run: run}
+	if err := p.Pause("the operator"); err != nil {
+		t.Fatal(err)
+	}
+	key, _ := delivery.PauseKey("shanks")
+	raw, _ := st.load(key)
+	if v, err := delivery.DecodePause(raw); err != nil || !v.Paused || v.By != "the operator" {
+		t.Fatalf("the pause key holds %s (%v)", raw, err)
+	}
+	if raw, _ := steps.load(key); raw != nil {
+		t.Fatalf("the pause was written in the steps state, whose keys age out: %s", raw)
+	}
+	// The restart: a new puller on the same state.
+	again := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: steps.put, PausePut: st.put, Load: st.load,
+		PullWait: 10 * time.Millisecond, Capacity: func() int { return 2 }, Run: run}
+	_ = src.PublishAsk(testAsk(delivery.AskDelivery))
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go again.Pull(ctx)
+	time.Sleep(50 * time.Millisecond)
+	if !again.Paused() || src.Waiting(delivery.AskDelivery) != 1 {
+		t.Fatalf("restarted: paused %v, waiting %d; want paused and 1", again.Paused(), src.Waiting(delivery.AskDelivery))
+	}
+	if err := again.Resume("the operator"); err != nil {
+		t.Fatal(err)
+	}
+	waitFor(t, "the ask taken after the resume", func() bool { a, _, _ := src.Fates(); return len(a) == 1 })
+
+	t.Run("a pause that cannot be read is said and pulled as not paused", func(t *testing.T) {
+		src := NewFakeAsks()
+		var said atomic.Value
+		p := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: steps.put, PausePut: st.put,
+			Load:     func(string) ([]byte, error) { return nil, errors.New("no runtime yet") },
+			PullWait: 10 * time.Millisecond, Capacity: func() int { return 2 }, Run: run,
+			Logf: func(f string, a ...any) {
+				if m := fmt.Sprintf(f, a...); strings.Contains(m, "cannot be read") {
+					said.Store(m)
+				}
+			}}
+		_ = src.PublishAsk(testAsk(delivery.AskDelivery))
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		go p.Pull(ctx)
+		waitFor(t, "the ask taken", func() bool { a, _, _ := src.Fates(); return len(a) == 1 })
+		if m, _ := said.Load().(string); !strings.Contains(m, "pulling as not paused") {
+			t.Fatalf("the unreadable pause was not said: %q", m)
+		}
+	})
+}
+
+// 1887/A2c: a long step tells the bus it is still being worked; a holder that stops mid-step neither ends nor
+// acknowledges its ask, so the stream gives it to another node.
+func TestPullHeartbeatAndStop(t *testing.T) {
+	src, st := NewFakeAsks(), newSteps()
+	a := testAsk(delivery.AskDelivery)
+	_ = src.PublishAsk(a)
+	running := make(chan struct{})
+	p := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: st.put, Capacity: func() int { return 1 },
+		PullWait: 10 * time.Millisecond, Heartbeat: 5 * time.Millisecond,
+		Run: func(ctx context.Context, a delivery.StepAsk) (any, error) {
+			close(running)
+			<-ctx.Done()
+			return nil, ctx.Err()
+		}}
+	ctx, cancel := context.WithCancel(context.Background())
+	stopped := make(chan struct{})
+	go func() { p.Pull(ctx); close(stopped) }()
+	<-running
+	waitFor(t, "two heartbeats", func() bool { src.mu.Lock(); defer src.mu.Unlock(); return src.InProgress >= 2 })
+	cancel()
+	<-stopped
+	waitFor(t, "the step's goroutine gone", func() bool { return p.InHand() == 0 })
+	acked, termed, naked := src.Fates()
+	if len(acked)+len(termed)+len(naked) != 0 {
+		t.Fatalf("a stopped holder gave its ask a fate: acked %v termed %v naked %v", acked, termed, naked)
+	}
+	key, _ := delivery.AskStepKey("shanks", a.ID)
+	if s, ok := st.get(key); !ok || s.State != delivery.StepRunning {
+		t.Fatalf("the step %s = %+v, want left running", key, s)
+	}
+}
+
+// 1907: an ask taken past AskRuns (each run took its node down) is run no more: its step ends failed saying why, so the
+// asker's key fails, and it is ended on the stream, not offered to another node.
+func TestAPoisonedAskIsSaidAndRunNoMore(t *testing.T) {
+	src, st := NewFakeAsks(), newSteps()
+	src.Delivered = delivery.AskRuns + 1
+	a := testAsk(delivery.AskDelivery)
+	_ = src.PublishAsk(a)
+	ran := false
+	p := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: st.put, Capacity: func() int { return 1 },
+		PullWait: 10 * time.Millisecond, Run: func(ctx context.Context, a delivery.StepAsk) (any, error) { ran = true; return nil, nil }}
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go p.Pull(ctx)
+	waitFor(t, "the ask termed", func() bool { _, tm, _ := src.Fates(); return len(tm) == 1 })
+	key, _ := delivery.AskStepKey("shanks", a.ID)
+	s, ok := st.get(key)
+	if ran || !ok || s.State != delivery.StepFailed || !strings.Contains(s.Reason, "taken 3 times") || !strings.Contains(s.Reason, "poison") {
+		t.Fatalf("ran %v, step %+v", ran, s)
+	}
+	if acked, _, naked := src.Fates(); len(acked)+len(naked) != 0 {
+		t.Errorf("acked %v naked %v, want it termed alone", acked, naked)
+	}
+}

go/buildstep/refusal.go

@@ -0,0 +1,18 @@
+package buildstep
+
+import "fmt"
+
+// Refusal is a step that is not run on purpose, as against one that failed: the toolchain installed is not the
+// recipe's, the integration level's postgres major is not the one it is built for (novox/hq ADR 0469 §1, ADR 0470
+// §4; issue 1473). A step's run returns one and the runner ends the step refused with its text.
+type Refusal struct {
+	// Text is the reason, in words the operator reads.
+	Text string
+	// Want is the version the recipe asks for and Have the one found; either may be empty.
+	Want, Have string
+}
+
+func (r *Refusal) Error() string { return r.Text }
+
+// Refuse is a Refusal with its text formatted.
+func Refuse(format string, args ...any) *Refusal { return &Refusal{Text: fmt.Sprintf(format, args...)} }

go/buildstep/request.go

@@ -0,0 +1,115 @@
+package buildstep
+
+import (
+	"fmt"
+	"path"
+	"regexp"
+	"strings"
+)
+
+var (
+	requestCommitOK     = regexp.MustCompile(`^[0-9a-f]{40}$`)
+	requestRepositoryOK = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]*/[A-Za-z0-9][A-Za-z0-9._-]*$`)
+)
+
+// FetchRequest is what a build module's fetch tool is asked: the repository and the full commit, the pull request's
+// ref when only its head carries the commit, the trunk commit to merge onto for a merge preview, and, for a build of a
+// module whose every artifact names its paths, that module's directory and its named paths (novox/hq ADR 0499 clause 4).
+//
+// **The paths come from the builder, not from a manifest** (ADR 0495 clause 1; the lead's decision L8 of R4e): the
+// builder fills Dir and Paths from the indexer's Module value (Path, and KeptInputs2.Paths' keys), and the build module
+// gives the build and test steps a workspace holding those paths, the manifest and its lock files. A request without
+// them builds from the module's directory, as before.
+type FetchRequest struct {
+	Repository string   `json:"repository"`
+	Commit     string   `json:"commit"`
+	Ref        string   `json:"ref,omitempty"`
+	Base       string   `json:"base,omitempty"`
+	Dir        string   `json:"dir,omitempty"`
+	Paths      []string `json:"paths,omitempty"`
+}
+
+// FetchRequestProperties are the JSON schema properties of FetchRequest's dir and paths, for a fetch tool's Input.
+func FetchRequestProperties() map[string]any {
+	return map[string]any{
+		"dir": map[string]any{"type": "string", "description": "the module's directory in the repository (\".\" for its root), with paths"},
+		"paths": map[string]any{"type": "array", "items": map[string]any{"type": "string"},
+			"description": "the paths the module names, relative to dir, from the indexer's kept inputs: the build sees only these, the manifest and its lock files"},
+	}
+}
+
+// Args is r as a tool call's arguments.
+func (r FetchRequest) Args() map[string]any {
+	args := map[string]any{"repository": r.Repository, "commit": r.Commit}
+	for k, v := range map[string]string{"ref": r.Ref, "base": r.Base, "dir": r.Dir} {
+		if v != "" {
+			args[k] = v
+		}
+	}
+	if len(r.Paths) > 0 {
+		args["paths"] = append([]string(nil), r.Paths...)
+	}
+	return args
+}
+
+// ParseFetchRequest reads a fetch tool's arguments; arguments it does not know (a build module's own) are left to the
+// caller. It refuses a repository that is not <owner>/<name>, a commit or a base that is not 40 hex digits, paths with no
+// module directory or a directory with no path, a directory leaving the repository and a path leaving the directory,
+// naming each.
+func ParseFetchRequest(args map[string]any) (FetchRequest, error) {
+	var r FetchRequest
+	r.Repository, _ = args["repository"].(string)
+	r.Commit, _ = args["commit"].(string)
+	r.Ref, _ = args["ref"].(string)
+	r.Base, _ = args["base"].(string)
+	r.Dir, _ = args["dir"].(string)
+	switch v := args["paths"].(type) {
+	case nil:
+	case []string:
+		r.Paths = append([]string(nil), v...)
+	case []any:
+		for _, p := range v {
+			s, ok := p.(string)
+			if !ok {
+				return FetchRequest{}, fmt.Errorf("paths is a list of strings")
+			}
+			r.Paths = append(r.Paths, s)
+		}
+	default:
+		return FetchRequest{}, fmt.Errorf("paths is a list of strings")
+	}
+	return r, r.Check()
+}
+
+// Check is what ParseFetchRequest refuses.
+func (r FetchRequest) Check() error {
+	if !requestRepositoryOK.MatchString(r.Repository) || strings.Contains(r.Repository, "..") {
+		return fmt.Errorf("%q is not a repository, <owner>/<name>", r.Repository)
+	}
+	if !requestCommitOK.MatchString(r.Commit) {
+		return fmt.Errorf("%q is not a full commit (40 hex digits)", r.Commit)
+	}
+	if r.Base != "" && !requestCommitOK.MatchString(r.Base) {
+		return fmt.Errorf("%q is not a trunk commit (40 hex digits)", r.Base)
+	}
+	switch {
+	case len(r.Paths) > 0 && r.Dir == "":
+		return fmt.Errorf("the request names paths and names no module directory (dir) they are relative to")
+	case len(r.Paths) == 0 && r.Dir != "":
+		return fmt.Errorf("the request names a module directory and no path")
+	}
+	if r.Dir != "" && (outside(r.Dir) || strings.HasPrefix(r.Dir, "/")) {
+		return fmt.Errorf("the module directory %q leaves the repository", r.Dir)
+	}
+	for _, p := range r.Paths {
+		if p == "" || strings.HasPrefix(p, "/") || outside(p) || path.Clean(p) == "." {
+			return fmt.Errorf("the path %q leaves the module's directory or is not a path in it", p)
+		}
+	}
+	return nil
+}
+
+func outside(p string) bool {
+	c := path.Clean(p)
+	return c == ".." || strings.HasPrefix(c, "../")
+}

go/buildstep/request_test.go

@@ -0,0 +1,57 @@
+package buildstep
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+)
+
+// A build's fetch is handed the paths of a module that names them (novox/hq ADR 0499 clause 4): the builder fills them
+// from the indexer's kept inputs and the build module reads them from the call, never from the manifest (ADR 0495
+// clause 1). The request survives the trip through a tool call's arguments.
+func TestAFetchRequestCarriesTheNamedPathsThroughTheToolCall(t *testing.T) {
+	req := FetchRequest{Repository: "novox/mesh-sdk", Commit: strings.Repeat("a", 40), Ref: "refs/pull/7/head",
+		Dir: ".", Paths: []string{"package.json", "src"}}
+	args := req.Args()
+	// A tool call's arguments arrive as JSON: lists of any.
+	args["paths"] = []any{"package.json", "src"}
+	got, err := ParseFetchRequest(args)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(got, req) {
+		t.Fatalf("got %+v, want %+v", got, req)
+	}
+	plain, err := ParseFetchRequest(map[string]any{"repository": "novox/x", "commit": strings.Repeat("b", 40),
+		"base": strings.Repeat("c", 40), "beside": []any{}})
+	if err != nil || plain.Paths != nil || plain.Base != strings.Repeat("c", 40) {
+		t.Fatalf("a request without paths: %+v, %v", plain, err)
+	}
+
+	ok := map[string]any{"repository": "novox/x", "commit": strings.Repeat("b", 40)}
+	for _, c := range []struct {
+		set  map[string]any
+		says string
+	}{
+		{map[string]any{"repository": "novox"}, "is not a repository"},
+		{map[string]any{"repository": "novox/../x"}, "is not a repository"},
+		{map[string]any{"commit": "abc"}, "is not a full commit"},
+		{map[string]any{"base": "abc"}, "is not a trunk commit"},
+		{map[string]any{"paths": []any{"src"}}, "names no module directory"},
+		{map[string]any{"dir": "modules/a", "paths": []any{"../b"}}, "leaves the module's directory"},
+		{map[string]any{"dir": "../a", "paths": []any{"src"}}, "leaves the repository"},
+		{map[string]any{"dir": "modules/a", "paths": []any{3}}, "paths is a list of strings"},
+		{map[string]any{"dir": "modules/a"}, "names a module directory and no path"},
+	} {
+		args := map[string]any{}
+		for k, v := range ok {
+			args[k] = v
+		}
+		for k, v := range c.set {
+			args[k] = v
+		}
+		if _, err := ParseFetchRequest(args); err == nil || !strings.Contains(err.Error(), c.says) {
+			t.Errorf("%v: %v, wanted a refusal saying %q", c.set, err, c.says)
+		}
+	}
+}

go/buildstep/seat_tools.go

@@ -0,0 +1,36 @@
+package buildstep
+
+import (
+	stdio "git.novox.be/novox/mesh-sdk/go"
+)
+
+// SeatTools are a build seat's verbs on one node, as its holder serves them (novox/hq ADR 0525 §10; mesh-sdk catalogue
+// buildSeatVerbs): `<seat>.current` (what the node runs, its capacity, whether it is paused), `<seat>.pause` and
+// `<seat>.resume`, the pause kept on the node's pause key by the puller. what names the asks in the descriptions ("Go").
+func SeatTools(seat, what string, p *Puller) []stdio.Tool {
+	verb := func(name, description string, run func() (any, error)) stdio.Tool {
+		return stdio.Tool{Name: seat + "." + name, Description: description,
+			Input: map[string]any{"type": "object", "properties": map[string]any{}},
+			Run:   func(map[string]any) (any, error) { return run() }}
+	}
+	current := func() (any, error) {
+		return map[string]any{"node": p.Node, "capacity": p.CapacityNow(), "running": p.Running(), "paused": p.Paused()}, nil
+	}
+	return []stdio.Tool{
+		verb("current", "The "+what+" asks this node runs now (each one's id, kind and when it started), its build capacity, "+
+			"and whether it is paused.", current),
+		verb("pause", "Take no new "+what+" ask on this node until resumed; an ask running here ends in its place. Kept "+
+			"across a restart (the node's pause key).", func() (any, error) {
+			if err := p.Pause("the seat's pause verb"); err != nil {
+				return nil, err
+			}
+			return current()
+		}),
+		verb("resume", "Take "+what+" asks again on this node.", func() (any, error) {
+			if err := p.Resume("the seat's resume verb"); err != nil {
+				return nil, err
+			}
+			return current()
+		}),
+	}
+}

go/buildstep/seat_tools_test.go

@@ -0,0 +1,52 @@
+package buildstep
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// 1887/A9a, ADR 0525 §10: a build seat's verbs are <seat>.current, .pause and .resume; current names the ask running,
+// pause stops the puller taking asks, resume lets it take them again.
+func TestSeatToolsCurrentPauseResume(t *testing.T) {
+	src, st := NewFakeAsks(), newSteps()
+	release := make(chan struct{})
+	p := &Puller{Source: src, Language: delivery.AskGo, Node: "shanks", Put: st.put, Capacity: func() int { return 1 },
+		PullWait: 10 * time.Millisecond, Run: func(ctx context.Context, a delivery.StepAsk) (any, error) { <-release; return nil, nil }}
+	tools := map[string]func(map[string]any) (any, error){}
+	for _, tool := range SeatTools("node-build-go", "Go", p) {
+		tools[tool.Name] = tool.Run
+	}
+	for _, name := range []string{"node-build-go.current", "node-build-go.pause", "node-build-go.resume"} {
+		if tools[name] == nil {
+			t.Fatalf("no %s", name)
+		}
+	}
+	a := testAsk(delivery.AskDelivery)
+	_ = src.PublishAsk(a)
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	go p.Pull(ctx)
+	waitFor(t, "the ask running", func() bool { return p.InHand() == 1 })
+	out, _ := tools["node-build-go.current"](nil)
+	cur := out.(map[string]any)
+	running := cur["running"].([]RunningAsk)
+	if len(running) != 1 || running[0].ID != a.ID || running[0].Module != "m" || cur["capacity"] != 1 || cur["paused"] != false {
+		t.Fatalf("current = %+v", cur)
+	}
+	if out, err := tools["node-build-go.pause"](nil); err != nil || out.(map[string]any)["paused"] != true {
+		t.Fatalf("pause = %v, %v", out, err)
+	}
+	close(release)
+	_ = src.PublishAsk(testAsk(delivery.AskDelivery))
+	time.Sleep(50 * time.Millisecond)
+	if src.Waiting(delivery.AskDelivery) != 1 {
+		t.Fatal("a paused node took an ask")
+	}
+	if _, err := tools["node-build-go.resume"](nil); err != nil {
+		t.Fatal(err)
+	}
+	waitFor(t, "the ask taken after the resume", func() bool { return src.Waiting(delivery.AskDelivery) == 0 })
+}

go/buildstep/step.go

@@ -0,0 +1,146 @@
+// Package buildstep is what both build modules share: the runner of a long step that answers a tool call at once
+// and ends on its key in the module's `steps` state (novox/hq ADR 0469 §2; issue 1471), the toolchain guard
+// (issue 1473) and the fetch of one commit over SSH (issue 1474).
+package buildstep
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"log"
+	"strconv"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// Put writes one key of a state: stdio.State(delivery.StepsState).Put's shape (go/state.go).
+type Put func(key string, value any) (uint64, error)
+
+// EndAttempts and EndRetry bound how a step's end is written: a write that fails is tried again, since the end
+// is the only way the step's reader learns it is over.
+var (
+	EndAttempts = 5
+	EndRetry    = 2 * time.Second
+)
+
+var now = time.Now
+
+// NewID is a step id: the time in milliseconds in base 36 and six random hex digits, lower-case letters and
+// digits only, so it is one key token and differs between two steps of one node even in one millisecond.
+func NewID() string {
+	var b [3]byte
+	_, _ = rand.Read(b[:])
+	return strconv.FormatInt(now().UnixMilli(), 36) + hex.EncodeToString(b[:])
+}
+
+// Start begins a step of tool on node and answers its id at once: the key <node>.<id> holds state running when
+// Start returns. run is then called in a goroutine of its own, under ctx (the process's, not the tool call's: the
+// call is cut at 30 s, the step is not). When it returns, the key is written passed with run's result, failed with
+// the error's text, or refused when the error is a *Refusal; a panic in run ends the step failed, naming it, and
+// the process goes on. If the running write fails, nothing was started and Start answers the error.
+func Start(ctx context.Context, put Put, node, tool string, run func(ctx context.Context) (result any, err error)) (string, error) {
+	step, key, err := begin(put, node, tool, NewID())
+	if err != nil {
+		return "", err
+	}
+	go end(ctx, put, key, step, run)
+	return step.ID, nil
+}
+
+// begin writes the step running under id.
+func begin(put Put, node, tool, id string) (delivery.Step, string, error) {
+	step := delivery.Step{ID: id, Tool: tool, Node: node, State: delivery.StepRunning, Started: now().UTC()}
+	key, err := delivery.StepKey(node, step.ID)
+	if err != nil {
+		return delivery.Step{}, "", err
+	}
+	if err := write(put, key, step); err != nil {
+		return delivery.Step{}, "", fmt.Errorf("buildstep: writing the running step %s: %w", key, err)
+	}
+	return step, key, nil
+}
+
+// end runs run and writes the step's end.
+func end(ctx context.Context, put Put, key string, step delivery.Step, run func(ctx context.Context) (any, error)) {
+	result, err := protect(ctx, run)
+	_ = finish(put, key, step, result, err, log.Printf) // finish says a refused end itself
+}
+
+// finish writes the step's end from run's result or error: passed, failed or refused (a *Refusal). A write that fails is
+// tried EndAttempts times. When the whole end is refused every time (a result the state will not take: issue 1930), the
+// refusal is logged and a small failed end without the result is written instead, naming the write's error, so the
+// step's reader learns it is over and why. finish answers an error only when no end could be written at all, and then
+// the step's ask is not acknowledged as done.
+func finish(put Put, key string, step delivery.Step, result any, err error, logf func(format string, args ...any)) error {
+	step.Ended = now().UTC()
+	switch ref := (*Refusal)(nil); {
+	case err == nil:
+		step.State = delivery.StepPassed
+		if result != nil {
+			raw, merr := json.Marshal(result)
+			if merr != nil {
+				step.State, step.Reason = delivery.StepFailed, "the result is not JSON: "+merr.Error()
+			} else {
+				step.Result = raw
+			}
+		}
+	case errors.As(err, &ref):
+		step.State, step.Reason = delivery.StepRefused, err.Error()
+	default:
+		step.State, step.Reason = delivery.StepFailed, err.Error()
+	}
+	werr := writeEnd(put, key, step)
+	if werr == nil {
+		return nil
+	}
+	if logf != nil {
+		logf("the end of the step %s (%s) could not be written in %d tries: %v", key, step.State, EndAttempts, werr)
+	}
+	ended := step.State
+	why := fmt.Sprintf("the step ended %s, and its end could not be written: %v", ended, werr)
+	if step.Reason != "" {
+		why = fmt.Sprintf("the step ended %s (%s), and its end could not be written: %v", ended, step.Reason, werr)
+	}
+	step.State, step.Reason, step.Result = delivery.StepFailed, why, nil
+	if ferr := writeEnd(put, key, step); ferr != nil {
+		if logf != nil {
+			logf("the failed end of the step %s could not be written either: %v", key, ferr)
+		}
+		return fmt.Errorf("buildstep: no end of the step %s could be written: %w", key, ferr)
+	}
+	return nil
+}
+
+// writeEnd writes the step's end, trying EndAttempts times.
+func writeEnd(put Put, key string, step delivery.Step) error {
+	for attempt := 1; ; attempt++ {
+		werr := write(put, key, step)
+		if werr == nil || attempt >= EndAttempts {
+			return werr
+		}
+		time.Sleep(EndRetry)
+	}
+}
+
+// protect is run with a panic turned into the error that ends the step.
+func protect(ctx context.Context, run func(ctx context.Context) (any, error)) (result any, err error) {
+	defer func() {
+		if p := recover(); p != nil {
+			result, err = nil, fmt.Errorf("the step panicked: %v", p)
+		}
+	}()
+	return run(ctx)
+}
+
+func write(put Put, key string, step delivery.Step) error {
+	raw, err := delivery.EncodeStep(step)
+	if err != nil {
+		return err
+	}
+	_, err = put(key, json.RawMessage(raw))
+	return err
+}

go/buildstep/step_test.go

@@ -0,0 +1,154 @@
+package buildstep
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"sync"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// keys is a steps state in memory: every value put, in order, per key, and a signal for each end.
+type keys struct {
+	mu    sync.Mutex
+	puts  map[string][]delivery.Step
+	ended chan string
+}
+
+func newKeys() *keys { return &keys{puts: map[string][]delivery.Step{}, ended: make(chan string, 16)} }
+
+func (k *keys) put(key string, value any) (uint64, error) {
+	step, err := delivery.DecodeStep(value.(json.RawMessage))
+	if err != nil {
+		return 0, err
+	}
+	k.mu.Lock()
+	k.puts[key] = append(k.puts[key], step)
+	n := uint64(len(k.puts[key]))
+	k.mu.Unlock()
+	if step.State != delivery.StepRunning {
+		k.ended <- key
+	}
+	return n, nil
+}
+
+func (k *keys) last(key string) delivery.Step {
+	k.mu.Lock()
+	defer k.mu.Unlock()
+	s := k.puts[key]
+	return s[len(s)-1]
+}
+
+func (k *keys) waitEnd(t *testing.T) string {
+	t.Helper()
+	select {
+	case key := <-k.ended:
+		return key
+	case <-time.After(3 * time.Second):
+		t.Fatal("the step never ended on its key")
+		return ""
+	}
+}
+
+// 1471/AC1: a run that blocks: Start answers an id within 100 ms and the key holds running.
+func TestStartAnswersAtOnceWithTheStepRunning(t *testing.T) {
+	k := newKeys()
+	release := make(chan struct{})
+	defer close(release)
+	began := time.Now()
+	id, err := Start(context.Background(), k.put, "ace", "fetch", func(ctx context.Context) (any, error) {
+		<-release
+		return nil, nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if d := time.Since(began); d > 100*time.Millisecond {
+		t.Errorf("Start took %v", d)
+	}
+	s := k.last("ace." + id)
+	if s.State != delivery.StepRunning || s.Tool != "fetch" || s.Node != "ace" || s.ID != id || s.Started.IsZero() {
+		t.Errorf("step = %+v", s)
+	}
+}
+
+// 1471/AC2 and 1473/AC4: a result, an error and a Refusal end the step passed, failed and refused.
+func TestStepEndsPassedFailedOrRefusedOnItsKey(t *testing.T) {
+	for _, c := range []struct {
+		name   string
+		run    func(context.Context) (any, error)
+		state  string
+		reason string
+		result string
+	}{
+		{"result", func(context.Context) (any, error) { return map[string]string{"sha": "abc"}, nil }, delivery.StepPassed, "", `{"sha":"abc"}`},
+		{"error", func(context.Context) (any, error) { return nil, errors.New("exit 2") }, delivery.StepFailed, "exit 2", ""},
+		{"refusal", func(context.Context) (any, error) {
+			return nil, &Refusal{Text: "go 1.27.1 installed, the recipe builds with go 1.27.0", Want: "1.27.0", Have: "1.27.1"}
+		}, delivery.StepRefused, "go 1.27.1 installed, the recipe builds with go 1.27.0", ""},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			k := newKeys()
+			id, err := Start(context.Background(), k.put, "ace", "test", c.run)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got := k.waitEnd(t); got != "ace."+id {
+				t.Fatalf("ended key %q", got)
+			}
+			s := k.last("ace." + id)
+			if s.State != c.state || s.Reason != c.reason || string(s.Result) != c.result || s.Ended.IsZero() {
+				t.Errorf("step = %+v", s)
+			}
+		})
+	}
+}
+
+// 1471/AC3: a panic in run ends the step failed, naming it, and the test process goes on.
+func TestAPanicEndsTheStepFailed(t *testing.T) {
+	k := newKeys()
+	id, _ := Start(context.Background(), k.put, "ace", "build", func(context.Context) (any, error) { panic("boom") })
+	k.waitEnd(t)
+	s := k.last("ace." + id)
+	if s.State != delivery.StepFailed || s.Reason != "the step panicked: boom" {
+		t.Errorf("step = %+v", s)
+	}
+}
+
+// 1471/AC5: ids made in one and the same millisecond differ, and each is one key token. The clock is fixed
+// while no step runs, so no goroutine reads it meanwhile.
+func TestTwoIDsInOneMillisecondDiffer(t *testing.T) {
+	was := now
+	defer func() { now = was }()
+	at := time.Date(2026, 10, 20, 12, 0, 0, 0, time.UTC)
+	now = func() time.Time { return at }
+	seen := map[string]bool{}
+	for i := 0; i < 50; i++ {
+		id := NewID()
+		if seen[id] {
+			t.Fatalf("id %q handed out twice", id)
+		}
+		seen[id] = true
+		if _, err := delivery.StepKey("ace", id); err != nil {
+			t.Errorf("id %q: %v", id, err)
+		}
+	}
+}
+
+// A first write that fails starts nothing.
+func TestStartAnswersTheErrorWhenTheRunningWriteFails(t *testing.T) {
+	ran := make(chan struct{}, 1)
+	_, err := Start(context.Background(), func(string, any) (uint64, error) { return 0, errors.New("no grant") }, "ace", "fetch",
+		func(context.Context) (any, error) { ran <- struct{}{}; return nil, nil })
+	if err == nil {
+		t.Fatal("Start answered no error")
+	}
+	select {
+	case <-ran:
+		t.Error("run was called")
+	case <-time.After(50 * time.Millisecond):
+	}
+}

go/buildstep/testdata/isolated-probe/main.go

@@ -0,0 +1,49 @@
+// The probe a run step's isolation is proved with (novox/hq ADR 0448; issue 1309, S19): run inside the step, it says
+// on stdout every way it reached what a step must not, and "shut off" when it reached none. Its arguments: the files
+// it must not read (the forge key, a bus login), a TCP address and a unix socket of the machine it must not reach, a
+// name it must not resolve, and a cache file it writes, which must be unchanged after the step.
+package main
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"time"
+)
+
+func main() {
+	if len(os.Args) != 7 {
+		fmt.Println("usage: probe <key> <login> <tcp address> <unix socket> <name> <cache file>")
+		os.Exit(2)
+	}
+	key, login, tcp, socket, name, cache := os.Args[1], os.Args[2], os.Args[3], os.Args[4], os.Args[5], os.Args[6]
+	reached := 0
+	say := func(f string, a ...any) { reached++; fmt.Printf(f+"\n", a...) }
+	for _, f := range []string{key, login} {
+		if _, err := os.ReadFile(f); err == nil {
+			say("read %s", f)
+		}
+	}
+	if c, err := net.DialTimeout("tcp", tcp, 2*time.Second); err == nil {
+		c.Close()
+		say("reached %s", tcp)
+	}
+	if c, err := net.DialTimeout("unix", socket, 2*time.Second); err == nil {
+		c.Close()
+		say("reached %s", socket)
+	}
+	if addrs, err := net.LookupHost(name); err == nil {
+		say("resolved %s to %v", name, addrs)
+	}
+	if home, err := os.UserHomeDir(); err == nil {
+		if entries, err := os.ReadDir(home); err == nil && len(entries) > 0 {
+			say("the home %s holds %d entries", home, len(entries))
+		}
+	}
+	if err := os.WriteFile(cache, []byte("written by the step\n"), 0o644); err != nil {
+		say("could not write the cache under its throwaway layer: %v", err)
+	}
+	if reached == 0 {
+		fmt.Println("shut off")
+	}
+}

go/buildstep/trees.go

@@ -0,0 +1,123 @@
+package buildstep
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// ModuleTree is what a merge holds of one module directory: its tree id, the sha256 of its module.json and the sha256
+// of each lock file it has (go.sum, package-lock.json), from which the checker and the indexer take the module's inputs
+// (novox/hq ADR 0484 clause 3).
+type ModuleTree struct {
+	Tree     string            `json:"tree"`
+	Manifest string            `json:"manifest"`
+	Locks    map[string]string `json:"locks,omitempty"`
+	// Paths are, of a module whose every artifact names its paths, each named path's git object id at the commit; Tree
+	// is then their delivery.NamedTree with Manifest (novox/hq ADR 0499 clause 2). Absent otherwise.
+	Paths map[string]string `json:"paths,omitempty"`
+}
+
+var lockFiles = []string{"go.sum", "package-lock.json"}
+
+// ModuleTrees are the trees, in commit, of every directory of the workspace dir that holds a module.json, by directory
+// (the repository's root is "."); for a module whose every artifact names its paths, the named tree of those paths and
+// their objects (novox/hq ADR 0499 clause 2). The workspace is at commit, so the manifests and the lock files are read from it. env is
+// the environment git runs with (nil for none). Both build modules' fetch steps answer it for a merge.
+func ModuleTrees(ctx context.Context, run forgekey.Runner, env []string, dir, commit string) (map[string]ModuleTree, error) {
+	r := run(ctx, env, "git", "-C", dir, "ls-files", "--", "module.json", "*/module.json")
+	if r.Status != 0 || r.Err != "" {
+		return nil, fmt.Errorf("git ls-files: %s", firstLine(r.Err+" "+r.Stderr))
+	}
+	trees := map[string]ModuleTree{}
+	for _, l := range strings.Split(r.Stdout, "\n") {
+		if l = strings.TrimSpace(l); l == "" {
+			continue
+		}
+		mdir := filepath.ToSlash(filepath.Dir(l))
+		spec := commit + ":" + mdir
+		if mdir == "." {
+			spec = commit + "^{tree}"
+		}
+		t := run(ctx, env, "git", "-C", dir, "rev-parse", spec)
+		if t.Status != 0 || t.Err != "" {
+			return nil, fmt.Errorf("git rev-parse %s: %s", spec, firstLine(t.Err+" "+t.Stderr))
+		}
+		mt := ModuleTree{Tree: strings.TrimSpace(t.Stdout)}
+		raw, err := os.ReadFile(filepath.Join(dir, filepath.FromSlash(l)))
+		if err != nil {
+			return nil, err
+		}
+		mt.Manifest = sha256Hex(raw)
+		if err := narrow(ctx, run, env, dir, commit, mdir, raw, &mt); err != nil {
+			return nil, err
+		}
+		for _, lock := range lockFiles {
+			if raw, err := os.ReadFile(filepath.Join(dir, filepath.FromSlash(mdir), lock)); err == nil {
+				if mt.Locks == nil {
+					mt.Locks = map[string]string{}
+				}
+				mt.Locks[lock] = sha256Hex(raw)
+			}
+		}
+		trees[mdir] = mt
+	}
+	return trees, nil
+}
+
+// narrow sets mt's Paths and its named Tree when the module's manifest names paths on every artifact (novox/hq ADR 0499
+// clause 2): one `git ls-tree -z` gives each named path's object at commit. The merge preview reads the manifest here, as
+// the indexer does, with catalogue.ParseManifestForInputs (issue 1751), and no other build step reads paths from one (ADR 0495 clause 1). A manifest that does not parse
+// is not narrowed: the indexer gives it none. A named path absent at commit fails, naming the module and the path.
+func narrow(ctx context.Context, run forgekey.Runner, env []string, dir, commit, mdir string, raw []byte, mt *ModuleTree) error {
+	m, err := catalogue.ParseManifestForInputs(raw)
+	if err != nil {
+		return nil
+	}
+	paths, every := m.NamedPaths()
+	if !every {
+		return nil
+	}
+	full := make([]string, len(paths))
+	for i, p := range paths {
+		full[i] = path.Join(mdir, p)
+	}
+	r := run(ctx, env, "git", append([]string{"-C", dir, "ls-tree", "-z", commit, "--"}, full...)...)
+	if r.Status != 0 || r.Err != "" {
+		return fmt.Errorf("git ls-tree %s of the module %s: %s", commit, mdir, firstLine(r.Err+" "+r.Stderr))
+	}
+	objects := map[string]string{}
+	for _, l := range strings.Split(r.Stdout, "\x00") {
+		meta, name, ok := strings.Cut(l, "\t")
+		fields := strings.Fields(meta)
+		if !ok || len(fields) != 3 {
+			continue
+		}
+		objects[name] = fields[2]
+	}
+	mt.Paths = map[string]string{}
+	for i, p := range paths {
+		object := objects[full[i]]
+		if object == "" {
+			return fmt.Errorf("the module %s names the path %q, which is not in %s", mdir, p, commit)
+		}
+		mt.Paths[p] = object
+	}
+	named, err := delivery.NamedTree(mt.Manifest, mt.Paths)
+	if err != nil {
+		return fmt.Errorf("the module %s: %w", mdir, err)
+	}
+	mt.Tree = named
+	return nil
+}
+
+func sha256Hex(b []byte) string { h := sha256.Sum256(b); return hex.EncodeToString(h[:]) }

go/buildstep/trees_integration_test.go

@@ -0,0 +1,63 @@
+//go:build integration
+
+package buildstep
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// On a real repository shaped like mesh-sdk (novox/hq ADR 0499 clauses 2 and 6), a commit touching only the Go package
+// leaves the TypeScript package's tree value equal, and a commit touching its source changes it; a module that names no
+// path keeps its directory's tree id.
+func TestAGoOnlyCommitLeavesTheNamedTreeEqualOnRealGit(t *testing.T) {
+	repo := t.TempDir()
+	realGit(t, repo, "init", "-q", "-b", "main")
+	writeFile(t, repo, "module.json", `{"module":"mesh-sdk","version":"1","build":{"artifacts":[`+
+		`{"name":"lib","kind":"package","language":"typescript","paths":["src","test","package.json","package-lock.json","tsconfig.json"]}]}}`)
+	writeFile(t, repo, "src/index.ts", "export const a = 1\n")
+	writeFile(t, repo, "test/a.test.ts", "// a\n")
+	writeFile(t, repo, "package.json", "{}\n")
+	writeFile(t, repo, "package-lock.json", "{}\n")
+	writeFile(t, repo, "tsconfig.json", "{}\n")
+	writeFile(t, repo, "go/delivery/x.go", "package delivery\n")
+	writeFile(t, repo, "other/module.json", `{"module":"other","version":"1"}`)
+	writeFile(t, repo, "other/a.txt", "a\n")
+	commit := func(msg string) string {
+		realGit(t, repo, "add", "-A")
+		realGit(t, repo, "commit", "-q", "-m", msg)
+		return realGit(t, repo, "rev-parse", "HEAD")
+	}
+	trees := func(c string) map[string]ModuleTree {
+		got, err := ModuleTrees(context.Background(), forgekey.ExecRunner, nil, repo, c)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return got
+	}
+	first := trees(commit("first"))
+	if !strings.HasPrefix(first["."].Tree, "named:") || len(first["."].Paths) != 5 {
+		t.Fatalf("the root module was not narrowed: %+v", first["."])
+	}
+	if want := realGit(t, repo, "rev-parse", "HEAD:other"); first["other"].Tree != want || first["other"].Paths != nil {
+		t.Fatalf("a module naming no path: %+v, want its directory's tree %s", first["other"], want)
+	}
+
+	writeFile(t, repo, "go/delivery/x.go", "package delivery\n\nconst B = 2\n")
+	goOnly := trees(commit("go only"))
+	if goOnly["."].Tree != first["."].Tree {
+		t.Fatalf("a Go-only commit changed the TypeScript package's tree: %s, was %s", goOnly["."].Tree, first["."].Tree)
+	}
+
+	writeFile(t, repo, "src/index.ts", "export const a = 2\n")
+	src := trees(commit("src"))
+	if src["."].Tree == first["."].Tree {
+		t.Fatal("a commit to src/ left the TypeScript package's tree equal")
+	}
+	if src["."].Paths["src"] != realGit(t, repo, "rev-parse", "HEAD:src") {
+		t.Fatalf("the object of src is %s, git says %s", src["."].Paths["src"], realGit(t, repo, "rev-parse", "HEAD:src"))
+	}
+}

go/buildstep/trees_named_test.go

@@ -0,0 +1,113 @@
+package buildstep
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/catalogue"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+// A module whose every artifact names its paths takes its tree from them (novox/hq ADR 0499 clause 2): ModuleTrees asks
+// git for each named path's object at the commit, keeps them in Paths and answers their delivery.NamedTree as Tree; a
+// module naming none keeps its directory's tree, as before.
+func TestModuleTreesNarrowsAModuleWhoseArtifactsNameTheirPaths(t *testing.T) {
+	root := t.TempDir()
+	sdk := `{"module":"mesh-sdk","version":"1","build":{"artifacts":[{"name":"lib","kind":"package","language":"typescript","paths":["src","package.json"]}]}}`
+	writeTreeFile(t, root, "module.json", sdk)
+	writeTreeFile(t, root, "modules/b/module.json", `{"module":"b","version":"1"}`)
+	merge := strings.Repeat("c", 40)
+	var lsTree []string
+	run := func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+		switch args[2] {
+		case "ls-files":
+			return forgekey.Ran{Stdout: "module.json\nmodules/b/module.json\n"}
+		case "rev-parse":
+			return forgekey.Ran{Stdout: "tree-of-" + args[3] + "\n"}
+		case "ls-tree":
+			lsTree = append(lsTree, strings.Join(args[4:], " "))
+			return forgekey.Ran{Stdout: "100644 blob " + strings.Repeat("b", 40) + "\tpackage.json\x00" +
+				"040000 tree " + strings.Repeat("a", 40) + "\tsrc\x00"}
+		}
+		return forgekey.Ran{Status: 1, Stderr: "unexpected " + args[2]}
+	}
+	got, err := ModuleTrees(context.Background(), run, nil, root, merge)
+	if err != nil {
+		t.Fatal(err)
+	}
+	paths := map[string]string{"src": strings.Repeat("a", 40), "package.json": strings.Repeat("b", 40)}
+	want, _ := delivery.NamedTree(hexOf(sdk), paths)
+	if g := got["."]; g.Tree != want || len(g.Paths) != 2 || g.Paths["src"] != paths["src"] || g.Paths["package.json"] != paths["package.json"] {
+		t.Fatalf("the root module = %+v, want tree %s and paths %v", g, want, paths)
+	}
+	if len(lsTree) != 1 || lsTree[0] != merge+" -- package.json src" {
+		t.Fatalf("git ls-tree ran as %v", lsTree)
+	}
+	if g := got["modules/b"]; g.Tree != "tree-of-"+merge+":modules/b" || g.Paths != nil {
+		t.Fatalf("a module naming no path was narrowed: %+v", g)
+	}
+}
+
+// A named path absent at the commit fails the answer, naming the module and the path: a tree computed without it would
+// pin a build source that does not exist.
+func TestModuleTreesFailsNamingANamedPathAbsentAtTheCommit(t *testing.T) {
+	root := t.TempDir()
+	writeTreeFile(t, root, "modules/a/module.json", `{"module":"a","version":"1","build":{"artifacts":[{"name":"lib","kind":"package","language":"typescript","paths":["src","gone"]}]}}`)
+	run := func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+		switch args[2] {
+		case "ls-files":
+			return forgekey.Ran{Stdout: "modules/a/module.json\n"}
+		case "rev-parse":
+			return forgekey.Ran{Stdout: "t\n"}
+		case "ls-tree":
+			if strings.Join(args[4:], " ") != strings.Repeat("c", 40)+" -- modules/a/gone modules/a/src" {
+				return forgekey.Ran{Status: 1, Stderr: "wrong arguments " + strings.Join(args[3:], " ")}
+			}
+			return forgekey.Ran{Stdout: "040000 tree " + strings.Repeat("a", 40) + "\tmodules/a/src\x00"}
+		}
+		return forgekey.Ran{Status: 1}
+	}
+	_, err := ModuleTrees(context.Background(), run, nil, root, strings.Repeat("c", 40))
+	if err == nil || !strings.Contains(err.Error(), `"gone"`) || !strings.Contains(err.Error(), "modules/a") {
+		t.Fatalf("an absent named path gave %v", err)
+	}
+}
+
+// A manifest whose config value falls back to a predefined key is narrowed here as the indexer narrows it: both read it
+// with catalogue.ParseManifestForInputs (issue 1751), so a build module holding no published list computes the same
+// tree (ADR 0499 clause 2).
+func TestModuleTreesNarrowsAManifestFallingBackToAPredefinedKey(t *testing.T) {
+	was := catalogue.ReplacePublished(nil) // the build modules' case: no published list
+	defer catalogue.ReplacePublished(was)
+	root := t.TempDir()
+	raw := `{"module":"xterm","version":"1","config":{"size":{"type":"number","description":"The text size.","predefined":"font-size","default":12,"runtime":true}},` +
+		`"build":{"artifacts":[{"name":"lib","kind":"package","language":"typescript","paths":["src"]}]}}`
+	if _, err := catalogue.ParseManifest([]byte(raw)); err == nil {
+		t.Fatal("ParseManifest reads the manifest with no list; the test proves nothing")
+	}
+	if _, err := catalogue.ParseManifestForInputs([]byte(raw)); err != nil {
+		t.Fatalf("the indexer's read refuses the manifest: %v", err)
+	}
+	writeTreeFile(t, root, "module.json", raw)
+	run := func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+		switch args[2] {
+		case "ls-files":
+			return forgekey.Ran{Stdout: "module.json\n"}
+		case "rev-parse":
+			return forgekey.Ran{Stdout: "whole\n"}
+		case "ls-tree":
+			return forgekey.Ran{Stdout: "040000 tree " + strings.Repeat("a", 40) + "\tsrc\x00"}
+		}
+		return forgekey.Ran{Status: 1}
+	}
+	got, err := ModuleTrees(context.Background(), run, nil, root, strings.Repeat("c", 40))
+	if err != nil {
+		t.Fatal(err)
+	}
+	want, _ := delivery.NamedTree(hexOf(raw), map[string]string{"src": strings.Repeat("a", 40)})
+	if g := got["."]; g.Tree != want || g.Paths["src"] == "" {
+		t.Fatalf("the module = %+v, want the named tree %s", g, want)
+	}
+}

go/buildstep/trees_test.go

@@ -0,0 +1,93 @@
+package buildstep
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"os"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/forgekey"
+)
+
+func hexOf(s string) string { h := sha256.Sum256([]byte(s)); return hex.EncodeToString(h[:]) }
+
+func writeTreeFile(t *testing.T, root, name, content string) {
+	t.Helper()
+	p := filepath.Join(root, filepath.FromSlash(name))
+	if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(p, []byte(content), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+// ModuleTrees answers, for each directory holding a module.json (the root as "."), the tree id git gives, the sha256 of
+// module.json and of each lock file present, and reads them from the workspace.
+func TestModuleTreesAnswersTreeManifestAndLocksPerModuleDirectory(t *testing.T) {
+	root := t.TempDir()
+	writeTreeFile(t, root, "module.json", `{"root":1}`)
+	writeTreeFile(t, root, "go.sum", "rootsum")
+	writeTreeFile(t, root, "modules/a/module.json", `{"a":1}`)
+	writeTreeFile(t, root, "modules/a/go.sum", "asum")
+	writeTreeFile(t, root, "modules/a/package-lock.json", "alock")
+	writeTreeFile(t, root, "modules/b/module.json", `{"b":1}`)
+	merge := strings.Repeat("c", 40)
+	var calls []string
+	var envs [][]string
+	run := func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+		calls = append(calls, name+" "+strings.Join(args[2:], " "))
+		envs = append(envs, env)
+		switch args[2] {
+		case "ls-files":
+			return forgekey.Ran{Stdout: "module.json\nmodules/a/module.json\nmodules/b/module.json\n"}
+		case "rev-parse":
+			return forgekey.Ran{Stdout: "tree-of-" + args[3] + "\n"}
+		}
+		return forgekey.Ran{Status: 1, Stderr: "unexpected"}
+	}
+	got, err := ModuleTrees(context.Background(), run, []string{"X=1"}, root, merge)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := map[string]ModuleTree{
+		".":         {Tree: "tree-of-" + merge + "^{tree}", Manifest: hexOf(`{"root":1}`), Locks: map[string]string{"go.sum": hexOf("rootsum")}},
+		"modules/a": {Tree: "tree-of-" + merge + ":modules/a", Manifest: hexOf(`{"a":1}`), Locks: map[string]string{"go.sum": hexOf("asum"), "package-lock.json": hexOf("alock")}},
+		"modules/b": {Tree: "tree-of-" + merge + ":modules/b", Manifest: hexOf(`{"b":1}`)},
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("trees = %+v\nwant %+v", got, want)
+	}
+	if got["modules/b"].Locks != nil {
+		t.Error("a module with no lock file carries a lock map")
+	}
+	for _, e := range envs {
+		if len(e) != 1 || e[0] != "X=1" {
+			t.Errorf("git ran with env %v, want the one given", e)
+		}
+	}
+}
+
+func TestModuleTreesFailsNamingTheGitCommandOrTheUnreadableManifest(t *testing.T) {
+	root := t.TempDir()
+	fail := func(on string) forgekey.Runner {
+		return func(ctx context.Context, env []string, name string, args ...string) forgekey.Ran {
+			if args[2] == on {
+				return forgekey.Ran{Status: 128, Stderr: "fatal: no\n"}
+			}
+			return forgekey.Ran{Stdout: "modules/a/module.json\n"}
+		}
+	}
+	for _, on := range []string{"ls-files", "rev-parse"} {
+		if _, err := ModuleTrees(context.Background(), fail(on), nil, root, sha); err == nil || !strings.Contains(err.Error(), on) || !strings.Contains(err.Error(), "fatal: no") {
+			t.Errorf("%s failing: %v", on, err)
+		}
+	}
+	if _, err := ModuleTrees(context.Background(), fail("none"), nil, root, sha); err == nil {
+		t.Error("a module.json that is not in the workspace was read")
+	}
+}

go/buildstep/workspaces.go

@@ -0,0 +1,160 @@
+package buildstep
+
+// A build module's room to work and its workspaces (novox/hq issue 1839, ADR 0509): a step is refused while the
+// filesystem it writes to has less free than the floor, and a workspace is removed when its caller releases it, or,
+// unheld, once its last use is past a bound (a lost caller's), never while a running step holds it.
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"sync"
+	"syscall"
+	"time"
+)
+
+// FreeSpaceFloor is the free space a build module needs on its work and cache filesystems to take a step: the floor
+// build-agent keeps (mesh-controller internal/builder/floor.go, issue 1834).
+const FreeSpaceFloor uint64 = 20 << 30
+
+// UnheldBound is how long a workspace no step holds is kept after its last use, when its caller never released it
+// (ADR 0509: a lost caller's workspace goes after two hours).
+const UnheldBound = 2 * time.Hour
+
+// FreeBytes reads the bytes an unprivileged writer can still use on the filesystem holding path.
+func FreeBytes(path string) (uint64, error) {
+	var s syscall.Statfs_t
+	if err := syscall.Statfs(path, &s); err != nil {
+		return 0, err
+	}
+	return s.Bavail * uint64(s.Bsize), nil
+}
+
+// Floor refuses a step while a filesystem it writes to has less free than Bytes. A zero Bytes checks nothing.
+type Floor struct {
+	// Node is named in the refusal.
+	Node  string
+	Bytes uint64
+	// Free reads a path's free bytes; FreeBytes when nil. A test answers for a disk it does not have.
+	Free func(path string) (uint64, error)
+}
+
+// Check answers a *Refusal, "refused: <node> has N GiB free under the floor of F GiB (on <path>)", when any path's
+// filesystem has less free than the floor, or its free space cannot be read; nil otherwise. A path not made yet is
+// read at its nearest folder that is; an empty path is skipped.
+func (f Floor) Check(paths ...string) error {
+	if f.Bytes == 0 {
+		return nil
+	}
+	free := f.Free
+	if free == nil {
+		free = FreeBytes
+	}
+	for _, p := range paths {
+		if p == "" {
+			continue
+		}
+		at := p
+		for {
+			if _, err := os.Stat(at); err == nil || filepath.Dir(at) == at {
+				break
+			}
+			at = filepath.Dir(at)
+		}
+		n, err := free(at)
+		if err != nil {
+			return &Refusal{Text: fmt.Sprintf("refused: the free space of %s on %s cannot be read: %v", p, f.Node, err)}
+		}
+		if n < f.Bytes {
+			return &Refusal{Text: fmt.Sprintf("refused: %s has %d GiB free under the floor of %d GiB (on %s)", f.Node, n>>30, f.Bytes>>30, p),
+				Want: fmt.Sprintf("%d GiB", f.Bytes>>30), Have: fmt.Sprintf("%d GiB", n>>30)}
+		}
+	}
+	return nil
+}
+
+var workspaceID = regexp.MustCompile(`^[a-z0-9]+$`)
+
+// Workspaces are a build module's workspaces, each <Dir>/<id>, and which of them running steps hold.
+type Workspaces struct {
+	Dir string
+
+	mu   sync.Mutex
+	held map[string]int
+}
+
+// Hold marks the workspace held by a running step until the answered func is called; both mark it used now, so the
+// sweep counts its bound from the step's end. An id that is not a workspace's holds nothing.
+func (w *Workspaces) Hold(id string) func() {
+	if !workspaceID.MatchString(id) {
+		return func() {}
+	}
+	w.mu.Lock()
+	if w.held == nil {
+		w.held = map[string]int{}
+	}
+	w.held[id]++
+	w.mu.Unlock()
+	w.touch(id)
+	var once sync.Once
+	return func() {
+		once.Do(func() {
+			w.touch(id)
+			w.mu.Lock()
+			if w.held[id]--; w.held[id] <= 0 {
+				delete(w.held, id)
+			}
+			w.mu.Unlock()
+		})
+	}
+}
+
+func (w *Workspaces) touch(id string) {
+	now := time.Now()
+	_ = os.Chtimes(filepath.Join(w.Dir, id), now, now) // a workspace not made yet has nothing to mark
+}
+
+// Release removes the workspace at once: its caller's chain of steps has ended. One already gone is no error; one a
+// running step holds is refused and kept; an id that is not a workspace's is refused.
+func (w *Workspaces) Release(id string) error {
+	if !workspaceID.MatchString(id) {
+		return fmt.Errorf("%q is not a workspace id", id)
+	}
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if w.held[id] > 0 {
+		return fmt.Errorf("the workspace %s is held by a running step", id)
+	}
+	if err := os.RemoveAll(filepath.Join(w.Dir, id)); err != nil {
+		return fmt.Errorf("the workspace %s could not be removed: %w", id, err)
+	}
+	return nil
+}
+
+// Sweep removes every workspace no step holds whose last use is older than bound, and answers the ids it removed,
+// sorted. It is the safety net for a caller that never released its workspace.
+func (w *Workspaces) Sweep(now time.Time, bound time.Duration) []string {
+	entries, err := os.ReadDir(w.Dir)
+	if err != nil {
+		return nil
+	}
+	removed := []string{}
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	for _, e := range entries {
+		if !e.IsDir() || !workspaceID.MatchString(e.Name()) || w.held[e.Name()] > 0 {
+			continue
+		}
+		info, err := e.Info()
+		if err != nil || now.Sub(info.ModTime()) < bound {
+			continue
+		}
+		if os.RemoveAll(filepath.Join(w.Dir, e.Name())) == nil {
+			removed = append(removed, e.Name())
+		}
+	}
+	sort.Strings(removed)
+	return removed
+}

go/buildstep/workspaces_test.go

@@ -0,0 +1,113 @@
+package buildstep
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+// 1839/AC1: a filesystem under the floor refuses the step, naming the node, what is free and the floor.
+func TestAFilesystemUnderTheFloorRefusesNamingNodeFreeAndFloor(t *testing.T) {
+	dir := t.TempDir()
+	f := Floor{Node: "ace", Bytes: 20 << 30, Free: func(string) (uint64, error) { return 4<<30 + 5, nil }}
+	err := f.Check(dir)
+	var ref *Refusal
+	if !errors.As(err, &ref) {
+		t.Fatalf("Check = %v, want a *Refusal", err)
+	}
+	if want := "refused: ace has 4 GiB free under the floor of 20 GiB (on " + dir + ")"; err.Error() != want {
+		t.Errorf("Check = %q, want %q", err, want)
+	}
+}
+
+// 1839/AC1: at or above the floor, and with no floor set, nothing is refused.
+func TestAtTheFloorOrWithNoFloorNothingIsRefused(t *testing.T) {
+	dir := t.TempDir()
+	if err := (Floor{Node: "ace", Bytes: 20 << 30, Free: func(string) (uint64, error) { return 20 << 30, nil }}).Check(dir); err != nil {
+		t.Errorf("at the floor: %v", err)
+	}
+	if err := (Floor{Node: "ace", Free: func(string) (uint64, error) { return 0, nil }}).Check(dir); err != nil {
+		t.Errorf("no floor: %v", err)
+	}
+}
+
+// 1839/AC1: a path not made yet is read at its nearest folder that is; a free space that cannot be read is a refusal.
+func TestAPathNotMadeIsReadAtItsParentAndAnUnreadableOneRefuses(t *testing.T) {
+	dir := t.TempDir()
+	var read string
+	f := Floor{Node: "ace", Bytes: 1, Free: func(p string) (uint64, error) { read = p; return 2, nil }}
+	if err := f.Check(filepath.Join(dir, "not", "made")); err != nil || read != dir {
+		t.Errorf("Check = %v, read %q, want nil and %q", err, read, dir)
+	}
+	f.Free = func(string) (uint64, error) { return 0, errors.New("statfs: boom") }
+	var ref *Refusal
+	if err := f.Check(dir); !errors.As(err, &ref) {
+		t.Errorf("Check = %v, want a refusal", err)
+	}
+}
+
+func makeWorkspace(t *testing.T, w *Workspaces, id string, age time.Duration) string {
+	t.Helper()
+	p := filepath.Join(w.Dir, id)
+	if err := os.MkdirAll(filepath.Join(p, "tree"), 0o700); err != nil {
+		t.Fatal(err)
+	}
+	at := time.Now().Add(-age)
+	if err := os.Chtimes(p, at, at); err != nil {
+		t.Fatal(err)
+	}
+	return p
+}
+
+func gone(p string) bool { _, err := os.Stat(p); return os.IsNotExist(err) }
+
+// 1839/AC2: a released workspace is gone at once; one already gone is no error; one a running step holds is refused
+// and kept; an id that is not a workspace's is refused.
+func TestReleaseRemovesAWorkspaceAtOnce(t *testing.T) {
+	w := &Workspaces{Dir: t.TempDir()}
+	p := makeWorkspace(t, w, "abc1", 0)
+	if err := w.Release("abc1"); err != nil || !gone(p) {
+		t.Fatalf("Release = %v, gone %v", err, gone(p))
+	}
+	if err := w.Release("abc1"); err != nil {
+		t.Errorf("a second release = %v, want nil", err)
+	}
+	held := makeWorkspace(t, w, "abc2", 0)
+	done := w.Hold("abc2")
+	if err := w.Release("abc2"); err == nil || gone(held) {
+		t.Errorf("Release of a held workspace = %v, gone %v; want refused and kept", err, gone(held))
+	}
+	done()
+	if err := w.Release("abc2"); err != nil || !gone(held) {
+		t.Errorf("Release after the hold ended = %v, gone %v", err, gone(held))
+	}
+	if err := w.Release("../etc"); err == nil {
+		t.Errorf("Release of ../etc answered nil")
+	}
+}
+
+// 1839/AC3: the sweep removes a workspace no step holds whose last use is past the bound, and keeps a held one and a
+// recent one; a hold ending counts as a use.
+func TestSweepRemovesUnheldWorkspacesPastTheBound(t *testing.T) {
+	w := &Workspaces{Dir: t.TempDir()}
+	old := makeWorkspace(t, w, "old1", 3*time.Hour)
+	heldOld := makeWorkspace(t, w, "held1", 3*time.Hour)
+	recent := makeWorkspace(t, w, "new1", time.Minute)
+	if err := os.WriteFile(filepath.Join(w.Dir, "not-a-workspace.txt"), nil, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	done := w.Hold("held1")
+	removed := w.Sweep(time.Now(), 2*time.Hour)
+	if !gone(old) || gone(heldOld) || gone(recent) {
+		t.Errorf("after the sweep: old gone %v, held kept %v, recent kept %v", gone(old), !gone(heldOld), !gone(recent))
+	}
+	if len(removed) != 1 || removed[0] != "old1" {
+		t.Errorf("Sweep answered %v, want [old1]", removed)
+	}
+	done()
+	if w.Sweep(time.Now(), 2*time.Hour); gone(heldOld) {
+		t.Errorf("a workspace whose hold just ended was swept: its end is a use")
+	}
+}

go/buscompose/agreement.go

@@ -0,0 +1,125 @@
+package buscompose
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// Do the emitters and the consumers of a catalogue agree?
+//
+// **The check that was missing** (novox/hq 04-ISSUES/127). Every manifest was individually
+// well-formed and every derivation individually correct, and no cross-module subscription in the
+// mesh matched anything: a consumer's declaration derived into a namespace nobody publishes to.
+// Nothing failed, because a subscription that matches nothing is not an error — it is silence.
+//
+// The comparison has to be over the whole catalogue, because the two halves live in different
+// manifests, and it cannot simply demand that every consumed event have a live emitter: a module
+// may be installed long before the one whose events it wants. So the rule is narrower and still
+// catches this: **where the emitter is present, it must emit what the consumer asked for.**
+
+// AConsumer is one module's interest in another's events, as this check needs it.
+type AConsumer struct {
+	Module   string
+	Consumes []string
+}
+
+// AnEmitter is one module's events.
+type AnEmitter struct {
+	Module string
+	Emits  []string
+}
+
+// Disagreements are the consumed events whose emitter is in the catalogue and does not emit them.
+//
+// Returned as sentences rather than as structs: every one of them is read by a person deciding
+// whether a manifest or a catalogue is wrong, and a pair of names without the reason is a puzzle.
+func Disagreements(emitters []AnEmitter, consumers []AConsumer, seats []DeclaredSeat) []string {
+	emits := map[string]map[string]bool{}
+	for _, e := range emitters {
+		if emits[e.Module] == nil {
+			emits[e.Module] = map[string]bool{}
+		}
+		for _, name := range e.Emits {
+			emits[e.Module][name] = true
+		}
+	}
+	// A seat's events are published by its holder under the seat's name, so a consumer naming the
+	// seat is naming something real even though no module declares it as its own.
+	for _, s := range seats {
+		if len(s.Emits) == 0 {
+			continue
+		}
+		if emits[s.Name] == nil {
+			emits[s.Name] = map[string]bool{}
+		}
+		for _, name := range s.Emits {
+			emits[s.Name][name] = true
+		}
+	}
+
+	var out []string
+	for _, c := range consumers {
+		for _, pattern := range c.Consumes {
+			emitter, event, named := strings.Cut(pattern, ".")
+			// Every event from everyone, or every event from one module: both are deliberate and
+			// neither names a particular event to check.
+			if !named || emitter == "*" || emitter == catalogueTheRest || event == catalogueTheRest {
+				continue
+			}
+			known, present := emits[emitter]
+			if !present {
+				// Not installed here, which is ordinary: a module lives in its own repository and
+				// may be registered later. Nothing to compare, so nothing to say.
+				continue
+			}
+			if matchesAny(event, known) {
+				continue
+			}
+			out = append(out, fmt.Sprintf(
+				"%s consumes %q and %s emits %s — so that subscription would match nothing, and "+
+					"nothing would report it",
+				c.Module, pattern, emitter, listOf(known)))
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+// matchesAny says whether one of an emitter's event names satisfies a consumer's pattern.
+func matchesAny(pattern string, emitted map[string]bool) bool {
+	want := strings.Split(pattern, ".")
+	for name := range emitted {
+		if matches(want, strings.Split(name, ".")) {
+			return true
+		}
+	}
+	return false
+}
+
+func matches(pattern, name []string) bool {
+	for i, part := range pattern {
+		if part == catalogueTheRest {
+			return i < len(name)
+		}
+		if i >= len(name) {
+			return false
+		}
+		if part != "*" && part != name[i] {
+			return false
+		}
+	}
+	return len(pattern) == len(name)
+}
+
+func listOf(names map[string]bool) string {
+	if len(names) == 0 {
+		return "nothing"
+	}
+	out := make([]string, 0, len(names))
+	for n := range names {
+		out = append(out, n)
+	}
+	sort.Strings(out)
+	return strings.Join(out, ", ")
+}

go/buscompose/announced.go

@@ -0,0 +1,82 @@
+package buscompose
+
+import (
+	"sort"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/announce"
+)
+
+// Who may read a module's state is what the module announced (novox/hq ADR 0495 clauses 2 and 3, ADR 0513 §3; issue
+// 1790). A module says on the bus which states it keeps and which others may read (announce.Subject); the controller
+// keeps the last word of each (announce.KeptBucket) and grants a reader's `reads: <owner>.<name>` only when the owner
+// announced that state readable. An owner that has announced nothing yet is read as before, from the reader's `reads`
+// (the transition, until every module announces), and is named as not yet announced.
+
+// StatesAnnouncedBucket is the controller's bucket of the last announcement of each module (announce.KeptBucket).
+const StatesAnnouncedBucket = announce.KeptBucket
+
+// controllerReadable are the controller's states others may read: the record mirrors (the packages each node declares
+// among them, which the pacman module reads, ADR 0507 §5), the chain's buckets, and the grants issued and the
+// compositions' digests, which the assigner reads (ADR 0528 clause 2, ADR 0539 clause 6).
+var controllerReadable = []string{MirrorAssignments, MirrorDeclaredConfig, MirrorPredefined, ChainBuilds, ChainRollouts,
+	MirrorDeclaredPackages, ControllerGrants, ControllerComposed}
+
+// ControllerAnnouncement is what the controller announces it keeps (ADR 0495 clause 2): every bucket of its own by its local
+// name, the ones others may read marked readable. It announces itself, as any module does from its code.
+func ControllerAnnouncement(node string) announce.States {
+	s := announce.States{Module: ControllerSeat, Node: node}
+	readable := map[string]bool{}
+	for _, n := range controllerReadable {
+		readable[n] = true
+	}
+	for _, bucket := range ControllerBuckets() {
+		local, mine := strings.CutPrefix(bucket, ControllerSeat+"_")
+		if !mine {
+			continue
+		}
+		s.States = append(s.States, announce.State{Name: local, Readable: readable[local]})
+	}
+	sort.Slice(s.States, func(i, j int) bool { return s.States[i].Name < s.States[j].Name })
+	return s
+}
+
+// ReadsAnnounced splits a reader's `reads` (`<owner>.<name>`) by what each owner announced: granted when the owner
+// announced the state readable, or announced nothing yet (the transition); refused when the owner announced and did
+// not announce that state readable.
+func ReadsAnnounced(reads []string, announced map[string]announce.States) (granted, refused []string) {
+	for _, r := range reads {
+		owner, name, ok := strings.Cut(r, ".")
+		s, said := announced[owner]
+		switch {
+		case !ok || !said || s.Readable(name):
+			granted = append(granted, r)
+		default:
+			refused = append(refused, r)
+		}
+	}
+	return granted, refused
+}
+
+// NotAnnounced are the owners some module reads the state of and that have announced nothing yet, sorted: read from the
+// readers' `reads` as before, until they announce.
+func NotAnnounced(r Records) []string {
+	seen := map[string]bool{}
+	var out []string
+	for _, ds := range r.Assigned {
+		for _, d := range ds {
+			for _, read := range append(append([]string(nil), d.Reads...), d.ReadsRefused...) {
+				owner, _, ok := strings.Cut(read, ".")
+				if !ok || seen[owner] {
+					continue
+				}
+				if _, said := r.Announced[owner]; !said {
+					seen[owner] = true
+					out = append(out, owner)
+				}
+			}
+		}
+	}
+	sort.Strings(out)
+	return out
+}

go/buscompose/buildbacklog.go

@@ -0,0 +1,47 @@
+package buscompose
+
+import "git.novox.be/novox/mesh-sdk/go/delivery"
+
+// The view alone reads the build seats' queues (novox/hq ADR 0525 §2, issue 1887 A8a): the shared workers' counts and the
+// oldest waiting ask, to show the backlog. It may not publish an ask: only the builder and the checker ask, by their seat use.
+// The watchman is granted nothing here: a waiting ask has no pulse, a taken one is read from the build module's steps (issue
+// 1908). Nothing is a wildcard over a stream or a worker.
+const (
+	// ViewModule is the module of the delivery view (mesh-delivery-view).
+	ViewModule = "mesh-delivery-view"
+	// BuilderModule is the module of the builder (mesh-delivery-builder).
+	BuilderModule = "mesh-delivery-builder"
+)
+
+// BuildAskReads are the API subjects the builder requests when it takes over, at its start, a key naming an ask (issue
+// 1910): each build seat's stream's information and its messages by sequence, to tell whether the ask is on its stream.
+// Reads only: no consumer, no pull, no acknowledgement; the builder puts its asks by its seat use, as before.
+func BuildAskReads() []string {
+	var out []string
+	for _, lang := range delivery.AskLanguages {
+		if stream, err := delivery.AskStream(lang); err == nil {
+			out = append(out, "$JS.API.STREAM.INFO."+stream, "$JS.API.STREAM.MSG.GET."+stream)
+		}
+	}
+	return out
+}
+
+// BuildBacklogReads are the API subjects the view requests: the information of each build seat's stream and of each of its
+// shared workers (delivery.AskStream, delivery.AskWorker), and the message of the stream by sequence. Reads only: no
+// message is pulled, none acknowledged, none published.
+func BuildBacklogReads() []string {
+	var out []string
+	for _, lang := range delivery.AskLanguages {
+		stream, err := delivery.AskStream(lang)
+		if err != nil {
+			continue
+		}
+		out = append(out, "$JS.API.STREAM.INFO."+stream, "$JS.API.STREAM.MSG.GET."+stream)
+		for _, kind := range delivery.AskKinds {
+			if w, err := delivery.AskWorker(lang, kind); err == nil {
+				out = append(out, "$JS.API.CONSUMER.INFO."+stream+"."+w)
+			}
+		}
+	}
+	return out
+}

go/buscompose/buscompose_test.go

@@ -0,0 +1,102 @@
+package buscompose
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+// Defends issue 1377 and novox/hq ADR 0547 §5: this is the controller's bus composer copied, and it composes byte for
+// byte what the controller's composes. testdata/controller-user-lists.json was written by the controller's own
+// internal/broker (mesh-controller branch fix/1945-mesh-grants-publishes-memberships), lists and memberships, from fixtures_test.go compiled there unchanged; composed.conf is the
+// controller's golden of the whole server configuration. A row that differs is the copy drifting from the controller,
+// which is a fault while both compose (until the controller loses its lease, ADR 0547 §13).
+func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
+	raw, err := os.ReadFile(filepath.Join("testdata", "controller-user-lists.json"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var want []struct {
+		Name, List  string
+		Missing     []string
+		Err         string
+		Memberships json.RawMessage
+	}
+	if err := json.Unmarshal(raw, &want); err != nil {
+		t.Fatal(err)
+	}
+	fixtures := UserListFixtures()
+	if len(want) != len(fixtures) {
+		t.Fatalf("%d fixtures, %d lists the controller composed", len(fixtures), len(want))
+	}
+	for i, f := range fixtures {
+		t.Run(f.Name, func(t *testing.T) {
+			if want[i].Name != f.Name {
+				t.Fatalf("fixture %q against the controller's %q", f.Name, want[i].Name)
+			}
+			list, missing, err := ComposedFor(f)
+			got := ""
+			if err != nil {
+				got = err.Error()
+			}
+			if got != want[i].Err {
+				t.Fatalf("error %q, the controller's %q", got, want[i].Err)
+			}
+			if strings.Join(missing, ",") != strings.Join(want[i].Missing, ",") {
+				t.Errorf("left out %v, the controller %v", missing, want[i].Missing)
+			}
+			if list != want[i].List {
+				t.Errorf("the list differs from the controller's:\n%s", list)
+			}
+			// And every membership the records issue, as the controller's MembershipFor makes it (ADR 0547 §5): the
+			// grants part publishes them.
+			raw, err := json.Marshal(MembershipsFor(f))
+			if err != nil {
+				t.Fatal(err)
+			}
+			var gotM, wasM any
+			if err := json.Unmarshal(raw, &gotM); err != nil {
+				t.Fatal(err)
+			}
+			if err := json.Unmarshal(want[i].Memberships, &wasM); err != nil {
+				t.Fatal(err)
+			}
+			if !reflect.DeepEqual(gotM, wasM) {
+				t.Errorf("the memberships differ from the controller's:\n%s", raw)
+			}
+		})
+	}
+	t.Run("the controller's golden server configuration", func(t *testing.T) {
+		seat := Seat{Name: "telegram-sender", Accepts: []string{"send"}, Emits: []string{"delivered", "failed"}}
+		got, err := Compose(
+			Server{ClientPort: 4222, MonitoringPort: 8222, StoreDir: "/data",
+				TLSCert: "/tls/tls.crt", TLSKey: "/tls/tls.key", TLSCA: "/tls/ca.crt"},
+			[]Principal{
+				{Kind: KindController, PasswordHash: "$2a$11$cccccccccccccccccccccc"},
+				{Kind: KindEnrolment, Node: "one", PasswordHash: "$2a$11$eeeeeeeeeeeeeeeeeeeeee"},
+				{Kind: KindNode, Node: "one", PasswordHash: "$2a$11$nnnnnnnnnnnnnnnnnnnnnn"},
+				{Kind: KindModule, Node: "one", Module: "telegram", Holds: []Seat{seat},
+					Serves: []string{"status"}, PasswordHash: "$2a$11$tttttttttttttttttttttt"},
+				{Kind: KindModule, Node: "two", Module: "shop", Uses: []Seat{seat},
+					Emits: []string{"order.placed"}, PasswordHash: "$2a$11$ssssssssssssssssssssss"},
+				{Kind: KindModule, Node: "two", Module: "audit",
+					Consumes: []string{"shop.order.placed"}, PasswordHash: "$2a$11$aaaaaaaaaaaaaaaaaaaaaa"},
+				{Kind: KindModule, Node: "one", Module: WatchmanModule, PasswordHash: "$2a$11$wwwwwwwwwwwwwwwwwwwwww"},
+				{Kind: KindModule, Node: "one", Module: "nats", SnapshotsTheBus: true,
+					Serves: []string{"nats_streams"}, PasswordHash: "$2a$11$bbbbbbbbbbbbbbbbbbbbbb"},
+			})
+		if err != nil {
+			t.Fatal(err)
+		}
+		want, err := os.ReadFile(filepath.Join("testdata", "composed.conf"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got != string(want) {
+			t.Errorf("the configuration differs from the controller's golden:\n%s", got)
+		}
+	})
+}

go/buscompose/callers.go

@@ -0,0 +1,117 @@
+package buscompose
+
+import (
+	"regexp"
+	"strings"
+)
+
+// A tool call names its caller (novox/hq issue 365, by ADR 0259 §3's precedent for asks).
+//
+//	mesh.mod.<module>.call.<tool>[.<node>].<caller>
+//	mesh.seat.<seat>.call.<verb>[.<node>].<caller>
+//
+// The last token is the bus user that published the call, and each user is granted these subjects with its own
+// name there and no other — the caller is a fact the server enforces, and the tool runtime hands it to the
+// module from the subject a call arrived on (mesh-tools node-tools internal/bus caller.go holds the same shape).
+//
+// **A kind of its own, `call`, not the `tool` subject with a token appended.** Every grant to call a tool is a
+// wildcard over the `tool` kind — `.tool.<t>.*` for the instance on any machine, `mesh.mod.*.tool.>` for every
+// tool — and either would match a `tool` subject with any caller appended, so a caller could name another.
+// Under `call` nothing is granted but the caller-named subjects. No stream's filter covers it: a tool call is
+// never persisted (design 25 §3).
+//
+// **Derived from the `tool` grants, in one place** (callerNamed): wherever a principal may call or answer a
+// tool, it may call it in its own name, or answer it naming any caller — so no kind of principal is left
+// unable to call in its own name, and a new grant to call is one in both shapes by construction.
+//
+// The `tool` grants stay beside these for one release, so every caller and every runtime moves without a gap:
+// their retirement is hq issue 464.
+const CallKind = "call"
+
+var userName = regexp.MustCompile(`^[A-Za-z0-9_-]+(\.[A-Za-z0-9_-]+)*$`)
+
+// CallerToken is a bus user's name as the last token of a call it publishes: each dot written `~`, which no part
+// of a user's name may hold (safeSubject), so the token names that user and no other. "" for a name that is not
+// a user's.
+func CallerToken(user string) string {
+	if !userName.MatchString(user) {
+		return ""
+	}
+	return strings.ReplaceAll(user, ".", "~")
+}
+
+// toolGrant splits a grant on the `tool` kind — `mesh.mod.<m>.tool.<rest>` or `mesh.seat.<s>.tool.<rest>`, any
+// part possibly a wildcard — at the kind; ok is false for any other subject.
+func toolGrant(subject string) (head, rest string, ok bool) {
+	parts := strings.SplitN(subject, ".", 5)
+	if len(parts) != 5 || parts[0] != "mesh" || (parts[1] != "mod" && parts[1] != "seat") || parts[3] != "tool" ||
+		parts[2] == "" || parts[4] == "" {
+		return "", "", false
+	}
+	return parts[0] + "." + parts[1] + "." + parts[2], parts[4], true
+}
+
+// CalledSubject is where a call to a tool subject goes naming its caller; "" when the subject is not a tool's
+// or the user is not a bus user.
+func CalledSubject(subject, user string) string {
+	head, rest, ok := toolGrant(subject)
+	token := CallerToken(user)
+	if !ok || token == "" || strings.ContainsAny(rest, "*>") {
+		return ""
+	}
+	return head + "." + CallKind + "." + rest + "." + token
+}
+
+// CalledPattern is what a holder answering a tool subject also subscribes, to hear the calls that name their
+// caller: the same address under the `call` kind, any caller last. "" for a subject that is not a tool's.
+func CalledPattern(subject string) string {
+	head, rest, ok := toolGrant(subject)
+	if !ok || strings.ContainsAny(rest, "*>") {
+		return ""
+	}
+	return head + "." + CallKind + "." + rest + ".*"
+}
+
+// calledPublish is a grant to call on the `tool` kind, as the same grant in the caller's own name: its last
+// token the caller's, and nothing that reaches past it. A `>` is every tail a call carries — the tool alone or
+// the tool and the machine — so it becomes both, each ending in the caller.
+func calledPublish(grant, token string) []string {
+	head, rest, ok := toolGrant(grant)
+	if !ok || token == "" {
+		return nil
+	}
+	base := head + "." + CallKind + "."
+	switch {
+	case rest == ">":
+		return []string{base + "*." + token, base + "*.*." + token}
+	case strings.HasSuffix(rest, ".>"):
+		return []string{base + strings.TrimSuffix(rest, ">") + "*." + token}
+	}
+	return []string{base + rest + "." + token}
+}
+
+// calledSubscribe is a grant to answer on the `tool` kind, as the same grant for the calls naming any caller.
+func calledSubscribe(grant string) []string {
+	head, rest, ok := toolGrant(grant)
+	if !ok {
+		return nil
+	}
+	base := head + "." + CallKind + "."
+	if strings.HasSuffix(rest, ">") {
+		return []string{base + rest}
+	}
+	return []string{base + rest + ".*"}
+}
+
+// callerNamed adds, beside a principal's grants on the `tool` kind, the same grants under `call`: to publish in
+// its own name, to subscribe naming anybody.
+func callerNamed(user string, pub, sub []string) ([]string, []string) {
+	token := CallerToken(user)
+	for _, g := range pub {
+		pub = append(pub, calledPublish(g, token)...)
+	}
+	for _, g := range sub {
+		sub = append(sub, calledSubscribe(g)...)
+	}
+	return unique(pub), unique(sub)
+}

go/buscompose/cancelled.go

@@ -0,0 +1,11 @@
+package buscompose
+
+import "strings"
+
+// A seat's cancelled set (novox/hq ADR 0219) is a bucket the mesh no longer raises or grants (R4g, ADR 0525 clause 6): the
+// controller asks no work queue, so nothing is cancelled. A bus that still holds one is not reported as state nothing declares.
+
+// IsCancelledSet says a bucket is a seat's cancelled set rather than a module's state.
+func IsCancelledSet(bucket string) bool {
+	return strings.HasPrefix(bucket, "SEAT_") && strings.HasSuffix(bucket, "_cancelled")
+}

go/buscompose/composed.go

@@ -0,0 +1,196 @@
+package buscompose
+
+import (
+	"context"
+	"fmt"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+// The compositions' buckets (novox/hq ADR 0539 clauses 2 and 4): one per node, `composed-<node>`, holding that node's
+// compositions, which only that node's node-engine reads, since a composition can carry a sealed value (ADR 0488 §2's
+// reason); and `mesh-controller_composed`, holding each composition's digest and the judgement of its move, which the
+// assigner reads. The controller writes both, by compare-and-set while it holds the lease; each keeps five revisions
+// of a key. The names and layouts are mesh-sdk's (delivery.ComposedBucketFor, ControllerComposedBucket, ComposedKey).
+
+// ControllerComposed is the local name of the compositions' digests, as a reader names it in `reads` after
+// `mesh-controller.`: delivery.ControllerComposedBucket.
+const ControllerComposed = "composed"
+
+// ComposedValueBytes is the most a composition may hold: a file over 64 KiB travels by digest, so a module's
+// composition is far smaller; just under the server's largest message, which also carries the subject and headers.
+const ComposedValueBytes = 1<<20 - 8<<10
+
+// ComposedBucketBytes is a node's composition bucket's size: five revisions of every module's compositions of the node.
+const ComposedBucketBytes = 256 << 20
+
+// ComposedDigestsBytes is the size of the bucket of digests: a value of a few hundred bytes per node, module and
+// fingerprint kept.
+const ComposedDigestsBytes = 64 << 20
+
+// ComposedConfig is a node's composition bucket as the controller asserts it.
+func ComposedConfig(node string) (jetstream.KeyValueConfig, error) {
+	bucket, err := delivery.ComposedBucketFor(node)
+	if err != nil {
+		return jetstream.KeyValueConfig{}, err
+	}
+	return jetstream.KeyValueConfig{
+		Bucket: bucket,
+		Description: "the compositions of " + node + " (novox/hq ADR 0539): each module's resources for this node at one " +
+			"fingerprint, and the node's own, signed; written by the controller alone, read by this node's node-engine " +
+			"alone; deleted when outside the module's five newest fingerprints and named by no want",
+		History:      delivery.ComposedHistory,
+		MaxValueSize: ComposedValueBytes,
+		MaxBytes:     ComposedBucketBytes,
+		Storage:      jetstream.FileStorage,
+	}, nil
+}
+
+// ComposedDigestsConfig is the bucket of the compositions' digests as the controller asserts it.
+func ComposedDigestsConfig() jetstream.KeyValueConfig {
+	return jetstream.KeyValueConfig{
+		Bucket: delivery.ControllerComposedBucket,
+		Description: "each composition's digest and the judgement of its move from what the node runs (novox/hq ADR 0539 " +
+			"clauses 2 and 14): written by the controller alone, read by the assigner",
+		History:      delivery.ControllerComposedHistory,
+		MaxValueSize: 4 << 10,
+		MaxBytes:     ComposedDigestsBytes,
+		Storage:      jetstream.FileStorage,
+	}
+}
+
+// EnsureComposed creates the bucket of digests and each named node's composition bucket if absent and brings their
+// options to match. An update, never a delete.
+func EnsureComposed(ctx context.Context, js jetstream.JetStream, nodes ...string) error {
+	if _, err := js.CreateOrUpdateKeyValue(ctx, ComposedDigestsConfig()); err != nil {
+		return fmt.Errorf("asserting bucket %s: %w", delivery.ControllerComposedBucket, err)
+	}
+	for _, node := range nodes {
+		cfg, err := ComposedConfig(node)
+		if err != nil {
+			return err
+		}
+		if _, err := js.CreateOrUpdateKeyValue(ctx, cfg); err != nil {
+			return fmt.Errorf("asserting bucket %s: %w", cfg.Bucket, err)
+		}
+	}
+	return nil
+}
+
+// ComposedWrites is what the controller publishes to write a node's compositions: the bucket's own subjects.
+func ComposedWrites(node string) (string, error) {
+	bucket, err := delivery.ComposedBucketFor(node)
+	if err != nil {
+		return "", err
+	}
+	return "$KV." + bucket + ".>", nil
+}
+
+// ComposedReads is what a node's node-engine publishes to follow its wants and compositions (ADR 0539 clauses 1, 2 and
+// 9): every key of its own composition bucket, and its own wants (`want.<node>.<module>` and `want.<node>.node`) in the
+// assigner's bucket; nothing of another node's, nor the bucket of digests.
+func ComposedReads(node string) ([]string, error) {
+	bucket, err := delivery.ComposedBucketFor(node)
+	if err != nil {
+		return nil, err
+	}
+	if !safeSubject.MatchString(node) {
+		return nil, fmt.Errorf("%q cannot be part of a subject: a permission is a subject pattern, and this would widen it", node)
+	}
+	return append(readGrants(bucket, ""), readGrants(delivery.AssignerWantsBucket, "want."+node+".>")...), nil
+}
+
+// VerbsTheNodeAgentAsks are the seat verbs a node's node-engine calls of its own machine while it applies a want (ADR
+// 0539 clause 16, ADR 0429 §14): its backup holder backs a data module up before it moves, and says when it was. Asked
+// of its own machine only, `mesh.seat.<seat>.tool.<verb>.<node>`.
+var VerbsTheNodeAgentAsks = []SeatVerb{{Seat: "node-backup", Verb: "now"}, {Seat: "node-backup", Verb: "backed-up"}}
+
+// NodeAgentAsks are the subjects of VerbsTheNodeAgentAsks for one node.
+func NodeAgentAsks(node string) ([]string, error) {
+	if !safeSubject.MatchString(node) {
+		return nil, fmt.Errorf("%q cannot be part of a subject: a permission is a subject pattern, and this would widen it", node)
+	}
+	var out []string
+	for _, v := range VerbsTheNodeAgentAsks {
+		out = append(out, "mesh.seat."+v.Seat+".tool."+v.Verb+"."+node)
+	}
+	return out, nil
+}
+
+// NodeAgentHears are the events a node's node-engine subscribes while it applies a want: the backup holder's word that a
+// backup is taken (`backed-up`), from whichever module holds node-backup on its machine (restic today).
+var NodeAgentHears = []string{"mesh.mod." + BackupHolderModule + ".event.backed-up"}
+
+// BackupHolderModule is the module that holds node-backup on every node, restic: the one whose word a node-engine hears.
+// A second holder of the seat is a change of this grant.
+const BackupHolderModule = "restic"
+
+// administers says a person may invoke every tool (`*`): the operator.
+func administers(invokes []string) bool {
+	for _, i := range invokes {
+		if i == "*" {
+			return true
+		}
+	}
+	return false
+}
+
+// HandPathWrites is what the operator's account publishes for release 6's hand path (ADR 0539 clauses 2 and 10): a want
+// of any node, written and read back, in the assigner's bucket; each named node's compositions; the digests; and each
+// node's object bucket for a file over 64 KiB, whose put reads an object's metadata and purges a replaced one's chunks.
+func HandPathWrites(nodes []string) ([]string, error) {
+	out := append([]string{"$KV." + delivery.AssignerWantsBucket + ".want.>"}, readGrants(delivery.AssignerWantsBucket, "want.>")...)
+	out = append(out, "$KV."+delivery.ControllerComposedBucket+".>")
+	out = append(out, readGrants(delivery.ControllerComposedBucket, "")...)
+	for _, node := range nodes {
+		w, err := ComposedWrites(node)
+		if err != nil {
+			return nil, err
+		}
+		bucket, _ := delivery.ComposedBucketFor(node)
+		out = append(out, w)
+		out = append(out, readGrants(bucket, "")...)
+		files, err := DeclarationFilesWrites(node)
+		if err != nil {
+			return nil, err
+		}
+		stream := "OBJ_" + DeclarationFilesBucket + node
+		out = append(out, files, "$JS.API.STREAM.INFO."+stream, "$JS.API.DIRECT.GET."+stream+".>",
+			"$JS.API.STREAM.MSG.GET."+stream, "$JS.API.STREAM.PURGE."+stream)
+	}
+	return out, nil
+}
+
+// DeclarationsStream is the stream of each node's last declaration, `mesh.node.<node>.declare` (issue 107). Release 6
+// sends none (ADR 0539 clauses 5 and 11): the stream is kept, with each node's consumer, only so a node away during the
+// switch finds its last declaration and with it the new node-engine; the controller deletes it once every node's have
+// names the new node-engine, and from then on neither asserts it nor any node's consumer on it; nor makes it again once
+// it is gone from the bus for any reason, since a stream made anew would hold no node's last declaration (issue 1945).
+const DeclarationsStream = "NODES"
+
+// RaiseAfterDeclarations is Raise once the declarations' stream is retired: the mesh's streams and consumers but the
+// declarations' stream, and no node's consumer of a declaration.
+func RaiseAfterDeclarations(r Raiser) error {
+	for _, s := range MeshStreams() {
+		if s.Name == DeclarationsStream {
+			continue
+		}
+		if err := r.EnsureStream(s); err != nil {
+			return fmt.Errorf("asserting stream %s: %w", s.Name, err)
+		}
+	}
+	return AssertMeshConsumers(r)
+}
+
+// TakeInConsumer is the durable consumer the controller takes done keys in from, on the stream of each of TakeInBuckets
+// (novox/hq ADR 0544 §1).
+const TakeInConsumer = "mesh-controller-take-in"
+
+// TakeInBuckets are the buckets the take-in consumes: the indexer's modules (each module's trunk value) and the builder's
+// builds (each build's key).
+var TakeInBuckets = []string{delivery.ModulesBucket, delivery.BuilderBuildsBucket}
+
+// ConfigFollowConsumer is the durable consumer the controller follows mesh-config's resolved values with, on that
+// bucket's stream (novox/hq ADR 0545).
+const ConfigFollowConsumer = "mesh-controller-config-follow"

go/buscompose/controller_buckets.go

@@ -0,0 +1,247 @@
+package buscompose
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+// The controller's own key-value buckets (novox/hq to-be 45 §1, §6, §7).
+//
+// **What the controller must remember across its own restart, it keeps on the bus.** A call's
+// outcome lived in the memory of the process that served it (novox/hq issue 265), so a controller
+// replaced while a push ran answered "no such call" for the one thing its caller had been told to
+// ask about. The bus already outlives the controller and is the shape ADR 0201 gives a module's
+// current state: one value per key, written by one owner, read by anybody granted it. These are the
+// controller's, written by it alone — the writers table of to-be 45 §1 — and asserted on every start
+// like the streams, so a bus raised from nothing has them before the first call is served.
+
+// CallsBucket keeps every call of the mesh's own verbs and what came of it; HandActsBucket every act
+// a person did by hand, with why; ConditionsBucket every condition open now (to-be 45 §2), one key
+// each, and ConditionHistoryBucket every transition of one — raised, changed, silenced, cleared —
+// for ninety days.
+//
+// **The history is a bucket of its own** because its keys expire and an open condition's must not:
+// a bucket has one age for every key, and a condition open longer than the history is kept would
+// otherwise vanish from the store while still true.
+var (
+	CallsBucket            = BucketName(ControllerSeat, "calls")
+	HandActsBucket         = BucketName(ControllerSeat, "hand-acts")
+	ConditionsBucket       = BucketName(ControllerSeat, "conditions")
+	ConditionHistoryBucket = BucketName(ControllerSeat, "condition-history")
+	// LeaseBucket holds the controller's lease (to-be 45 §6): one key, `holder`, which the instance
+	// allowed to act writes by compare-and-set and renews; its revision when taken is the epoch.
+	LeaseBucket = BucketName(ControllerSeat, "lease")
+	// AskedBucket keeps what the controller asked the operator about its conditions (novox/hq ADR 0259):
+	// each ask by its id, its options and the actions they stand for, how it ended and whether the
+	// controller acted on its warrant — so a restart neither asks twice nor acts twice.
+	AskedBucket = BucketName(ControllerSeat, "asked")
+	// DeliveryMergesBucket holds the merges mesh-delivery announced it made, each with the ask whose Approve it merged
+	// on (novox/hq ADR 0420 §7, issue 1025): per merge a key `<owner>/<repo>/<number>/<head sha>` holding the
+	// announcement, kept DeliveryMergesKeptFor. What lets the build of a moved module register it from its new
+	// repository: the controller reads the ask's warrant from the router and accepts only the operator's Approve of
+	// those heads. Written by the controller alone, from the announcement, when it holds the lease.
+	DeliveryMergesBucket = BucketName(ControllerSeat, "delivery-merges")
+)
+
+// DeliveryMergesKeptFor is how long a merge mesh-delivery announced is kept: a week, as the events are.
+const DeliveryMergesKeptFor = 7 * 24 * time.Hour
+
+// The controller's record mirrors (novox/hq ADR 0289, design 54, design 57 package F3): a bucket per kind of
+// record, one key per record, written from the store by the lease holder only when the record changed, with
+// one event on the controller's seat per write. Read by whatever names them in `reads` as
+// `mesh-controller.<mirror>` (ADR 0201 §1), written by nobody else. **No secret in either** (ADR 0201): an
+// assignment's value names its module and node; a module's declared config is what its manifest, which is
+// public, declares.
+//
+// AssignmentsBucket holds which module is assigned to which node, keyed `<node>.<module>`; and
+// DeclaredConfigBucket each registered module's config declarations as its manifest holds them, keyed by
+// the module: what mesh-config resolves a config value from (ADR 0348 clauses 2 and 4); and PredefinedBucket the
+// list of predefined keys the mesh published (the newest trunk build's of the catalogue, ADR 0348 §7), one key
+// `list`: what mesh-config publishes as mesh-config_predefined (design 57 K3, issue 662).
+var (
+	AssignmentsBucket    = BucketName(ControllerSeat, MirrorAssignments)
+	DeclaredConfigBucket = BucketName(ControllerSeat, MirrorDeclaredConfig)
+	PredefinedBucket     = BucketName(ControllerSeat, MirrorPredefined)
+	// DeclaredPackagesBucket holds, keyed by the node, each package the modules assigned to it declare, present or absent,
+	// with the declaring modules: what the pacman module's verbs read to say a package is declared (ADR 0507 §5).
+	DeclaredPackagesBucket = BucketName(ControllerSeat, MirrorDeclaredPackages)
+)
+
+// The mirrors' local names, as a reader names them in `reads` after `mesh-controller.`.
+const (
+	MirrorAssignments    = "assignments"
+	MirrorDeclaredConfig = "declared-config"
+	MirrorPredefined     = "predefined"
+	// MirrorDeclaredPackages is the local name of the packages each node's modules declare (ADR 0507 §5, issue 1840/S3).
+	MirrorDeclaredPackages = "declared-packages"
+)
+
+// The chain's buckets (novox/hq ADR 0408, issue 1089): builds, rollouts and assignments are one chain kept on the bus
+// alone, one bucket each, one key per record, written by the lease holder by compare-and-set. The assignments bucket is
+// AssignmentsBucket above, which keeps its name and its readers (ADR 0408 §3). Nothing is removed from them (§4), they keep
+// ChainHistory earlier revisions of every key (§5), and a value is never cut (§6).
+var (
+	BuildsBucket   = BucketName(ControllerSeat, ChainBuilds)
+	RolloutsBucket = BucketName(ControllerSeat, ChainRollouts)
+)
+
+// **The assignments bucket keeps the marker age (MirrorMarkerTTL) it was made with as a mirror.** A stream that allows
+// messages an age cannot be made to disallow them (the server refuses the update: "message TTL status can not be
+// disabled", nats-server stream.go), so asserting the bucket without the age would fail the controller's start on a
+// mesh that has the bucket. The chain never purges or removes a key (ADR 0408 §4), so no marker is ever written and the
+// age ends nothing; it is kept only so the stream's configuration stays one the server accepts.
+//
+// The chain buckets' local names, as a reader names them in `reads` after `mesh-controller.`.
+const (
+	ChainBuilds   = "builds"
+	ChainRollouts = "rollouts"
+)
+
+// The chain buckets' bounds. ChainHistory is the bus's largest history (ADR 0408 §5). A value is at most ChainValueBytes,
+// just under the server's largest message of a mebibyte, which also carries the subject and the headers (ADR 0408 §6):
+// the controller writes none larger and the move refuses to. The buckets' size is the arithmetic of the survey of
+// issue 981: 8585 builds of 1 to 40 KB, 1049 rollouts of about 2 KB a revision and 64 revisions, so 512 MiB for the two
+// that grow, and the assignments, 285 of under a kilobyte, 64 MiB.
+const (
+	ChainHistory         = 64
+	ChainValueBytes      = 1<<20 - 8<<10
+	ChainBuildsBytes     = 512 << 20
+	ChainRolloutsBytes   = 512 << 20
+	ChainAssignmentBytes = 64 << 20
+)
+
+// GrantsBucket holds, keyed `<module>.<fingerprint hex>`, each fingerprint of a module whose bus credential the controller
+// has issued (novox/hq ADR 0528 clause 2, ADR 0429 §6 rule 6, issue 1394): written by the controller alone once the bus's
+// user list composed with the module's manifest at that fingerprint was sent to the bus's machine; read by the assigner,
+// whose sixth rule moves a node's want to a fingerprint only once its grant exists. The name and layout are mesh-sdk's
+// (delivery.ControllerGrantsBucket, ControllerGrantKey).
+var GrantsBucket = BucketName(ControllerSeat, ControllerGrants)
+
+// ControllerGrants is the grants bucket's local name, as a reader names it in `reads` after `mesh-controller.`.
+const ControllerGrants = "grants"
+
+// ChainBuckets are the three buckets of the chain: builds, rollouts and assignments.
+func ChainBuckets() []string { return []string{BuildsBucket, RolloutsBucket, AssignmentsBucket} }
+
+// MirrorsWrittenByAnother are the controller's mirrors whose writer is not the controller, each with its reason: the rule
+// that a mirror is written by the controller alone (TestTheMirrorsListAndTheWritersTableAgree) has these exceptions and no
+// other.
+var MirrorsWrittenByAnother = map[string]string{}
+
+// The mirrors' caps (design 54 §5): one value per key, no age, 64 KiB a value, 64 MiB a bucket.
+const (
+	MirrorValueBytes = 64 << 10
+	MirrorBytes      = 64 << 20
+	// MirrorMarkerTTL is the longest a purge's marker is kept (design 54 §2): the bucket allows a
+	// per-message age for it, and the writer gives each marker a day.
+	MirrorMarkerTTL = 24 * time.Hour
+)
+
+// PlanStateBuckets are the buckets of the plans' state that release 6 deletes (novox/hq ADR 0539 clause 13): the merge
+// window's clock, the silent sends' waits and the building plans' hold. The controller deletes each at its first start
+// and says it once (composed_start.go); none is asserted, granted or written any more.
+var PlanStateBuckets = []string{BucketName(ControllerSeat, "merge-window"), BucketName(ControllerSeat, "rollout-silent"),
+	BucketName(ControllerSeat, "plans-building")}
+
+// AskedKeptFor is how long an ask is kept after it was made: a month, as the router keeps its own.
+const AskedKeptFor = 30 * 24 * time.Hour
+
+// LeaseTTL is how long the lease's key lives unrenewed (to-be 45 §6): fifteen seconds, renewed
+// every five. The bucket's age, so the bus forgets a holder that stopped renewing.
+const LeaseTTL = 15 * time.Second
+
+// The bounds to-be 45 §6 sets for calls: the last thousand, or fourteen days, whichever is fewer.
+// A call is two keys — its record, and its answer apart so a listing does not read every answer —
+// so the stream holds twice as many messages as it keeps calls.
+const (
+	KeptCallsDurably = 1000
+	CallsKeptFor     = 14 * 24 * time.Hour
+	// CallAnswerBytes is the most of one answer kept: a whole declaration is far smaller, and an
+	// answer larger is cut and says so.
+	CallAnswerBytes = 64 << 10
+	// HandActsKeptFor is as long as a condition's history (to-be 45 §2): an act by hand is read
+	// back beside what it addressed.
+	HandActsKeptFor = 90 * 24 * time.Hour
+	// ConditionHistoryKeptFor is how long a condition's transitions are kept (to-be 45 §2).
+	ConditionHistoryKeptFor = 90 * 24 * time.Hour
+)
+
+// IsControllerBucket says a bucket is the controller's own, not a module's state nothing declares.
+func IsControllerBucket(bucket string) bool {
+	return bucket == CallsBucket || bucket == HandActsBucket || bucket == ConditionsBucket ||
+		bucket == ConditionHistoryBucket || bucket == LeaseBucket || bucket == AskedBucket ||
+		bucket == AssignmentsBucket || bucket == DeclaredConfigBucket || bucket == PredefinedBucket ||
+		bucket == DeclaredPackagesBucket ||
+		bucket == DeliveryMergesBucket || bucket == BuildsBucket || bucket == RolloutsBucket ||
+		bucket == delivery.HaveBucket || bucket == StatesAnnouncedBucket ||
+		bucket == GrantsBucket || bucket == delivery.ControllerComposedBucket
+}
+
+// ControllerBuckets are the controller's own buckets, in the order they are asserted.
+func ControllerBuckets() []string {
+	return []string{LeaseBucket, CallsBucket, HandActsBucket, ConditionsBucket, ConditionHistoryBucket, AskedBucket,
+		AssignmentsBucket, DeclaredConfigBucket, PredefinedBucket, DeclaredPackagesBucket,
+		DeliveryMergesBucket, BuildsBucket, RolloutsBucket, delivery.HaveBucket, StatesAnnouncedBucket, GrantsBucket,
+		delivery.ControllerComposedBucket}
+}
+
+// ControllerBucketsAsserter is what raising the controller's buckets needs of a connection.
+type ControllerBucketsAsserter interface {
+	EnsureControllerBuckets() error
+}
+
+// chainBucket is the options of a bucket of the chain: sixty-four revisions of each key, no age, a value up to
+// ChainValueBytes, on disk.
+func chainBucket(bucket, why string, bytes int64, markers time.Duration) jetstream.KeyValueConfig {
+	return jetstream.KeyValueConfig{
+		Bucket:         bucket,
+		Description:    why,
+		History:        ChainHistory,
+		MaxValueSize:   ChainValueBytes,
+		MaxBytes:       bytes,
+		Storage:        jetstream.FileStorage,
+		LimitMarkerTTL: markers,
+	}
+}
+
+// EnsureLeaseBucket creates the lease's bucket if absent and brings its options to match (to-be 45
+// §6). **Before the lease is taken, by any candidate**: it is the lease's own precondition, and asserting
+// a bucket that exists changes nothing. File storage, so its revisions — the epochs — outlive a restart of
+// the bus; one raised again from nothing is moved past the highest epoch issued when the lease is taken.
+func EnsureLeaseBucket(ctx context.Context, js jetstream.JetStream) error {
+	if _, err := js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{
+		Bucket: LeaseBucket,
+		Description: "the controller's lease (novox/hq to-be 45 §6): the key `holder`, written by compare-and-set " +
+			"by the one controller instance that may act and renewed every five seconds; its revision when taken " +
+			"is the epoch every declaration and plan write carries",
+		History:      1,
+		TTL:          LeaseTTL,
+		MaxValueSize: 4 << 10,
+		MaxBytes:     1 << 20,
+		Storage:      jetstream.FileStorage,
+	}); err != nil {
+		return fmt.Errorf("asserting bucket %s: %w", LeaseBucket, err)
+	}
+	return nil
+}
+
+// HaveBucketConfig is the options of the have bucket (novox/hq ADR 0429 §1): delivery.HaveHistory revisions of each
+// key, no age, 64 MiB on disk like the assignments. A module's have is JSON of about 500 bytes, but a node's own key
+// carries its whole facts (its profile among them), several kilobytes on a desktop: a value is as large as the chain's
+// buckets take, since a value is never cut (novox/hq ADR 0408 §6, issue 1162).
+func HaveBucketConfig() jetstream.KeyValueConfig {
+	return jetstream.KeyValueConfig{
+		Bucket: delivery.HaveBucket,
+		Description: "what each machine has of each module, one key `<node>.<module>` (and `<node>.node` for the machine's " +
+			"own facts) (novox/hq ADR 0429, design 47): written by each machine's node-engine under its own node's keys " +
+			"alone, never by the controller; read by the delivery view and the watchman",
+		History:      delivery.HaveHistory,
+		MaxValueSize: ChainValueBytes,
+		MaxBytes:     64 << 20,
+		Storage:      jetstream.FileStorage,
+	}
+}

go/buscompose/declaration_files.go

@@ -0,0 +1,111 @@
+package buscompose
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/declaration"
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+// The object buckets a declaration's large files travel in (novox/hq ADR 0486, issues 1696 and 1697): **one bucket for each
+// node**, `declaration-files-<node>`.
+//
+// **The controller alone writes them, and a node-engine reads an object by its name from its own bucket** (ADR 0486 §2): its
+// account may neither list the bucket nor write it, no account may touch another node's, and no other account has any access.
+// Why a bucket each: a subject pattern cannot tell a name from a wildcard. A grant of `...M.*` matches a publish to the literal
+// subject `...M.*` too (probed on nats-server 2.11.17 by the review of this issue: a node created a consumer filtered on
+// `$O.<bucket>.C.*` and read every object of the bucket), so in one shared bucket a node could read every other node's files.
+// With a bucket each, the same trick reads only the node's own files, which are the files of its own declaration.
+//
+// A bucket of the bus's object store is a stream, OBJ_<bucket>, whose messages are the objects' metadata
+// (`$O.<bucket>.M.<base64 of the name>`) and chunks (`$O.<bucket>.C.<nuid>`).
+
+// DeclarationFilesBucket is the prefix of the buckets' names, which mesh-sdk fixes for the node-engine and the controller alike.
+const DeclarationFilesBucket = declaration.FileBucketPrefix
+
+// DeclarationFilesBucketOf is the bucket a node's files are in: mesh-sdk's FileBucketFor, the one place the name is composed. A
+// node name it refuses (one that could carry a subject wildcard or separator into a grant) is an error, never a bucket.
+func DeclarationFilesBucketOf(node string) (string, error) { return declaration.FileBucketFor(node) }
+
+// DeclarationFilesStreamOf is the stream under a node's bucket: mesh-sdk's FileStreamFor.
+func DeclarationFilesStreamOf(node string) (string, error) { return declaration.FileStreamFor(node) }
+
+// DeclarationFilesMaxBytes is a bucket's size: the objects are immutable and regenerable, and one node's hold well under a hundred
+// megabytes.
+const DeclarationFilesMaxBytes = 1 << 30
+
+// DeclarationFilesKeptFor is how long an object stays after no node's latest declaration names it (ADR 0486 §3).
+const DeclarationFilesKeptFor = 24 * time.Hour
+
+// DeclarationFilesWrites is the one pattern the controller may publish to write a node's bucket: every object's metadata and
+// chunks. The server's API for the stream is the controller's `$JS.API.>`.
+func DeclarationFilesWrites(node string) (string, error) {
+	bucket, err := DeclarationFilesBucketOf(node)
+	if err != nil {
+		return "", err
+	}
+	return "$O." + bucket + ".>", nil
+}
+
+// DeclarationFilesReads is what a node-engine's account may publish to read an object of its own bucket by its name, and nothing
+// more. The set is the one node-engine's own call (mesh-host internal/link FileObject) makes, for B the node's bucket and S its
+// stream (issue 1697, notes 4 and 5):
+//
+//   - the object's metadata, by a direct get of the last message of the one subject that names it. **Only the suffixed
+//     form**: the bare `$JS.API.DIRECT.GET.S` takes a sequence number and would read any message of the stream.
+//   - the ordered consumer on that object's chunks: `$JS.API.CONSUMER.CREATE.S.<name>.$O.B.C.<nuid>`. **Not `S.>`**:
+//     a consumer filtered on `$O.B.M.>` would read every object's name.
+//   - the flow-control replies of that consumer, without which a large object stalls at the flow-control window.
+//   - the consumer's deletion, best effort: the consumer's inactivity threshold removes it if this is refused.
+//
+// **Never granted:** STREAM.INFO (a `subjects_filter` of `>` lists every name), STREAM.MSG.GET (any message by its sequence), a
+// publish to `$O.B.>` (a write), and any subject of another node's stream. A literal `*` in a subject matches the grant's `*`: it
+// reaches the objects of this node's own bucket and no other (above).
+func DeclarationFilesReads(node string) ([]string, error) {
+	bucket, err := DeclarationFilesBucketOf(node)
+	if err != nil {
+		return nil, err
+	}
+	stream, err := DeclarationFilesStreamOf(node)
+	if err != nil {
+		return nil, err
+	}
+	return []string{
+		"$JS.API.DIRECT.GET." + stream + ".$O." + bucket + ".M.*",
+		"$JS.API.CONSUMER.CREATE." + stream + ".*.$O." + bucket + ".C.*",
+		"$JS.API.CONSUMER.DELETE." + stream + ".*",
+		"$JS.FC." + stream + ".>",
+	}, nil
+}
+
+// EnsureDeclarationFiles is the same on a JetStream the caller holds.
+func EnsureDeclarationFiles(ctx context.Context, js jetstream.JetStream, nodes ...string) error {
+	for _, node := range nodes {
+		cfg, err := DeclarationFilesConfig(node)
+		if err != nil {
+			return err
+		}
+		if _, err := js.CreateOrUpdateObjectStore(ctx, cfg); err != nil {
+			return fmt.Errorf("asserting the object bucket %s: %w", cfg.Bucket, err)
+		}
+	}
+	return nil
+}
+
+// DeclarationFilesConfig is a node's bucket as the controller asserts it.
+func DeclarationFilesConfig(node string) (jetstream.ObjectStoreConfig, error) {
+	bucket, err := DeclarationFilesBucketOf(node)
+	if err != nil {
+		return jetstream.ObjectStoreConfig{}, err
+	}
+	return jetstream.ObjectStoreConfig{
+		Bucket: bucket,
+		Description: "the contents of the files over 64 KiB of the declaration of " + node + ", each under the hex of its sha256 " +
+			"digest (novox/hq ADR 0486): written by the controller alone, read by the node-engine of that node by name, removed " +
+			"a day after the node's latest declaration no longer names it",
+		MaxBytes: DeclarationFilesMaxBytes,
+		Storage:  jetstream.FileStorage,
+	}, nil
+}

go/buscompose/derived.go

@@ -0,0 +1,357 @@
+package buscompose
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// Streams and consumers derived from what modules declare.
+//
+// The mesh's own four exist before any module does (streams.go). Everything here is the other
+// half: a seat's stream comes into being when the module declaring it is **registered**, and a
+// consumer when a module is **assigned** — which is why ADR 0116's task 1.4 had to be narrowed to
+// the foundation set. Neither has happened at genesis.
+//
+// All of it is a pure function of declarations. The controller is still the only writer; this is
+// only what it writes.
+
+// A Consumer is a durable subscription the controller creates on a module's behalf. A module
+// declares what it reacts to, never how delivery works, so it does not name these and cannot
+// misconfigure them.
+type Consumer struct {
+	Name   string
+	Stream string
+	// Filters are the subjects this consumer receives. One consumer per module with several
+	// filters, rather than one per consumed event: its ack subject is derived from its name, and
+	// a module with five consumers would need five ack permissions to ack its own deliveries.
+	Filters []string
+	// Queue is the queue group, set for a seat's worker so that "exactly one holder" survives a
+	// seat later being relaxed to several. Authority and delivery are kept separate on purpose.
+	Queue string
+	// Push asks the server to deliver to a subject rather than wait to be pulled.
+	//
+	// For the mesh's own consumer, where the controller wants every message to arrive in the one
+	// loop it already runs: pulling would mean a second goroutine fetching batches and handing
+	// them over, and a loop that acts on one message at a time is the property the store window
+	// depends on. A queue group implies this, because a group has nothing to pull from.
+	Push bool
+	// TakesOverFrom names a consumer of the same stream whose filter this one takes over (issue 973): made while
+	// that consumer still filters this one's subject, it starts after what that consumer has acknowledged, so a
+	// message the old one held unacknowledged is not lost to the change. Otherwise it starts as FromNow says.
+	TakesOverFrom string
+	// DeliverSubject, when set, is where a push consumer delivers instead of DeliverSubjectFor's.
+	DeliverSubject string
+	// AckWaitSeconds before an unacknowledged delivery is redelivered.
+	AckWaitSeconds int
+	// MaxDeliver is how often a message is handed over before the consumer gives it up; zero for no
+	// bound. What a consumer gives up is kept in DEAD_LETTERS by the controller (novox/hq issue 330).
+	MaxDeliver int
+	// MaxAckPending is how many deliveries the server lets stand unacknowledged at once; zero for
+	// the server's default, which is many. **One, for a consumer handled one at a time**
+	// (novox/hq issue 175): a handler that builds for minutes keeps its own message alive with a
+	// heartbeat, but everything handed over behind it times out unacknowledged and comes back —
+	// and a merge that came back rebuilt what it had just built, five times over on 2026-09-30.
+	// With one outstanding, the server holds the rest, and the heartbeat is keeping the message.
+	MaxAckPending int
+	// FromNow makes a consumer that does not exist yet start at the stream's end rather than its
+	// beginning (novox/hq issue 248). For a consumer that reacts to announcements — a merge, a build's
+	// outcome — on a stream that keeps a week of them: the server's default, everything the stream
+	// holds, replays every merge and every build of that week as if it had just happened. A consumer
+	// that exists keeps where it is, whatever this says; only its making is decided here.
+	FromNow bool
+	Why     string
+	// Resettable says why this consumer may be re-made to deliver from now by the mesh itself, with
+	// nobody asked (novox/hq to-be 45 §7, healer H4): what a reset drops, something else catches up.
+	// Empty for every consumer where nothing would — a module's, whose events would be lost to it.
+	// Not a property of the consumer on the bus: nothing here is sent to the server.
+	Resettable string
+}
+
+// seatStreamName is the stream holding a seat's inbound work. Named after the seat rather than
+// the module holding it, because the holder can change and the queued work must not care — which
+// is the whole reason a caller addresses a seat instead of a module.
+func seatStreamName(seat string) string { return "SEAT_" + upperSnake(seat) }
+
+// SeatStreams is one work queue per declared seat, created when the declaring module is
+// registered rather than when it is assigned.
+//
+// **The stream exists before anyone holds the seat, and that is the point.** Work queues until a
+// holder appears, so installing the telegram module a week after something started sending to it
+// flushes the backlog instead of having lost it. A stream created at assignment would make "the
+// holder is not here yet" mean "your messages are gone".
+func SeatStreams(seats []DeclaredSeat) []Stream {
+	sorted := append([]DeclaredSeat(nil), seats...)
+	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Name < sorted[j].Name })
+
+	var out []Stream
+	for _, s := range sorted {
+		if len(s.Accepts) == 0 {
+			// A seat that only emits and serves needs no stream: its events ride EVENTS and its
+			// tools are core request/reply, which is never persisted.
+			continue
+		}
+		retain := s.RetainSeconds
+		if retain == 0 {
+			retain = 7 * 24 * 60 * 60
+		}
+		out = append(out, Stream{
+			Name:      seatStreamName(s.Name),
+			Subjects:  []string{"mesh.seat." + s.Name + ".accept.>"},
+			Retention: RetentionWorkQueue,
+			MaxAge:    retain,
+			Why: fmt.Sprintf("work submitted to the %s seat; one holder consumes it, and it "+
+				"queues while nobody does", s.Name),
+		})
+	}
+	return out
+}
+
+// A DeclaredSeat is a seat as the catalogue knows it. Mirrored here rather than imported so this
+// package stays free of the catalogue's own types — the same reason the host mirrors the
+// contracts instead of importing the sdk.
+type DeclaredSeat struct {
+	Name    string
+	Accepts []string
+	// Emits are the verbs the seat's holder publishes under the seat's own name. An event about a
+	// role belongs here rather than in the holder's namespace, because the name then outlives
+	// whoever fills it (novox/hq ADR 0121, 04-ISSUES/127).
+	Emits []string
+	// Serves are the verbs the holder answers, request and reply.
+	Serves        []string
+	RetainSeconds int
+	// PulledByKind is Seat's: a worker per accepted kind, derived from the holders' seat traffic, not here.
+	PulledByKind bool
+}
+
+// ConsumerFor is the durable consumer a module's declarations imply, or false when it subscribes
+// to nothing and needs none.
+//
+// One per module, with every consumed subject as a filter, because its ack permission is derived
+// from its name: a module with a consumer per event would need an ack permission per consumer,
+// and the permission list would stop being derivable from the declaration.
+func ConsumerFor(p Principal) (Consumer, bool) {
+	// A module that reacts to anything — a module's events or a role's (novox/hq ADR 0121). Watching
+	// a role was missing here, so the one module that does it got no consumer at all: it started,
+	// connected, and its graph stayed empty with nothing anywhere reporting why.
+	// And one that hears its own answers on a seat it uses (novox/hq ADR 0259 §3): an asker's warrants.
+	hearsItsOwn := len(SeatTrafficOf(p.Module, nil, p.Uses, nil).Subscribe) > 0
+	hearsAStream := false
+	for _, h := range p.Hears {
+		if len(h.Filters) > 0 {
+			hearsAStream = true
+		}
+	}
+	if p.Kind != KindModule || (len(p.Consumes) == 0 && len(p.Watches) == 0 && !hearsItsOwn && !hearsAStream) {
+		return Consumer{}, false
+	}
+	perms, err := PermissionsFor(p)
+	if err != nil {
+		return Consumer{}, false
+	}
+	// Events, wherever they live: a module's own namespace, and the namespace of any role it watches
+	// (novox/hq ADR 0121). Tool subjects and inboxes are subscribed directly and are not a consumer's
+	// business, which is why this is a filter and not the whole list.
+	var filters []string
+	for _, s := range perms.Subscribe {
+		// Not a module stream's, which its own consumer on that stream hears (novox/hq ADR 0363).
+		if strings.Contains(s, ".event.") && !strings.HasPrefix(s, moduleStreamPrefix) {
+			filters = append(filters, s)
+		}
+	}
+	// **A module that hears only a module's stream still has one here** (novox/hq ADR 0363 §7): what it
+	// gives up on there is delivered again under `mesh.again.<consumer>.` on EVENTS, and only this filters it.
+	if len(filters) == 0 && !hearsAStream {
+		return Consumer{}, false
+	}
+	sort.Strings(filters)
+	// And the events given up on and delivered again to this consumer alone (novox/hq issue 330).
+	filters = append(filters, AgainFilter(consumerDurable(p)))
+	return Consumer{
+		Name:           consumerDurable(p),
+		Stream:         consumerStream(p),
+		Filters:        filters,
+		AckWaitSeconds: 30,
+		MaxDeliver:     5,
+		// From now, as the controller's own consumers have been since issue 248: a module made on a stream that
+		// keeps a week replays none of it. What a part needs of the present it reads from its owner
+		// (novox/hq ADR 0443 §1, §3). A consumer that exists keeps its place whatever this says.
+		FromNow: true,
+		Why: "what " + p.Module + " declared it consumes; after max-deliver it gives an event up, and the " +
+			"controller keeps it in DEAD_LETTERS until a person delivers it again or drops it",
+	}, true
+}
+
+// ModuleConsumer is one module's durable consumer, with the module and node it is for.
+type ModuleConsumer struct {
+	Node, Module string
+	Consumer     Consumer
+}
+
+// ConsumersOf is every module's durable consumer the composed users imply: each module user's, and
+// each module a runtime carries — a carried module with no account of its own is no user (novox/hq
+// issue 195), and its consumer is still the controller's to make, since the runtime reads it on the
+// module's behalf (ADR 0198). One per module and node, whichever of the two named it first.
+func ConsumersOf(users []Principal) []ModuleConsumer {
+	var out []ModuleConsumer
+	seen := map[string]bool{}
+	add := func(p Principal) {
+		key := p.Node + "/" + p.Module
+		if seen[key] {
+			return
+		}
+		c, needed := ConsumerFor(p)
+		// **A module with a work-queue consumer of its own needs no other reason to be visited here**
+		// (novox/hq ADR 0436 §1, §2, §6): mesh-mail's sender consumes and watches nothing of its own, so
+		// ConsumerFor alone would have found nothing needed and skipped it before its one queue consumer
+		// was ever composed.
+		if !needed && len(p.Queues) == 0 {
+			return
+		}
+		seen[key] = true
+		if needed {
+			out = append(out, ModuleConsumer{Node: p.Node, Module: p.Module, Consumer: c})
+			// And one on each module stream it hears (novox/hq ADR 0363 §5).
+			for _, h := range p.Hears {
+				if len(h.Filters) == 0 {
+					continue
+				}
+				out = append(out, ModuleConsumer{Node: p.Node, Module: p.Module, Consumer: heardConsumer(p, h)})
+			}
+		}
+		// And the one durable consumer of each of its own work-queue streams, for the one process its
+		// bus.queues names (novox/hq ADR 0436 §1, §2, §6).
+		for _, q := range p.Queues {
+			out = append(out, ModuleConsumer{Node: p.Node, Module: p.Module, Consumer: QueueConsumer(p, q)})
+		}
+	}
+	for _, p := range users {
+		if p.Kind == KindModule {
+			add(p)
+		}
+	}
+	for _, p := range users {
+		if p.Kind != KindNodeTools {
+			continue
+		}
+		for _, d := range p.Carries {
+			// **A carried module's work-queue consumer is still the controller's to make** (novox/hq ADR
+			// 0436 §1, §2, §6), the same reason its ordinary consumer is (ADR 0198): mesh-mail has no
+			// account of its own (NoAccount) and is carried here, but its process does, and the consumer
+			// it reads through must exist and survive PruneHeard whether or not the module itself speaks.
+			add(Principal{Kind: KindModule, Node: p.Node, Module: d.Module, Emits: d.Emits,
+				Consumes: d.Consumes, Serves: d.Serves, Holds: d.Holds, Uses: d.Uses, Watches: d.Watches,
+				Streams: d.Streams, Hears: ComposedHears(d), Queues: d.Queues})
+		}
+	}
+	return out
+}
+
+// HolderConsumerFor is the worker a seat's holders share on that seat's work queue.
+//
+// **One worker for every holder, and each holder pulls one ask when it is idle** (novox/hq ADR
+// 0190). The seat is *authority* — who may be the telegram sender — and the worker is *delivery*,
+// kept separate so that relaxing one changes nothing about the other: a node-scoped seat has a
+// holder per machine, and all of them take from this one consumer, so the work is shared without
+// any holder knowing about the others. Pulled rather than pushed because a push consumer hands the
+// next ask to whichever subscriber the server picks, busy or not, and a pulled one is asked for by
+// a holder that has just become free. Which is also what ends the race issue 186 describes — asks
+// delivered behind the one being worked, expiring unacknowledged and dropped after the fifth
+// redelivery: nothing is delivered that nobody asked for. A long build keeps its own ask alive
+// (stillWorking); the ack wait is for a holder that died.
+func HolderConsumerFor(node, module string, seat DeclaredSeat) (Consumer, bool) {
+	if len(seat.Accepts) == 0 || seat.PulledByKind {
+		// A seat pulled by kind has a worker per kind, which its holders' seat traffic derives (SeatTrafficObjects): one
+		// worker filtered on every accept would overlap them on the work queue.
+		return Consumer{}, false
+	}
+	return Consumer{
+		Name:           "SEAT_" + upperSnake(seat.Name) + "_worker",
+		Stream:         seatStreamName(seat.Name),
+		Filters:        []string{"mesh.seat." + seat.Name + ".accept.>"},
+		AckWaitSeconds: 60,
+		MaxDeliver:     5,
+		// As many in flight as there are holders working, which pulling bounds by itself: a holder
+		// fetches one and fetches again only after it acknowledged. The server's default stands.
+		Why: fmt.Sprintf("%s on %s holds %s; every holder pulls one ask at a time from this worker "+
+			"and acknowledges after the work is done, so a crash mid-work redelivers rather than "+
+			"loses and an idle holder is the one that takes the next ask", module, node, seat.Name),
+	}, true
+}
+
+// NodeConsumer is the durable consumer a node reads its own declaration through.
+//
+// **Derived from a node existing, and created by the controller, because a host cannot create it.**
+// A host's account may subscribe its own declaration subject and publish its own ack subject, and
+// reaches no part of the JetStream API — which is correct (the controller is the only writer of
+// consumer definitions, design 25 §3) and means the consumer must be waiting before the host binds
+// to it. Named after the node, because the node's ack grant is `$JS.ACK.NODES.<node>.>` and a
+// consumer named anything else is one the host cannot acknowledge a delivery from.
+//
+// **No max-deliver, and a long ack wait.** A declaration is settled only after the node has applied
+// it and reported, which is minutes on a machine pulling images; and a declaration the mesh cannot
+// get a node to accept is not one to give up on, because the stream keeps only the newest per node
+// anyway — so there is exactly one message per node to redeliver, for as long as that node is away.
+func NodeConsumer(node string) Consumer {
+	return Consumer{
+		Name:           node,
+		Stream:         "NODES",
+		Filters:        []string{"mesh.node." + node + ".declare"},
+		Push:           true,
+		AckWaitSeconds: 300,
+		Why: "how " + node + " hears what it should be; last-per-subject, so a node that was away " +
+			"gets exactly the current declaration and nothing older",
+	}
+}
+
+// AssertNodeConsumers brings every known node's declaration consumer into being.
+//
+// Asserted on start as well as created at enrolment, for the reason the streams are: a mesh raised
+// from a restored backup, or one whose bus was recreated, has node records and no consumers, and a
+// node whose consumer is missing hears nothing while everything else about it looks correct.
+func AssertNodeConsumers(e Ensurer, nodes []string) error {
+	for _, n := range nodes {
+		if err := e.EnsureConsumer(NodeConsumer(n)); err != nil {
+			return fmt.Errorf("asserting how %s hears its declaration: %w", n, err)
+		}
+	}
+	return nil
+}
+
+// AllOverlaps reports subject filters claimed by more than one stream, across the mesh's own and
+// every derived one.
+//
+// NATS refuses an overlapping stream rather than merging it (verified against nats-server 2.10:
+// "subjects overlap with an existing stream"), so this is not a subtle divergence — it is a
+// registration that fails. Catching it here names both streams, before a half-applied mesh does.
+func AllOverlaps(seats []DeclaredSeat) []string {
+	all := append(MeshStreams(), SeatStreams(seats)...)
+	seen := map[string]string{}
+	var clashes []string
+	for _, s := range all {
+		for _, subject := range s.Subjects {
+			if first, ok := seen[subject]; ok {
+				clashes = append(clashes, fmt.Sprintf("%s and %s both claim %s", first, s.Name, subject))
+				continue
+			}
+			seen[subject] = s.Name
+		}
+	}
+	sort.Strings(clashes)
+	return clashes
+}
+
+// upperSnake makes a stream name from a seat name. NATS stream names may not contain a dot,
+// a space or a wildcard, and a hyphen is legal but reads badly beside the mesh's own.
+func upperSnake(s string) string {
+	out := []rune(s)
+	for i, r := range out {
+		switch {
+		case r >= 'a' && r <= 'z':
+			out[i] = r - 32
+		case r == '-' || r == '.':
+			out[i] = '_'
+		}
+	}
+	return string(out)
+}

go/buscompose/doc.go

@@ -0,0 +1,12 @@
+// Package buscompose is the bus's composer: who may say what on the bus, as the user list and the server configuration
+// the bus loads, derived from the mesh's records (Users, WithPasswords, ComposeAccounts, Compose), with the grants,
+// streams, state and logs it composes them from.
+//
+// **A copy of the controller's internal/broker, composer half** (issue 1377, novox/hq ADR 0547 §5), taken at
+// mesh-controller 7cd4d18b with the grants part's membership grant of f67d1553 (ADR 0547 §5): the bus client (jetstream.go), the broker's address from the environment (broker.go, onnats.go
+// but its one constant) and the two methods on that client are left out; the lease's two subjects are copied in
+// (nats.go). The controller keeps its own copy, unchanged, until it loses its lease at ADR 0547's third milestone, so
+// for that time two composers state who may say what and must say the same: TestTheCopiedComposerComposesAsTheControllers
+// holds this copy to lists the controller's own code wrote from the same fixtures. A change to what is granted is made
+// here and, while the controller composes, in the controller's copy too, never in one alone.
+package buscompose

go/buscompose/fixtures_test.go

@@ -0,0 +1,116 @@
+package buscompose
+
+// The fixtures the copied bus composer is held to (issue 1377, ADR 0547 §5): the same source is compiled into the
+// controller's internal/broker to write the expected lists, and into mesh-sdk's buscompose to compare against them.
+
+// UserListFixture is one mesh's records, and the hashes its accounts carry.
+type UserListFixture struct {
+	Name    string
+	Records Records
+	// Hashless are users given no hash, so they are left out and named.
+	Hashless []string
+}
+
+func fixtureTelegramSeat() Seat {
+	return Seat{Name: "telegram-sender", Accepts: []string{"send"}, Emits: []string{"delivered", "failed"}}
+}
+
+// UserListFixtures are the meshes, from the controller's own tests' records outward.
+func UserListFixtures() []UserListFixture {
+	return []UserListFixture{
+		{Name: "empty"},
+		{Name: "the controller's someRecords", Records: Records{
+			Nodes: []string{"two", "one"},
+			Assigned: map[string][]Declared{
+				"one": {{Module: "telegram", Serves: []string{"status"}}},
+				"two": {{Module: "shop", Emits: []string{"order.placed"}}},
+			},
+			Enrolling: []string{"three"},
+			People:    map[string][]string{"ada": {"mesh-catalog.catalog_tools"}},
+		}},
+		{Name: "seats, consumers, people and a hashless user", Hashless: []string{"two.audit"}, Records: Records{
+			Nodes: []string{"one", "two"},
+			Assigned: map[string][]Declared{
+				"one": {
+					{Module: "telegram", Holds: []Seat{fixtureTelegramSeat()}, Serves: []string{"status"}},
+					{Module: "nats", SnapshotsTheBus: true, Serves: []string{"nats_streams"}},
+					{Module: "mesh-watchman"},
+					{Module: "mesh-grants", Emits: []string{"membership-changed"}},
+				},
+				"two": {
+					{Module: "shop", Uses: []Seat{fixtureTelegramSeat()}, Emits: []string{"order.placed"}},
+					{Module: "audit", Consumes: []string{"shop.order.placed"}},
+				},
+			},
+			People:          map[string][]string{"ada": {"*"}, "bob": {"shop.status"}},
+			Interchangeable: map[string]bool{"shop": true},
+		}},
+		{Name: "state, logs, streams, queues and processes", Records: Records{
+			Nodes: []string{"ace", "novox"},
+			Assigned: map[string][]Declared{
+				"novox": {
+					{Module: "mesh-delivery-builder", Emits: []string{"built"},
+						State: []Bucket{{Module: "mesh-delivery-builder", Name: "steps", History: 5},
+							{Module: "mesh-delivery-builder", Name: "presence", PerMachine: true, KeyTTL: true, TTLSeconds: 60}},
+						Logs:    []Log{{Module: "mesh-delivery-builder", Name: "builds", MaxMiB: 64}},
+						Streams: []ModuleStream{{Module: "mesh-delivery-builder", Name: "asks", Events: []string{"ask"}, MaxAgeDays: 7, MaxMiB: 32, WorkQueue: true}},
+						Queues:  []QueueOwner{{Process: "worker", Stream: "asks", MaxDeliver: 5}},
+						Processes: []ProcessPrincipal{{Process: "worker", Emits: []string{"built"},
+							Queues: []QueueOwner{{Process: "worker", Stream: "asks", MaxDeliver: 5}},
+							State:  []string{"steps"}, Invokes: []string{"gitea.gitea_commit"}}},
+						Invokes: []string{"gitea.gitea_commit"},
+					},
+					{Module: "mesh-delivery-view", Reads: []string{"mesh-delivery-builder.steps"},
+						KeyedReads: []KeyedRead{{Read: "mesh-delivery-builder.presence", Key: "novox"}}},
+				},
+				"ace": {
+					{Module: "plex", Serves: []string{"plex_status"}, Checks: []string{"plex.plex_status"}},
+					{Module: "silent", NoAccount: true},
+				},
+			},
+			RootFree: map[string]bool{"ace": true},
+		}},
+	}
+}
+
+// HashOf is the stand-in hash a fixture's user carries.
+func HashOf(user string) string {
+	h := "$2a$11$"
+	for len(h) < 29 {
+		h += user
+	}
+	return h[:29] + "fixturefixturefixturefixture00"
+}
+
+// ComposedFor is a fixture's user list as the composer writes it, and the users left out.
+func ComposedFor(f UserListFixture) (string, []string, error) {
+	users, err := Users(f.Records)
+	if err != nil {
+		return "", nil, err
+	}
+	hashes := map[string]string{}
+	skip := map[string]bool{}
+	for _, u := range f.Hashless {
+		skip[u] = true
+	}
+	for _, u := range users {
+		if !skip[u.Username()] {
+			hashes[u.Username()] = HashOf(u.Username())
+		}
+	}
+	filled, missing := WithPasswords(users, hashes)
+	list, err := ComposeAccounts(filled)
+	return list, missing, err
+}
+
+// MembershipsFor is every membership a fixture's records issue, by `<node>.<module>`, as the composer makes them.
+func MembershipsFor(f UserListFixture) map[string]Membership {
+	where := PlacementsOf(f.Records, f.Records.Interchangeable)
+	out := map[string]Membership{}
+	for node, ds := range f.Records.Assigned {
+		for _, d := range ds {
+			out[node+"."+d.Module] = MembershipFor(node, d, where)
+		}
+	}
+	return out
+}

go/buscompose/log.go

@@ -0,0 +1,184 @@
+package buscompose
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+// A module's log on the bus (novox/hq ADR 0297): its record of operations, each entry appended under
+// a key and kept as long as the log is.
+//
+// A log follows a bucket in every respect (ADR 0201): the module names it locally, the mesh derives
+// its stream and subjects, the controller creates it from the catalogue on every raise and from
+// registration, never a module, and **no path of the mesh removes one** — a log whose declaration
+// is gone is reported, as a bucket is. Unlike a bucket, a log is its owner's alone: no other module
+// reads it, so there is no read of a log to grant or issue.
+//
+// Pure, but for the stream's configuration, which is the server's own type so that what is tested
+// is exactly what is sent; jetstream.go is the part that asks a server.
+
+// The mesh's caps on a log: what an entry's value may weigh, what a message on the log's stream may
+// weigh — the value and its headers, which the server counts in a message's size, so a value of the
+// full size still fits with the expected-last-sequence header an append carries — and what a log holds
+// when its module says nothing and at most.
+const (
+	LogMaxEntryBytes   = 256 * 1024
+	LogMaxMessageBytes = LogMaxEntryBytes + 4*1024
+	LogDefaultMiB      = 1024
+	LogMostMiB         = 8192
+)
+
+// A Log is one module's declared log as the bus holds it.
+type Log struct {
+	Module string
+	Name   string
+	// MaxMiB is its cap in MiB; zero is LogDefaultMiB.
+	MaxMiB int
+}
+
+// LogStreamPrefix starts every log's stream name, which no other stream of the mesh's starts with.
+const LogStreamPrefix = "LOG_"
+
+// LogStreamName is the stream a module's log lives in: `LOG_<module>_<name>`. The module and the
+// local name are each one token with no underscore, so two modules can never derive one stream.
+func LogStreamName(module, name string) string { return LogStreamPrefix + module + "_" + name }
+
+// LogSubject is the subject a log's entries are published under, without the key: an entry for key K
+// is on `<LogSubject>.<K>`.
+func LogSubject(module, name string) string { return "mesh.log." + module + "." + name }
+
+// Stream is this log's stream name.
+func (l Log) Stream() string { return LogStreamName(l.Module, l.Name) }
+
+// Subject is this log's subject, without the key.
+func (l Log) Subject() string { return LogSubject(l.Module, l.Name) }
+
+// MaxBytes is this log's cap in bytes.
+func (l Log) MaxBytes() int64 {
+	mib := l.MaxMiB
+	if mib <= 0 {
+		mib = LogDefaultMiB
+	}
+	return int64(mib) * 1024 * 1024
+}
+
+// Why is carried into the server's description of the stream, so somebody reading the server's own
+// state finds whose it is and why it is kept.
+func (l Log) Why() string {
+	return fmt.Sprintf("%s's log %q (novox/hq ADR 0297): its record of operations, one entry per operation "+
+		"under its key, appended by %s alone and kept as long as the log; never removed by the mesh, because "+
+		"it is data", l.Module, l.Name, l.Module)
+}
+
+// Config is the stream a log is, field by field as novox/hq ADR 0297 fixes it: a file stream kept by
+// limits, with no maximum age and no cap per key, whose message is an entry's value and 4 KiB of
+// headers at most, that refuses a new entry when full rather than
+// drop an old one, and that refuses deleting an entry or purging it. Direct gets are allowed, which
+// is how the runtime reads it.
+func (l Log) Config() jetstream.StreamConfig {
+	return jetstream.StreamConfig{
+		Name:              l.Stream(),
+		Description:       l.Why(),
+		Subjects:          []string{l.Subject() + ".>"},
+		Storage:           jetstream.FileStorage,
+		Retention:         jetstream.LimitsPolicy,
+		MaxAge:            0,
+		MaxMsgs:           -1,
+		MaxMsgsPerSubject: -1,
+		MaxBytes:          l.MaxBytes(),
+		MaxMsgSize:        LogMaxMessageBytes,
+		Discard:           jetstream.DiscardNew,
+		AllowDirect:       true,
+		DenyDelete:        true,
+		DenyPurge:         true,
+		Replicas:          1,
+	}
+}
+
+// logsIssuedFor is every log a module's code may reach, as its membership lists them: its own.
+func logsIssuedFor(d Declared) []LogIssued {
+	var out []LogIssued
+	for _, l := range d.Logs {
+		if !safeSubject.MatchString(d.Module) || !safeSubject.MatchString(l.Name) {
+			continue
+		}
+		out = append(out, LogIssued{Name: l.Name, Stream: LogStreamName(d.Module, l.Name),
+			Subject: LogSubject(d.Module, l.Name), Writes: true})
+	}
+	return out
+}
+
+// logGrants is what a principal publishes to reach the logs its module keeps: for each, appending
+// under the log's subjects, binding to its stream, and reading it directly. Nothing more — the
+// runtime reads a log by direct gets alone and makes no consumer on it — and nothing of any other
+// module's log, because a log is its owner's alone. Replies come on the principal's inbox, as for a
+// bucket.
+func logGrants(module string, names []string) []string {
+	if !safeSubject.MatchString(module) {
+		return nil
+	}
+	var out []string
+	for _, name := range names {
+		if !safeSubject.MatchString(name) {
+			continue
+		}
+		stream := LogStreamName(module, name)
+		out = append(out,
+			LogSubject(module, name)+".>",
+			"$JS.API.STREAM.INFO."+stream,
+			"$JS.API.DIRECT.GET."+stream,
+			"$JS.API.DIRECT.GET."+stream+".>")
+	}
+	return out
+}
+
+// logNames is the local names of a module's logs.
+func logNames(logs []Log) []string {
+	out := make([]string, 0, len(logs))
+	for _, l := range logs {
+		out = append(out, l.Name)
+	}
+	return out
+}
+
+// A LogAsserter is the part of a JetStream connection log assertion needs. It has no way to remove a
+// log, by design: nothing the mesh runs asks for one.
+type LogAsserter interface {
+	// EnsureLog creates the log's stream if absent and brings its configuration to match if present,
+	// never deleting or recreating it.
+	EnsureLog(l Log) error
+	// LogStreams is every log stream on the server: every stream named with LogStreamPrefix.
+	LogStreams() ([]string, error)
+}
+
+// RaiseLogs asserts every declared log and answers the log streams on the server that nothing
+// declares any more.
+//
+// **Those are reported, never removed** (novox/hq ADR 0297 §2, ADR 0201 §15–16): a log is a module's
+// record, and a manifest edited, a module renamed or unassigned is an ordinary day's work that must
+// not take a record with it. Removing one is a person's act, outside the mesh.
+func RaiseLogs(a LogAsserter, logs []Log) (undeclared []string, err error) {
+	sorted := append([]Log(nil), logs...)
+	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Stream() < sorted[j].Stream() })
+	declared := map[string]bool{}
+	for _, l := range sorted {
+		if err := a.EnsureLog(l); err != nil {
+			return nil, fmt.Errorf("asserting %s's log %q: %w", l.Module, l.Name, err)
+		}
+		declared[l.Stream()] = true
+	}
+	names, err := a.LogStreams()
+	if err != nil {
+		return nil, fmt.Errorf("listing the bus's logs: %w", err)
+	}
+	for _, n := range names {
+		if strings.HasPrefix(n, LogStreamPrefix) && !declared[n] {
+			undeclared = append(undeclared, n)
+		}
+	}
+	sort.Strings(undeclared)
+	return undeclared, nil
+}

go/buscompose/membership.go

@@ -0,0 +1,178 @@
+package buscompose
+
+import (
+	"slices"
+	"sort"
+	"strings"
+)
+
+// What the mesh issues an assignment to serve and to reach (novox/hq ADR 0160).
+//
+// A module's code names its tools and its events; **where they land is the mesh's to decide**, and
+// it decided it twice — once in the runtime, once here, by one rule compiled into both. Now the
+// controller composes a membership for every module on every machine and publishes it to a subject
+// only that assignment reads; the runtime serves exactly what the membership says, and the account's
+// grant is the same composition read the other way. The shape issued today is the shape the mesh
+// already had, so nothing moves when a membership first arrives; only who decides it moves.
+
+// Placements is where every module runs, for deciding which instance answers for the module.
+type Placements struct {
+	// Nodes is each module's machines.
+	Nodes map[string][]string
+	// Interchangeable is each module whose definition says its instances are the same anywhere,
+	// so the module's plain subject is issued to all of them in one queue.
+	Interchangeable map[string]bool
+	// Kinds is every kind held of a kinded bench, by whom and with what capabilities (ADR 0259 §5).
+	Kinds []KindHeld
+}
+
+// AnswersForTheModule says whether an instance of a module on one machine is issued the module's
+// plain subject: when it is the only instance, or when the definition says instances are
+// interchangeable. A stateful module on two machines gets only its machines' subjects, so a call
+// that names none reaches nothing rather than the wrong store.
+func (p Placements) AnswersForTheModule(module string) bool {
+	return len(p.Nodes[module]) <= 1 || p.Interchangeable[module]
+}
+
+// MembershipFor composes one assignment's membership from what it declared and where everything
+// runs. The subjects are the ones PermissionsFor grants, derived here once more only until the
+// grant itself is read from the membership — which is the next step, not this one.
+func MembershipFor(node string, d Declared, where Placements) Membership {
+	own := "mesh.mod." + d.Module
+	m := Membership{
+		Node: node, Module: d.Module,
+		Emits: own + ".event.{event}",
+		Tools: own + ".tool.tools",
+	}
+	// This machine's address always; the module's when this instance answers for the module.
+	m.Serves = append(m.Serves, Served{Subject: own + ".tool.{tool}." + node})
+	if where.AnswersForTheModule(d.Module) {
+		m.Serves = append(m.Serves, Served{Subject: own + ".tool.{tool}", Queue: "serve." + d.Module})
+	}
+	for _, s := range d.Holds {
+		if servedOnlyByTheController(s) {
+			continue // answered by the serving controller alone, never through a membership
+		}
+		for _, verb := range s.Serves {
+			m.Seats = append(m.Seats, SeatServed{Seat: s.Name, Verb: verb, Subject: seatToolSubject(s, verb, node)})
+		}
+	}
+	m.State = stateIssuedFor(d, node)
+	m.Logs = logsIssuedFor(d)
+	m.Streams = streamsIssuedFor(d)
+	m.Hears = HeardIssuedFor(node, d)
+	m.Waits = waitsIssuedFor(d)
+	t := SeatTrafficOf(d.Module, d.Holds, d.Uses, d.Watches)
+	for _, s := range append(append([]Seat{}, d.Uses...), d.Watches...) {
+		if !s.Kinded {
+			continue
+		}
+		for _, k := range where.Kinds {
+			if k.Seat == s.Name && !kindListed(t.Kinds, k) {
+				t.Kinds = append(t.Kinds, k)
+			}
+		}
+	}
+	if len(t.Publish)+len(t.Subscribe)+len(t.Answers)+len(t.Workers)+len(t.Records)+len(t.Kinds) > 0 {
+		m.SeatTraffic = &t
+	}
+	if len(d.Invokes) > 0 {
+		m.Reaches = map[string][]string{}
+		for _, t := range d.Invokes {
+			if t == "*" || strings.HasPrefix(t, "seat:") {
+				continue // every tool, or a role's: addressed by name, not resolved per instance
+			}
+			module, tool, ok := strings.Cut(t, ".")
+			if !ok {
+				continue
+			}
+			var reach []string
+			if where.AnswersForTheModule(module) {
+				reach = append(reach, "mesh.mod."+module+".tool."+tool)
+			}
+			nodes := append([]string{}, where.Nodes[module]...)
+			sort.Strings(nodes)
+			for _, n := range nodes {
+				reach = append(reach, "mesh.mod."+module+".tool."+tool+"."+n)
+			}
+			m.Reaches[t] = reach
+		}
+	}
+	return m
+}
+
+// PlacementsOf reads where everything runs from the records the bus's accounts are composed from.
+func PlacementsOf(r Records, interchangeable map[string]bool) Placements {
+	p := Placements{Nodes: map[string][]string{}, Interchangeable: interchangeable}
+	for node, declared := range r.Assigned {
+		for _, d := range declared {
+			p.Nodes[d.Module] = append(p.Nodes[d.Module], node)
+		}
+	}
+	for _, nodes := range p.Nodes {
+		sort.Strings(nodes)
+	}
+	// Where the router runs: a verified sender is believed only while its machine is root-free too. A router
+	// placed nowhere, or on more than one machine, frees nothing.
+	var routerNodes []string
+	for node, declared := range r.Assigned {
+		for _, d := range declared {
+			for _, s := range d.Holds {
+				if s.Name == routerSeat && !slices.Contains(routerNodes, node) {
+					routerNodes = append(routerNodes, node)
+				}
+			}
+		}
+	}
+	routerFree := len(routerNodes) == 1 && r.RootFree[routerNodes[0]]
+	for node, declared := range r.Assigned {
+		for _, d := range declared {
+			for _, s := range d.Holds {
+				if s.Kinded && s.Kind != "" {
+					p.Kinds = append(p.Kinds, KindHeld{Seat: s.Name, Kind: s.Kind, Module: d.Module, Node: node,
+						Capabilities: placedCapabilities(s.Capabilities, d.RunsAs, routerFree && r.RootFree[node])})
+				}
+			}
+		}
+	}
+	sort.Slice(p.Kinds, func(i, j int) bool {
+		a, b := p.Kinds[i], p.Kinds[j]
+		if a.Seat != b.Seat {
+			return a.Seat < b.Seat
+		}
+		if a.Kind != b.Kind {
+			return a.Kind < b.Kind
+		}
+		return a.Node < b.Node
+	})
+	return p
+}
+
+// routerSeat is the seat the router of asks holds (novox/hq ADR 0259 §3).
+const routerSeat = "operator-channel"
+
+// placedCapabilities is what a kind's claim promises, as far as its placement lets the router believe it
+// (novox/hq ADR 0259 §8): `verified-sender` only from a holder that runs as an account of its own, on a bus
+// account of its own — never one the machine's runtime carries as the operator's account — and only while
+// its machine and the router's were root-free when composed (rootFree; the review of 2026-10-09, H3). The
+// membership carrying it is composed at a push, so it can outlive a pass that later fails: the router asks
+// the controller's root-free verb again before it honours an approval, and that is the check that holds.
+func placedCapabilities(declared []string, runsAs string, rootFree bool) []string {
+	var out []string
+	for _, c := range declared {
+		if c == "verified-sender" && (runsAs == "" || !rootFree) {
+			continue
+		}
+		out = append(out, c)
+	}
+	return out
+}
+
+func kindListed(list []KindHeld, k KindHeld) bool {
+	for _, x := range list {
+		if x.Seat == k.Seat && x.Kind == k.Kind && x.Module == k.Module && x.Node == k.Node {
+			return true
+		}
+	}
+	return false
+}

go/buscompose/modstreams.go

@@ -0,0 +1,343 @@
+package buscompose
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// A module's own stream on the bus (novox/hq ADR 0363).
+//
+// A module declares a stream as it declares a log: named locally, created by the controller from the
+// catalogue on every raise and every send, never removed by the mesh. Its events are published on
+// `mesh.stream.<module>.event.<event>`, a subject space the shared EVENTS stream (`mesh.mod.*.event.>`)
+// does not take — the bus refuses two streams claiming one subject, so a module's stream cannot share
+// EVENTS' — and a consumer hears it through a durable consumer of its own on that stream, named as on
+// EVENTS. Pure; the controller's raise asserts what is composed here.
+
+// moduleStreamPrefix starts every subject a module's own stream takes.
+const moduleStreamPrefix = "mesh.stream."
+
+// ModuleStreamSubject is where a module's event on its own stream lands: `mesh.stream.<module>.event.<event>`.
+// The token before `.event.` is the emitter, as on EVENTS, so a runtime reads the same key from it.
+func ModuleStreamSubject(module, event string) string {
+	return moduleStreamPrefix + module + ".event." + event
+}
+
+// OnAModuleStream says a subject is one a module's own stream takes.
+func OnAModuleStream(subject string) bool { return strings.HasPrefix(subject, moduleStreamPrefix) }
+
+// WirePattern is a local event pattern as the bus spells it: `**` is `>`.
+func WirePattern(local string) string {
+	parts := strings.Split(local, ".")
+	for i, p := range parts {
+		if p == "**" {
+			parts[i] = ">"
+		}
+	}
+	return strings.Join(parts, ".")
+}
+
+// A ModuleStream is one module's declared stream as the bus holds it.
+type ModuleStream struct {
+	Module string
+	// Name is its name on the bus, `MAIL`.
+	Name string
+	// Events are the events it carries, as the bus spells them (WirePattern).
+	Events     []string
+	MaxAgeDays int
+	MaxMiB     int
+	// Restricted says a trusted config value of the module grants who hears it (ADR 0363 §4).
+	Restricted bool
+	// WorkQueue says this stream holds ADR 0436 §6's work-queue retention: a message is removed once a
+	// consumer acknowledges it, and the bus refuses a new one when full rather than dropping its oldest.
+	WorkQueue bool
+	// Duplicates is the work-queue's duplicate window in hours (novox/hq ADR 0436 §6); meaningless unless
+	// WorkQueue.
+	Duplicates int
+}
+
+// Subjects are the subjects the stream takes.
+func (s ModuleStream) Subjects() []string {
+	var out []string
+	for _, e := range s.Events {
+		out = append(out, ModuleStreamSubject(s.Module, e))
+	}
+	sort.Strings(out)
+	return out
+}
+
+// Stream is the stream the controller asserts: kept by limits, its age and size the module's, dropping
+// its oldest when full — a consumer that was away catches up within the age, and the module's own record
+// answers for anything older.
+func (s ModuleStream) Stream() Stream {
+	why := fmt.Sprintf("%s's own stream (novox/hq ADR 0363): its events, kept %d days and at most %d MiB so a "+
+		"consumer that was away catches up", s.Module, s.MaxAgeDays, s.MaxMiB)
+	if s.Restricted {
+		why += "; heard only by the consumers its trusted config value grants"
+	}
+	if s.WorkQueue {
+		why += "; a work-queue (novox/hq ADR 0436 §6): a message is removed once its one consumer " +
+			"acknowledges it, and a full stream refuses a new one rather than dropping what it holds"
+	}
+	out := Stream{
+		Name:      s.Name,
+		Subjects:  s.Subjects(),
+		Retention: RetentionLimits,
+		MaxAge:    s.MaxAgeDays * 24 * 60 * 60,
+		MaxBytes:  int64(s.MaxMiB) * 1024 * 1024,
+		Why:       why,
+		// Said on the bus, so a dead letter kept from it ages out with it (novox/hq ADR 0376 §3).
+		Restricted: s.Restricted,
+	}
+	if s.WorkQueue {
+		out.Retention = RetentionWorkQueue
+		out.DiscardNew = true
+		out.DuplicatesSeconds = s.Duplicates * 60 * 60
+		// Said on the bus too, reusing the one flag a restricted stream's dead letters already age and hide
+		// by (novox/hq ADR 0436 §6, ADR 0376 §3-4): a work-queue stream's grant is always empty (ADR 0436
+		// §6 refuses one that carries a grant), so this never collides with a trusted-config restriction.
+		out.Restricted = true
+		// And its own metadata, apart from the bus's work-queue retention SEAT_* and other mesh-internal
+		// streams share without being one of this clause's: only this flag says a dead letter kept from the
+		// stream is drop-only (novox/hq ADR 0436 §6), never the stream's Retention alone.
+		out.WorkQueue = true
+	}
+	return out
+}
+
+// QueueOwner is the one process of a module that is the durable consumer of one of its own work-queue
+// streams (novox/hq ADR 0436 §1, §2, §6): named in that process's bus.queues, and checked at registration
+// to be the only one (catalogue.WorkQueueStreamProblems).
+type QueueOwner struct {
+	// Process is the process resource's id — its bus account's name, with the node and module (novox/hq ADR
+	// 0436 §2).
+	Process string
+	// Stream is the work-queue stream's name on the bus.
+	Stream string
+	// MaxDeliver bounds how many times a message is handed over before it is given up as a dead letter
+	// (novox/hq ADR 0436 §6).
+	MaxDeliver int
+}
+
+// QueueConsumer is the durable consumer the one process a module's bus.queues names is granted on its own
+// work-queue stream (novox/hq ADR 0436 §1, §2, §6): no filter, since it is the stream's only consumer —
+// unlike heardConsumer, which is one of possibly several hearing a module's ordinary stream.
+func QueueConsumer(p Principal, q QueueOwner) Consumer {
+	return Consumer{
+		Name:           p.Node + "_" + p.Module + "_" + q.Process,
+		Stream:         q.Stream,
+		AckWaitSeconds: 30,
+		MaxDeliver:     q.MaxDeliver,
+		Why: fmt.Sprintf("%s's process %s is the one consumer %s's bus.queues names for its work-queue "+
+			"stream %s (novox/hq ADR 0436 §6); after max-deliver %d it gives a message up, and the "+
+			"controller keeps it in %s, offered only drop", p.Module, q.Process, p.Module, q.Stream,
+			q.MaxDeliver, DeadLettersStream),
+	}
+}
+
+// ModuleStreams is every declared module stream as the controller asserts it, in name order.
+func ModuleStreams(declared []ModuleStream) []Stream {
+	sorted := append([]ModuleStream(nil), declared...)
+	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Name < sorted[j].Name })
+	out := make([]Stream, 0, len(sorted))
+	for _, s := range sorted {
+		out = append(out, s.Stream())
+	}
+	return out
+}
+
+// Heard is a module's stream another module hears, and the subjects it hears of it: its `consumes`
+// within the stream and, for a restricted stream, within what the provider's trusted config value grants it
+// (ADR 0363 §5). Composed only with at least one subject.
+type Heard struct {
+	Stream  string
+	Emitter string
+	Filters []string
+	// Restricted says the stream is restricted by its provider's trusted config value (ADR 0363 §4): then it
+	// is heard only by a module on an account of its own (ADR 0376 §1, ComposedHears).
+	Restricted bool
+}
+
+// ComposedHears is what of a module's hearing the controller composes (novox/hq ADR 0376 §1): every stream it
+// hears, but a restricted one only for a module that runs in a runtime of its own on a bus account of its own
+// (`runs-as`, ADR 0259). **The tool runner never hears a restricted stream**: a module it carries reaches the bus
+// through the tool runner's account, which every agent session on that machine reaches the bus as too, so a
+// consumer, its grants or its bind word composed there would hand the stream to any session. A module that
+// declares no `runs-as` and keeps its own container credential gets none either: only `runs-as` is an account
+// the mesh keeps from agents.
+func ComposedHears(d Declared) []Heard {
+	if d.RunsAs != "" {
+		return d.Hears
+	}
+	var out []Heard
+	for _, h := range d.Hears {
+		if !h.Restricted {
+			out = append(out, h)
+		}
+	}
+	return out
+}
+
+// Withheld is a restricted stream a grant gives a module that the controller composes nothing for, because the
+// module has no account of its own (novox/hq ADR 0376 §2): said in `doctor` and in the controller's log, never
+// silent.
+type Withheld struct {
+	Node, Module, Stream, Emitter string
+}
+
+// Said is a withheld hearing in the operator's words: the module, the stream and the remedy.
+func (w Withheld) Said() string {
+	return fmt.Sprintf("%s on %s is granted part of %s's restricted stream %s, and hears none of it: it is carried "+
+		"by the machine's tool runner, whose bus account every agent session there shares, so nothing is composed "+
+		"for it. Declare runs-as in %s's manifest, so it runs as an account of its own (novox/hq ADR 0376)",
+		w.Module, w.Node, w.Emitter, w.Stream, w.Module)
+}
+
+// WithheldOf is every granted hearing of a restricted stream composed for nothing, by machine and module.
+func WithheldOf(r Records) []Withheld {
+	var out []Withheld
+	for _, node := range sortedCopy(r.Nodes) {
+		for _, d := range r.Assigned[node] {
+			if d.RunsAs != "" {
+				continue
+			}
+			for _, h := range d.Hears {
+				if h.Restricted && len(h.Filters) > 0 {
+					out = append(out, Withheld{Node: node, Module: d.Module, Stream: h.Stream, Emitter: h.Emitter})
+				}
+			}
+		}
+	}
+	return out
+}
+
+// heardConsumer is the durable consumer a module hears a module's stream through: named as its consumer
+// on EVENTS, on that stream, with the subjects it was granted as its filters.
+func heardConsumer(p Principal, h Heard) Consumer {
+	filters := append([]string(nil), h.Filters...)
+	sort.Strings(filters)
+	return Consumer{
+		Name:           consumerDurable(p),
+		Stream:         h.Stream,
+		Filters:        filters,
+		AckWaitSeconds: 30,
+		MaxDeliver:     5,
+		// From now, like a module's consumer on EVENTS (novox/hq ADR 0443 §1).
+		FromNow: true,
+		Why: "what " + p.Module + " consumes of " + h.Emitter + "'s stream " + h.Stream + " and is granted " +
+			"(novox/hq ADR 0363); after max-deliver it gives an event up, and the controller keeps it in " +
+			"DEAD_LETTERS until a person delivers it again or drops it",
+	}
+}
+
+// heardGrants are what a principal publishes to read and acknowledge the consumers it hears module streams
+// through: asking about each, pulling from it, acknowledging it — its own name on each stream, no other's.
+func heardGrants(p Principal, hears []Heard) []string {
+	var out []string
+	durable := consumerDurable(p)
+	for _, h := range hears {
+		if !safeSubject.MatchString(h.Stream) || len(h.Filters) == 0 {
+			continue
+		}
+		out = append(out,
+			"$JS.API.CONSUMER.INFO."+h.Stream+"."+durable,
+			"$JS.API.CONSUMER.MSG.NEXT."+h.Stream+"."+durable,
+			"$JS.ACK."+h.Stream+"."+durable+".>")
+	}
+	return out
+}
+
+// ownStreamGrants are the subjects a module publishes its own streams' events on, and no other's.
+func ownStreamGrants(module string, streams []ModuleStream) []string {
+	var out []string
+	for _, s := range streams {
+		if s.Module != module {
+			continue
+		}
+		out = append(out, s.Subjects()...)
+	}
+	return out
+}
+
+// streamsIssuedFor is every stream of its own a module's membership names.
+func streamsIssuedFor(d Declared) []StreamIssued {
+	var out []StreamIssued
+	for _, s := range d.Streams {
+		if s.Module != d.Module || !safeSubject.MatchString(d.Module) {
+			continue
+		}
+		out = append(out, StreamIssued{Stream: s.Name, Events: append([]string(nil), s.Events...),
+			Subject: ModuleStreamSubject(d.Module, "{event}")})
+	}
+	return out
+}
+
+// HeardIssuedFor is every module stream an assignment hears, as its membership names it.
+func HeardIssuedFor(node string, d Declared) []HeardIssued {
+	var out []HeardIssued
+	// A restricted stream's bind word only for a module of its own account (novox/hq ADR 0376 §1).
+	for _, h := range ComposedHears(d) {
+		if len(h.Filters) == 0 {
+			continue
+		}
+		out = append(out, HeardIssued{Stream: h.Stream, Consumer: node + "_" + d.Module})
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Stream < out[j].Stream })
+	return out
+}
+
+// Pruner is the part of a JetStream connection that removes a module's consumer on a module's stream it
+// may no longer hear (ADR 0363 §6). Optional: what only records what it is asked to assert has none.
+type Pruner interface {
+	ConsumerNames(stream string) ([]string, error)
+	RemoveConsumer(stream, name string) error
+}
+
+// PruneHeard removes, from each module stream, every durable consumer the composition no longer asks for,
+// and answers what it removed as `<stream>/<consumer>`. A consumer that loses its grant loses what it reads
+// through, whatever its runtime still holds; a stream that does not exist yet has nothing to remove.
+func PruneHeard(p Pruner, streams []ModuleStream, wanted []Consumer) ([]string, error) {
+	keep := map[string]bool{}
+	for _, c := range wanted {
+		keep[c.Stream+"/"+c.Name] = true
+	}
+	var removed []string
+	for _, s := range streams {
+		names, err := p.ConsumerNames(s.Name)
+		if err != nil {
+			return removed, fmt.Errorf("listing the consumers on %s: %w", s.Name, err)
+		}
+		for _, n := range names {
+			if keep[s.Name+"/"+n] {
+				continue
+			}
+			if err := p.RemoveConsumer(s.Name, n); err != nil {
+				return removed, fmt.Errorf("removing %s's consumer on %s, which is no longer granted: %w", n, s.Name, err)
+			}
+			removed = append(removed, s.Name+"/"+n)
+		}
+	}
+	return removed, nil
+}
+
+// EnsureHeard asserts a consumer on a module's stream (ADR 0363 §5, §6). **On a restricted stream, a consumer
+// the bus will not bring to match is removed**: a pull consumer delivers to whoever pulls it, so one left with
+// its wider filters after a narrowing was refused would keep handing over what the grant no longer names,
+// whatever the user list now says. The next assertion makes it again with the granted filters. The refusal is
+// returned either way, saying what was done, so the send says it and raises it.
+func EnsureHeard(r Raiser, c Consumer, restricted bool) error {
+	err := r.EnsureConsumer(c)
+	if err == nil || !restricted {
+		return err
+	}
+	p, prunes := r.(Pruner)
+	if !prunes {
+		return fmt.Errorf("%w; it could not be removed here, and may still deliver more than it is granted", err)
+	}
+	if rerr := p.RemoveConsumer(c.Stream, c.Name); rerr != nil {
+		return fmt.Errorf("%w; REMOVING IT FAILED TOO, so it may still deliver more than it is granted: %v", err, rerr)
+	}
+	return fmt.Errorf("%w; REMOVED, so it delivers nothing it is no longer granted: the next assertion makes it "+
+		"again with its granted filters (novox/hq ADR 0363 §6)", err)
+}

go/buscompose/onnats.go

@@ -0,0 +1,5 @@
+package buscompose
+
+// NATSVar names the environment variable that says the controller is on the bus (mesh-controller internal/broker
+// onnats.go); kept with the composer for the readiness it composes.
+const NATSVar = "MESH_BUS_NATS"

go/buscompose/process_grants.go

@@ -0,0 +1,52 @@
+package buscompose
+
+// The bus account of one process of a module that declares bus (novox/hq ADR 0436 §1, §2, §3, §5).
+//
+// **Never the module's own account's grants, never the tool runner's.** A process's authority is read
+// straight from its bus declaration — its emits, its queue's consumer, its state, whether it reads the
+// records of its module's own asks, and the tools and seat verbs it calls — and nothing else: it holds no
+// seat, serves no tool, hears no module stream, and answers nothing a caller asked (§3). Modelled on
+// provisionerGrants, the other kind of process account the mesh mints (ADR 0349 clauses 6 and 11).
+
+// processGrants is one process's whole authority: to publish, and to subscribe.
+func processGrants(p Principal) (pub, sub []string, err error) {
+	// 1. Its own events, under its module's own namespace — the same subjects the module's own principal
+	// would publish them on, had it declared them there instead (novox/hq ADR 0436 §1).
+	own := "mesh.mod." + p.Module
+	for _, e := range p.Emits {
+		pub = append(pub, own+".event."+e)
+	}
+
+	// 2. The one durable consumer of each work-queue stream its bus names (novox/hq ADR 0436 §1, §2, §6):
+	// asked about, pulled from and acknowledged, by the same name ConsumersOf composes the consumer under
+	// (QueueConsumer) — and no other stream's.
+	for _, q := range p.Queues {
+		consumer := p.Node + "_" + p.Module + "_" + q.Process
+		pub = append(pub,
+			"$JS.API.CONSUMER.INFO."+q.Stream+"."+consumer,
+			"$JS.API.CONSUMER.MSG.NEXT."+q.Stream+"."+consumer,
+			"$JS.ACK."+q.Stream+"."+consumer+".>")
+	}
+
+	// 3. Its module's own state, by the local names its bus names alone — never the whole of what the
+	// module keeps (novox/hq ADR 0436 §1), read and written as stateGrants gives any module's own bucket.
+	pub = append(pub, stateGrants(stateAccess{Module: p.Module, Node: p.Node, Keeps: p.State})...)
+
+	// 4. The router's records of its module's own asks (novox/hq ADR 0436 §1, ADR 0259 §3): the same
+	// direct-get subjects a module's own principal reads for the seats its Uses names that keep them —
+	// read here from the one list, so the two cannot disagree.
+	if p.Asks {
+		pub = append(pub, SeatTrafficOf(p.Module, nil, p.Uses, nil).Records...)
+	}
+
+	// 5. The tools and seat verbs it calls (novox/hq ADR 0152, ADR 0436 §1): the same derivation a
+	// module's own principal's invokes takes, so `callerNamed` (applied to every non-controller principal)
+	// adds the caller-named `call` variants for it exactly as it would for a module.
+	invoked, err := invokedSubjects(p.Invokes)
+	if err != nil {
+		return nil, nil, err
+	}
+	pub = append(pub, invoked...)
+
+	return pub, sub, nil
+}

go/buscompose/provisioner.go

@@ -0,0 +1,217 @@
+package buscompose
+
+import (
+	"errors"
+	"fmt"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"strings"
+
+	"github.com/nats-io/nats.go"
+)
+
+// The provisioner client's own bus account (novox/hq ADR 0349 clauses 6 and 11, design 57 package P3).
+//
+// **Not the tool runner's account.** The client fills a machine's files and asks the vault for the secrets that
+// machine's declaration names; the vault hands a secret only to an account of its own, because a call under the
+// tool runner's account cannot be told from an agent's on that machine (ADR 0305 §3, §12). So each machine that
+// runs the client has a principal of its own, KindProvisioner, named for the machine, and granted what the client
+// does and nothing else: read its own machine's keys in each domain's bucket, write its own machine's keys of the
+// provisioner server's needs, applied and collections (design 57 P4), read the server's registry, say what it
+// applied on its own machine, and ask the vault in its own name.
+
+// NodeProvisionerSeat is the seat the provisioner client holds on every machine (ADR 0349 clause 3).
+const NodeProvisionerSeat = "node-provisioner"
+
+// ProvisionerSecret is the own secret of the module running the client that its bus account is delivered in, as
+// `broker` is a module's own (novox/hq issue 195): a module that claims NodeProvisionerSeat and declares no own
+// secret of this name has nowhere to read an account, and is given none.
+const ProvisionerSecret = "provisioner-broker"
+
+// ConfigResolvedBucket is the config domain's resolved values, keyed `<node>.<module>.<key>` (ADR 0348, research
+// 051): mesh-config's state `resolved`, written by mesh-config alone.
+var ConfigResolvedBucket = BucketName("mesh-config", "resolved")
+
+// ProvisionerReads are the domains' buckets a provisioner client reads its own machine's keys of, each keyed
+// `<node>.…` (research 051): placement, the controller's assignments mirror (`<node>.<module>`), whose value carries
+// the provisioner's plan of a module handed to it (inventory.Provisioning, design 57 P5); and config,
+// mesh-config's resolved values. **Named one by one**, as the controller's asks are: a domain that moves to the
+// provisioner adds its bucket here, and a bucket not named is one the client cannot read.
+var ProvisionerReads = []string{ConfigResolvedBucket}
+
+// ProvisionerReadsWhole are the buckets a provisioner client reads every key of: the controller's assignments mirror,
+// where a provider's consumers are bound to it in their own machines' plans, which the provider machine's client
+// reads to fill ${consumers:<provision>} with each one's credential (novox/hq ADR 0373, issue 679). It holds placement
+// and plans, never a secret's value; the client writes none of it.
+var ProvisionerReadsWhole = []string{AssignmentsBucket}
+
+// BoundState is a providing module's state of entries, one per consumer (mesh-sdk go/provider, issue 678): a
+// consumer's machine's client reads its own keys of it, `<node>.<module>.<provision>[.<local>]`, to fill
+// ${bound:<provision>:<key>} (issue 679).
+const BoundState = "bound"
+
+// ProvisionerServerModule is the module holding the seat mesh-provisioner once for the mesh (ADR 0349 clause 3,
+// design 57 P4), whose buckets the clients write their own machine's keys of.
+const ProvisionerServerModule = "mesh-provisioner"
+
+// The provisioner server's buckets (ADR 0349 clause 3): its state, created by the controller from its manifest
+// like any module's, and written by its own account whole.
+var (
+	// ProvisionerRegistryBucket is which domain answers which kind of placeholder, keyed by the kind; the
+	// server's alone, read whole by every client.
+	ProvisionerRegistryBucket = BucketName(ProvisionerServerModule, "registry")
+	// ProvisionerNeedsBucket is what each module on each machine needs, `<node>.<module>.<kind>.<name>`.
+	ProvisionerNeedsBucket = BucketName(ProvisionerServerModule, "needs")
+	// ProvisionerAppliedBucket is what is applied where, `<node>.<module>`.
+	ProvisionerAppliedBucket = BucketName(ProvisionerServerModule, "applied")
+	// ProvisionerCollectBucket is the items of every collection, `<node>.<collection>.<contributor>`.
+	ProvisionerCollectBucket = BucketName(ProvisionerServerModule, "collect")
+)
+
+// ProvisionerWrites are the server's buckets a client writes, and reads, its own machine's keys of (`<node>.>`)
+// and no other's: the needs it records, what it applied, and the items of the collections on its machine. A
+// client cannot write another machine's needs, or say another machine applied a file.
+var ProvisionerWrites = []string{ProvisionerNeedsBucket, ProvisionerAppliedBucket, ProvisionerCollectBucket}
+
+// VerbsTheProvisionerAsksTheVault are the vault's verbs a provisioner client asks in its own name (ADR 0349
+// clause 11): `get`, a secret its machine's declaration names, answered sealed to the asker's key. On the subject
+// that names its caller, so the vault knows which machine's client asks from the bus's word.
+var VerbsTheProvisionerAsksTheVault = []SeatVerb{{Seat: "mesh-vault", Verb: "get"}}
+
+// VaultSecretChangedSubject is where the vault says a secret it holds changed (`secret-changed`: which, by whom,
+// when, its generation; never a value, ADR 0349 clause 11), as link.EventSubject addresses mesh-vault's event. A
+// provisioner client listens to it so a rotated secret reaches its file without a new declaration (design 57 V4):
+// it asks the vault again, in its own name, for a secret its machine's declaration names.
+const VaultSecretChangedSubject = "mesh.mod.mesh-vault.event.secret-changed"
+
+// ProvisionerAppliedSubject is where a machine's client says what it applied for one module, applied or failed
+// with the reason (ADR 0349 clauses 4 and 15): `prov.applied.<node>.<module>`.
+func ProvisionerAppliedSubject(node, module string) string {
+	return "prov.applied." + node + "." + module
+}
+
+// ProvisionerAskSubject is where a machine's tool runner asks that machine's provisioner client for a config value
+// or a non-secret bound value of a module it carries, naming the module from the bundle that asks (novox/hq ADR
+// 0370 §1, §3, §4; issue 685): `prov.ask.<node>`, which the client subscribes and the tool runner's account of the
+// same machine alone may publish. The bus proves only that the tool runner asks; the module is the runtime's word,
+// so the client answers no secret here (ADR 0370 §2).
+func ProvisionerAskSubject(node string) string { return "prov.ask." + node }
+
+// ProvisionerChangedSubject is where a machine's client says that a value of one module it answers moved, so the
+// tool runner asks again for the module's code's watches (ADR 0349 §14, ADR 0370 §1): `prov.changed.<node>.<module>`,
+// carrying which value and never the value itself, heard by that machine's tool runner alone.
+func ProvisionerChangedSubject(node, module string) string {
+	return "prov.changed." + node + "." + module
+}
+
+// provisionerGrants is a provisioner client's whole authority: to publish, and to subscribe.
+func provisionerGrants(p Principal) (pub, sub []string, err error) {
+	if p.Node == "" {
+		// Refused rather than composed into `$KV.<bucket>..>`, a pattern no machine's keys are under, and a
+		// name every nameless client would share.
+		return nil, nil, errors.New("a provisioner client names no machine, so it would have no keys of its own " +
+			"to read and an account it shared with every other")
+	}
+	for _, bucket := range ProvisionerReads {
+		pub = append(pub, machineKeysRead(bucket, p.Node)...)
+	}
+	for _, bucket := range ProvisionerReadsWhole {
+		pub = append(pub, wholeBucketRead(bucket)...)
+	}
+	for _, bucket := range p.BoundBuckets {
+		module, name, ok := strings.Cut(bucket, "_")
+		if !ok || name != BoundState || !safeSubject.MatchString(module) || strings.Contains(module, "_") {
+			return nil, nil, fmt.Errorf("%q is not a provider's bucket of entries, <module>_%s", bucket, BoundState)
+		}
+		pub = append(pub, machineKeysRead(bucket, p.Node)...)
+	}
+	// The server's buckets (design 57 P4): its own machine's keys of the needs, the applied and the
+	// collections, read and written, `$KV.<bucket>.<node>.>` and nothing wider; and the registry, read whole,
+	// which says which domain answers which kind and is the same for every machine.
+	for _, bucket := range ProvisionerWrites {
+		pub = append(pub, machineKeysRead(bucket, p.Node)...)
+		pub = append(pub, "$KV."+bucket+"."+p.Node+".>")
+	}
+	pub = append(pub, wholeBucketRead(ProvisionerRegistryBucket)...)
+	// Its own node's own have, `<node>.node`, read and never written, and no other key of the bucket: it fills every
+	// module again when the node-engine moves to a new composition of the node's own (issue 1945), since an apply can
+	// leave a filled file as the composition had it.
+	pub = append(pub, readGrants(delivery.HaveBucket, p.Node+".node")...)
+	pub = append(pub, "prov.applied."+p.Node+".>")
+	token := CallerToken(p.Username())
+	if token == "" {
+		return nil, nil, fmt.Errorf("%q cannot name a caller", p.Username())
+	}
+	for _, v := range VerbsTheProvisionerAsksTheVault {
+		pub = append(pub, "mesh.seat."+v.Seat+"."+CallKind+"."+v.Verb+"."+token)
+	}
+	// What moved of a value it answers its own machine's tool runner (ADR 0370 §1), under its own machine's name.
+	pub = append(pub, "prov.changed."+p.Node+".>")
+	// Its own reply space, for the vault's answers and its reads' and watches' deliveries; what the vault says
+	// changed; and its own machine's tool runner asking it for a module's config and non-secret bound values (ADR
+	// 0370 §3), which it answers on the ask's reply and nowhere else.
+	return pub, []string{p.inbox(), VaultSecretChangedSubject, ProvisionerAskSubject(p.Node)}, nil
+}
+
+// machineKeysRead is reading every key of a bucket under one machine's name, `<node>.>`, and no other key: a
+// direct get of a key's own subject, and a consumer whose filter is under it — the server's create-with-filter
+// form, which it holds to the filter the subject names (as stateGrants does for one key, novox/hq ADR 0260).
+// Binding, deleting a consumer and flow control cannot be narrowed by key and read no value.
+func machineKeysRead(bucket, node string) []string {
+	stream := "KV_" + bucket
+	keys := "$KV." + bucket + "." + node + ".>"
+	return []string{
+		"$JS.API.STREAM.INFO." + stream,
+		"$JS.API.DIRECT.GET." + stream + "." + keys,
+		"$JS.API.CONSUMER.CREATE." + stream + ".*." + keys,
+		"$JS.API.CONSUMER.DELETE." + stream + ".>",
+		"$JS.FC." + stream + ".>",
+	}
+}
+
+// wholeBucketRead is reading every key of a bucket and writing none: what stateGrants grants a module for a
+// bucket it `reads`.
+func wholeBucketRead(bucket string) []string {
+	stream := "KV_" + bucket
+	return []string{
+		"$JS.API.STREAM.INFO." + stream,
+		"$JS.API.DIRECT.GET." + stream + ".>",
+		"$JS.API.CONSUMER.CREATE." + stream + ".>",
+		"$JS.API.CONSUMER.DELETE." + stream + ".>",
+		"$JS.FC." + stream + ".>",
+	}
+}
+
+// LastProvApplied is what a machine's provisioner client last said of one module's files, as it published it on
+// ProvisionerAppliedSubject and ProvAppliedStream keeps it (design 57 P6): false when it has said nothing of it in
+// the stream's week.
+func LastProvApplied(js nats.JetStreamContext, node, module string) ([]byte, bool, error) {
+	msg, err := js.GetLastMsg(ProvAppliedStream, ProvisionerAppliedSubject(node, module))
+	if errors.Is(err, nats.ErrMsgNotFound) {
+		return nil, false, nil
+	}
+	if err != nil {
+		return nil, false, fmt.Errorf("what %s's provisioner client said of %s cannot be read: %w", node, module, err)
+	}
+	return msg.Data, true, nil
+}
+
+// ProvAppliedReports is the newest word of every machine's provisioner client on every module it said one of, kept by
+// ProvAppliedStream, by subject (`prov.applied.<node>.<module>`).
+func ProvAppliedReports(js nats.JetStreamContext) (map[string][]byte, error) {
+	info, err := js.StreamInfo(ProvAppliedStream, &nats.StreamInfoRequest{SubjectsFilter: ProvAppliedSubjects})
+	if err != nil {
+		return nil, fmt.Errorf("the provisioner clients' reports cannot be listed: %w", err)
+	}
+	out := map[string][]byte{}
+	for subject := range info.State.Subjects {
+		msg, err := js.GetLastMsg(ProvAppliedStream, subject)
+		if errors.Is(err, nats.ErrMsgNotFound) {
+			continue // aged out between the two reads
+		}
+		if err != nil {
+			return nil, fmt.Errorf("the provisioner client's report on %s cannot be read: %w", subject, err)
+		}
+		out[subject] = msg.Data
+	}
+	return out, nil
+}

go/buscompose/raise.go

@@ -0,0 +1,73 @@
+package buscompose
+
+import "fmt"
+
+// Bringing the bus's own objects into being, in the one order that works.
+//
+// **Asserted on every start rather than created once at genesis.** A stream somebody deleted, a mesh
+// raised from a restored backup, or a bus whose data directory was replaced all have records and no
+// objects — and a node whose consumer is missing hears nothing while everything else about it looks
+// correct. Idempotence is the whole requirement, and the parts are already idempotent; this is the
+// order they have to be asked in.
+
+// Raiser is everything asserting the bus's objects needs of a connection to it.
+type Raiser interface {
+	Asserter
+	Ensurer
+}
+
+// Raise asserts the mesh's streams, the controller's own consumers, and one consumer per node.
+//
+// **The order is not a preference.** A consumer on a stream that does not exist is refused, and the
+// refusal names the stream rather than the order — so somebody reading it goes looking for a deleted
+// stream instead of a reversed pair of lines. Nodes last, because the one a node reads lives on a
+// stream the mesh's own set defines.
+func Raise(r Raiser, nodes []string) error {
+	if err := AssertMeshStreams(r); err != nil {
+		return err
+	}
+	if err := AssertMeshConsumers(r); err != nil {
+		return err
+	}
+	if err := AssertNodeConsumers(r, nodes); err != nil {
+		return err
+	}
+	return nil
+}
+
+// RaiseSeats asserts one work queue per declared seat, and the worker of whoever holds it.
+//
+// Separate from Raise because it is answered by a different question: the mesh's own objects exist
+// because the mesh does, and a seat's exist because a module declaring one was registered. Kept
+// beside it so the order is visible — a holder's worker needs the seat's stream, and a seat's stream
+// needs nothing.
+func RaiseSeats(r Raiser, seats []DeclaredSeat, holders map[string]Holder) error {
+	for _, s := range SeatStreams(seats) {
+		if err := r.EnsureStream(s); err != nil {
+			return fmt.Errorf("asserting the work queue for %s: %w", s.Name, err)
+		}
+	}
+	for _, s := range seats {
+		h, held := holders[s.Name]
+		if !held {
+			// **The stream exists and the consumer does not, on purpose.** Work queues until a
+			// holder appears, so installing the module a week after something started sending to it
+			// flushes the backlog instead of having lost it.
+			continue
+		}
+		c, needed := HolderConsumerFor(h.Node, h.Module, s)
+		if !needed {
+			continue
+		}
+		if err := r.EnsureConsumer(c); err != nil {
+			return fmt.Errorf("asserting how %s on %s works %s: %w", h.Module, h.Node, s.Name, err)
+		}
+	}
+	return nil
+}
+
+// Holder is which module on which machine holds a seat.
+type Holder struct {
+	Node   string
+	Module string
+}

go/buscompose/readiness.go

@@ -0,0 +1,139 @@
+package buscompose
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// Whether a mesh could move its bus, and what is missing if not.
+//
+// **Asked before anything moves, and answerable from records alone.** The rollout moves every node at
+// once (novox/hq ADR 0116 step 5), so there is no partial state to inspect afterwards and no half to
+// roll back: either the mesh was ready or it was not. That makes a readiness question the most
+// valuable thing here — it costs nothing, it can be asked of a running mesh any number of times, and
+// every answer is a thing somebody can go and fix.
+//
+// Deliberately pure. It is handed what the mesh knows and returns sentences; nothing here connects to
+// anything, so it can be asked on a workstation about a mesh it has never reached.
+
+// Readiness is what the mesh knows about its own ability to move.
+type Readiness struct {
+	// TheBus is the address the mesh's own traffic would move to, empty when nothing names one.
+	TheBus string
+	// ServerStanding is whether a bus is reachable at that address, as somebody checked.
+	ServerStanding bool
+	// Holder is the node running the module that holds the bus seat, empty when nothing does.
+	Holder string
+	// AccountsComposed is whether that node has been sent the composed user list.
+	AccountsComposed bool
+	// Nodes is every machine the mesh knows.
+	Nodes []string
+	// Credentialled is which of them has a credential for the new bus.
+	Credentialled map[string]bool
+	// Modules is every assigned module, as `<node>/<module>`.
+	Modules []string
+	// ModuleCredentialled is which of those has one.
+	ModuleCredentialled map[string]bool
+}
+
+// NotReady is every reason this mesh cannot move its bus yet, in the order somebody would fix them.
+//
+// Empty means ready. **Each entry names one thing and what to do about it**, because a readiness check
+// that says "not ready" is a check nobody can act on — and this is read at the point where the next
+// step is irreversible.
+func NotReady(r Readiness) []string {
+	var why []string
+
+	if strings.TrimSpace(r.TheBus) == "" {
+		why = append(why, "nothing names the bus to move to: set "+NATSVar+" on the control node "+
+			"to the address the new server answers on")
+	}
+	if !r.ServerStanding {
+		why = append(why, "no bus is answering at that address. Step 2 of the change raises it beside "+
+			"the one the mesh is on, carrying nothing — assign the module that holds "+
+			"mesh-broker and push the machine that runs it")
+	}
+	if r.Holder == "" {
+		why = append(why, "no machine holds mesh-broker, so nothing would compose the bus's user "+
+			"list. Assign the module that claims it")
+	} else if !r.AccountsComposed {
+		why = append(why, fmt.Sprintf(
+			"%s holds mesh-broker and has not been sent the composed user list, so the bus would "+
+				"refuse every connection. `push %s`", r.Holder, r.Holder))
+	}
+
+	// A node with no credential cannot come back after the move, and a node that cannot come back is
+	// a machine the mesh has lost until somebody goes to it.
+	var missing []string
+	for _, n := range r.Nodes {
+		if !r.Credentialled[n] {
+			missing = append(missing, n)
+		}
+	}
+	sort.Strings(missing)
+	if len(missing) > 0 {
+		why = append(why, fmt.Sprintf(
+			"%d machine(s) have no credential for the new bus and would not come back: %s. Each needs "+
+				"one minted before the move, not after — after, there is no bus to ask over",
+			len(missing), strings.Join(missing, ", ")))
+	}
+
+	// A module without one keeps running and stops being reachable, which is a smaller fault and still
+	// one somebody should choose rather than discover.
+	var quiet []string
+	for _, m := range r.Modules {
+		if !r.ModuleCredentialled[m] {
+			quiet = append(quiet, m)
+		}
+	}
+	sort.Strings(quiet)
+	if len(quiet) > 0 {
+		why = append(why, fmt.Sprintf(
+			"%d module(s) have no credential for the new bus: %s. Each keeps serving and stops "+
+				"answering tools and hearing events until it is issued one",
+			len(quiet), strings.Join(quiet, ", ")))
+	}
+
+	return why
+}
+
+// WhatMoves is what the rollout would do, in order, for somebody reading before they commit.
+//
+// **Written out rather than summarised.** This is the one step with nothing to inspect afterwards, so
+// the last useful moment to disagree with it is while reading this.
+func WhatMoves(r Readiness) []string {
+	out := []string{
+		fmt.Sprintf("compose the bus's user list and send it to %s", holderOr(r.Holder)),
+		fmt.Sprintf("move this control plane to %s, and confirm it is heard", busOr(r.TheBus)),
+	}
+	nodes := append([]string(nil), r.Nodes...)
+	sort.Strings(nodes)
+	for _, n := range nodes {
+		out = append(out, fmt.Sprintf("move %s, and confirm it reports", n))
+	}
+	if len(r.Modules) > 0 {
+		out = append(out, fmt.Sprintf("move %d module runtime(s), and confirm each answers",
+			len(r.Modules)))
+	}
+	// **The old broker goes, and it goes last** (novox/hq ADR 0131). AMQP is not a provision, so once
+	// every machine reports on the new bus nothing of the mesh is left speaking to it, and its module
+	// is unassigned. Said as a step so nobody reads the move as leaving a second bus behind.
+	out = append(out, "then unassign the old broker's module: AMQP is not a provision (ADR 0131), and "+
+		"once every machine reports on the new bus nothing of the mesh speaks to it")
+	return out
+}
+
+func holderOr(node string) string {
+	if node == "" {
+		return "whichever machine holds mesh-broker"
+	}
+	return node
+}
+
+func busOr(address string) string {
+	if address == "" {
+		return "the new bus"
+	}
+	return address
+}

go/buscompose/sdk_membership.go

@@ -0,0 +1,38 @@
+package buscompose
+
+import (
+	"git.novox.be/novox/mesh-sdk/go/membership"
+	"git.novox.be/novox/mesh-sdk/go/process"
+)
+
+// The membership the mesh issues an assignment (novox/hq ADR 0160), its subject, its stream, the bare address and the
+// pin are mesh-sdk's, public so that a module's program outside this Go module, the route proxy, reads them too
+// (novox/hq ADR 0480 clause 4, issue 1633). This package keeps no second copy: what follows only names them where the
+// controller already did.
+type (
+	Membership   = membership.Membership
+	Served       = membership.Served
+	SeatServed   = membership.SeatServed
+	StateIssued  = membership.StateIssued
+	LogIssued    = membership.LogIssued
+	Worker       = membership.Worker
+	SeatTraffic  = membership.SeatTraffic
+	KindHeld     = membership.KindHeld
+	StreamIssued = membership.StreamIssued
+	HeardIssued  = membership.HeardIssued
+	WaitIssued   = membership.WaitIssued
+)
+
+// AssignmentsStream holds every assignment's membership, the newest per subject.
+const AssignmentsStream = membership.AssignmentsStream
+
+var (
+	// MembershipSubject is where an assignment's own membership is published.
+	MembershipSubject = membership.Subject
+	// CredentialIn reads the user and password out of a bus address, and the address without them.
+	CredentialIn = membership.CredentialIn
+	// BareAddress is a bus address with any credential stripped.
+	BareAddress = membership.BareAddress
+	// PinnedToFingerprint accepts exactly the certificate with this SHA-256 and no other.
+	PinnedToFingerprint = process.PinnedToFingerprint
+)

go/buscompose/seattraffic.go

@@ -0,0 +1,290 @@
+package buscompose
+
+import (
+	"fmt"
+	"sort"
+)
+
+// What a module may say and take on the seats it holds, uses and watches, beyond tools (novox/hq ADR
+// 0259 §3, to-be 46 §10).
+//
+// Three rules are added to the ones a seat always had, each a subject whose last token names who may
+// publish it, granted to that publisher alone — the way a node seat's event about a machine carries the
+// machine (ADR 0219):
+//
+//   - **A verb named by its caller** (`by-caller`). A user of the seat submits that accept, and hears that
+//     event, under its own module's name and no other: `accept.ask.<module>`, `event.decided.<module>`. The
+//     holder takes every caller's accept and says the event to any caller. So an ask's asker is a fact the
+//     server enforces, and a warrant reaches only the asker it is for.
+//   - **A kinded bench** (ADR 0234 §2). A holder claims one kind and takes its own kind's accepts, says its
+//     own kind's events and asks its own kind's proofs, and nothing of another kind; a user submits to any
+//     kind. Each kind has its own worker on the seat's queue, so a holder that is away keeps its work and
+//     holds up no other kind.
+//   - **A proof** (`proofs`): core request and reply on `mesh.seat.<seat>.proof.<verb>.<kind>`. No stream's
+//     subjects cover it, so what travels there — a code typed by the operator — is never persisted. A kinded
+//     holder asks with its own kind; the modules that watch the seat answer.
+//
+// And one read: **a holder's records**, a bucket the seat names, read by each user under its own name only
+// (`$KV.<bucket>.<module>.>`), so an asker reads the state of its own asks and no other asker's.
+
+// BuildAskMaxDeliver bounds the deliveries of a build seat's ask (issue 1907): mesh-sdk delivery.AskMaxDeliver, written
+// here as the broker mirrors the catalogue rather than importing it.
+const BuildAskMaxDeliver = 5
+
+// KindedBenches are the seats that may be kinded (ADR 0234 §2): making another is a decision, recorded.
+var KindedBenches = map[string]bool{"channel": true, "intake": true}
+
+// WorkerName is the worker a seat's holders pull from: one for the seat, or one per kind on a kinded bench.
+func WorkerName(seat, kind string) string {
+	if kind == "" {
+		return "SEAT_" + upperSnake(seat) + "_worker"
+	}
+	return "SEAT_" + upperSnake(seat) + "_" + upperSnake(kind) + "_worker"
+}
+
+func namesVerb(list []string, s string) bool {
+	for _, x := range list {
+		if x == s {
+			return true
+		}
+	}
+	return false
+}
+
+// SeatTrafficOf derives one module's seat traffic from the seats it holds, uses and watches. Only seats
+// carrying one of the rules above are read: every other seat is composed as it always was.
+func SeatTrafficOf(module string, holds, uses, watches []Seat) SeatTraffic {
+	var t SeatTraffic
+	for _, s := range holds {
+		if !s.isNewTraffic() {
+			continue
+		}
+		kind := ""
+		if s.Kinded {
+			kind = s.Kind
+			if kind == "" || !safeSubject.MatchString(kind) {
+				// A kinded claim without a usable kind is refused at registration; here it is granted
+				// nothing, which is the same answer at the last place it could be asked.
+				continue
+			}
+		}
+		if len(s.Accepts) > 0 && s.PulledByKind {
+			// One worker per accepted kind, which every holder pulls in the order of Accepts (ADR 0525 §4, ADR 0536 §4):
+			// `SEAT_<SEAT>_<KIND>_worker`, filtered to `accept.<kind>` (mesh-sdk delivery.AskWorker).
+			for _, a := range s.Accepts {
+				t.Workers = append(t.Workers, Worker{Stream: seatStreamName(s.Name), Consumer: WorkerName(s.Name, a),
+					Filter: "mesh.seat." + s.Name + ".accept." + a})
+			}
+		} else if len(s.Accepts) > 0 {
+			stream := seatStreamName(s.Name)
+			filter := "mesh.seat." + s.Name + ".accept.>"
+			if kind != "" {
+				filter = "mesh.seat." + s.Name + ".accept.*." + kind
+			}
+			t.Workers = append(t.Workers, Worker{Stream: stream, Consumer: WorkerName(s.Name, kind), Filter: filter})
+		}
+		for _, a := range s.Accepts {
+			switch {
+			case kind != "":
+				t.Subscribe = append(t.Subscribe, seatSubject(s, "accept", a+"."+kind))
+			case namesVerb(s.ByCaller, a):
+				t.Subscribe = append(t.Subscribe, seatSubject(s, "accept", a+".*"))
+			}
+		}
+		for _, e := range s.Emits {
+			switch {
+			case kind != "":
+				t.Publish = append(t.Publish, seatSubject(s, "event", e+"."+kind))
+			case namesVerb(s.ByCaller, e):
+				t.Publish = append(t.Publish, seatSubject(s, "event", e+".*"))
+			}
+		}
+		if kind != "" {
+			for _, v := range s.Proofs {
+				t.Publish = append(t.Publish, seatSubject(s, "proof", v+"."+kind))
+			}
+		}
+	}
+	for _, s := range uses {
+		if !s.isNewTraffic() {
+			continue
+		}
+		for _, a := range s.Accepts {
+			switch {
+			case namesVerb(s.ByCaller, a):
+				t.Publish = append(t.Publish, seatSubject(s, "accept", a+"."+module))
+			case s.Kinded && module == s.DeclaredBy:
+				// Work for a kind is put on its queue by the bench's own router, and by no other user.
+				t.Publish = append(t.Publish, seatSubject(s, "accept", a+".*"))
+			}
+		}
+		for _, e := range s.Emits {
+			if namesVerb(s.ByCaller, e) {
+				t.Subscribe = append(t.Subscribe, seatSubject(s, "event", e+"."+module))
+			}
+		}
+		for _, b := range s.Records {
+			if !safeSubject.MatchString(b) {
+				continue
+			}
+			t.Records = append(t.Records, "$JS.API.DIRECT.GET.KV_"+b+".$KV."+b+"."+module+".>")
+		}
+	}
+	for _, w := range watches {
+		if w.Kinded {
+			for _, e := range w.Emits {
+				t.Subscribe = append(t.Subscribe, seatSubject(w, "event", e+".*"))
+			}
+			if module == w.DeclaredBy {
+				// A code is answered by the bench's own router, and by no other watcher.
+				for _, v := range w.Proofs {
+					t.Answers = append(t.Answers, seatSubject(w, "proof", v+".*"))
+				}
+			}
+		}
+	}
+	t.Publish = unique(t.Publish)
+	t.Subscribe = unique(t.Subscribe)
+	t.Answers = unique(t.Answers)
+	t.Records = unique(t.Records)
+	sort.Slice(t.Workers, func(i, j int) bool { return t.Workers[i].Consumer < t.Workers[j].Consumer })
+	return t
+}
+
+// seatTrafficGrants is the bus permissions seat traffic needs: the subjects themselves, and the JetStream API a
+// worker is pulled and acknowledged through and a record is read through.
+func seatTrafficGrants(t SeatTraffic) (pub, sub []string) {
+	pub = append(pub, t.Publish...)
+	sub = append(sub, t.Subscribe...)
+	sub = append(sub, t.Answers...)
+	for _, w := range t.Workers {
+		pub = append(pub,
+			"$JS.API.CONSUMER.INFO."+w.Stream+"."+w.Consumer,
+			"$JS.API.CONSUMER.MSG.NEXT."+w.Stream+"."+w.Consumer,
+			"$JS.ACK."+w.Stream+"."+w.Consumer+".>")
+	}
+	pub = append(pub, t.Records...)
+	return pub, sub
+}
+
+// isNewTraffic says whether a seat carries any of the rules above, so a seat that carries none is
+// composed exactly as before them.
+func (s Seat) isNewTraffic() bool {
+	return s.Kinded || len(s.ByCaller) > 0 || len(s.Proofs) > 0 || len(s.Records) > 0 || s.PulledByKind
+}
+
+// plainVerbs is a seat's accepts or emits with those the rules above compose taken out: a verb named by
+// its caller and every verb of a kinded bench are composed by SeatTrafficOf and nowhere else.
+func plainVerbs(s Seat, verbs []string) []string {
+	if s.Kinded {
+		return nil
+	}
+	var out []string
+	for _, v := range verbs {
+		if !namesVerb(s.ByCaller, v) {
+			out = append(out, v)
+		}
+	}
+	return out
+}
+
+// SeatTrafficObjects is the work queues and workers the seat traffic of every composed user implies
+// (novox/hq ADR 0259 §3): a queue for each seat a holder takes work from, and each holder's worker on it —
+// one per kind on a kinded bench, filtered to that kind, so the kinds never take each other's work. Only
+// seats carrying the rules above; the mesh's own seats' queues are RaiseSeats'.
+func SeatTrafficObjects(users []Principal) ([]Stream, []Consumer) {
+	streams := map[string]Stream{}
+	consumers := map[string]Consumer{}
+	add := func(module string, holds []Seat) {
+		for _, w := range SeatTrafficOf(module, holds, nil, nil).Workers {
+			seat, byKind := "", false
+			for _, s := range holds {
+				if seatStreamName(s.Name) == w.Stream {
+					seat, byKind = s.Name, s.PulledByKind
+				}
+			}
+			streams[w.Stream] = Stream{
+				Name:      w.Stream,
+				Subjects:  []string{"mesh.seat." + seat + ".accept.>"},
+				Retention: RetentionWorkQueue,
+				MaxAge:    7 * 24 * 60 * 60,
+				Why:       "work submitted to the " + seat + " seat; its holders take it, each kind its own, and it queues while nobody does",
+			}
+			c := Consumer{
+				Name:           w.Consumer,
+				Stream:         w.Stream,
+				Filters:        []string{w.Filter},
+				AckWaitSeconds: 60,
+				// No bound on redelivery: a channel away for a day keeps its work, offered again later and
+				// later by its holder's runtime (novox/hq ADR 0259; the correctness review of 2026-10-08).
+				MaxDeliver: 0,
+				Why: module + " holds " + seat + "; it pulls one ask at a time and acknowledges once it has " +
+					"recorded it, so a crash redelivers rather than loses",
+			}
+			if byKind {
+				// A build seat's ask is offered a bounded number of times (issue 1907): the holder that takes it past
+				// mesh-sdk delivery.AskRuns ends it failed saying it is poison, and the bound stops a run that kills
+				// every node it reaches even when that holder dies too.
+				c.MaxDeliver = BuildAskMaxDeliver
+				c.Why = module + " holds " + seat + "; each holder pulls an ask when it has a free slot, and an ask that " +
+					"no run ends is offered at most " + fmt.Sprint(BuildAskMaxDeliver) + " times, its step failed as poison"
+			}
+			consumers[w.Consumer] = c
+		}
+	}
+	for _, p := range users {
+		switch p.Kind {
+		case KindModule:
+			add(p.Module, p.Holds)
+		case KindNodeTools:
+			for _, d := range p.Carries {
+				add(d.Module, d.Holds)
+			}
+		}
+	}
+	var ss []Stream
+	for _, s := range streams {
+		ss = append(ss, s)
+	}
+	sort.Slice(ss, func(i, j int) bool { return ss[i].Name < ss[j].Name })
+	var cs []Consumer
+	for _, c := range consumers {
+		cs = append(cs, c)
+	}
+	sort.Slice(cs, func(i, j int) bool { return cs[i].Name < cs[j].Name })
+	return ss, cs
+}
+
+// trustedTraffic is why a module's seat traffic is the trusted holder's (novox/hq ADR 0259 §8), or "": it
+// says a seat's event to one caller each (a warrant), or holds a kind of a kinded bench that proves its sender.
+func trustedTraffic(d Declared) string {
+	for _, s := range d.Holds {
+		for _, e := range s.Emits {
+			if namesVerb(s.ByCaller, e) {
+				return "it says " + s.Name + "'s " + e + " to one caller each"
+			}
+		}
+		if s.Kinded && namesVerb(s.Capabilities, "verified-sender") {
+			return "it holds " + s.Name + " of kind " + s.Kind + ", which proves its sender"
+		}
+	}
+	return ""
+}
+
+// TrafficQueues is the work queue of every seat naming its caller or its kind that accepts work, held or not
+// (novox/hq ADR 0259 §3): what is submitted before a holder is assigned waits for it.
+func TrafficQueues(seats []Seat) []Stream {
+	var out []Stream
+	seen := map[string]bool{}
+	for _, s := range seats {
+		if len(s.Accepts) == 0 || !s.isNewTraffic() || seen[s.Name] {
+			continue
+		}
+		seen[s.Name] = true
+		out = append(out, Stream{Name: seatStreamName(s.Name), Subjects: []string{"mesh.seat." + s.Name + ".accept.>"},
+			Retention: RetentionWorkQueue, MaxAge: 7 * 24 * 60 * 60,
+			Why: "work submitted to the " + s.Name + " seat; its holders take it, each kind its own, and it queues while nobody does"})
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
+	return out
+}

go/buscompose/state.go

@@ -0,0 +1,265 @@
+package buscompose
+
+import (
+	"fmt"
+	"git.novox.be/novox/mesh-sdk/go/announce"
+	"sort"
+	"strings"
+	"time"
+)
+
+// A module's state on the bus (novox/hq ADR 0201, design 32 §4, design 25 §3).
+//
+// A module names the state it keeps (`state`) and the state of others it reads (`reads`), and each
+// is a key-value bucket: the server's own last-per-subject stream with direct reads, delete markers
+// and watches, which is the state relationship the mesh already uses for declarations, opened to
+// modules. The controller creates every bucket from the catalogue — from registration, like a
+// seat's stream, so a reader may watch before the owner runs anywhere — and no module can.
+//
+// Pure, like everything else in this package that decides what the bus holds; jetstream.go is the
+// part that asks a server.
+
+// The mesh's caps on a bucket, the same for every module: a value is a piece of state, not a file,
+// and a bucket that grew without bound would be one module filling the bus's disk for everyone.
+const (
+	StateMaxValueBytes = 256 * 1024
+	StateMaxBytes      = 64 * 1024 * 1024
+)
+
+// A Bucket is one module's declared state as the bus holds it.
+type Bucket struct {
+	Module string
+	Name   string
+	// History is how many values a key keeps; zero is one.
+	History int
+	// TTLSeconds is how long a value lives; zero is until replaced or deleted.
+	TTLSeconds int
+	// PerMachine says each machine's instance writes only the key named for its machine (novox/hq ADR
+	// 0260), and is granted that key and no other.
+	PerMachine bool
+	// KeyTTL says the bucket allows a time to live per key (novox/hq ADR 0433 §1): its owner writes each key with its
+	// own, and the server writes a delete marker, kept KeyTTLMarkerTTL, when it ends.
+	KeyTTL bool
+}
+
+// KeyTTLMarkerTTL is how long the marker an expired key leaves is kept: long enough for a watcher to hear it.
+const KeyTTLMarkerTTL = time.Minute
+
+// BucketName is the bucket a module's state lives in: the module and the local name joined by an
+// underscore, which neither may contain, so two modules can never derive one bucket.
+func BucketName(module, name string) string { return module + "_" + name }
+
+// Bucket is this bucket's name on the bus.
+func (b Bucket) Bucket() string { return BucketName(b.Module, b.Name) }
+
+// Why is carried into the server's description of the bucket, so somebody reading the server's
+// own state finds whose it is and why it is kept.
+func (b Bucket) Why() string {
+	return fmt.Sprintf("%s's state %q (novox/hq ADR 0201): its current value per key, written by %s, "+
+		"read by whatever declares it reads it; kept when %s is unassigned, because it is data",
+		b.Module, b.Name, b.Module, b.Module)
+}
+
+// bucketOfRead is the bucket a read names, `<module>.<name>`, or false when it names none.
+func bucketOfRead(read string) (string, bool) {
+	at := strings.LastIndex(read, ".")
+	if at <= 0 || at == len(read)-1 {
+		return "", false
+	}
+	module, name := read[:at], read[at+1:]
+	if !safeSubject.MatchString(module) || !safeSubject.MatchString(name) {
+		return "", false
+	}
+	return BucketName(module, name), true
+}
+
+// readGrants is what reaching a bucket's keys needs: binding to it, a direct get, an ordered consumer for listing and
+// watching and the deletion of that consumer and its flow control. key is one key's subject tail, a pattern such as
+// `one.>` for a prefix of keys, or empty for every key. The bucket is made with AllowDirect, so a get is the direct get
+// and never the stream's message get.
+func readGrants(bucket, key string) []string {
+	stream := "KV_" + bucket
+	out := []string{"$JS.API.STREAM.INFO." + stream}
+	if key == "" {
+		out = append(out,
+			"$JS.API.DIRECT.GET."+stream+".>",
+			"$JS.API.CONSUMER.CREATE."+stream+".>")
+	} else {
+		out = append(out,
+			"$JS.API.DIRECT.GET."+stream+".$KV."+bucket+"."+key,
+			"$JS.API.CONSUMER.CREATE."+stream+".*.$KV."+bucket+"."+key)
+	}
+	return append(out,
+		"$JS.API.CONSUMER.DELETE."+stream+".>",
+		"$JS.FC."+stream+".>")
+}
+
+// NodeKeysGrants is what a node's node-engine is granted of a bucket it writes by node, `<node>.>` and no other key
+// (novox/hq ADR 0429 §1: each key one writer, enforced by credentials): the writes of those keys and what a get,
+// create, update and watch of them need. The node name is checked as every subject token is.
+func NodeKeysGrants(bucket, node string) ([]string, error) {
+	if !safeSubject.MatchString(node) {
+		return nil, fmt.Errorf("%q cannot be part of a subject: a permission is a subject pattern, and this would widen it", node)
+	}
+	return append([]string{"$KV." + bucket + "." + node + ".>"}, readGrants(bucket, node+".>")...), nil
+}
+
+// stateGrants is what a principal publishes to reach the state its modules keep and read: for every
+// bucket, binding to it, reading a key directly, and an ordered consumer for listing and watching,
+// created and deleted on the bucket's own stream, with its flow control answered; for a bucket an
+// owner keeps, writing under the bucket's own subjects too.
+//
+// **Measured against a running server, 2026-10-04** (novox/hq research 024), and each one is there
+// because leaving it out failed: without STREAM.INFO nothing binds; without DIRECT.GET nothing is
+// read; without CONSUMER.CREATE no key is listed and nothing is watched; without CONSUMER.DELETE a
+// watch cannot be stopped and lingers on the server. A write outside these is refused by the server
+// — and reaches the writer as a timeout, not a refusal, which is why the runtime refuses first.
+//
+// **One key, where the state is per machine** (novox/hq ADR 0260). The owner's instance on a machine
+// writes and reads the key named for that machine, and a holder granted a read for its machine reads
+// that key: a direct get of the key's own subject, and a consumer whose filter is that subject — the
+// server's create-with-filter form, which a client uses for a watch of one key and which the server
+// holds to the filter it names. What cannot be narrowed by key: binding (STREAM.INFO), deleting a
+// consumer (named at random by the client) and flow control; none of them reads or writes a value.
+func stateGrants(a stateAccess) []string {
+	var out []string
+	read := func(bucket, key string) { out = append(out, readGrants(bucket, key)...) }
+	machineKey := ""
+	if safeSubject.MatchString(a.Node) {
+		machineKey = a.Node
+	}
+	perMachine := map[string]bool{}
+	for _, n := range a.PerMachine {
+		perMachine[n] = true
+	}
+	for _, name := range a.Keeps {
+		if !safeSubject.MatchString(name) {
+			continue
+		}
+		bucket := BucketName(a.Module, name)
+		if perMachine[name] {
+			if machineKey == "" {
+				continue // a machine with no usable name reaches none of it
+			}
+			read(bucket, machineKey)
+			out = append(out, "$KV."+bucket+"."+machineKey)
+			continue
+		}
+		read(bucket, "")
+		out = append(out, "$KV."+bucket+".>")
+	}
+	// **And it says what it keeps** (novox/hq ADR 0495 clause 2, issue 1790): a module keeping state announces it on its
+	// own event subject, from its code; refused, its readers are read as before.
+	if len(a.Keeps) > 0 && safeSubject.MatchString(a.Module) {
+		out = append(out, announce.Subject(a.Module))
+	}
+	for _, r := range a.Reads {
+		if bucket, ok := bucketOfRead(r); ok {
+			read(bucket, "")
+		}
+	}
+	for _, k := range a.KeyedReads {
+		if bucket, ok := bucketOfRead(k.Read); ok && safeSubject.MatchString(k.Key) {
+			read(bucket, k.Key)
+		}
+	}
+	return out
+}
+
+// KeyedRead is one key of another module's state a principal reads, and no other key of it.
+type KeyedRead struct {
+	Read string `json:"read"`
+	Key  string `json:"key"`
+}
+
+// stateAccess is what one principal may do with state: the module's own buckets (some per machine),
+// what it reads whole, and what it reads for its machine's key alone.
+type stateAccess struct {
+	Module, Node      string
+	Keeps, PerMachine []string
+	Reads             []string
+	KeyedReads        []KeyedRead
+}
+
+// perMachineNames is the local names of a module's buckets keyed by machine.
+func perMachineNames(buckets []Bucket) []string {
+	var out []string
+	for _, b := range buckets {
+		if b.PerMachine {
+			out = append(out, b.Name)
+		}
+	}
+	return out
+}
+
+// stateIssuedFor is every bucket a module's code may reach on a machine, as its membership lists them.
+func stateIssuedFor(d Declared, node string) []StateIssued {
+	var out []StateIssued
+	for _, b := range d.State {
+		issued := StateIssued{Name: b.Name, Bucket: BucketName(d.Module, b.Name), Writes: true}
+		if b.PerMachine {
+			issued.Key = node
+		}
+		out = append(out, issued)
+	}
+	for _, r := range d.Reads {
+		if bucket, ok := bucketOfRead(r); ok {
+			out = append(out, StateIssued{Name: r, Bucket: bucket})
+		}
+	}
+	for _, k := range d.KeyedReads {
+		if bucket, ok := bucketOfRead(k.Read); ok {
+			out = append(out, StateIssued{Name: k.Read, Bucket: bucket, Key: k.Key})
+		}
+	}
+	return out
+}
+
+// stateNames is the local names of a module's own buckets.
+func stateNames(buckets []Bucket) []string {
+	out := make([]string, 0, len(buckets))
+	for _, b := range buckets {
+		out = append(out, b.Name)
+	}
+	return out
+}
+
+// A BucketAsserter is the part of a JetStream connection bucket assertion needs.
+type BucketAsserter interface {
+	// EnsureBucket creates the bucket if absent and brings its options to match if present, never
+	// discarding what it holds.
+	EnsureBucket(b Bucket) error
+	// BucketNames is every key-value bucket on the server.
+	BucketNames() ([]string, error)
+}
+
+// RaiseBuckets asserts every declared bucket and answers the buckets on the server that nothing
+// declares any more.
+//
+// **Those are reported, never removed** (novox/hq ADR 0201, ADR 0030): what a module stored is
+// data, and a manifest edited, a module renamed or a catalogue entry dropped is an ordinary day's
+// work that must not take data with it. Removing one is a person's act.
+func RaiseBuckets(a BucketAsserter, buckets []Bucket) (undeclared []string, err error) {
+	sorted := append([]Bucket(nil), buckets...)
+	sort.Slice(sorted, func(i, j int) bool { return sorted[i].Bucket() < sorted[j].Bucket() })
+	declared := map[string]bool{}
+	for _, b := range sorted {
+		if err := a.EnsureBucket(b); err != nil {
+			return nil, fmt.Errorf("asserting %s's state %q: %w", b.Module, b.Name, err)
+		}
+		declared[b.Bucket()] = true
+	}
+	names, err := a.BucketNames()
+	if err != nil {
+		return nil, fmt.Errorf("listing the bus's state: %w", err)
+	}
+	for _, n := range names {
+		// A seat's cancelled set is the mesh's own (novox/hq ADR 0219), not a module's state; so are
+		// the controller's own buckets (novox/hq to-be 45 §1).
+		if !declared[n] && !IsCancelledSet(n) && !IsControllerBucket(n) {
+			undeclared = append(undeclared, n)
+		}
+	}
+	sort.Strings(undeclared)
+	return undeclared, nil
+}

go/buscompose/streams.go

@@ -0,0 +1,612 @@
+package buscompose
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// The mesh's own streams.
+//
+// **These and no more** (novox/hq ADR 0116 task 1.4, as revised by ADR 0118; the two that keep what a
+// consumer gave up on added for issue 330). An earlier
+// reading had the controller create *every* stream at genesis, from a fixed set. That is only the
+// mesh's own half: a seat's streams are created when the module declaring it is registered, and a
+// module's durable consumers when it is assigned — neither of which has happened at genesis. What
+// is here is the foundation, which exists before any module does.
+//
+// The controller is the only writer of stream definitions (design 25 §3). A module declares
+// nothing about them and cannot reach the JetStream API to make one.
+
+// Retention is how a stream decides what to keep, which is the whole of what distinguishes the
+// mesh's four relationships on the wire (design 29 §4).
+type Retention string
+
+const (
+	// RetentionWorkQueue: a message is removed once a consumer acknowledges it. Exactly one
+	// worker does the work, and a worker that dies has its message redelivered.
+	RetentionWorkQueue Retention = "workqueue"
+	// RetentionLastPerSubject: only the newest message on each subject survives. This is the
+	// state shape — a node that was away gets exactly the current declaration and nothing older.
+	RetentionLastPerSubject Retention = "last_per_subject"
+	// RetentionLimits: kept until it ages or the stream fills. Events, where a subscriber that
+	// was down catches up and nobody is obliged to act.
+	RetentionLimits Retention = "limits"
+)
+
+// A Stream is one of the mesh's own, as the controller asserts it.
+type Stream struct {
+	Name      string
+	Subjects  []string
+	Retention Retention
+	// MaxAge in seconds, zero for unbounded. Per stream — JetStream has no per-subject age,
+	// which is why differing retention between modules would mean a stream each.
+	MaxAge int
+	// MaxMsgsPerSubject caps each subject independently, so one noisy emitter cannot push
+	// another's events out of a shared stream. Verified: with a cap of 3, ten messages on one
+	// subject and one on another leave four in the stream, not three.
+	MaxMsgsPerSubject int
+	// Why is carried into the assertion so an operator reading the server's own state finds the
+	// reason there, rather than only in a repository they may not have.
+	Why string
+	// Direct lets a client read a subject's last message without a consumer, which is how a
+	// runtime reads its own membership with no JetStream API beyond one request (ADR 0160).
+	Direct bool
+	// MaxBytes bounds the stream's size, zero for unbounded. With DiscardNew a full stream refuses
+	// what comes next rather than dropping what it holds: the publisher is told, and says so.
+	MaxBytes   int64
+	DiscardNew bool
+	// DuplicatesSeconds is the window in which a message id published twice is kept once; zero for the
+	// server's default (two minutes).
+	DuplicatesSeconds int
+	// AllowMsgTTL lets a message carry a time to live of its own (`Nats-TTL`), for what must not outlive the
+	// stream it came from (novox/hq ADR 0376 §3, §5).
+	AllowMsgTTL bool
+	// Restricted marks a module's stream restricted by a grant (novox/hq ADR 0363 §4), in the stream's own
+	// metadata, so whoever keeps one of its messages reads it from the bus (ADR 0376 §3).
+	Restricted bool
+	// WorkQueue marks a module stream declared retention: work-queue (novox/hq ADR 0436 §6), in the
+	// stream's own metadata, so a dead letter kept from it is read as drop-only from the bus, by the
+	// declaration and not by the bus's work-queue retention alone — which SEAT_* and other mesh-internal
+	// streams share without being one of ADR 0436's, and whose dead letters are still delivered again
+	// (ADR 0264 §4).
+	WorkQueue bool
+}
+
+// RestrictedMetadata is the key a restricted stream's metadata says it under.
+const RestrictedMetadata = "mesh-restricted"
+
+// WorkQueueMetadata is the key a module stream declared retention: work-queue (novox/hq ADR 0436 §6) says
+// it under: never set by a mesh-internal work-queue stream (a seat's, a check's), only by Stream.WorkQueue.
+const WorkQueueMetadata = "mesh-work-queue"
+
+// What a durable consumer gave up on is kept (novox/hq issue 330, design 25 §3).
+//
+// **The server says it and keeps it; the controller copies it.** A consumer that handed a message over
+// as often as it may stops offering it and publishes `$JS.EVENT.ADVISORY.CONSUMER.MAX_DELIVERIES` with
+// the stream and the message's sequence. DeadLetterNoticesStream captures those advisories as the
+// server publishes them, so one said while no controller listens is still there when one starts. The
+// controller's consumer on it fetches the given-up message by its sequence, while the source stream
+// still holds it, and keeps a copy in DeadLettersStream under DeadLetterSubject, with the consumer,
+// the subject, how often it was handed over and when it was given up. It stays there until a person
+// delivers it again or drops it, with why; a condition is open for as long as it does.
+const (
+	DeadLetterNoticesStream = "DEAD_LETTER_NOTICES"
+	DeadLettersStream       = "DEAD_LETTERS"
+	// MaxDeliveriesAdvisories is the subject the server says a given-up message on.
+	MaxDeliveriesAdvisories = "$JS.EVENT.ADVISORY.CONSUMER.MAX_DELIVERIES.>"
+	deadLetterPrefix        = "mesh.events.dead."
+	againPrefix             = "mesh.again."
+	// DeadLettersBytes bounds the kept copies. Full, the stream refuses the next copy, which is said
+	// as the consumer's condition; it never drops one it holds.
+	DeadLettersBytes = 256 << 20
+)
+
+// DeadLetterSubject is where a message one consumer gave up on is kept: `mesh.events.dead.<stream>.<consumer>`.
+func DeadLetterSubject(stream, consumer string) string {
+	return deadLetterPrefix + stream + "." + consumer
+}
+
+// DeadLetterOf is the stream and consumer a kept message's subject names; false for any other subject.
+func DeadLetterOf(subject string) (stream, consumer string, ok bool) {
+	rest, found := strings.CutPrefix(subject, deadLetterPrefix)
+	if !found {
+		return "", "", false
+	}
+	stream, consumer, ok = strings.Cut(rest, ".")
+	return stream, consumer, ok && stream != "" && consumer != "" && !strings.Contains(consumer, ".")
+}
+
+// AgainSubject is where an event given up on is delivered again to the one consumer that gave it up,
+// and to nobody else: `mesh.again.<consumer>.` and the original subject without its `mesh.`. Every
+// consumer on EVENTS filters its own (AgainFilter), and a module's runtime reads the event's key from
+// the tokens around `.event.`, so the handler sees the same key it saw the first time.
+func AgainSubject(consumer, original string) string {
+	return againPrefix + consumer + "." + strings.TrimPrefix(original, "mesh.")
+}
+
+// AgainFilter is the one consumer's share of the subjects events are delivered again on.
+func AgainFilter(consumer string) string { return againPrefix + consumer + ".>" }
+
+// OriginalOfAgain is the subject an event delivered again was first published on; false for a subject
+// that is not one delivered again.
+func OriginalOfAgain(subject string) (string, bool) {
+	rest, found := strings.CutPrefix(subject, againPrefix)
+	if !found {
+		return "", false
+	}
+	_, original, ok := strings.Cut(rest, ".")
+	if !ok || original == "" {
+		return "", false
+	}
+	return "mesh." + original, true
+}
+
+// MeshStreams is the foundation set, in the order a person reads it.
+//
+// **CONTROL names its subjects rather than taking `mesh.control.>`**, because heartbeats live
+// under that prefix and must not be persisted: a lost heartbeat is the next heartbeat, and a
+// stream of them is a stream of the least valuable messages the mesh sends, competing for the
+// same retention as the ones that matter.
+//
+// **EVENTS filters on the `event` token**, which is the reason that token exists. A module's
+// namespace carries both its events and its tool calls; a filter of `mesh.mod.*.>` would persist
+// every tool invocation in the mesh, and a tool call must never be persisted (design 25 §3 keeps
+// tools on core NATS, where a lost call is a timeout the caller already handles).
+func MeshStreams() []Stream {
+	return []Stream{
+		{
+			Name: "CONTROL",
+			// A build's outcome is no longer here: it is the build-machine seat's own event, so one
+			// publish reaches whoever asked, the controller and the catalogue (novox/hq ADR 0121).
+			Subjects:  []string{"mesh.control.*.report", "mesh.control.enrol"},
+			Retention: RetentionWorkQueue,
+			Why: "the store-window guarantee (ADR 0083): the controller naks with a delay while its " +
+				"store is away and the message is redelivered; nothing is dropped",
+		},
+		{
+			Name:      "NODES",
+			Subjects:  []string{"mesh.node.*.declare"},
+			Retention: RetentionLastPerSubject,
+			Why: "one declaration per node, always the newest; a node that sees sequence n refuses " +
+				"n-1 by construction (issue 107)",
+		},
+		{
+			Name:      AssignmentsStream,
+			Subjects:  []string{"mesh.assignment.*.*"},
+			Retention: RetentionLastPerSubject,
+			Direct:    true,
+			Why: "one membership per assignment, always the newest: what the mesh issued this module " +
+				"on this machine to serve and to reach (ADR 0160); read directly by the runtime it is for",
+		},
+		{
+			Name: EventsStream,
+			// A seat's own events ride here too: they are 1:many like any event, and the
+			// `event` token keeps them clear of both the seat's work queue (`accept`) and its
+			// tools (`tool`), which must not be persisted.
+			// And an event given up on, delivered again to the one consumer that gave it up
+			// (novox/hq issue 330): under `mesh.again.<consumer>.`, which only that consumer filters.
+			Subjects:          []string{"mesh.mod.*.event.>", "mesh.seat.*.event.>", againPrefix + ">"},
+			Retention:         RetentionLimits,
+			MaxAge:            7 * 24 * 60 * 60,
+			MaxMsgsPerSubject: 10000,
+			// A restricted dead letter delivered again keeps what is left of its stream's age (ADR 0376 §5).
+			AllowMsgTTL: true,
+			Why: "a subscriber that was down catches up; tool traffic under the same prefix is " +
+				"excluded by the event token; per-subject caps keep a noisy emitter from " +
+				"evicting a quiet one without splitting the stream",
+		},
+		{
+			Name:      DeadLetterNoticesStream,
+			Subjects:  []string{MaxDeliveriesAdvisories},
+			Retention: RetentionWorkQueue,
+			MaxAge:    7 * 24 * 60 * 60,
+			Why: "the server's word that a consumer gave up on a message, kept until the controller has " +
+				"copied the message into DEAD_LETTERS (novox/hq issue 330); a week, the longest the source " +
+				"streams keep what they are about",
+		},
+		{
+			Name:              DeadLettersStream,
+			Subjects:          []string{deadLetterPrefix + ">"},
+			Retention:         RetentionLimits,
+			MaxBytes:          DeadLettersBytes,
+			DiscardNew:        true,
+			DuplicatesSeconds: 24 * 60 * 60,
+			AllowMsgTTL:       true,
+			Why: "every message a consumer gave up on, with its consumer, subject, deliveries and when, kept " +
+				"until a person delivers it again or drops it with why (novox/hq issue 330); no age but a restricted " +
+				"stream's message, which ages out with its stream (ADR 0376), and full it refuses the next copy " +
+				"rather than drop one it holds",
+		},
+		{
+			Name:      ProvAppliedStream,
+			Subjects:  []string{ProvAppliedSubjects},
+			Retention: RetentionLastPerSubject,
+			Direct:    true,
+			MaxAge:    7 * 24 * 60 * 60,
+			Why: "each machine's provisioner client's newest word on each module's files, applied, waiting or " +
+				"failed with the reason (novox/hq ADR 0349 §4): what a walk's end and a gate wait for (ADR 0362, " +
+				"ADR 0349 §15), read by subject; a week, as the events are",
+		},
+	}
+}
+
+// ProvAppliedStream keeps what each machine's provisioner client last said of each module's files, newest per
+// subject (novox/hq ADR 0349 §4, ADR 0362, design 57 P6): `prov.applied.<node>.<module>` lies outside `mesh.*`, so
+// no other stream captures it, and a report said while no controller listened is still there to be read.
+const ProvAppliedStream = "PROV_APPLIED"
+
+// ProvAppliedSubjects is every machine's client's reports: `prov.applied.<node>.<module>`, a module's name dots and
+// all (ProvisionerAppliedSubject).
+const ProvAppliedSubjects = "prov.applied.>"
+
+// eventsTheControllerFollows are the events the controller's events consumer takes: all it follows but the forge's
+// merges, which the merges consumer takes (MergesConsumerName).
+func eventsTheControllerFollows() []string {
+	var out []string
+	for _, subject := range ControllerFollows {
+		if subject != ControllerFollows[3] {
+			out = append(out, subject)
+		}
+	}
+	return append(out, ControllerHears...)
+}
+
+// DeliverSubjectFor is where a push consumer's messages land.
+//
+// **Per consumer, which means per stream as well as per name** (novox/hq 04-ISSUES/146). A push
+// consumer delivers onto an ordinary subject, and everything subscribed to that subject gets a
+// copy. The controller holds a consumer called `controller` on CONTROL and another called
+// `controller` on EVENTS; while both were given `_DELIVER.controller`, the one process holding
+// both subscriptions acted on every message twice — a joining machine was enrolled twice from one
+// request, and the second enrolment minted a credential that replaced the one the machine had just
+// been handed. Every report and every followed event doubled the same way, silently: nothing is
+// redelivered, no count is wrong, the work simply happens twice.
+//
+// The stream belongs in it because the pair is what identifies a consumer — the server scopes a
+// durable's name to its stream, and this subject was the one place that scoping was dropped. It
+// stays inside what a controller may already subscribe (`_DELIVER.controller.>`).
+func DeliverSubjectFor(c Consumer) string {
+	if c.DeliverSubject != "" {
+		return c.DeliverSubject
+	}
+	return "_DELIVER." + c.Name + "." + c.Stream
+}
+
+// An Asserter is the part of a JetStream connection stream assertion needs. Narrow on purpose: it
+// keeps this testable without a server, and keeps the client library out of everything that only
+// wants to know what the streams are.
+type Asserter interface {
+	// EnsureStream creates the stream if absent and updates it to match if present. It must be
+	// idempotent: the controller asserts on every start, not only at genesis.
+	EnsureStream(s Stream) error
+}
+
+// AssertMeshStreams brings the foundation set into being, in order, and says which one failed
+// rather than that something did.
+//
+// Asserted on every start rather than created once at genesis, because a stream that was deleted,
+// or a mesh raised from a restored backup, must converge rather than run without the guarantee
+// its messages assume. Idempotence is the whole requirement.
+func AssertMeshStreams(a Asserter) error {
+	for _, s := range MeshStreams() {
+		if err := a.EnsureStream(s); err != nil {
+			return fmt.Errorf("asserting stream %s: %w", s.Name, err)
+		}
+	}
+	return nil
+}
+
+// Overlaps reports subject filters claimed by more than one stream.
+//
+// **Corrected against the server**: an earlier version of this comment said NATS accepts
+// overlapping streams and stores the message twice. It does not — it refuses the second stream
+// with "subjects overlap with an existing stream" (verified against nats-server 2.10). The check
+// still earns its place, for a different reason: the server's refusal arrives when the controller
+// is applying, naming one stream, at a moment when the mesh is half-configured. This one arrives
+// where the set is written, names both, and cannot reach a running mesh.
+//
+// It also decides a design question. Because overlap is refused rather than merged, a shared
+// EVENTS stream and a per-module stream cannot coexist — the module's would be refused — so
+// "one stream for most, its own for a module that wants different retention" is not an option
+// the server allows. It is all of one or all of the other.
+func Overlaps() []string {
+	seen := map[string]string{}
+	var clashes []string
+	for _, s := range MeshStreams() {
+		for _, subject := range s.Subjects {
+			if first, ok := seen[subject]; ok {
+				clashes = append(clashes, fmt.Sprintf("%s and %s both claim %s", first, s.Name, subject))
+				continue
+			}
+			seen[subject] = s.Name
+		}
+	}
+	sort.Strings(clashes)
+	return clashes
+}
+
+// The mesh's own consumers.
+//
+// A seat's streams and a module's consumers are derived from declarations (derived.go). These two
+// are not: **the controller is not a module and files no manifest**, so its authority and its
+// subscriptions cannot come from a declaration that does not exist. They are named here, where the
+// mesh's own streams are named, and narrowly — a controller subscribing `mesh.mod.*.event.>` would
+// hear every event in the mesh, which it has no business doing and which would make its permission
+// list stop explaining anything.
+
+// ControllerName is the controller's durable consumer on each stream it reads, and the name its
+// ack subject is derived from (nats.go: `$JS.ACK.<stream>.controller.>`).
+const ControllerName = "controller"
+
+// MergesConsumerName is the controller's durable consumer of the forge's merged event on EVENTS, apart from the
+// events consumer (novox/hq ADR 0407 decision 3, issue 973). A merge is never dropped, so this consumer has no
+// max-deliver, which would send a merge held five times to DEAD_LETTERS to wait for a person, and no healer
+// resets it, which would drop the merges it holds. A consumer of its own because both of those are properties of
+// a consumer, not of a subject.
+const MergesConsumerName = "controller-merges"
+
+// ControllerSeat is the role the control plane holds, and ControllerStates are the facts it states
+// under it (novox/hq ADR 0134).
+//
+// **Written here as well as in `link`, and a test keeps them agreeing.** `link` imports `broker`, so
+// `broker` cannot import `link`; a grant naming a subject the controller never publishes is authority
+// nobody uses, and a controller publishing one the grant omits is refused at the moment it has
+// something to say.
+const ControllerSeat = "mesh-controller"
+
+var ControllerStates = []string{"applied", "refused", "built-before",
+	// What is wrong, said as it changes (novox/hq to-be 45 §2): a condition raised, changed in
+	// severity, resolver or silence, and cleared. The operator-channel's holder and any other surface
+	// consume them; the controller tells nobody itself.
+	"condition-raised", "condition-changed", "condition-cleared",
+	// And the self-check's heartbeat, at the end of every run (to-be 45 §4, S10): watched from a
+	// machine that is not the control node, so the controller going quiet is itself said.
+	"doctor-heartbeat",
+	// And a value given by hand, replaced after its module's first good start (novox/hq ADR 0228).
+	"secret-replaced",
+	// And every act a healer takes on a condition (novox/hq to-be 45 §7, Phase 3): a repair the mesh
+	// made by itself is said like one a person made, never quietly.
+	"healer-acted",
+	// And a build put back after its gate failed on its first machine (novox/hq ADR 0236, to-be 45 §8).
+	"rolled-back",
+	// And a pull request's merge check, judged (novox/hq to-be 45 §9): what the forge's holder sets as
+	// the pull request's status, and anybody else may read.
+	"checked",
+	// (A walk kept in a new state and a tier sent to a machine are gone with the plans, novox/hq ADR 0539.)
+	// And a key of a record mirror written or removed (novox/hq ADR 0289, design 54 §3): the assignments and
+	// each registered module's declared config (design 57 F3).
+	"assignment-changed", "declared-config-changed", "predefined-changed",
+	// And a builder's key not taken in because the artifact store does not hold what it names (novox/hq issue 1937).
+	"artifacts-gone",
+	// And a bucket of the plans' state deleted at the controller's first start, and the declarations' stream once no node
+	// reads one (novox/hq ADR 0539 clauses 11 and 13).
+	"bucket-deleted"}
+
+// BusAdvisories are what the bus server says about the mesh's own account that the controller
+// reads (novox/hq to-be 45 §3, S9): a durable consumer that handed a message over as often as it
+// may and gave up on it, and one that was deleted. Read-only: an advisory is the server's to
+// publish, and the controller's subscription changes nothing on the bus.
+var BusAdvisories = []string{
+	"$JS.EVENT.ADVISORY.CONSUMER.MAX_DELIVERIES.>",
+	"$JS.EVENT.ADVISORY.CONSUMER.DELETED.>",
+}
+
+// ControllerFollows are the events the controller reacts to: the catalogue saying a module's
+// current version moved, and a catalogue that has just started saying it may have missed builds.
+//
+// **Derived the same way a module's subscription is**, from the emitter and the bare local event
+// name, rather than written out. They were written out while the catalogue still spelled its events
+// as the old bus's routing keys, and the moment those were converted (novox/hq 04-ISSUES/127) a
+// hard-coded pair became a controller listening to a subject nothing publishes — the same fault, from
+// the other side. Deriving them means the conversion could not leave these behind.
+var ControllerFollows = []string{
+	moduleEventSubject("mesh-catalog", "upgraded"),
+	moduleEventSubject("mesh-catalog", "catching-up"),
+	// A build's outcome, which is the build-machine role's own event now (ADR 0121) rather than a
+	// message on the control branch. Same three audiences, one publish: whoever asked, this, and the
+	// catalogue.
+	seatEventSubject("node-build-agent", "built"),
+	// The forge's merges: what moved a source, so the mesh builds what that source produces
+	// without anybody telling it (novox/hq 04-ISSUES/131). Appended, because the index is a name.
+	moduleEventSubject("gitea", "pull.merged"),
+	// The retired build role's outcome too, while the handover runs (novox/hq ADR 0190): the one
+	// build machine keeps answering on its seat until build-agent replaces it, and the outcome that
+	// registers build-agent itself comes from there. Appended, for the same reason as above; goes
+	// with the retired seat row.
+	seatEventSubject("mesh-build-machine", "built"),
+	// **Every provider's standing** (novox/hq ADR 0224): a consumer it has failed for minutes, and
+	// that consumer recovered. The one pattern on this list, and a narrow one — two named events,
+	// from whichever module provides — because the rule is about every provider, and a list of
+	// providers here would be a list somebody forgets to extend. On 2026-10-05 the identity provider
+	// failed every consumer for a day and only its journal said so (issue 179). Appended, because
+	// the index is a name.
+	moduleEventSubject("*", ProvisionerFailing),
+	moduleEventSubject("*", ProvisionerRecovered),
+	// **What becomes of a consumer the mesh stopped asking for** (novox/hq ADR 0230): retired, waiting
+	// for a person, re-enabled, deleted — a provider's third word, from whichever module provides.
+	// Appended, because the index is a name.
+	moduleEventSubject("*", ProvisionerRetirement),
+	// **A pull request's head, announced** (novox/hq to-be 45 §9): what the controller asks the build
+	// seat to check before it merges — every machine of the facts snapshot composed with the change.
+	// Appended, because the index is a name.
+	moduleEventSubject("gitea", "pull.updated"),
+	// **The operator's answers to what the controller asked** (novox/hq ADR 0259): the router's warrant, or
+	// the end of an ask without one, said to the controller alone under its own name. On the stream, so a
+	// controller that was away hears what was decided meanwhile. Appended, because the index is a name.
+	DecidedSubject,
+}
+
+// ControllerHears are events the controller's events consumer takes beside the ones it follows, and that need no
+// subscribe grant of their own. **A push consumer delivers onto its deliver subject** (`_DELIVER.controller.>`, already
+// granted), so the subject a consumer filters on is never one the controller subscribes: listing this one in
+// ControllerFollows would add a subscribe grant the installer's carried user list, which lives in mesh-host, would
+// have to carry too (TestTheInstallersFirstUserListIsWhatTheControllerWouldCompose), for nothing the consumer uses.
+//
+// A merge mesh-delivery made, announced (novox/hq ADR 0420 §7, issue 1025): with the ask whose Approve it merged on and
+// the heads that Approve covered, kept a week to read the warrant a moved module's registration needs.
+var ControllerHears = []string{DeliveryMergedSubject}
+
+// DeliveryMergedEvent is the event a module says when it merged a pull request.
+const DeliveryMergedEvent = "merged"
+
+// DeliveryMergedSubject is where the delivery's owner says it merged a pull request: one wildcard subject, the
+// module that claims the delivery seat being whichever the catalogue says (novox/hq ADR 0437 §3). Who said it is
+// read from the subject, and whether it claims the seat is the controller's to check.
+var DeliveryMergedSubject = moduleEventSubject("*", DeliveryMergedEvent)
+
+// DeliveryMergedSubjectOf is where one module says it merged a pull request.
+func DeliveryMergedSubjectOf(module string) string {
+	return moduleEventSubject(module, DeliveryMergedEvent)
+}
+
+// AsksSeat is the seat an ask is made on and its warrant heard from (novox/hq ADR 0259): the router's.
+const AsksSeat = "operator-channel"
+
+// DecidedSubject is where the router says the controller's warrants: the seat's event named by the
+// controller as its caller.
+var DecidedSubject = seatEventSubject(AsksSeat, "decided."+ControllerSeat)
+
+// The provider standing events, by their local names. Written here as well as in the catalogue
+// (catalogue.ProvisionerEvents), which this package cannot import; a test keeps them agreeing.
+const (
+	ProvisionerFailing    = "provisioner.failing"
+	ProvisionerRecovered  = "provisioner.recovered"
+	ProvisionerRetirement = "provisioner.retirement"
+)
+
+// moduleEventSubject is where one module's event lands. The same derivation PermissionsFor uses, so
+// what the controller subscribes and what the emitter is permitted to publish cannot drift apart.
+func moduleEventSubject(module, event string) string {
+	return "mesh.mod." + module + ".event." + event
+}
+
+// seatEventSubject is where a role's own event lands, derived the same way a holder's permission is.
+func seatEventSubject(seat, verb string) string {
+	return "mesh.seat." + seat + ".event." + verb
+}
+
+// EventsStream holds every module's and every role's events, a build's log among them.
+const EventsStream = "EVENTS"
+
+// MeshConsumers is what the controller consumes, in the order a person reads it.
+//
+// **Unlimited redelivery on CONTROL, deliberately.** The store window's bound is the controller's,
+// not the server's (window.go): a message is held with a nak-and-delay until the controller either
+// takes it or gives up and says so. A max-deliver here would give up on a push that was being
+// held through a store restart — the exact message the stream exists to protect — some minutes
+// before the controller had finished deciding about it.
+func MeshConsumers() []Consumer {
+	return ControllerConsumers()
+}
+
+// ControllerConsumers are the consumers the controller's own event loop takes from: MeshConsumers without the build
+// seat's check workers, which the builders take from and the loop never does (issue 1063). A consumer added to the
+// controller is counted here without a change elsewhere.
+func ControllerConsumers() []Consumer {
+	return []Consumer{
+		{
+			Name:           ControllerName,
+			Stream:         "CONTROL",
+			Push:           true,
+			AckWaitSeconds: 30,
+			Why: "the controller is the single consumer of what nodes say; explicit ack and no " +
+				"max-deliver, because the store window's bound is the controller's own",
+		},
+		// The forge's merges (novox/hq ADR 0407 decision 3, issue 973): never dropped, so no max-deliver and no
+		// reset; a merge the controller cannot record yet is held with a growing delay until it can. **Asserted before
+		// the events consumer**, which stops filtering merges: the order of this list is the order of assertion.
+		{
+			Name:   MergesConsumerName,
+			Stream: "EVENTS",
+			// Within what the controller may subscribe already (`_DELIVER.controller.>`).
+			DeliverSubject: "_DELIVER." + ControllerName + ".merges",
+			Filters:        []string{ControllerFollows[3]},
+			Push:           true,
+			AckWaitSeconds: 30,
+			MaxAckPending:  1,
+			FromNow:        true,
+			TakesOverFrom:  ControllerName,
+			Why: "the forge's merges, one at a time; no max-deliver and never reset, because a merge is never " +
+				"dropped and no person releases one",
+		},
+		{
+			Name:           ControllerName,
+			Stream:         "EVENTS",
+			Filters:        append(eventsTheControllerFollows(), AgainFilter(ControllerName)),
+			Push:           true,
+			AckWaitSeconds: 30,
+			MaxDeliver:     5,
+			// One at a time (novox/hq issue 175): acting on a merge builds for minutes, and an
+			// announcement handed over behind it must wait on the server, not time out on the
+			// client and come back to be acted on again.
+			MaxAckPending: 1,
+			FromNow:       true,
+			// **The one consumer the mesh resets by itself** (healer H4, issue 248): it fell a week
+			// behind once and held every merge after it. What a reset drops is caught up elsewhere — a
+			// build's outcome from the build records a plan settles from (issue 214), a provider's failing
+			// word by the provider saying it again every quarter of an hour (ADR 0224). **Not the merges**:
+			// they are the merges consumer's below, which a reset leaves alone (ADR 0407 decision 3).
+			Resettable: "what it drops is caught up: build outcomes from the build records (issue 214), a " +
+				"provider's failing word said again (ADR 0224); the forge's merges are not its, they have a " +
+				"consumer of their own that no reset touches",
+			Why: "the events the mesh's own controller reacts to, one at a time; after " +
+				"max-deliver it gives the event up, and the controller keeps it in DEAD_LETTERS until " +
+				"a person delivers it again or drops it",
+		},
+		// What the server said a consumer gave up on (novox/hq issue 330): copied into DEAD_LETTERS and
+		// acknowledged. No max-deliver: a notice the controller could not copy is offered again, and said.
+		{
+			Name:           ControllerName,
+			Stream:         DeadLetterNoticesStream,
+			Push:           true,
+			AckWaitSeconds: 30,
+			Why: "the controller copies each message a consumer gave up on into DEAD_LETTERS; no max-deliver, " +
+				"because a notice it gave up on would lose the message it is about",
+		},
+	}
+}
+
+// NoticesConsumer is the controller's consumer on DEAD_LETTER_NOTICES (novox/hq issue 330).
+func NoticesConsumer() Consumer {
+	for _, c := range MeshConsumers() {
+		if c.Stream == DeadLetterNoticesStream {
+			return c
+		}
+	}
+	panic("the mesh's consumers carry none on " + DeadLetterNoticesStream)
+}
+
+// AssertServingConsumers are the controller's own consumers its serving cannot go without: all but the
+// one on DEAD_LETTER_NOTICES, which the keeper of dead letters asserts and retries by itself, so a fault
+// there never stops the controller serving (novox/hq issue 330).
+func AssertServingConsumers(e Ensurer) error {
+	for _, c := range MeshConsumers() {
+		if c.Stream == DeadLetterNoticesStream {
+			continue
+		}
+		if err := e.EnsureConsumer(c); err != nil {
+			return fmt.Errorf("asserting consumer %s on %s: %w", c.Name, c.Stream, err)
+		}
+	}
+	return nil
+}
+
+// Ensurer is the part of a JetStream connection consumer assertion needs, narrow for the reason
+// Asserter is.
+type Ensurer interface {
+	EnsureConsumer(c Consumer) error
+}
+
+// AssertMeshConsumers brings the controller's own consumers into being, and says which one failed.
+//
+// After the streams, necessarily: a consumer on a stream that does not exist is refused, and the
+// refusal names the stream rather than the order.
+func AssertMeshConsumers(e Ensurer) error {
+	for _, c := range MeshConsumers() {
+		if err := e.EnsureConsumer(c); err != nil {
+			return fmt.Errorf("asserting consumer %s on %s: %w", c.Name, c.Stream, err)
+		}
+	}
+	return nil
+}

go/buscompose/testdata/composed.conf

@@ -0,0 +1,78 @@
+# Composed by the mesh controller. Do not edit: the next composition overwrites it.
+# Accounts and permissions are derived from what each module declares and nothing
+# else (novox/hq ADR 0043, design 29 §2).
+
+port: 4222
+http: 127.0.0.1:8222
+
+tls {
+  cert_file: "/tls/tls.crt"
+  key_file: "/tls/tls.key"
+  ca_file: "/tls/ca.crt"
+}
+
+jetstream {
+  store_dir: "/data"
+}
+
+# The mesh's users, composed by the controller. Do not edit: the next
+# composition overwrites it. Permissions are derived from what each module
+# declares and nothing else (novox/hq ADR 0043, design 29 §2).
+
+accounts {
+  MESH {
+    jetstream: enabled
+    imports = [
+      { stream: { account: "$SYS", subject: "$SYS.ACCOUNT.MESH.CONNECT" }, to: "mesh.bus.connect" }
+      { stream: { account: "$SYS", subject: "$SYS.ACCOUNT.MESH.DISCONNECT" }, to: "mesh.bus.disconnect" }
+      { service: { account: "$SYS", subject: "$SYS.REQ.ACCOUNT.MESH.CONNZ" }, to: "mesh.bus.connz" }
+    ]
+    users = [
+      { user: "controller", password: "$2a$11$cccccccccccccccccccccc", permissions: {
+        publish: { allow: ["$JS.ACK.CONTROL.controller.>", "$JS.ACK.DEAD_LETTER_NOTICES.controller.>", "$JS.ACK.EVENTS.controller-merges.>", "$JS.ACK.EVENTS.controller.>", "$JS.ACK.KV_mesh-delivery-builder_builds.mesh-controller-take-in.>", "$JS.ACK.KV_mesh-delivery-indexer_modules.mesh-controller-take-in.>", "$JS.API.>", "$KV.mesh-controller_asked.>", "$KV.mesh-controller_assignments.>", "$KV.mesh-controller_builds.>", "$KV.mesh-controller_calls.>", "$KV.mesh-controller_composed.>", "$KV.mesh-controller_condition-history.>", "$KV.mesh-controller_conditions.>", "$KV.mesh-controller_declared-config.>", "$KV.mesh-controller_declared-packages.>", "$KV.mesh-controller_delivery-merges.>", "$KV.mesh-controller_grants.>", "$KV.mesh-controller_hand-acts.>", "$KV.mesh-controller_lease.>", "$KV.mesh-controller_predefined.>", "$KV.mesh-controller_rollouts.>", "$KV.mesh-controller_states-announced.>", "$SRV.INFO", "_INBOX.enrol.>", "mesh.again.>", "mesh.assignment.>", "mesh.events.dead.>", "mesh.mod.*.tool.>", "mesh.mod.mesh-controller.event.states", "mesh.node.>", "mesh.seat.mesh-controller.event.applied", "mesh.seat.mesh-controller.event.artifacts-gone", "mesh.seat.mesh-controller.event.assignment-changed", "mesh.seat.mesh-controller.event.bucket-deleted", "mesh.seat.mesh-controller.event.built-before", "mesh.seat.mesh-controller.event.checked", "mesh.seat.mesh-controller.event.condition-changed", "mesh.seat.mesh-controller.event.condition-cleared", "mesh.seat.mesh-controller.event.condition-raised", "mesh.seat.mesh-controller.event.declared-config-changed", "mesh.seat.mesh-controller.event.doctor-heartbeat", "mesh.seat.mesh-controller.event.healer-acted", "mesh.seat.mesh-controller.event.predefined-changed", "mesh.seat.mesh-controller.event.refused", "mesh.seat.mesh-controller.event.rolled-back", "mesh.seat.mesh-controller.event.secret-replaced", "mesh.seat.mesh-controller.tool.plans", "mesh.seat.mesh-controller.tool.push", "mesh.seat.mesh-controller.tool.upgrade", "mesh.seat.mesh-delivery.tool.close", "mesh.seat.mesh-delivery.tool.groups", "mesh.seat.mesh-delivery.tool.release", "mesh.seat.mesh-delivery.tool.stalled", "mesh.seat.mesh-delivery.tool.stop", "mesh.seat.mesh-delivery.tool.times", "mesh.seat.node-backup.tool.backed-up.*", "mesh.seat.node-backup.tool.now.*", "mesh.seat.node-intrusion-prevention.tool.banned.*", "mesh.seat.node-launcher.tool.secret.*", "mesh.seat.node-service-manager.tool.restart.*", "mesh.seat.operator-channel.tool.tell"] }
+        subscribe: { allow: ["$JS.API.>", "$JS.EVENT.ADVISORY.CONSUMER.DELETED.>", "$JS.EVENT.ADVISORY.CONSUMER.MAX_DELIVERIES.>", "$SRV.INFO", "$SRV.INFO.mesh-controller", "$SRV.INFO.mesh-controller.>", "$SRV.PING", "$SRV.PING.mesh-controller", "$SRV.PING.mesh-controller.>", "$SRV.STATS", "$SRV.STATS.mesh-controller", "$SRV.STATS.mesh-controller.>", "_DELIVER.controller", "_DELIVER.controller.>", "_INBOX.controller.>", "mesh.control.>", "mesh.mod.*.event.provisioner.failing", "mesh.mod.*.event.provisioner.recovered", "mesh.mod.*.event.provisioner.retirement", "mesh.mod.gitea.event.pull.merged", "mesh.mod.gitea.event.pull.updated", "mesh.mod.mesh-catalog.event.catching-up", "mesh.mod.mesh-catalog.event.upgraded", "mesh.seat.mesh-build-machine.event.built", "mesh.seat.mesh-controller.tool.>", "mesh.seat.node-build-agent.event.built", "mesh.seat.operator-channel.event.decided.mesh-controller"] }
+        allow_responses: { max: 1, ttl: "1m" }
+      } }
+      { user: "enrol.one", password: "$2a$11$eeeeeeeeeeeeeeeeeeeeee", permissions: {
+        publish: { allow: ["mesh.control.enrol"] }
+        subscribe: { allow: ["_INBOX.enrol.one.>"] }
+      } }
+      { user: "node.one", password: "$2a$11$nnnnnnnnnnnnnnnnnnnnnn", permissions: {
+        publish: { allow: ["$JS.ACK.NODES.one.>", "$JS.API.CONSUMER.CREATE.KV_composed-one.>", "$JS.API.CONSUMER.CREATE.KV_mesh-delivery-assigner_wants.*.$KV.mesh-delivery-assigner_wants.want.one.>", "$JS.API.CONSUMER.CREATE.KV_node-engine_have.*.$KV.node-engine_have.one.>", "$JS.API.CONSUMER.CREATE.OBJ_declaration-files-one.*.$O.declaration-files-one.C.*", "$JS.API.CONSUMER.DELETE.KV_composed-one.>", "$JS.API.CONSUMER.DELETE.KV_mesh-delivery-assigner_wants.>", "$JS.API.CONSUMER.DELETE.KV_node-engine_have.>", "$JS.API.CONSUMER.DELETE.OBJ_declaration-files-one.*", "$JS.API.CONSUMER.INFO.NODES.one", "$JS.API.DIRECT.GET.KV_composed-one.>", "$JS.API.DIRECT.GET.KV_mesh-delivery-assigner_wants.$KV.mesh-delivery-assigner_wants.want.one.>", "$JS.API.DIRECT.GET.KV_node-engine_have.$KV.node-engine_have.one.>", "$JS.API.DIRECT.GET.OBJ_declaration-files-one.$O.declaration-files-one.M.*", "$JS.API.STREAM.INFO.KV_composed-one", "$JS.API.STREAM.INFO.KV_mesh-delivery-assigner_wants", "$JS.API.STREAM.INFO.KV_node-engine_have", "$JS.FC.KV_composed-one.>", "$JS.FC.KV_mesh-delivery-assigner_wants.>", "$JS.FC.KV_node-engine_have.>", "$JS.FC.OBJ_declaration-files-one.>", "$KV.node-engine_have.one.>", "$SRV.PING.node-tools.one", "mesh.control.one.>", "mesh.seat.node-backup.call.backed-up.one.node~one", "mesh.seat.node-backup.call.now.one.node~one", "mesh.seat.node-backup.tool.backed-up.one", "mesh.seat.node-backup.tool.now.one"] }
+        subscribe: { allow: ["_DELIVER.one", "_DELIVER.one.>", "_INBOX.node.one.>", "mesh.mod.restic.event.backed-up", "mesh.node.one.ask.access-act", "mesh.node.one.ask.hand-over", "mesh.node.one.ask.judge-directories", "mesh.node.one.ask.move-secret", "mesh.node.one.ask.report", "mesh.node.one.ask.setuid-search", "mesh.node.one.declare"] }
+        allow_responses: { max: 1, ttl: "1m" }
+      } }
+      { user: "one.mesh-delivery-watchman", password: "$2a$11$wwwwwwwwwwwwwwwwwwwwww", permissions: {
+        publish: { allow: ["$JS.ACK.EVENTS.one_mesh-delivery-watchman.>", "$JS.API.CONSUMER.INFO.EVENTS.one_mesh-delivery-watchman", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.one_mesh-delivery-watchman", "$JS.API.DIRECT.GET.ASSIGNMENTS.mesh.assignment.one.mesh-delivery-watchman", "mesh.bus.connz"] }
+        subscribe: { allow: ["$SRV.INFO", "$SRV.INFO.mesh-delivery-watchman", "$SRV.INFO.mesh-delivery-watchman.>", "$SRV.PING", "$SRV.PING.mesh-delivery-watchman", "$SRV.PING.mesh-delivery-watchman.>", "$SRV.STATS", "$SRV.STATS.mesh-delivery-watchman", "$SRV.STATS.mesh-delivery-watchman.>", "_INBOX.one.mesh-delivery-watchman.>", "mesh.assignment.one.mesh-delivery-watchman", "mesh.bus.connect", "mesh.bus.disconnect", "mesh.mod.mesh-delivery-watchman.call.>", "mesh.mod.mesh-delivery-watchman.tool.>"] }
+        allow_responses: { max: 1, ttl: "1m" }
+      } }
+      { user: "one.nats", password: "$2a$11$bbbbbbbbbbbbbbbbbbbbbb", permissions: {
+        publish: { allow: ["$JS.API.STREAM.INFO.*", "$JS.API.STREAM.NAMES", "$JS.API.STREAM.SNAPSHOT.*", "$JS.SNAPSHOT.ACK.>"] }
+        subscribe: { allow: ["_INBOX.one.nats.>"] }
+      } }
+      { user: "one.telegram", password: "$2a$11$tttttttttttttttttttttt", permissions: {
+        publish: { allow: ["$JS.ACK.EVENTS.one_telegram.>", "$JS.ACK.SEAT_TELEGRAM_SENDER.SEAT_TELEGRAM_SENDER_worker.>", "$JS.API.CONSUMER.INFO.EVENTS.one_telegram", "$JS.API.CONSUMER.INFO.SEAT_TELEGRAM_SENDER.SEAT_TELEGRAM_SENDER_worker", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.one_telegram", "$JS.API.CONSUMER.MSG.NEXT.SEAT_TELEGRAM_SENDER.SEAT_TELEGRAM_SENDER_worker", "$JS.API.DIRECT.GET.ASSIGNMENTS.mesh.assignment.one.telegram", "mesh.seat.telegram-sender.event.delivered", "mesh.seat.telegram-sender.event.failed"] }
+        subscribe: { allow: ["$SRV.INFO", "$SRV.INFO.telegram", "$SRV.INFO.telegram.>", "$SRV.PING", "$SRV.PING.telegram", "$SRV.PING.telegram.>", "$SRV.STATS", "$SRV.STATS.telegram", "$SRV.STATS.telegram.>", "_INBOX.one.telegram.>", "mesh.assignment.one.telegram", "mesh.mod.telegram.call.>", "mesh.mod.telegram.tool.>", "mesh.seat.telegram-sender.accept.send"] }
+        allow_responses: { max: 1, ttl: "1m" }
+      } }
+      { user: "two.audit", password: "$2a$11$aaaaaaaaaaaaaaaaaaaaaa", permissions: {
+        publish: { allow: ["$JS.ACK.EVENTS.two_audit.>", "$JS.API.CONSUMER.INFO.EVENTS.two_audit", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.two_audit", "$JS.API.DIRECT.GET.ASSIGNMENTS.mesh.assignment.two.audit"] }
+        subscribe: { allow: ["$SRV.INFO", "$SRV.INFO.audit", "$SRV.INFO.audit.>", "$SRV.PING", "$SRV.PING.audit", "$SRV.PING.audit.>", "$SRV.STATS", "$SRV.STATS.audit", "$SRV.STATS.audit.>", "_INBOX.two.audit.>", "mesh.assignment.two.audit", "mesh.mod.audit.call.>", "mesh.mod.audit.tool.>", "mesh.mod.shop.event.order.placed"] }
+        allow_responses: { max: 1, ttl: "1m" }
+      } }
+      { user: "two.shop", password: "$2a$11$ssssssssssssssssssssss", permissions: {
+        publish: { allow: ["$JS.ACK.EVENTS.two_shop.>", "$JS.API.CONSUMER.INFO.EVENTS.two_shop", "$JS.API.CONSUMER.MSG.NEXT.EVENTS.two_shop", "$JS.API.DIRECT.GET.ASSIGNMENTS.mesh.assignment.two.shop", "mesh.mod.shop.event.order.placed", "mesh.seat.telegram-sender.accept.send"] }
+        subscribe: { allow: ["$SRV.INFO", "$SRV.INFO.shop", "$SRV.INFO.shop.>", "$SRV.PING", "$SRV.PING.shop", "$SRV.PING.shop.>", "$SRV.STATS", "$SRV.STATS.shop", "$SRV.STATS.shop.>", "_INBOX.two.shop.>", "mesh.assignment.two.shop", "mesh.mod.shop.call.>", "mesh.mod.shop.tool.>"] }
+        allow_responses: { max: 1, ttl: "1m" }
+      } }
+    ]
+  }
+  "$SYS" {
+    exports = [
+      { stream: "$SYS.ACCOUNT.MESH.CONNECT", accounts: ["MESH"] }
+      { stream: "$SYS.ACCOUNT.MESH.DISCONNECT", accounts: ["MESH"] }
+      { service: "$SYS.REQ.ACCOUNT.MESH.CONNZ", accounts: ["MESH"] }
+    ]
+  }
+}

go/buscompose/users.go

@@ -0,0 +1,420 @@
+package buscompose
+
+import (
+	"fmt"
+	"git.novox.be/novox/mesh-sdk/go/announce"
+	"slices"
+	"sort"
+)
+
+// Every user the composed file should contain, derived from what the mesh knows.
+//
+// **The list is derived, never kept.** A stored user list would be a second account of who may
+// reach the bus, able to disagree with the records it came from — and the disagreement would be
+// invisible, because both would look internally consistent. So this is a pure function of the
+// mesh's records, run again every time the file is written.
+//
+// Records are mirrored into this package's own types rather than imported from the catalogue, for
+// the reason DeclaredSeat is: composing authority is a different job from parsing a manifest, and
+// this package stays free of the other's types so a change to a manifest field cannot quietly widen
+// a permission.
+
+// Declared is one module on one node, as composing its authority needs it.
+type Declared struct {
+	Module   string
+	Emits    []string
+	Consumes []string
+	Serves   []string
+	// Holds are the seats this module claims, with the protocol each seat declares. A seat the
+	// mesh defines for itself declares no protocol, so holding one grants nothing on the bus —
+	// which is right: those seats are about who does a job, not about who may say what.
+	Holds []Seat
+	// Uses are the seats this module sends to.
+	Uses []Seat
+	// Issued are the tools that answer a credential its software issued, one per offer that says so (novox/hq
+	// ADR 0305): the controller is granted to ask each in its own name, and no other tool so.
+	Issued []string
+	// Watches are the seats whose events it consumes.
+	Watches []Seat
+	// Invokes are the tools it calls, `<module>.<tool>` or `*` (novox/hq ADR 0152).
+	Invokes []string
+	// Waits are the event families a session may wait on through the tool runner, the tool runner's module's
+	// alone (novox/hq ADR 0367 §2): its account subscribes them for a call, through no consumer.
+	Waits []Wait
+	// State is the state it keeps, each a bucket its instances write (novox/hq ADR 0201).
+	State []Bucket
+	// Logs are the logs it keeps, each a stream its instances append to (novox/hq ADR 0297).
+	Logs []Log
+	// Streams are the streams it owns, each its events' one place (novox/hq ADR 0363).
+	Streams []ModuleStream
+	// Queues are its own work-queue streams and the one process each is the consumer of (novox/hq ADR 0436
+	// §1, §2, §6): one durable consumer per entry, named `<node>_<module>_<process id>`.
+	Queues []QueueOwner
+	// Hears are the module streams it hears on this machine, each with the subjects it was granted
+	// (novox/hq ADR 0363 §5); HearsAStream says its `consumes` names a module that owns a stream, granted
+	// or not, so its membership is issued again when a grant changes.
+	Hears        []Heard
+	HearsAStream bool
+	// Reads are other modules' state it reads, each `<module>.<name>` (novox/hq ADR 0201).
+	Reads []string
+	// ReadsRefused are the reads its manifest names that the owner's announcement does not make readable (novox/hq ADR
+	// 0495 clause 3, issue 1790): granted nothing, kept to be said.
+	ReadsRefused []string
+	// KeyedReads are keys of other modules' state it reads, each one key alone: what a seat's holder is
+	// granted for the pieces the modules beside it offer (novox/hq ADR 0260).
+	KeyedReads []KeyedRead
+	// NoAccount says the module declares no own secret named broker, so no account could ever be
+	// delivered to it and nothing can connect as it (novox/hq issue 195). Said in the negative so a
+	// record that does not say is composed as it always was.
+	NoAccount bool
+	// SnapshotsTheBus says the module holds mesh-broker — it is the bus — and so is the one module
+	// granted the snapshot API, to copy the bus's streams for the night's backup (novox/hq ADR 0235).
+	SnapshotsTheBus bool
+	// Checks are the module's own tools its health asks, each `<module>.<tool>` (novox/hq ADR 0240, to-be
+	// 48 §3): the machine's node-engine asks them of its own node tools, and is granted that and no more.
+	Checks []string
+	// Loads says the module has a compiled bundle whose entrypoints the machine's tool runtime loads and runs
+	// (novox/hq ADR 0175; issue 1329): a helper that reaches the bus on the runner's account, so the runner
+	// must carry the module although it declares no tools.
+	Loads bool
+	// RunsAs is the account the module runs as in a runtime of its own (novox/hq ADR 0259 §8): it is never
+	// carried by the machine's runtime, and reaches the bus on its own account.
+	RunsAs string
+	// ProvisionsNode says the module runs the machine's provisioner client: it claims NodeProvisionerSeat and
+	// declares the own secret ProvisionerSecret its account is delivered in (novox/hq ADR 0349 clause 11, design 57
+	// P3). The client is given a bus account of its own, never the module's or the tool runner's.
+	ProvisionsNode bool
+	// Processes are this module's own processes that declare bus (novox/hq ADR 0436 §1), each getting a
+	// principal of its own: granted exactly what its bus says, and nothing of this module's other grants —
+	// composed whether or not the module itself has an account (NoAccount), because a process account is
+	// delivered in its own secret, broker-<process id>, never the module's `broker`.
+	Processes []ProcessPrincipal
+}
+
+// ProcessPrincipal is one process of a module that declares bus (novox/hq ADR 0436 §1, §2), as the broker
+// composes its own account from: its own emits, its own work-queue consumers, its own state, whether it
+// reads the router's records of its module's own asks, and the tools and seat verbs it calls.
+type ProcessPrincipal struct {
+	// Process is the process resource's id, naming the account <node>.<module>.<process id>.
+	Process string
+	// Emits are the events this process may publish, named as the module's own Emits are.
+	Emits []string
+	// Queues are the module's own work-queue streams this process is the one consumer of.
+	Queues []QueueOwner
+	// State is the module's own state, by local name, this process reads and writes.
+	State []string
+	// Asks says whether this process reads the records of its module's own asks (novox/hq ADR 0259 §3), on
+	// whichever seats the module uses that keep them (the router's, operator-channel, among others).
+	Asks bool
+	// Invokes are the tools and seat verbs this process calls, each <module>.<tool> or a role's
+	// seat:<seat>.<verb>, or * for every tool on the mesh.
+	Invokes []string
+}
+
+// Records is what composing a user list needs to know about the mesh, and nothing more.
+type Records struct {
+	// Nodes is every machine the mesh knows. Each gets a host user.
+	Nodes []string
+	// Assigned is the modules on each node, as they declare themselves.
+	Assigned map[string][]Declared
+	// Enrolling is every node with a live token — one enrolment user each, because the inbox an
+	// answer goes to is scoped to the token and a shared one is one machine reading another's
+	// sealed credentials (design 25 §6).
+	Enrolling []string
+	// People is each person's name against the tools they may invoke, `*` for an administrator.
+	People map[string][]string
+	// Interchangeable is each module whose definition says its instances are the same anywhere
+	// (ADR 0160), which decides whether the module's plain subject is issued to every instance.
+	Interchangeable map[string]bool
+	// RootFree is each machine judged root-free when this was composed (novox/hq ADR 0259 §8): it names an
+	// account agents run as, judged unable to become root by its node-engine, and serves no login shell
+	// execute. A machine absent is not free: no record of a pass is no pass.
+	RootFree map[string]bool
+	// Announced is each module's last announcement of the states it keeps (novox/hq ADR 0495, issue 1790), as the
+	// controller keeps it; a module absent has announced nothing yet. Nil where none was read.
+	Announced map[string]announce.States
+}
+
+// Users is every user the composed file should contain, in the order it will be written.
+//
+// The controller is always first and always present: a mesh whose own controller is not in the file
+// is a mesh that cannot be told anything, and there is no state of the records in which that is
+// correct.
+func Users(r Records) ([]Principal, error) {
+	out := []Principal{{Kind: KindController, Uses: asksSeatOf(r), AsksIssued: issuedOf(r), AsksTheVault: vaultVerbsOf(r),
+		AsksTheConfig: servedOf(r, VerbsTheControllerAsksTheConfig), FilesFor: sortedCopy(r.Nodes)}}
+
+	for _, node := range sortedCopy(r.Nodes) {
+		witness := false
+		var checks []string
+		for _, d := range r.Assigned[node] {
+			if d.Module == controllerModule {
+				witness = true
+			}
+			checks = append(checks, d.Checks...)
+		}
+		out = append(out, Principal{Kind: KindNode, Node: node, WitnessesController: witness, Checks: checks,
+			MovesIntoTheVault: servesMoveIn(r), StatesItsKeyToTheVault: servesVerb(r, VaultNodeKey)})
+		// **And the machine's provisioner client, on an account of its own** (novox/hq ADR 0349 clause 11): one
+		// per machine that runs it, delivered to the module running it.
+		for _, d := range r.Assigned[node] {
+			if d.ProvisionsNode {
+				out = append(out, Principal{Kind: KindProvisioner, Node: node, Module: d.Module,
+					BoundBuckets: boundBucketsOf(r)})
+				break
+			}
+		}
+		// **Where the runtime is assigned, the machine gets one runtime principal in place of the
+		// runtime module's own** (novox/hq ADR 0175, to-be 38). It carries every module on the
+		// node: its serving grants are the union of theirs. Every other module keeps its own
+		// principal — a module still serving tools from its own container holds its own
+		// credential until it moves, and the two serve side by side in the meantime.
+		runtimeHere := false
+		for _, d := range r.Assigned[node] {
+			if d.Module == RuntimeModule {
+				runtimeHere = true
+			}
+		}
+		for _, d := range r.Assigned[node] {
+			// **A process account is its own, delivered in its own secret** (broker-<process id>, novox/hq
+			// ADR 0436 §1, §2), never the module's `broker` — so it is composed whether or not the module
+			// itself has an account, and is never carried by the machine's runtime, which runs as the
+			// operator's account (ADR 0436 §5): added here, before either of those is judged.
+			for _, pr := range d.Processes {
+				out = append(out, Principal{
+					Kind: KindProcess, Node: node, Module: d.Module, Process: pr.Process,
+					Emits: pr.Emits, Queues: pr.Queues, State: pr.State, Uses: d.Uses, Asks: pr.Asks,
+					Invokes: pr.Invokes,
+				})
+			}
+			if runtimeHere && d.Module == RuntimeModule {
+				continue
+			}
+			// **A module with nowhere to read an account is no user** (novox/hq issue 195). `module
+			// issue` refuses it one (issue 078: an account nothing reads is an orphan), so its user
+			// could only ever be left out of the file for want of a password — and every such module
+			// was named, on every status and plan, as a credential the mesh had not minted. Where the
+			// runtime is, it speaks for the module; where it is not, the module cannot speak at all,
+			// and a user would not change that.
+			if d.NoAccount {
+				continue
+			}
+			out = append(out, Principal{
+				Kind: KindModule, Node: node, Module: d.Module,
+				Emits: d.Emits, Consumes: d.Consumes, Serves: d.Serves,
+				Holds: d.Holds, Uses: d.Uses, Watches: d.Watches, Invokes: d.Invokes,
+				State: stateNames(d.State), Reads: d.Reads, SnapshotsTheBus: d.SnapshotsTheBus,
+				PerMachine: perMachineNames(d.State), KeyedReads: d.KeyedReads,
+				Logs: logNames(d.Logs), Streams: d.Streams, Hears: ComposedHears(d), Queues: d.Queues,
+			})
+			// **The vault's holder asks the desks and the issuing providers itself** (issue 723), under the
+			// account its own runtime runs on (ADR 0259 §8's runs-as): the one module granted it.
+			if holdsSeat(d, VaultSeat) {
+				out[len(out)-1].AsksTheDesk = true
+				out[len(out)-1].AsksIssued = issuedOf(r)
+			}
+		}
+		if runtimeHere {
+			var carried []Declared
+			for _, d := range r.Assigned[node] {
+				if d.RunsAs == "" && runnerServes(d) {
+					// Never a restricted stream for what the tool runner carries (novox/hq ADR 0376 §1).
+					d.Hears = ComposedHears(d)
+					carried = append(carried, d)
+				}
+			}
+			out = append(out, Principal{Kind: KindNodeTools, Node: node, Module: RuntimeModule, Carries: carried})
+		}
+	}
+	for _, node := range sortedCopy(r.Enrolling) {
+		out = append(out, Principal{Kind: KindEnrolment, Node: node})
+	}
+	for _, person := range sortedNames(r.People) {
+		p := Principal{Kind: KindPerson, Module: person, Invokes: r.People[person]}
+		if administers(p.Invokes) {
+			// The operator's hand path writes each node's compositions (ADR 0539 clause 10).
+			p.FilesFor = sortedCopy(r.Nodes)
+		}
+		out = append(out, p)
+	}
+
+	// Refused here rather than discovered by the server. Two users with one name is a file the
+	// server reads as one of them, and which one depends on the order — so a module assigned to a
+	// node twice, or a person named after nothing, is a composition that must not be written.
+	seen := map[string]string{}
+	for _, p := range out {
+		name := p.Username()
+		if name == "" || name == "." {
+			return nil, fmt.Errorf("a %s user has no name, so nothing could authenticate as it", p.Kind)
+		}
+		if first, already := seen[name]; already {
+			return nil, fmt.Errorf(
+				"two users would be called %q (a %s and a %s): the server would read the file as "+
+					"one of them, and which one depends on the order", name, first, p.Kind)
+		}
+		seen[name] = string(p.Kind)
+	}
+	return out, nil
+}
+
+// WithPasswords fills each user's hash from what the mesh minted, and says which users have none.
+//
+// **Separated from Users because they fail differently.** A user missing from the records is a bug
+// in deriving them; a user with no password is a step that has not happened yet — a module assigned
+// but never given a credential, a node enrolled before this existed. The second is ordinary and its
+// remedy is to mint one, so it is named rather than returned as an error, and the caller decides
+// whether a partial composition is worth writing.
+func WithPasswords(principals []Principal, hashes map[string]string) (filled []Principal, missing []string) {
+	for _, p := range principals {
+		hash, ok := hashes[p.Username()]
+		if !ok || hash == "" {
+			missing = append(missing, p.Username())
+			continue
+		}
+		p.PasswordHash = hash
+		filled = append(filled, p)
+	}
+	return filled, missing
+}
+
+func sortedCopy(in []string) []string {
+	out := append([]string(nil), in...)
+	sort.Strings(out)
+	return out
+}
+
+func sortedNames(in map[string][]string) []string {
+	out := make([]string, 0, len(in))
+	for k := range in {
+		out = append(out, k)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// controllerModule is the controller's module: the machine assigned it witnesses its upgrades.
+const controllerModule = "mesh-controller"
+
+// asksSeatOf is the seat an ask is made on, as its holder declares it (novox/hq ADR 0259): the controller
+// asks the operator through it like any other user, and is granted what its declaration names for a caller.
+// None while nothing holds it.
+// issuedOf is every tool of a module assigned anywhere that answers a credential its software issued, as
+// `<module>.<tool>` (novox/hq ADR 0305): what the controller asks in its own name, and nothing beside.
+func issuedOf(r Records) []string {
+	seen := map[string]bool{}
+	var out []string
+	for _, node := range sortedCopy(r.Nodes) {
+		for _, d := range r.Assigned[node] {
+			for _, t := range d.Issued {
+				if key := d.Module + "." + t; !seen[key] {
+					seen[key] = true
+					out = append(out, key)
+				}
+			}
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+func asksSeatOf(r Records) []Seat {
+	for _, node := range sortedCopy(r.Nodes) {
+		for _, d := range r.Assigned[node] {
+			for _, s := range d.Holds {
+				if s.Name == AsksSeat && namesVerb(s.ByCaller, "ask") {
+					seat := s
+					seat.Kind, seat.Capabilities = "", nil
+					return []Seat{seat}
+				}
+			}
+		}
+	}
+	return nil
+}
+
+// VaultSeat is the vault's seat: its holder alone asks the desks and the issuing providers in its own name.
+const VaultSeat = "mesh-vault"
+
+func holdsSeat(d Declared, seat string) bool {
+	for _, s := range d.Holds {
+		if s.Name == seat {
+			return true
+		}
+	}
+	return false
+}
+
+// vaultVerbsOf are the vault's intake verbs its holder serves, as the records say (issue 675): what the controller
+// is granted to ask it in its own name. None while no holder serves them.
+func vaultVerbsOf(r Records) []string { return servedOf(r, VerbsTheControllerAsksTheVault) }
+
+// servedOf are the verbs of asked that a seat's holder serves, as the records say, by name.
+func servedOf(r Records, asked []SeatVerb) []string {
+	seen := map[string]bool{}
+	var out []string
+	for _, node := range sortedCopy(r.Nodes) {
+		for _, d := range r.Assigned[node] {
+			for _, s := range d.Holds {
+				for _, v := range asked {
+					if s.Name == v.Seat && slices.Contains(s.Serves, v.Verb) && !seen[v.Verb] {
+						seen[v.Verb] = true
+						out = append(out, v.Verb)
+					}
+				}
+			}
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
+// servesMoveIn says the vault's holder serves move-in, as the records say (issue 676): what lets each machine's
+// node-engine ask it in its own name.
+func servesMoveIn(r Records) bool { return servesVerb(r, VaultMoveIn) }
+
+// servesVerb says a holder of verb's seat serves it, as the records say.
+func servesVerb(r Records, verb SeatVerb) bool {
+	for _, node := range r.Nodes {
+		for _, d := range r.Assigned[node] {
+			for _, s := range d.Holds {
+				if s.Name == verb.Seat && slices.Contains(s.Serves, verb.Verb) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+// boundBucketsOf is every provider's bucket of entries, `<module>_bound` (mesh-sdk go/provider, issue 678): the state
+// named bound of every module placed anywhere, once each, in name order. A consumer on any machine may be bound to
+// it, so each machine's provisioner client reads its own keys of each (issue 679).
+func boundBucketsOf(r Records) []string {
+	seen := map[string]bool{}
+	for _, mods := range r.Assigned {
+		for _, d := range mods {
+			for _, b := range d.State {
+				if b.Name == BoundState {
+					seen[b.Bucket()] = true
+				}
+			}
+		}
+	}
+	out := make([]string, 0, len(seen))
+	for b := range seen {
+		out = append(out, b)
+	}
+	sort.Strings(out)
+	return out
+}
+
+// runnerServes says the machine's tool runner has something of this module to serve (novox/hq ADR 0436 §1,
+// ADR 0437 §4, issue 1329): tools or loads it answers, a seat it holds, event families a session waits on,
+// a bundle the runtime loads (Loads), or a check its health asks. A module with none of these is a process of its own on its own credential, and
+// carrying it would hand every session on the machine the runner's account with that module's state, seat
+// traffic and streams. A module with no account of its own (NoAccount) is spoken for by the runner, so it
+// stays carried, and so does the runtime module itself. Whether the module has its own broker secret is not
+// the test: a module with tools and its own credential is still carried (ADR 0175).
+func runnerServes(d Declared) bool {
+	return d.Module == RuntimeModule || d.NoAccount || d.Loads || len(d.Serves) > 0 || len(d.Holds) > 0 || len(d.Waits) > 0 || len(d.Checks) > 0
+}

go/buscompose/waits.go

@@ -0,0 +1,94 @@
+package buscompose
+
+import (
+	"fmt"
+	"strings"
+)
+
+// What a session may wait on through the mesh MCP server (novox/hq ADR 0367).
+//
+// **A grant apart from `consumes`, and the tool runner's alone.** The tool runner's module names in its
+// manifest the event families a session may wait on, one by one; the runtime's account is granted a plain
+// subscription on those subjects and nothing wider — no durable consumer, no queue of its own — and its
+// membership names the same list, from which `mesh_wait` refuses any other. Both are read from this one
+// composition, so the grant and what the tool runner offers cannot disagree, and nothing but the manifest
+// adds a family (§6).
+
+// Wait is one event family the tool runner's module declares: its name as the manifest gives it, and the
+// emitter — a seat or a module — and the event, as the inventory resolved them.
+type Wait struct {
+	// Name is the family as the manifest names it, `<emitter>.<event>`: what a session asks for.
+	Name    string
+	Emitter string
+	// Seat says the emitter is a seat, whose events live under the seat's namespace (novox/hq ADR 0121).
+	Seat bool
+	// Event is the event, with any further token the subject carries: `decided.claude-code`, the asker of a
+	// seat that names it last (ADR 0259 §3).
+	Event string
+	// Last names what the seat's event subject ends in — "kind" for a kinded bench, "asker" for a seat naming
+	// its caller (ADR 0259 §3) — and is empty for an event that ends at its name. A family needing it is waited
+	// on with it given, and refused without.
+	Last string
+}
+
+// WaitSubject is where a family's events land. Each token is checked before it becomes a subject: a
+// wildcard, a dot inside a name or an empty token would widen the grant.
+func WaitSubject(w Wait) (string, error) {
+	if !safeSubject.MatchString(w.Emitter) {
+		return "", fmt.Errorf("%q cannot name an emitter of a waited event: it would widen the subject", w.Emitter)
+	}
+	for _, t := range strings.Split(w.Event, ".") {
+		if !safeSubject.MatchString(t) {
+			return "", fmt.Errorf("%q cannot name a waited event: each of its names is plain, never a wildcard "+
+				"(novox/hq ADR 0367 §2)", w.Event)
+		}
+	}
+	if w.Last != "" && !strings.Contains(w.Event, ".") {
+		return "", fmt.Errorf("%s names no %s: %s's events are said for each %s, so a family is %s.%s.<%s>; "+
+			"without it no event would ever be heard (novox/hq ADR 0367 §5)",
+			w.Name, w.Last, w.Emitter, w.Last, w.Emitter, w.Event, w.Last)
+	}
+	if w.Seat {
+		return "mesh.seat." + w.Emitter + ".event." + w.Event, nil
+	}
+	return "mesh.mod." + w.Emitter + ".event." + w.Event, nil
+}
+
+// waitGrants is the subscription the tool runner's account is granted for its module's families, and an
+// error for a carried module other than the tool runner's that declares any (ADR 0367 §2).
+func waitGrants(carries []Declared) ([]string, error) {
+	var sub []string
+	for _, d := range carries {
+		if len(d.Waits) == 0 {
+			continue
+		}
+		if d.Module != RuntimeModule {
+			return nil, fmt.Errorf("%s declares what a session waits on; only %s, the tool runner's module, "+
+				"does (novox/hq ADR 0367 §2)", d.Module, RuntimeModule)
+		}
+		for _, w := range d.Waits {
+			s, err := WaitSubject(w)
+			if err != nil {
+				return nil, err
+			}
+			sub = append(sub, s)
+		}
+	}
+	return sub, nil
+}
+
+// waitsIssuedFor is the families a membership names: the tool runner's module's, and nobody else's.
+func waitsIssuedFor(d Declared) []WaitIssued {
+	if d.Module != RuntimeModule {
+		return nil
+	}
+	var out []WaitIssued
+	for _, w := range d.Waits {
+		s, err := WaitSubject(w)
+		if err != nil {
+			continue // refused where the account is composed, which names it
+		}
+		out = append(out, WaitIssued{Event: w.Name, Subject: s})
+	}
+	return out
+}

go/buscompose/writers.go

@@ -0,0 +1,308 @@
+package buscompose
+
+import (
+	"fmt"
+	"slices"
+	"strings"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// The writers table (novox/hq to-be 45 §1, ADR 0227 rule 1), compiled in.
+//
+// **Every kind of state the core keeps has one writer; anyone else asks it.** The table is the design's,
+// row for row, with what each row writes on the bus where it writes there. Two things read it: the
+// composition of every principal's grants (PermissionsFor), which **refuses a grant that lets a
+// principal publish on a subject another writes** — so a second writer cannot be granted by accident,
+// and the composition says which state and whose — and the test beside it, which walks the rows
+// against the design's list and the composition of a whole mesh. Changing a writer is a change to
+// this table, through a decision.
+
+// WriterRow is one row of the writers table.
+type WriterRow struct {
+	State  string
+	Writer string
+	KeptIn string
+	Others string
+	// Subjects are the bus subjects a write of this state is a publish to; none for state kept off the
+	// bus (the controller's store, a module's own) or not built yet.
+	Subjects []string
+	// Writes says a principal granted a publish pattern overlapping Subjects is this state's writer —
+	// given the pattern, because a machine writes its own report and no other's.
+	Writes func(p Principal, pattern string) bool
+	// Shared says why more than one principal may publish here; empty for one writer.
+	Shared string
+}
+
+// isController, and the other writers' tests, are who a row's writer is as a principal.
+func isController(p Principal, _ string) bool { return p.Kind == KindController }
+
+// ownMachine is a node writing a subject whose third token is its own name, and no wildcard there.
+func ownMachine(p Principal, pattern string) bool {
+	tokens := strings.Split(pattern, ".")
+	return p.Kind == KindNode && len(tokens) > 2 && tokens[2] == p.Node
+}
+
+// holdsSeatOf is a principal holding the seat a `mesh.seat.<seat>.…` pattern names: its module's own
+// principal, or the node tools carrying a module that holds it (ADR 0175, the runtime is its modules).
+func holdsSeatOf(p Principal, pattern string) bool {
+	tokens := strings.Split(pattern, ".")
+	if len(tokens) < 3 {
+		return false
+	}
+	seat := tokens[2]
+	holds := func(seats []Seat) bool {
+		return slices.ContainsFunc(seats, func(s Seat) bool { return s.Name == seat })
+	}
+	switch p.Kind {
+	case KindModule:
+		return holds(p.Holds)
+	case KindNodeTools:
+		return slices.ContainsFunc(p.Carries, func(d Declared) bool { return holds(d.Holds) })
+	}
+	return false
+}
+
+// ownModule is a module publishing under its own name, or the node tools carrying it.
+func ownModule(p Principal, pattern string) bool {
+	tokens := strings.Split(pattern, ".")
+	if len(tokens) < 3 {
+		return false
+	}
+	module := tokens[2]
+	switch p.Kind {
+	case KindModule:
+		return p.Module == module
+	case KindNodeTools:
+		return slices.ContainsFunc(p.Carries, func(d Declared) bool { return d.Module == module })
+	}
+	return false
+}
+
+// ownAnnouncer is a module, a process of it or the node tools carrying it saying what that module keeps, or the
+// controller saying what it keeps itself (novox/hq ADR 0495 clause 2): each under its own name alone.
+func ownAnnouncer(p Principal, pattern string) bool {
+	tokens := strings.Split(pattern, ".")
+	if len(tokens) < 3 {
+		return false
+	}
+	switch p.Kind {
+	case KindController:
+		return tokens[2] == ControllerSeat
+	case KindProcess:
+		return p.Module == tokens[2]
+	}
+	return ownModule(p, pattern)
+}
+
+// ownProvisioner is a machine's provisioner client saying a report about its own machine: the third token of
+// `prov.applied.<node>.…` is its machine (novox/hq ADR 0349 §4, design 57 P3).
+func ownProvisioner(p Principal, pattern string) bool {
+	tokens := strings.Split(pattern, ".")
+	return p.Kind == KindProvisioner && len(tokens) > 3 && tokens[2] == p.Node
+}
+
+// ownNodeKeys is a node writing the have keys of its own node: `$KV.<bucket>.<node>.…`, the node in the third token
+// and no wildcard there (novox/hq ADR 0429 §1).
+func ownNodeKeys(p Principal, pattern string) bool {
+	tokens := strings.Split(pattern, ".")
+	return p.Kind == KindNode && len(tokens) > 2 && tokens[2] == p.Node
+}
+
+// kvOf is a bucket's write subjects.
+func kvOf(bucket string) []string { return []string{"$KV." + bucket + ".>"} }
+
+// WritersTable is to-be 45 §1, in its order.
+var WritersTable = []WriterRow{
+	{State: "a machine's declaration", Writer: "controller (lease holder)", KeptIn: "the bus, last per subject",
+		Others: "read", Subjects: []string{"mesh.node.*.declare"}, Writes: isController},
+	// The operator's hand-over of a directory used as found, asked of the machine's engine at the controller's
+	// terminal (novox/hq issue 356). One publisher; and because a responder can still reach the subject through a
+	// reply, the ask is signed with the mesh's key and the engine verifies it — the row bounds who is granted the
+	// publish, the signature who is believed.
+	{State: "a hand-over asked of a machine", Writer: "controller, at its terminal", KeptIn: "the machine, beside its state",
+		Others:   "the engine verifies the mesh's signature and records it, or refuses",
+		Subjects: []string{"mesh.node.*.ask.hand-over"}, Writes: isController},
+	// The operator asking a machine's engine for a fresh search for setuid programs, at the controller's
+	// terminal (novox/hq issue 361): signed as a hand-over is, under a signing context of its own.
+	{State: "a fresh setuid search asked of a machine", Writer: "controller, at its terminal",
+		KeptIn: "the machine, which throws its last search away", Others: "the engine verifies the mesh's signature and starts it, or refuses",
+		Subjects: []string{"mesh.node.*.ask.setuid-search"}, Writes: isController},
+	// A read-only judgement of a machine's declared directories asked of its engine (novox/hq issue 358): signed as a
+	// hand-over is, under a signing context of its own. It changes nothing on the machine.
+	{State: "a judgement of a machine's directories asked of it", Writer: "controller",
+		KeptIn: "nowhere: the engine answers it and keeps nothing", Others: "the engine verifies the mesh's signature and answers, or refuses",
+		Subjects: []string{"mesh.node.*.ask.judge-directories"}, Writes: isController},
+	{State: "a machine's applied state and its report", Writer: "the node-engine's apply queue",
+		KeptIn: "the machine; the report on the bus", Others: "the reconcile and a delivery enqueue, never apply",
+		// And its health statement between reports (novox/hq ADR 0240): the same writer stating the same
+		// machine, inside the grant it already had (`mesh.control.<its own>.>`). And a line mesh-cli was given
+		// on the machine (novox/hq ADR 0272): the node is what the controller judges the terminal by, so that
+		// subject is this machine's engine's alone.
+		Subjects: []string{"mesh.control.*.report", "mesh.control.*.health", "mesh.control.*.cli"}, Writes: ownMachine},
+	{State: "the controller lease", Writer: "the controller instance holding it", KeptIn: "key-value " + LeaseBucket,
+		Others: "a candidate waits", Subjects: kvOf(LeaseBucket), Writes: isController},
+	// The merges mesh-delivery announced, for a moved module's registration (ADR 0420 §7), written by the lease holder.
+	{State: "the merges mesh-delivery announced", Writer: "controller (lease holder)",
+		KeptIn: "key-value " + DeliveryMergesBucket, Others: "read at a moved module's registration",
+		Subjects: kvOf(DeliveryMergesBucket), Writes: isController},
+	// And the compositions (novox/hq ADR 0539 clauses 2 and 4): each node's in its own bucket, which only that node's
+	// node-engine reads, and each digest with the judgement of its move, which the assigner reads.
+	{State: "the compositions and their digests", Writer: "controller (lease holder), compare-and-set",
+		KeptIn:   "key-value composed-<node> for each node, and " + delivery.ControllerComposedBucket,
+		Others:   "a node-engine reads its own node's; the assigner reads the digests",
+		Subjects: kvOf(delivery.ControllerComposedBucket), Writes: isControllerOrTheHandPath},
+	{State: "conditions", Writer: "controller", KeptIn: "key-value " + ConditionsBucket + " (and its history, " +
+		ConditionHistoryBucket + "); how often each was observed, when last and its newest evidence in the " +
+		"controller's store, so a look that changes nothing writes no bucket", Others: "raise or clear only through observations the controller reads",
+		Subjects: append(kvOf(ConditionsBucket), kvOf(ConditionHistoryBucket)...), Writes: isController},
+	{State: "calls and their outcomes", Writer: "controller", KeptIn: "key-value " + CallsBucket,
+		Others: "read by id", Subjects: kvOf(CallsBucket), Writes: isController},
+	{State: "the hand-act log", Writer: "controller, through the verbs that act", KeptIn: "key-value " + HandActsBucket,
+		Others: "—", Subjects: kvOf(HandActsBucket), Writes: isController},
+	// What the healers did (novox/hq to-be 45 §7, Phase 3): the controller's alone, in its store — the
+	// budgets and the mesh-wide brake are counted from it, so a controller restarting cannot reset them.
+	{State: "the healers' acts and their brake", Writer: "controller (lease holder), each act begun before it is made",
+		KeptIn: "the controller's store", Others: "read through healers; each act said as healer-acted and in its condition's tried"},
+	{State: "stream definitions and bus permissions", Writer: "controller", KeptIn: "the bus", Others: "—",
+		// A stream's definition, and a durable consumer's by the API that names it so. Not every
+		// consumer create: a module watching its own bucket makes and deletes an ordered consumer on the
+		// bucket's stream (ADR 0201), which defines nothing the mesh keeps.
+		Subjects: []string{"$JS.API.STREAM.CREATE.>", "$JS.API.STREAM.UPDATE.>", "$JS.API.STREAM.DELETE.>",
+			"$JS.API.CONSUMER.DURABLE.CREATE.>"},
+		Writes: isController},
+	{State: "builds and their outcomes", Writer: "the build seat's holder", KeptIn: "its own state",
+		Others:   "the controller asks",
+		Subjects: []string{"mesh.seat.node-build-agent.event.built", "mesh.seat.mesh-build-machine.event.built"},
+		Writes:   holdsSeatOf,
+		Shared:   "every machine holding the build seat answers the asks it took; each outcome names its ask"},
+	// What a module keeps and who may read it (novox/hq ADR 0495 clauses 2 and 3, issue 1790): said by the module, kept by
+	// the controller.
+	{State: "a module's states announced", Writer: "the module itself, from its code, under its own name",
+		KeptIn: "the bus (EVENTS)", Others: "the controller keeps the last of each and grants readers from it",
+		Subjects: []string{"mesh.mod.*.event.states"}, Writes: ownAnnouncer},
+	{State: "the states announced", Writer: "controller, from each module's announcement",
+		KeptIn: "key-value " + StatesAnnouncedBucket, Others: "the composition of the bus's users reads it",
+		Subjects: kvOf(StatesAnnouncedBucket), Writes: isController},
+	{State: "a merge announced", Writer: "one announcer per forge (the hook, or the poll when the hook is absent — never both)",
+		KeptIn: "the bus", Others: "—", Subjects: []string{"mesh.mod.*.event.pull.merged"}, Writes: ownModule},
+	// A pull request's head, before it merges (novox/hq to-be 45 §9): the same one announcer.
+	{State: "a pull request's head announced", Writer: "the forge's announcer, the one that announces its merges",
+		KeptIn: "the bus", Others: "the controller asks the build seat to check it", Subjects: []string{"mesh.mod.*.event.pull.updated"},
+		Writes: ownModule},
+	{State: "a pull request's merge check", Writer: "the build seat's holder that ran it, said as the controller's `checked`",
+		KeptIn: "the bus", Others: "the forge's holder sets it as the pull request's status"},
+	{State: "a provider's standing", Writer: "the provider", KeptIn: "the provider's events",
+		Others: "the controller keeps the newest word as a condition",
+		Subjects: []string{"mesh.mod.*.event.provisioner.failing", "mesh.mod.*.event.provisioner.recovered",
+			"mesh.mod.*.event.provisioner.retirement"},
+		Writes: ownModule},
+	{State: "the operator-channel's open messages", Writer: "the seat's holder", KeptIn: "its own key-value state",
+		Others: "—"},
+	{State: "the facts snapshot", Writer: "controller", KeptIn: "the artifact store, facts/latest",
+		Others: "the build seat reads"},
+	// What a consumer gave up on (novox/hq issue 330): copied by the controller from the server's notice,
+	// and delivered again or dropped only through its verb, with why.
+	{State: "a message a consumer gave up on", Writer: "controller", KeptIn: "the bus, the stream " + DeadLettersStream,
+		Others:   "read, delivered again or dropped through the controller's dead-letters verb",
+		Subjects: []string{deadLetterPrefix + ">", againPrefix + ">"}, Writes: isController},
+	// The record mirrors (novox/hq ADR 0289 §9, design 54 §2): rows of this table, so a grant that lets
+	// anything else write them is refused at composition. Built so far: the assignments and each registered
+	// module's declared config (design 57 F3), and the list of predefined keys kept (design 57 K3).
+	{State: "the assignments mirror", Writer: "controller (lease holder): the verbs that assign, and the sends that record what runs; " +
+		"a mirror of its store only until the assignments are moved to the bus (novox/hq ADR 0408)",
+		KeptIn: "key-value " + AssignmentsBucket + ", the record once moved", Others: "read through `reads` as mesh-controller." + MirrorAssignments,
+		Subjects: kvOf(AssignmentsBucket), Writes: isController},
+	// The chain (novox/hq ADR 0408): builds and rollouts beside the assignments above, which keep their bucket. Not
+	// mirrors of the store but the record, written by the lease holder by compare-and-set and removed by nobody.
+	{State: "the builds of the chain", Writer: "controller (lease holder), compare-and-set on the key's revision",
+		KeptIn: "key-value " + BuildsBucket + ", sixty-four revisions of each key, none removed",
+		Others: "read through `reads` as mesh-controller." + ChainBuilds, Subjects: kvOf(BuildsBucket), Writes: isController},
+	{State: "the rollouts of the chain", Writer: "controller (lease holder), compare-and-set on the key's revision",
+		KeptIn: "key-value " + RolloutsBucket + ", sixty-four revisions of each key, none removed",
+		Others: "read through `reads` as mesh-controller." + ChainRollouts, Subjects: kvOf(RolloutsBucket), Writes: isController},
+	// The grants issued (novox/hq ADR 0528 clause 2, issue 1394): the controller's, read by the assigner for its sixth rule.
+	{State: "the grants issued", Writer: "controller (lease holder), once the bus's user list carrying a module's manifest at a fingerprint was sent",
+		KeptIn: "key-value " + GrantsBucket + ", one key a module's fingerprint, none removed",
+		Others: "read through `reads` as mesh-controller." + ControllerGrants, Subjects: kvOf(GrantsBucket), Writes: isController},
+	// What each machine has of each module (novox/hq ADR 0429 §1, design 47): written by that machine's node-engine under
+	// its own node's keys, never by the controller; the view and the watchman read it.
+	{State: "a machine's have", Writer: "the node-engine of the machine, under its own keys `<node>.>`",
+		KeptIn: "key-value " + delivery.HaveBucket + ", twenty revisions of each key",
+		Others: "read through `reads` as node-engine.have", Subjects: kvOf(delivery.HaveBucket), Writes: ownNodeKeys},
+	// The contents of a declaration's files over 64 KiB (novox/hq ADR 0486 §2): the controller alone writes the bucket, each
+	// object under the digest of its content; a node-engine reads one by its name, with no list and no write.
+	{State: "a declaration's large files", Writer: "controller, each object under the sha256 digest of its content; the " +
+		"operator's account on release 6's hand path alone (ADR 0539 clause 10)",
+		KeptIn: "the object bucket " + DeclarationFilesBucket + "-<node> of each node, an object removed a day after the " +
+			"node's latest declaration no longer names it",
+		Others:   "a node-engine reads an object of its own bucket by its name and may neither list the bucket nor write it",
+		Subjects: []string{"$O.*.>"}, Writes: isControllerOrTheHandPath},
+	{State: "the declared-config mirror", Writer: "controller (lease holder), from its store, only on a change",
+		KeptIn: "key-value " + DeclaredConfigBucket, Others: "read through `reads` as mesh-controller." + MirrorDeclaredConfig,
+		Subjects: kvOf(DeclaredConfigBucket), Writes: isController},
+	{State: "the predefined-keys mirror", Writer: "controller (lease holder), from its store, only on a change",
+		KeptIn: "key-value " + PredefinedBucket, Others: "read through `reads` as mesh-controller." + MirrorPredefined,
+		Subjects: kvOf(PredefinedBucket), Writes: isController},
+	{State: "the declared-packages mirror", Writer: "controller (lease holder), from the composition of each node, only on a change",
+		KeptIn: "key-value " + DeclaredPackagesBucket, Others: "read through `reads` as mesh-controller." + MirrorDeclaredPackages,
+		Subjects: kvOf(DeclaredPackagesBucket), Writes: isController},
+	// What a machine's provisioner client placed of a module's files (novox/hq ADR 0349 §4, design 57 P6): its own
+	// machine's word alone, which a walk's end and a gate wait for (ADR 0362, ADR 0349 §15). Kept newest per module
+	// in the stream ProvAppliedStream, and by the client in the provisioner server's `applied` bucket.
+	{State: "a module's files placed on a machine", Writer: "that machine's provisioner client",
+		KeptIn: "the bus, the stream " + ProvAppliedStream + ", newest per module; and key-value " +
+			ProvisionerAppliedBucket,
+		Others:   "the controller reads it at a walk's end and a gate; a failure is that machine's failed apply",
+		Subjects: []string{"prov.applied.*.>"}, Writes: ownProvisioner},
+}
+
+// CheckWriters refuses a grant that lets a principal publish on a subject the writers table gives
+// another writer (to-be 45 §1): which state, whose, and the pattern that would make a second writer.
+func CheckWriters(p Principal, publish []string) error {
+	var problems []string
+	for _, pattern := range publish {
+		for _, row := range WritersTable {
+			if row.Writes == nil {
+				continue
+			}
+			for _, subject := range row.Subjects {
+				if !SubjectsOverlap(pattern, subject) || row.Writes(p, pattern) {
+					continue
+				}
+				problems = append(problems, fmt.Sprintf("%s may publish %s, which writes %s (%s), whose writer is %s",
+					p.Username(), pattern, row.State, subject, row.Writer))
+			}
+		}
+	}
+	if len(problems) == 0 {
+		return nil
+	}
+	return fmt.Errorf("a second writer would be granted (novox/hq to-be 45 §1, one writer per piece of state):\n  %s",
+		strings.Join(problems, "\n  "))
+}
+
+// SubjectsOverlap says some subject matches both patterns: `*` is one token, `>` one or more to the end.
+func SubjectsOverlap(a, b string) bool {
+	x, y := strings.Split(a, "."), strings.Split(b, ".")
+	for i := 0; ; i++ {
+		switch {
+		case i == len(x) && i == len(y):
+			return true
+		case i == len(x) || i == len(y):
+			return false
+		case x[i] == ">" || y[i] == ">":
+			return true
+		case x[i] == "*" || y[i] == "*" || x[i] == y[i]:
+			continue
+		default:
+			return false
+		}
+	}
+}
+
+// isControllerOrTheHandPath is the controller, or the operator's account (a person who may invoke every tool) writing
+// release 6's hand path: the one second writer ADR 0539 clauses 2 and 10 name, for a composition made by hand.
+func isControllerOrTheHandPath(p Principal, pattern string) bool {
+	return isController(p, pattern) || (p.Kind == KindPerson && administers(p.Invokes))
+}

go/catalogue/a_service_process_test.go

@@ -0,0 +1,166 @@
+package catalogue
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+// novox/hq issue 213 (ADR 0188 §1, §3): a module's own Go service is a bundle the host runs as a
+// process, not an image. Each test holds one thing that had to change in the composer for the
+// controller to be declared that way.
+
+const aServiceDigest = "sha256:dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd"
+
+// aServiceModule is the controller's shape in miniature: it answers tools of its own, its code is a
+// Go bundle a process runs as an account it declares, its secrets belong to that account, it
+// prepares its state, and its process replaces the container it used to run as.
+func aServiceModule(t *testing.T) Manifest {
+	t.Helper()
+	raw := `{
+	  "module": "svc", "version": "1", "tools": ["status"], "prepares": true,
+	  "own-secrets": {"store": "${dir:state}/store"},
+	  "secrets-owner": "svc",
+	  "resources": [
+	    {"id": "state", "type": "directory", "mode": "0700", "place": "mesh", "owner": "svc"},
+	    {"id": "service", "type": "process", "name": "svc", "artifact": "code",
+	     "run": ["./svc", "serve"], "user": "svc", "replaces": ["server"],
+	     "env": {"SVC_STORE_FILE": "${dir:state}/store", "SVC_STORE_PORT": "${seat:mesh-store:5432}"}},
+	    {"id": "account", "type": "user", "name": "svc", "shell": "/usr/bin/nologin", "home": "/var/lib/svc"}
+	  ],
+	  "build": {"artifacts": [{"name": "code", "kind": "bundle", "language": "go", "system": "arch",
+	    "from": "cmd/svc", "binary": "svc"}]}
+	}`
+	m, err := ParseManifest([]byte(raw))
+	if err != nil {
+		t.Fatalf("the service's manifest is refused: %v", err)
+	}
+	resolved, err := m.Resolve([]Built{{Name: "code", Kind: ArtifactBundle,
+		Reference: ArtifactStoreScheme + "svc/code@" + aServiceDigest, Digest: aServiceDigest}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return resolved
+}
+
+func composeTheService(t *testing.T, with Rendering) []map[string]any {
+	t.Helper()
+	with.Needed = map[string]map[string]string{"svc": {"store": "sealed-store"}}
+	with.ArtifactStore = "anchor.internal:5100"
+	out, err := Resolution{Node: "anchor", Modules: []Manifest{aServiceModule(t)}}.Declaration(with)
+	if err != nil {
+		t.Fatalf("the service does not compose: %v", err)
+	}
+	return out
+}
+
+func indexOf(out []map[string]any, id string) int {
+	for i, r := range out {
+		if r["id"] == id {
+			return i
+		}
+	}
+	return -1
+}
+
+// A module that declares tools has every bundle served by the node's runtime unless it says
+// otherwise — and the controller declares the verbs it answers as tools. Its service bundle is run
+// by its own process; launched a second time by the runtime it would be a second controller
+// pretending to be an MCP server.
+func TestABundleItsOwnProcessRunsIsNotServedByTheRuntime(t *testing.T) {
+	m := aServiceModule(t)
+	if len(m.Bundles) != 1 {
+		t.Fatalf("the service's bundle was not kept: %+v", m.Bundles)
+	}
+	if loads := m.Bundles[0].Loads; len(loads) != 0 {
+		t.Fatalf("the runtime would launch the service's own bundle as tools: %v", loads)
+	}
+	// And a bundle no resource runs still is served, as a module declaring tools always had it.
+	tools := Manifest{Module: "t", Version: "1", Tools: []string{"x"},
+		Build: &Build{Artifacts: []Artifact{{Name: "tools", Kind: ArtifactBundle, Language: "go",
+			System: "arch", From: "cmd/t"}}}}
+	resolved, err := tools.Resolve([]Built{{Name: "tools", Kind: ArtifactBundle,
+		Reference: ArtifactStoreScheme + "t/tools@" + aServiceDigest, Digest: aServiceDigest}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if loads := resolved.Bundles[0].Loads; len(loads) != 1 || loads[0] != "t" {
+		t.Fatalf("a tools bundle nothing runs is no longer served: %v", loads)
+	}
+}
+
+// The account is created before anything is given to it. Its secrets are mesh-computed and so
+// placed before the module's own resources; given to a user the machine did not have yet, they were
+// refused on the first apply and the process started without them.
+func TestAModulesAccountComesBeforeWhatBelongsToIt(t *testing.T) {
+	out := composeTheService(t, Rendering{})
+	account, secret := indexOf(out, "svc.account"), indexOf(out, "svc."+NeedID("store"))
+	if account < 0 || secret < 0 {
+		t.Fatalf("the account or the secret is missing: %v", out)
+	}
+	if account > secret {
+		t.Fatalf("the secret owned by svc is written before svc exists: account at %d, secret at %d",
+			account, secret)
+	}
+	if owner := out[secret]["owner"]; owner != "svc" {
+		t.Errorf("the secret belongs to %v, not the account its process runs as", owner)
+	}
+}
+
+// The process is the module's program; its preparation is the same program asked to prepare, as a
+// step before it — with the same account and environment, and handing nothing over.
+func TestAProcessIsPreparedByItsOwnProgram(t *testing.T) {
+	out := composeTheService(t, Rendering{})
+	step, process := indexOf(out, "svc.service-prepare"), indexOf(out, "svc.service")
+	if step < 0 || process < 0 || step > process {
+		t.Fatalf("the preparation is not a step before the process (%d, %d): %v", step, process, out)
+	}
+	s := out[step]
+	if s["type"] != "process" || s["run-once"] != true || s["name"] != "svc-prepare" {
+		t.Errorf("the preparation is not a run-once process: %v", s)
+	}
+	if run, _ := json.Marshal(s["run"]); string(run) != `["./svc","prepare"]` {
+		t.Errorf("the preparation runs %s", run)
+	}
+	if s["user"] != "svc" || s["source"] != out[process]["source"] {
+		t.Errorf("the preparation does not run the same bundle as the same account: %v", s)
+	}
+	if env, _ := s["env"].(map[string]any); env["SVC_STORE_FILE"] == nil {
+		t.Errorf("the preparation is not given the process's environment: %v", s["env"])
+	}
+	if _, has := s["replaces"]; has {
+		t.Errorf("the preparation would hand over what the process replaces: %v", s)
+	}
+	if _, has := s["args"]; has {
+		t.Errorf("the preparation carries a container's args: %v", s)
+	}
+}
+
+// What the process replaces is named as the host recorded it, `<module>.<id>`; unprefixed, the host
+// matches nothing and removes the container first, as before.
+func TestWhatAProcessReplacesIsNamedAsTheHostRecordedIt(t *testing.T) {
+	out := composeTheService(t, Rendering{})
+	p := out[indexOf(out, "svc.service")]
+	if got, _ := json.Marshal(p["replaces"]); string(got) != `["svc.server"]` {
+		t.Fatalf("the process replaces %s", got)
+	}
+}
+
+func TestWhatReplacesMayNameIsRefusedNearItsAuthor(t *testing.T) {
+	for what, resource := range map[string]string{
+		"a container":        `{"id":"c","type":"container","name":"c","image":"x@` + aServiceDigest + `","replaces":["old"]}`,
+		"a step":             `{"id":"p","type":"process","name":"p","run":["./p"],"run-once":true,"replaces":["old"]}`,
+		"something declared": `{"id":"p","type":"process","name":"p","run":["./p"],"replaces":["p"]}`,
+		"another module's":   `{"id":"p","type":"process","name":"p","run":["./p"],"replaces":["other.old"]}`,
+		"not a list":         `{"id":"p","type":"process","name":"p","run":["./p"],"replaces":"old"}`,
+	} {
+		raw := `{"module":"m","version":"1","resources":[` + resource + `]}`
+		if _, err := ParseManifest([]byte(raw)); err == nil || !strings.Contains(err.Error(), "replace") {
+			t.Errorf("replaces on %s was accepted: %v", what, err)
+		}
+	}
+	ok := `{"module":"m","version":"1","resources":[{"id":"p","type":"process","name":"p","run":["./p"],"replaces":["old"]}]}`
+	if _, err := ParseManifest([]byte(ok)); err != nil {
+		t.Errorf("a process replacing what its module no longer declares was refused: %v", err)
+	}
+}

go/catalogue/accesses_test.go

@@ -0,0 +1,108 @@
+package catalogue
+
+import (
+	"strings"
+	"testing"
+)
+
+// The fault 04-ISSUES/036 records: a media stack is several modules — a library server, the
+// acquisition managers, a download client — that must share directories on one machine. Written
+// as owned `directory` resources, two of them on one node are refused as rivalrous owners, which
+// is right in general and wrong here: sharing those directories is the whole point of the stack.
+//
+// Declared as accesses to an operator-owned path (novox/hq ADR 0051), they co-resolve. An access
+// is not a resource and never enters the duplicate-owner map, so this is the exact case the
+// resolver refuses above when the same path is owned — and does not, when it is merely accessed.
+func TestTwoModulesAccessingOnePathCoResolve(t *testing.T) {
+	a := mod("a", nil, nil, nil)
+	a.Accesses = []Access{{Path: "/services/media/downloads", Mode: AccessReadWrite}}
+	b := mod("b", nil, nil, nil)
+	b.Accesses = []Access{{Path: "/services/media/downloads", Mode: AccessRead}}
+
+	got, err := Resolve(shelf(a, b), []string{"a", "b"}, workstation(), World{})
+	if err != nil {
+		t.Fatalf("two modules accessing one operator-owned path were refused: %v", err)
+	}
+
+	// And each accessing module's grant reaches the machine as its own `access` resource, so the
+	// host can find the path present or refuse — both naming the one operator-owned path.
+	var accesses int
+	for _, r := range mustDeclare(t, got) {
+		if r["type"] == "access" && r["path"] == "/services/media/downloads" {
+			accesses++
+		}
+	}
+	if accesses != 2 {
+		t.Errorf("expected both modules' accesses in the declaration, got %d", accesses)
+	}
+}
+
+// The mirror of the case above, so the sharing vocabulary does not weaken the rule it sits beside:
+// two modules OWNING one path is still refused, exactly as before accesses existed.
+func TestTwoModulesOwningOnePathAreStillRefused(t *testing.T) {
+	a := mod("a", nil, nil, nil)
+	a.Resources = []map[string]any{
+		{"id": "lib", "type": "directory", "path": "/services/media/movies", "mode": "0755"}}
+	b := mod("b", nil, nil, nil)
+	b.Resources = []map[string]any{
+		{"id": "lib", "type": "directory", "path": "/services/media/movies", "mode": "0755"}}
+
+	_, err := Resolve(shelf(a, b), []string{"a", "b"}, workstation(), World{})
+	if err == nil {
+		t.Fatal("two modules owning the same directory were both assigned")
+	}
+	if !strings.Contains(err.Error(), "/services/media/movies") {
+		t.Errorf("the refusal does not name the path: %v", err)
+	}
+}
+
+// Shared data is the operator's, owned by no module (novox/hq ADR 0051). A module owning the path
+// another module was told to expect the operator to provide would create and chown it — and the
+// two intentions cannot both hold, so it is refused by name. This is what keeps the distinction
+// machine-checkable rather than a convention nobody enforces.
+func TestAModuleMayNotOwnWhatAnotherAccesses(t *testing.T) {
+	owns := mod("owns", nil, nil, nil)
+	owns.Resources = []map[string]any{
+		{"id": "lib", "type": "directory", "path": "/services/media/movies", "mode": "0755"}}
+	uses := mod("uses", nil, nil, nil)
+	uses.Accesses = []Access{{Path: "/services/media/movies", Mode: AccessRead}}
+
+	_, err := Resolve(shelf(owns, uses), []string{"owns", "uses"}, workstation(), World{})
+	if err == nil {
+		t.Fatal("a module owning a path another accesses was allowed")
+	}
+	if !strings.Contains(err.Error(), "/services/media/movies") ||
+		!strings.Contains(err.Error(), "the operator's") {
+		t.Errorf("the refusal does not explain the ownership conflict: %v", err)
+	}
+}
+
+// A manifest states an access's extent, the way a listening port states its source. An absolute
+// path and a mode of read or read-write; anything else is refused rather than acted on wrongly.
+func TestAnAccessIsValidated(t *testing.T) {
+	good := []byte(`{"module":"m","accesses":[{"path":"/services/media","mode":"read-write"}]}`)
+	if _, err := ParseManifest(good); err != nil {
+		t.Fatalf("a valid access was refused: %v", err)
+	}
+
+	// Mode is optional and narrows to read — the safe default, because the danger with an access
+	// is being given more than was meant, not less.
+	bare := []byte(`{"module":"m","accesses":[{"path":"/services/media"}]}`)
+	m, err := ParseManifest(bare)
+	if err != nil {
+		t.Fatalf("an access with no mode was refused: %v", err)
+	}
+	if m.Accesses[0].At() != AccessRead {
+		t.Errorf("an access with no mode is %q, want %q", m.Accesses[0].At(), AccessRead)
+	}
+
+	relative := []byte(`{"module":"m","accesses":[{"path":"services/media","mode":"read"}]}`)
+	if _, err := ParseManifest(relative); err == nil {
+		t.Error("a relative access path was accepted")
+	}
+
+	wrong := []byte(`{"module":"m","accesses":[{"path":"/services/media","mode":"append"}]}`)
+	if _, err := ParseManifest(wrong); err == nil {
+		t.Error("an access with an unknown mode was accepted")
+	}
+}

go/catalogue/adoption.go

@@ -0,0 +1,242 @@
+package catalogue
+
+import (
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+// What an adopted node is declared in place of a filter (novox/hq ADR 0100).
+//
+// On an adopted node the firewall found on the machine stays in force: the mesh loads no table
+// that drops by default or holds an accept. What the mesh needs reachable is declared as
+// openings, which the host converges through the found firewall in its own terms; and the mesh
+// guards its own foundation ports itself, in a table that only refuses.
+
+// AdoptionPrefix is the id prefix of what the mesh declares of its own on an adopted node. It is
+// never a module's, so none of it is ever held as found.
+const AdoptionPrefix = "adoption."
+
+// Where an opening admits from, on the wire.
+const (
+	OpeningFromEverywhere = "everywhere"
+	OpeningFromMesh       = "mesh"
+)
+
+// The two paths a packet reaches a port by: received by the machine, or forwarded to a
+// container that publishes it.
+const (
+	PathIncoming  = "incoming"
+	PathForwarded = "forwarded"
+)
+
+// Guard resources: the refusal-only table, the unit that loads it, and that unit running.
+const (
+	GuardPath = "/etc/mesh/guard.nft"
+	GuardUnit = "mesh-guard.service"
+	// GuardUnitPath is where the unit is written.
+	GuardUnitPath = "/etc/systemd/system/" + GuardUnit
+)
+
+// GuardID, GuardUnitID and GuardRunningID are the guard's resource identities. The installer
+// raises the same three on an adopted genesis, so the first push finds them already there.
+func GuardID() string        { return AdoptionPrefix + "guard" }
+func GuardUnitID() string    { return AdoptionPrefix + "guard-unit" }
+func GuardRunningID() string { return AdoptionPrefix + "guard-running" }
+
+// GuardPackageID is the tool that loads the guard, declared first: a node joining adopted has
+// no filter module and may have no nft at all, and a table nothing can load guards nothing.
+func GuardPackageID() string { return AdoptionPrefix + "guard-package" }
+
+// GuardPackage is the package that carries nft.
+const GuardPackage = "nftables"
+
+// OpeningID is an opening's resource identity: its protocol, port and path say what it is.
+func OpeningID(protocol string, port int, path string) string {
+	return fmt.Sprintf("%sopening-%s-%d-%s", AdoptionPrefix, protocol, port, path)
+}
+
+// Openings are what the mesh needs reachable on an adopted node, from the same inputs as the
+// filter it would load were the node converged, each from where that filter would admit it.
+//
+// `rules` is Filtering's answer — every module's listens, the hub's port, the per-node exposure —
+// and `foundation` is the ports the mesh itself needs, from everywhere. A rule for this machine
+// only opens nothing. `published` maps a machine port a container publishes to the container's
+// port: a published port is forwarded, not received, so its opening names the forwarded path and
+// the port the packet is forwarded to.
+func Openings(rules []Rule, foundation []int, published map[string]map[int]int) []map[string]any {
+	type key struct {
+		protocol string
+		port     int
+	}
+	from := map[key]string{}
+	var order []key
+	widen := func(k key, f string) {
+		was, seen := from[k]
+		if !seen {
+			order = append(order, k)
+		}
+		if !seen || was != OpeningFromEverywhere {
+			from[k] = f
+		}
+	}
+	for _, rule := range rules {
+		switch rule.From {
+		case FromEverywhere:
+			widen(key{rule.Protocol, rule.Port}, OpeningFromEverywhere)
+		case FromMesh:
+			widen(key{rule.Protocol, rule.Port}, OpeningFromMesh)
+		case FromLocalNetwork:
+			// The private network's part only (novox/hq ADR 0340). An adopted node's found firewall
+			// stays, and it is what admits the machine's local network; an opening has no word for a
+			// local network, and widening it to everywhere would open the port to the internet.
+			widen(key{rule.Protocol, rule.Port}, OpeningFromMesh)
+		}
+	}
+	for _, port := range foundation {
+		widen(key{"tcp", port}, OpeningFromEverywhere)
+	}
+	sort.Slice(order, func(a, b int) bool {
+		if order[a].port != order[b].port {
+			return order[a].port < order[b].port
+		}
+		return order[a].protocol < order[b].protocol
+	})
+	out := make([]map[string]any, 0, len(order))
+	for _, k := range order {
+		opening := map[string]any{"type": "opening", "port": k.port, "protocol": k.protocol,
+			"from": from[k]}
+		if to, forwarded := published[k.protocol][k.port]; forwarded {
+			opening["id"] = OpeningID(k.protocol, k.port, PathForwarded)
+			opening["path"] = PathForwarded
+			opening["to"] = to
+		} else {
+			opening["id"] = OpeningID(k.protocol, k.port, PathIncoming)
+			opening["path"] = PathIncoming
+		}
+		out = append(out, opening)
+	}
+	return out
+}
+
+// Published is every port the given containers publish on the machine, by protocol and machine
+// port, mapped to the container's own port. A mapping bound to loopback is left out: nothing off
+// the machine reaches it, forwarded or not.
+func Published(resources []map[string]any) map[string]map[int]int {
+	out := map[string]map[int]int{}
+	for _, r := range resources {
+		if fmt.Sprint(r["type"]) != "container" {
+			continue
+		}
+		listed, _ := r["ports"].([]any)
+		for _, entry := range listed {
+			written := strings.TrimSpace(fmt.Sprint(entry))
+			protocol := "tcp"
+			if cut := strings.LastIndex(written, "/"); cut >= 0 {
+				protocol = written[cut+1:]
+			}
+			// Indexed from the end, so an IPv6 address's own colons never shift the ports.
+			outer, inner, address, ok := mapping(written)
+			if !ok {
+				continue
+			}
+			switch strings.Trim(address, "[]") {
+			case "127.0.0.1", "localhost", "::1":
+				continue
+			}
+			if out[protocol] == nil {
+				out[protocol] = map[int]int{}
+			}
+			out[protocol][outer] = inner
+		}
+	}
+	return out
+}
+
+// AsGuard renders the mesh's refusal-only table for the given machine ports.
+//
+// It passes everything by default and holds nothing but a refusal, so it cannot close anything
+// the machine serves; and it is the mesh's own table, so the found firewall reloading does not
+// touch it. It refuses only packets addressed to this machine, and the ports except from the
+// machine itself — its loopback and the container runtime's own networks — and from the private
+// network, known by the interface a packet arrives on and never by its source address. At
+// prerouting, ahead of the runtime's destination translation, so it matches the port the packet
+// was sent to; in the inet family, so both address families.
+//
+// **The machine's own interfaces are named, where the derived filter names address ranges.** The
+// filter accepts the container runtime's networks by CIDR; this excludes its bridges by name — lo,
+// docker0, the br-* a compose network gets, and the mesh's own mesh0. A runtime whose bridge is
+// named anything else (a podman or libvirt bridge, or a docker network created with a fixed name)
+// would have its containers' traffic to a guarded port refused, which reads as the port being
+// down. Names rather than addresses is deliberate: a source address can be claimed by whoever
+// sends the packet, and this table exists to refuse what the found firewall never sees. Widening
+// it means adding names here and in the installer's copy together, which the golden test holds to
+// one text.
+//
+// The same text the installer raises on an adopted genesis; a test holds both to it.
+func AsGuard(ports []int) string {
+	sorted := append([]int{}, ports...)
+	sort.Ints(sorted)
+	listed := make([]string, len(sorted))
+	for i, p := range sorted {
+		listed[i] = strconv.Itoa(p)
+	}
+	var b strings.Builder
+	b.WriteString("table inet mesh_guard {}\n")
+	b.WriteString("delete table inet mesh_guard\n")
+	b.WriteString("table inet mesh_guard {\n")
+	b.WriteString("\tchain prerouting {\n")
+	b.WriteString("\t\ttype filter hook prerouting priority raw; policy accept;\n")
+	// Only packets addressed to this machine: traffic it routes for others — a predecessor's hub,
+	// say — is never the guard's business (novox/hq ADR 0103).
+	fmt.Fprintf(&b, "\t\tfib daddr type local iifname != \"lo\" iifname != \"docker0\" "+
+		"iifname != \"br-*\" iifname != \"mesh0\" tcp dport { %s } drop\n",
+		strings.Join(listed, ", "))
+	b.WriteString("\t}\n")
+	b.WriteString("}\n")
+	return b.String()
+}
+
+// GuardUnitText is the unit that loads the guard. Stopping it deletes only its own table: never
+// a flush, which would take the container runtime's rules and the found firewall with it.
+func GuardUnitText() string {
+	return "[Unit]\n" +
+		"Description=The mesh's guard: refuses its own ports from outside (novox/hq ADR 0100)\n" +
+		// Early, before the network is up, and without the default dependencies that would
+		// order it after the network; stopped at shutdown like any unit.
+		"DefaultDependencies=no\n" +
+		"Wants=network-pre.target\n" +
+		"Before=network-pre.target shutdown.target\n" +
+		"Conflicts=shutdown.target\n" +
+		"\n" +
+		"[Service]\n" +
+		"Type=oneshot\n" +
+		"RemainAfterExit=yes\n" +
+		"ExecStart=nft -f " + GuardPath + "\n" +
+		"ExecReload=nft -f " + GuardPath + "\n" +
+		"ExecStop=nft delete table inet mesh_guard\n" +
+		"\n" +
+		"[Install]\n" +
+		"WantedBy=multi-user.target\n"
+}
+
+// GuardResources are the guard as four resources of the existing kinds: the tool that loads it,
+// the table, the unit, and the unit running — reloaded when the table changes, so the new table
+// replaces the old in one `nft -f` through the unit's ExecReload with no moment unguarded, and
+// restarted only when the unit itself changes. Nothing when there is nothing to guard: an empty
+// set is not a table nft loads.
+func GuardResources(ports []int) []map[string]any {
+	if len(ports) == 0 {
+		return nil
+	}
+	return []map[string]any{
+		{"id": GuardPackageID(), "type": "package", "package": GuardPackage},
+		{"id": GuardID(), "type": "file", "path": GuardPath, "content": AsGuard(ports),
+			"mode": "0644"},
+		{"id": GuardUnitID(), "type": "file", "path": GuardUnitPath, "content": GuardUnitText(),
+			"mode": "0644"},
+		{"id": GuardRunningID(), "type": "service", "unit": GuardUnit, "state": "running",
+			"boot": "enabled", "restart-on": []any{GuardUnitID()}, "reload-on": []any{GuardID()}},
+	}
+}

go/catalogue/adoption_test.go

@@ -0,0 +1,683 @@
+package catalogue
+
+import (
+	"encoding/json"
+	"reflect"
+	"slices"
+	"strings"
+	"testing"
+)
+
+// novox/hq ADR 0100: on an adopted node the found firewall stays in force. The mesh declares
+// openings where it would have loaded a filter, and guards its own ports in a table that only
+// refuses.
+
+// hub is the private network's generator on the hub: it opens the hub's port from anywhere.
+type hub struct{}
+
+func (hub) Resources(string) ([]map[string]any, bool, error) {
+	return []map[string]any{{"id": "config", "type": "file", "path": "/etc/wireguard/mesh0.conf",
+		"content": "[Interface]\n"}}, true, nil
+}
+func (hub) Listens(string) ([]Listening, error) {
+	return []Listening{{Port: 51820, Protocol: "udp", From: FromEverywhere}}, nil
+}
+
+// anAdoptedAnchor is the control-node's set: the store, the bus, the registry, the private network,
+// a served module and the filter module.
+func anAdoptedAnchor() Resolution {
+	return Resolution{Node: "anchor", Modules: []Manifest{
+		{Module: "network", Computed: "overlay"},
+		{Module: "postgres", Guards: []int{5432},
+			Listens: []Listening{{Port: 5432, From: FromMesh}},
+			Resources: []map[string]any{{"id": "server", "type": "container", "name": "mesh-store",
+				"ports": []any{"5432:5432"}}}},
+		{Module: "lavinmq", Guards: []int{15672},
+			Listens: []Listening{{Port: 5671, From: FromMesh}, {Port: 5672, From: FromMesh}},
+			Resources: []map[string]any{{"id": "server", "type": "container", "name": "mesh-broker",
+				"ports": []any{"5671:5671", "5672:5672", "127.0.0.1:15672:15672"}}}},
+		{Module: "distribution",
+			Listens: []Listening{{Port: 5000, From: FromMesh}},
+			Resources: []map[string]any{{"id": "store", "type": "container", "name": "registry",
+				"ports": []any{"5000"}}}},
+		{Module: "hello-web",
+			Listens: []Listening{{Port: 8080, From: FromEverywhere}},
+			Resources: []map[string]any{{"id": "server", "type": "container", "name": "hello-web",
+				"ports": []any{"8080"}}}},
+		{Module: "helper", Listens: []Listening{{Port: 9000, From: FromMachine}}},
+		{Module: "nftables", Filtering: &Filtering{Into: "/etc/nftables.conf"},
+			Resources: []map[string]any{{"id": "load", "type": "service", "unit": "mesh-filter.service",
+				"state": "running", "restart-on": []any{"filtering"}}}},
+	}}
+}
+
+func anchorRendering(adopted bool) Rendering {
+	return Rendering{
+		Generators: map[string]Generator{"overlay": hub{}},
+		Ports:      map[string]map[int]int{"distribution": {5000: 5000}, "hello-web": {8080: 20001}},
+		Settings: SettingsBy{"distribution": {{From: "node anchor",
+			Placement: map[string]any{ExposeSetting: map[string]any{"5000": FromEverywhere}}}}},
+		Mesh:       []string{"10.42.0.1"},
+		Foundation: []int{5671},
+		// What the machine reported faces outside, which every rule in the filter is written
+		// around (novox/hq ADR 0140).
+		OutwardLinks:    []string{"eth0"},
+		TunnelInterface: "mesh0",
+		Adopted:         adopted,
+		// Genesis takes the foundation's modules.
+		Taken: map[string]bool{"postgres": true, "lavinmq": true},
+	}
+}
+
+func byID(resources []map[string]any) map[string]map[string]any {
+	out := map[string]map[string]any{}
+	for _, r := range resources {
+		out[r["id"].(string)] = r
+	}
+	return out
+}
+
+func TestAnAdoptedNodeIsDeclaredOpeningsFromTheSameInputsAsTheFilter(t *testing.T) {
+	composed, err := anAdoptedAnchor().Compose(anchorRendering(true))
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := byID(composed.Resources)
+	want := map[string]map[string]any{
+		// The hub's port, from anywhere, received.
+		"adoption.opening-udp-51820-incoming": {"port": 51820, "protocol": "udp",
+			"from": "everywhere", "path": "incoming"},
+		// The store's port from the private network only, and forwarded: a container publishes it.
+		"adoption.opening-tcp-5432-forwarded": {"port": 5432, "protocol": "tcp", "from": "mesh",
+			"path": "forwarded", "to": 5432},
+		// The bus from anywhere: a node enrols over it before it has a private address.
+		"adoption.opening-tcp-5671-forwarded": {"port": 5671, "protocol": "tcp",
+			"from": "everywhere", "path": "forwarded", "to": 5671},
+		"adoption.opening-tcp-5672-forwarded": {"port": 5672, "protocol": "tcp", "from": "mesh",
+			"path": "forwarded", "to": 5672},
+		// The registry from anywhere, by its node's exposure setting.
+		"adoption.opening-tcp-5000-forwarded": {"port": 5000, "protocol": "tcp",
+			"from": "everywhere", "path": "forwarded", "to": 5000},
+		// A published port names the machine port and the container port it is forwarded to.
+		"adoption.opening-tcp-20001-forwarded": {"port": 20001, "protocol": "tcp",
+			"from": "everywhere", "path": "forwarded", "to": 8080},
+	}
+	for id, fields := range want {
+		opening, ok := got[id]
+		if !ok {
+			t.Errorf("no %s among %v", id, keys(got))
+			continue
+		}
+		if opening["type"] != "opening" {
+			t.Errorf("%s is a %v", id, opening["type"])
+		}
+		for k, v := range fields {
+			if opening[k] != v {
+				t.Errorf("%s: %s is %v, want %v", id, k, opening[k], v)
+			}
+		}
+	}
+	for id := range got {
+		if strings.HasPrefix(id, "adoption.opening-") && want[id] == nil {
+			t.Errorf("an opening nothing asked for: %s", id)
+		}
+	}
+	// A port for this machine only opens nothing, and the management port is not opened at all.
+	for id := range got {
+		if strings.Contains(id, "-9000-") || strings.Contains(id, "-15672-") {
+			t.Errorf("%s is opened", id)
+		}
+	}
+
+	// And openings come first, in the order the machine applies them.
+	if !strings.HasPrefix(composed.Resources[0]["id"].(string), "adoption.opening-") {
+		t.Errorf("openings are not first: %v", composed.Resources[0]["id"])
+	}
+}
+
+func TestAnAdoptedNodeLoadsNoFilterOfTheMeshs(t *testing.T) {
+	composed, err := anAdoptedAnchor().Compose(anchorRendering(true))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, r := range composed.Resources {
+		if r["path"] == "/etc/nftables.conf" || strings.HasPrefix(r["id"].(string), "nftables.") {
+			t.Fatalf("an adopted node is declared the filter module's %v", r["id"])
+		}
+		if content, _ := r["content"].(string); strings.Contains(content, "policy drop") {
+			t.Fatalf("an adopted node is declared a table that drops by default: %v", r["id"])
+		}
+		// Nothing but refusals: the only accept in the guard is its policy.
+		if content, _ := r["content"].(string); r["id"] == GuardID() &&
+			strings.Count(content, "accept") != 1 {
+			t.Fatalf("the guard holds an accept:\n%s", content)
+		}
+	}
+	got := byID(composed.Resources)
+	guard := got[GuardID()]
+	if guard == nil || got[GuardUnitID()] == nil || got[GuardRunningID()] == nil {
+		t.Fatalf("no guard: %v", keys(got))
+	}
+	if guard["content"] != AsGuard([]int{5432, 5672, 15672}) {
+		t.Fatalf("the guard does not guard the store, the broker and its management port:\n%s",
+			guard["content"])
+	}
+	// The tool that loads it comes first, and the table after it: a node joining adopted has no
+	// filter module and may have no nft.
+	pkg, table := -1, -1
+	for i, r := range composed.Resources {
+		switch r["id"] {
+		case GuardPackageID():
+			pkg = i
+			if r["type"] != "package" || r["package"] != "nftables" {
+				t.Fatalf("the guard's package is %v", r)
+			}
+		case GuardID():
+			table = i
+		}
+	}
+	if pkg < 0 || pkg > table {
+		t.Fatalf("nftables is not declared before the guard's table (%d, %d)", pkg, table)
+	}
+	// A changed table is reloaded — one `nft -f`, atomic — never restarted, which would delete the
+	// table and leave the ports unguarded until it is loaded again. Only a changed unit restarts.
+	if !reflect.DeepEqual(got[GuardRunningID()]["reload-on"], []any{GuardID()}) ||
+		!reflect.DeepEqual(got[GuardRunningID()]["restart-on"], []any{GuardUnitID()}) {
+		t.Fatalf("the guard is not reloaded on its table and restarted on its unit: %v",
+			got[GuardRunningID()])
+	}
+	// Nothing of the mesh's own is anybody's to hold.
+	for id, module := range composed.Owner {
+		if strings.HasPrefix(id, AdoptionPrefix) {
+			t.Fatalf("%s is owned by %s", id, module)
+		}
+	}
+}
+
+func TestAConvergedNodeIsDeclaredItsFilterAndNoOpenings(t *testing.T) {
+	composed, err := anAdoptedAnchor().Compose(anchorRendering(false))
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := byID(composed.Resources)
+	if got["nftables.filtering"] == nil || got["nftables.load"] == nil {
+		t.Fatalf("a converged node lost its filter: %v", keys(got))
+	}
+	for id := range got {
+		if strings.HasPrefix(id, AdoptionPrefix) {
+			t.Fatalf("a converged node is declared %s", id)
+		}
+	}
+	plain, err := anAdoptedAnchor().Declaration(anchorRendering(false))
+	if err != nil {
+		t.Fatal(err)
+	}
+	a, _ := json.Marshal(plain)
+	b, _ := json.Marshal(composed.Resources)
+	if string(a) != string(b) {
+		t.Fatal("Compose and Declaration disagree on a converged node")
+	}
+}
+
+// The table the installer raises and the controller declares, character for character.
+func TestTheGuardIsExactlyThisTable(t *testing.T) {
+	const golden = `table inet mesh_guard {}
+delete table inet mesh_guard
+table inet mesh_guard {
+	chain prerouting {
+		type filter hook prerouting priority raw; policy accept;
+		fib daddr type local iifname != "lo" iifname != "docker0" iifname != "br-*" iifname != "mesh0" tcp dport { 5432, 15672 } drop
+	}
+}
+`
+	if got := AsGuard([]int{15672, 5432}); got != golden {
+		t.Fatalf("the guard changed:\n%s", got)
+	}
+	const unit = `[Unit]
+Description=The mesh's guard: refuses its own ports from outside (novox/hq ADR 0100)
+DefaultDependencies=no
+Wants=network-pre.target
+Before=network-pre.target shutdown.target
+Conflicts=shutdown.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=nft -f /etc/mesh/guard.nft
+ExecReload=nft -f /etc/mesh/guard.nft
+ExecStop=nft delete table inet mesh_guard
+
+[Install]
+WantedBy=multi-user.target
+`
+	if got := GuardUnitText(); got != unit {
+		t.Fatalf("the guard's unit changed:\n%s", got)
+	}
+	if GuardResources(nil) != nil {
+		t.Fatal("a guard with nothing to guard is an empty set nft refuses to load")
+	}
+}
+
+func TestAGuardedPortMustBeAPort(t *testing.T) {
+	if _, err := ParseManifest([]byte(`{"module":"postgres","guards":[5432]}`)); err != nil {
+		t.Fatalf("guards is refused: %v", err)
+	}
+	if _, err := ParseManifest([]byte(`{"module":"postgres","guards":[0]}`)); err == nil {
+		t.Fatal("guarding port 0 was accepted")
+	}
+}
+
+func keys[V any](m map[string]V) []string {
+	return sortedKeys(m)
+}
+
+// novox/hq ADR 0100: the foundation's ports are the node's. Given 5433 for the store, every place
+// that uses the port reads it from there: the container, the filter, the openings, the guard.
+func TestAGivenPortIsUsedEverywhereThePortIs(t *testing.T) {
+	given := map[string]map[int]int{"postgres": {5432: 5433}, "lavinmq": {15672: 15673}}
+	for _, adopted := range []bool{true, false} {
+		with := anchorRendering(adopted)
+		with.Given = given
+		with.Ports["postgres"] = map[int]int{5432: 5433}
+		composed, err := anAdoptedAnchor().Compose(with)
+		if err != nil {
+			t.Fatal(err)
+		}
+		got := byID(composed.Resources)
+		if ports := got["postgres.server"]["ports"]; !reflect.DeepEqual(ports, []any{"5433:5432"}) {
+			t.Fatalf("the store's container publishes %v", ports)
+		}
+		if ports := got["lavinmq.server"]["ports"]; !reflect.DeepEqual(ports,
+			[]any{"5671:5671", "5672:5672", "127.0.0.1:15673:15672"}) {
+			t.Fatalf("the broker's container publishes %v", ports)
+		}
+		if !adopted {
+			filter, _ := got["nftables.filtering"]["content"].(string)
+			if !strings.Contains(filter, "tcp dport 5433 accept") || strings.Contains(filter, "5432") {
+				t.Fatalf("the filter does not use the given port:\n%s", filter)
+			}
+			continue
+		}
+		if o := got["adoption.opening-tcp-5433-forwarded"]; o == nil || o["to"] != 5432 {
+			t.Fatalf("no opening for the given port: %v", keys(got))
+		}
+		if guard := got[GuardID()]["content"]; guard != AsGuard([]int{5433, 5672, 15673}) {
+			t.Fatalf("the guard does not guard the given ports:\n%s", guard)
+		}
+	}
+}
+
+func TestAGivenPortIsTheNodesAndReachesSomething(t *testing.T) {
+	store := anAdoptedAnchor().Modules[1]
+	node := func(v any) []Layer {
+		return []Layer{{From: "anchor", Placement: map[string]any{PortsSetting: v}}}
+	}
+	if got, err := GivenPorts(store, node(map[string]any{"5432": float64(5433)})); err != nil ||
+		got[5432] != 5433 {
+		t.Fatalf("a node's given port was not read: %v %v", got, err)
+	}
+	if _, err := GivenPorts(store, []Layer{{From: MeshWideLayer,
+		Placement: map[string]any{PortsSetting: map[string]any{"5432": float64(5433)}}}}); err == nil {
+		t.Fatal("a port given for the whole mesh was accepted")
+	}
+	if _, err := GivenPorts(store, node(map[string]any{"6000": float64(6001)})); err == nil {
+		t.Fatal("a port the module neither listens on, publishes nor guards was given")
+	}
+	if _, err := GivenPorts(store, node(map[string]any{"5432": float64(70000)})); err == nil {
+		t.Fatal("a machine port that is not a port was given")
+	}
+	if _, err := GivenPorts(store, node(map[string]any{"5432": float64(22)})); err == nil {
+		t.Fatal("ssh's port was given")
+	}
+	broker := anAdoptedAnchor().Modules[2]
+	if _, err := GivenPorts(broker, node(map[string]any{"5671": float64(5700),
+		"5672": float64(5700)})); err == nil {
+		t.Fatal("one machine port was given for two of the module's ports")
+	}
+	if stray := UnusedSettings(store, node(map[string]any{"5432": float64(5433)})); len(stray) != 0 {
+		t.Fatalf("a given port is called stray: %v", stray)
+	}
+}
+
+// novox/hq ADR 0103: the guard is derived, and from taken modules only — every machine port a taken
+// module publishes that the filter admits from the private network only, and the ports its
+// manifest guards. A module assigned but not taken is not guarded: its port may still be the
+// predecessor's.
+func TestTheGuardIsDerivedFromTakenModulesOnly(t *testing.T) {
+	guardOf := func(with Rendering) string {
+		t.Helper()
+		composed, err := anAdoptedAnchor().Compose(with)
+		if err != nil {
+			t.Fatal(err)
+		}
+		content, _ := byID(composed.Resources)[GuardID()]["content"].(string)
+		return content
+	}
+
+	// The broker taken, the store not: the broker's plain port follows from its listens (from
+	// the mesh, published), its management port from its manifest; the store is not guarded, and
+	// neither is the bus, which the mesh needs from everywhere.
+	with := anchorRendering(true)
+	with.Taken = map[string]bool{"lavinmq": true}
+	if got := guardOf(with); got != AsGuard([]int{5672, 15672}) {
+		t.Fatalf("the guard is not the taken broker's ports:\n%s", got)
+	}
+
+	// A taken module publishing a port admitted from everywhere is not guarded; one admitted from
+	// the mesh is. The registry is exposed everywhere on this node, and hello-web listens from
+	// everywhere.
+	with.Taken = map[string]bool{"distribution": true, "hello-web": true}
+	if got := guardOf(with); got != "" {
+		t.Fatalf("a port admitted from everywhere is guarded:\n%s", got)
+	}
+	with.Settings = nil
+	if got := guardOf(with); got != AsGuard([]int{5000}) {
+		t.Fatalf("the registry, from the mesh only, is not guarded:\n%s", got)
+	}
+
+	// Nothing taken, nothing guarded — and no guard at all rather than an empty set.
+	with = anchorRendering(true)
+	with.Taken = nil
+	if got := guardOf(with); got != "" {
+		t.Fatalf("an untaken store is guarded:\n%s", got)
+	}
+
+	// A given port is followed: where the machine put it is what is refused.
+	with = anchorRendering(true)
+	with.Given = map[string]map[int]int{"lavinmq": {5672: 5682, 15672: 15673}}
+	with.Ports["lavinmq"] = map[int]int{5671: 5671, 5672: 5682}
+	if got := guardOf(with); got != AsGuard([]int{5432, 5682, 15673}) {
+		t.Fatalf("the guard does not follow the given ports:\n%s", got)
+	}
+}
+
+// A mapping bound to loopback is not published to anything off the machine — in either address
+// family — and an address's own colons never shift the ports.
+func TestPublishedLeavesOutLoopbackInBothFamilies(t *testing.T) {
+	got := Published([]map[string]any{{"type": "container", "ports": []any{
+		"127.0.0.1:15672:15672", "[::1]:8080:80", "localhost:9090:90",
+		"[::]:8443:443", "0.0.0.0:5000:5000", "5353:53/udp"}}})
+	want := map[string]map[int]int{"tcp": {8443: 443, 5000: 5000}, "udp": {5353: 53}}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("published is %v, want %v", got, want)
+	}
+}
+
+// novox/hq ADR 0038: only a published port is the mesh's to move. A module that binds the machine
+// itself listens where its software was told to, so giving it a machine port is refused.
+func TestAGivenPortIsRefusedForAPortNoContainerPublishes(t *testing.T) {
+	onTheMachine := Manifest{Module: "daemon",
+		Listens: []Listening{{Port: 9000, From: FromMesh}}, Guards: []int{9000}}
+	layers := []Layer{{From: "node anchor",
+		Placement: map[string]any{PortsSetting: map[string]any{"9000": float64(9100)}}}}
+	_, err := GivenPorts(onTheMachine, layers)
+	if err == nil || !strings.Contains(err.Error(), "does not publish") {
+		t.Fatalf("a port no container publishes was given: %v", err)
+	}
+}
+
+// novox/hq ADR 0103: a guarded port this node is told to open to everyone is opened, not guarded.
+// An opening from everywhere beside a guard dropping it is one statement refusing the other.
+func TestAGuardedPortOpenedToEveryoneIsNotGuarded(t *testing.T) {
+	with := anchorRendering(true)
+	with.Settings["postgres"] = []Layer{{From: "node anchor",
+		Placement: map[string]any{ExposeSetting: map[string]any{"5432": FromEverywhere}}}}
+	composed, err := anAdoptedAnchor().Compose(with)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := byID(composed.Resources)
+	if o := got["adoption.opening-tcp-5432-forwarded"]; o == nil || o["from"] != OpeningFromEverywhere {
+		t.Fatalf("the store's port is not opened to everyone: %v", o)
+	}
+	if guard, _ := got[GuardID()]["content"].(string); guard != AsGuard([]int{5672, 15672}) {
+		t.Fatalf("a port opened to everyone is still guarded:\n%s", guard)
+	}
+}
+
+// A module that publishes its ssh port the long way — `2222:22`, because the machine's own daemon
+// holds 22 — and says it listens on the machine side of that mapping, which is what anything
+// reaching it dials.
+func aForge() Manifest {
+	return Manifest{Module: "forge",
+		Provides: []Offer{{Name: "git-over-ssh", Scope: ScopeMesh}},
+		Serves:   map[string]map[string]any{"git-over-ssh": {"port": 2222}},
+		Listens:  []Listening{{Port: 3000, From: FromMesh}, {Port: 2222, From: FromMesh}},
+		Resources: []map[string]any{{"id": "server", "type": "container", "name": "forge",
+			"ports": []any{"3000", "2222:22"}}}}
+}
+
+// portsAsThePlanWould is where this machine puts each of a module's ports, derived the way
+// cmd/mesh-controller/plan.go derives it: a given port first, looked up by the port the module
+// says it listens on, and otherwise wherever the manifest's own mapping already put it. Written
+// here because everything below — the filter, the openings, the guard, what a consumer is told —
+// reads that map, and a given port that the lookup does not find moves the container's mapping
+// and nothing else.
+//
+// It stands in for the plan only where the plan does not allocate: a port the manifest already
+// placed, or one a node was given. For a short form with no given port the real plan asks the
+// inventory for a machine port and may come back with one from the pool, which needs a store and
+// is what cmd/mesh-controller's own tests exercise. So an assertion here about such a port asserts
+// this helper, not the mesh; keep the assertions to the ports under test.
+func portsAsThePlanWould(m Manifest, given map[int]int) map[int]int {
+	out := map[int]int{}
+	for _, l := range m.Listens {
+		if at, is := given[l.Port]; is {
+			out[l.Port] = at
+			continue
+		}
+		at, _ := m.MachineSide(l.Port)
+		out[l.Port] = at
+	}
+	return out
+}
+
+// novox/hq ADR 0100 and 0038: the machine side of a long-form mapping is a port the module
+// publishes, so a node may move it — and a module may name a mapping by either end.
+func TestAGivenPortNamesEitherEndOfWhatTheModulePublishes(t *testing.T) {
+	forge := aForge()
+	node := func(v any) []Layer {
+		return []Layer{{From: "node anchor", Placement: map[string]any{PortsSetting: v}}}
+	}
+
+	// The machine side — the number this module says it listens on, and the one the predecessor
+	// had somewhere else. Answered under 2222, the end the module itself names, which is what
+	// every reader of this map asks for. One entry, not two: a second key for the same answer is
+	// an entry another mapping's reader could find instead.
+	given, err := GivenPorts(forge, node(map[string]any{"2222": float64(222)}))
+	if err != nil {
+		t.Fatalf("the machine side of a mapping cannot be given a port: %v", err)
+	}
+	if want := map[int]int{2222: 222}; !reflect.DeepEqual(given, want) {
+		t.Fatalf("the forge was given %v; the mapping it names is filed under %v", given, want)
+	}
+
+	// The container's own port names the same mapping and means the same thing — and is filed
+	// under the same name, because the module's name for it has not changed.
+	if inside, err := GivenPorts(forge, node(map[string]any{"22": float64(222)})); err != nil ||
+		!reflect.DeepEqual(inside, map[int]int{2222: 222}) {
+		t.Fatalf("the container's end of the mapping was given %v: %v", inside, err)
+	}
+
+	// A short form is published on the number it names, and is unchanged by any of this.
+	if short, err := GivenPorts(forge, node(map[string]any{"3000": float64(2999)})); err != nil ||
+		short[3000] != 2999 {
+		t.Fatalf("the short form was given %v: %v", short, err)
+	}
+
+	// A port no container publishes is still refused, in the same words.
+	if _, err := GivenPorts(forge, node(map[string]any{"9000": float64(9100)})); err == nil ||
+		!strings.Contains(err.Error(), "does not publish") {
+		t.Fatalf("a port the forge does not publish was given: %v", err)
+	}
+
+	// And the two ends of one mapping given two different numbers is one setting contradicting
+	// the other: the machine publishes it once.
+	if _, err := GivenPorts(forge, node(map[string]any{
+		"2222": float64(222), "22": float64(300)})); err == nil ||
+		!strings.Contains(err.Error(), "one mapping") {
+		t.Fatalf("the two ends of one mapping were given different ports: %v", err)
+	}
+	// Said at both ends with the same number, it is still said twice, and refused where every
+	// other repeated machine port is — as the inventory refuses it when the setting is stored,
+	// which is the layer that sees it first.
+	if _, err := GivenPorts(forge, node(map[string]any{
+		"2222": float64(222), "22": float64(222)})); err == nil ||
+		!strings.Contains(err.Error(), "to both its 22 and its 2222") {
+		t.Fatalf("one mapping given one machine port at both ends: %v", err)
+	}
+	// A number that names two different mappings names neither: which one to move is not said.
+	twice := aForge()
+	twice.Resources[0]["ports"] = []any{"22", "2222:22"}
+	if _, err := GivenPorts(twice, node(map[string]any{"22": float64(222)})); err == nil ||
+		!strings.Contains(err.Error(), "twice") {
+		t.Fatalf("a number naming two of the module's mappings was accepted: %v", err)
+	}
+
+	// And the same refusal when the number naming two mappings is not the one the setting used
+	// but the one the answer would be filed under. Here `80` is the module's own name for a
+	// mapping, and two mappings wear it; filing an answer there is one container's port standing
+	// where the other's is read, and both containers then publish it.
+	shared := Manifest{Module: "gallery",
+		Listens: []Listening{{Port: 80, From: FromMesh}},
+		Resources: []map[string]any{
+			{"id": "a", "type": "container", "name": "a", "ports": []any{"4001:80"}},
+			{"id": "b", "type": "container", "name": "b", "ports": []any{"4002:80"}}}}
+	if _, err := GivenPorts(shared, node(map[string]any{"4001": float64(1234)})); err == nil ||
+		!strings.Contains(err.Error(), "twice") {
+		t.Fatalf("two containers were put on one machine port: %v", err)
+	}
+
+	// A module whose mappings chain — one's machine side is another's container port — keeps them
+	// apart, because each is filed under the port the module names it by and neither name is
+	// shared. Given both, each moves on its own and neither overwrites the other.
+	chained := Manifest{Module: "chain",
+		Listens: []Listening{{Port: 80, From: FromMesh}, {Port: 9090, From: FromMesh}},
+		Resources: []map[string]any{{"id": "server", "type": "container", "name": "chain",
+			"ports": []any{"8080:80", "9090:8080"}}}}
+	both, err := GivenPorts(chained, node(map[string]any{"80": float64(1234), "9090": float64(5678)}))
+	if err != nil || !reflect.DeepEqual(both, map[int]int{80: 1234, 9090: 5678}) {
+		t.Fatalf("chained mappings were given %v: %v", both, err)
+	}
+	if moved := givenOuter("8080:80", both); moved != "1234:80" {
+		t.Fatalf("the first mapping moved to %q, and it was given 1234", moved)
+	}
+	if moved := givenOuter("9090:8080", both); moved != "5678:8080" {
+		t.Fatalf("the second mapping moved to %q, and it was given 5678", moved)
+	}
+}
+
+// And the number reaches everything derived from it. The fault this is written against moved the
+// container's mapping alone: the filter opened the port the software had left, the adopted node's
+// opening named it too, the guard refused it, and a consumer was sent to it.
+func TestAGivenMachineSideReachesTheFilterTheOpeningAndTheConsumer(t *testing.T) {
+	forge := aForge()
+	given, err := GivenPorts(forge, []Layer{{From: "node anchor",
+		Placement: map[string]any{PortsSetting: map[string]any{"2222": float64(222)}}}})
+	if err != nil {
+		t.Fatalf("the machine side of a mapping cannot be given a port: %v", err)
+	}
+	r := Resolution{Node: "anchor", Modules: []Manifest{forge}}
+	with := Rendering{
+		Ports:           map[string]map[int]int{"forge": portsAsThePlanWould(forge, given)},
+		Given:           map[string]map[int]int{"forge": given},
+		Mesh:            []string{"10.77.0.1"},
+		Adopted:         true,
+		OutwardLinks:    []string{"eth0"},
+		TunnelInterface: "mesh0",
+		Taken:           map[string]bool{"forge": true},
+	}
+
+	// What the runtime is handed: the machine's own port on the outside, the container's within.
+	composed, err := r.Compose(with)
+	if err != nil {
+		t.Fatalf("the forge does not compose: %v", err)
+	}
+	got := byID(composed.Resources)
+	if ports := got["forge.server"]["ports"]; !reflect.DeepEqual(ports, []any{"3000:3000", "222:22"}) {
+		t.Fatalf("the forge's container publishes %v", ports)
+	}
+
+	// What the filter would open, were the node converged.
+	rules, err := r.Rules(with)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var opened []int
+	for _, rule := range rules {
+		opened = append(opened, rule.Port)
+	}
+	// Only the moved port is asserted: the forge's other port is a short form the real plan would
+	// allocate rather than read off the manifest, so its number here is portsAsThePlanWould's and
+	// not the mesh's.
+	if !slices.Contains(opened, 222) || slices.Contains(opened, 2222) {
+		t.Fatalf("the filter opens %v, not where the machine puts the forge", opened)
+	}
+
+	// And what it is declared instead, adopted: an opening on the machine's port, naming the
+	// container's port on the forwarded path — a published port is forwarded, never received.
+	opening := got[OpeningID("tcp", 222, PathForwarded)]
+	if opening == nil || opening["to"] != 22 || opening["from"] != OpeningFromMesh {
+		t.Fatalf("no opening for the port this node gave the forge: %v", keys(got))
+	}
+	for id := range got {
+		if strings.HasPrefix(id, "adoption.opening-tcp-2222-") {
+			t.Errorf("an opening for the port the forge was moved off: %s", id)
+		}
+	}
+
+	// The guard refuses it where the machine put it, and nothing where it used to be.
+	guard, _ := got[GuardID()]["content"].(string)
+	if !strings.Contains(guard, "222") || strings.Contains(guard, "2222") {
+		t.Fatalf("the guard does not follow the given port:\n%s", guard)
+	}
+
+	// And a consumer is sent to the same number, which is read from what the module serves.
+	if told := ServedOn(forge, "git-over-ssh", with.Ports["forge"])["port"]; told != 222 {
+		t.Fatalf("a consumer is told the forge answers on %v", told)
+	}
+}
+
+// And the mapping itself moves under either name, because Rendering.Given is a map anybody
+// composing a declaration hands in: keyed by the machine side, which is what a module declaring
+// 2222 calls its port, only the outside moves and the container's own port stays as written.
+func TestAMappingIsMovedUnderEitherOfItsNames(t *testing.T) {
+	for _, c := range []struct {
+		written string
+		given   map[int]int
+		want    string
+	}{
+		{"2222:22", map[int]int{2222: 222}, "222:22"},
+		{"2222:22", map[int]int{22: 222}, "222:22"},
+		{"127.0.0.1:15672:15672/tcp", map[int]int{15672: 15673}, "127.0.0.1:15673:15672/tcp"},
+		{"2222:22", map[int]int{3000: 2999}, "2222:22"},
+		{"2222:22", nil, "2222:22"},
+	} {
+		if got := givenOuter(c.written, c.given); got != c.want {
+			t.Errorf("%s given %v is published as %s, want %s", c.written, c.given, got, c.want)
+		}
+	}
+}
+
+// The same on a node that was given nothing, which is where the derivation was never at fault:
+// a long-form mapping is published where the manifest put it, and an adopted node opens that port
+// on the forwarded path like any other. What broke it was the number reaching only the mapping.
+func TestALongFormPortIsOpenedWhereTheManifestPublishesIt(t *testing.T) {
+	forge := aForge()
+	r := Resolution{Node: "anchor", Modules: []Manifest{forge}}
+	composed, err := r.Compose(Rendering{
+		Ports:           map[string]map[int]int{"forge": portsAsThePlanWould(forge, nil)},
+		Mesh:            []string{"10.77.0.1"},
+		Adopted:         true,
+		OutwardLinks:    []string{"eth0"},
+		TunnelInterface: "mesh0",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := byID(composed.Resources)
+	opening := got[OpeningID("tcp", 2222, PathForwarded)]
+	if opening == nil || opening["to"] != 22 {
+		t.Fatalf("no opening for the forge's published ssh port: %v", keys(got))
+	}
+}

go/catalogue/agent_account_test.go

@@ -0,0 +1,119 @@
+package catalogue
+
+import (
+	"testing"
+)
+
+// The account agents run as (novox/hq ADR 0266): a module names it as a machine fact — the agent account
+// where the node names one, the operator's otherwise — and asks the node-engine to judge it never to become
+// root only where it is the agents' own.
+
+func TestTheAgentAccountFactFallsBackToTheOperatorAndIsNeverRootOnlyWhenItsOwn(t *testing.T) {
+	facts := machineFacts(Resolution{Node: "anchor", Account: "ops"}, nil, "")
+	if facts["agent-account"] != "ops" || facts["agent-home"] != "/home/ops" || facts["agent-root"] != "" {
+		t.Errorf("with no agent account named, agents run as the operator: %v", facts)
+	}
+	facts = machineFacts(Resolution{Node: "anchor", Account: "ops", AccountHome: "/srv/ops"}, nil, "")
+	if facts["agent-home"] != "/srv/ops" {
+		t.Errorf("the operator's stated home is the agent's home when they are one account: %v", facts)
+	}
+	facts = machineFacts(Resolution{Node: "anchor", Account: "ops", AgentAccount: "agent"}, nil, "")
+	if facts["agent-account"] != "agent" || facts["agent-home"] != "/home/agent" || facts["agent-root"] != RootNever {
+		t.Errorf("a named agent account is the agents', never root: %v", facts)
+	}
+	if facts["account"] != "ops" {
+		t.Errorf("the operator account is still the operator's: %v", facts)
+	}
+	facts = machineFacts(Resolution{Node: "anchor", AgentAccount: "agent", AgentAccountHome: "/var/lib/agent"}, nil, "")
+	if facts["agent-home"] != "/var/lib/agent" || facts["agent-root"] != RootNever {
+		t.Errorf("an agent account with a stated home on a machine with no operator: %v", facts)
+	}
+	if _, has := machineFacts(Resolution{Node: "anchor"}, nil, "")["agent-account"]; has {
+		t.Error("a machine with no account at all names an agent account")
+	}
+}
+
+// The agent's module, in the shape the catalogue's declares it: the account, never root where it is its
+// own; its directory under that home, owned by it.
+const agentModule = `{"module": "agent", "version": "1", "resources": [
+  {"id": "account", "type": "user", "name": "${machine:agent-account}", "home": "${machine:agent-home}",
+   "root": "${machine:agent-root}"},
+  {"id": "home", "type": "directory", "path": "${machine:agent-home}/.agent", "mode": "0700",
+   "owner": "${machine:agent-account}"}
+]}`
+
+func TestTheAgentAccountIsDeclaredNeverRootOnlyToAnEngineThatJudgesIt(t *testing.T) {
+	m, err := ParseManifest([]byte(agentModule))
+	if err != nil {
+		t.Fatal(err)
+	}
+	compose := func(r Resolution, with Rendering) (user, home map[string]any) {
+		t.Helper()
+		r.Node, r.Modules = "anchor", []Manifest{m}
+		out, err := r.Declaration(with)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return fileNamed(out, "agent.account"), fileNamed(out, "agent.home")
+	}
+
+	user, home := compose(Resolution{Account: "ops", AgentAccount: "agent"}, Rendering{JudgesRoot: true})
+	if user["name"] != "agent" || user[RootField] != RootNever || user["home"] != "/home/agent" {
+		t.Errorf("an engine that judges root is sent the agent account never to become root: %v", user)
+	}
+	if home["path"] != "/home/agent/.agent" || home["owner"] != "agent" {
+		t.Errorf("the agent's directory is under its own home, its own: %v", home)
+	}
+
+	user, _ = compose(Resolution{Account: "ops", AgentAccount: "agent", AgentAccountHome: "/srv/agent"}, Rendering{JudgesRoot: true})
+	if user["home"] != "/srv/agent" {
+		t.Errorf("an agent account named with a home of its own is made there: %v", user)
+	}
+
+	user, _ = compose(Resolution{Account: "ops", AgentAccount: "agent"}, Rendering{})
+	if _, sent := user[RootField]; sent || user["name"] != "agent" {
+		t.Errorf("an older engine, which parses strictly, is sent root: %v", user)
+	}
+
+	user, home = compose(Resolution{Account: "ops"}, Rendering{JudgesRoot: true})
+	if _, sent := user[RootField]; sent || user["name"] != "ops" {
+		t.Errorf("where agents run as the operator, root asserts nothing and is not sent: %v", user)
+	}
+	if home["path"] != "/home/ops/.agent" || home["owner"] != "ops" {
+		t.Errorf("with no agent account, the agent's directory is the operator's: %v", home)
+	}
+}
+
+func TestTheRuntimeIsToldTheAgentAccount(t *testing.T) {
+	with := Rendering{ArtifactStore: "anchor.internal:5101",
+		Needed: map[string]map[string]string{RuntimeModule: {"broker": "sealed-credential"}}}
+	envOf := func(r Resolution) map[string]string {
+		t.Helper()
+		r.Node, r.Modules = "anchor", []Manifest{aToolsModule(t, "nftables", "tools/index.js"), theRuntime(t)}
+		out, err := r.Declaration(with)
+		if err != nil {
+			t.Fatal(err)
+		}
+		process := fileNamed(out, RuntimeModule+"."+RuntimeProcessID())
+		if process == nil {
+			t.Fatal("no runtime process was composed")
+		}
+		return process["env"].(map[string]string)
+	}
+	env := envOf(Resolution{Account: "ops", AgentAccount: "agent"})
+	if env[RuntimeAgentAccount] != "agent" || env[RuntimeAgentHome] != "/home/agent" || env[RuntimeOperatorAccount] != "ops" {
+		t.Errorf("the runtime is not told whom agents run as: %v", env)
+	}
+	env = envOf(Resolution{Account: "ops"})
+	if env[RuntimeAgentAccount] != "ops" || env[RuntimeAgentHome] != "/home/ops" {
+		t.Errorf("with no agent account, agents run as the operator: %v", env)
+	}
+	env = envOf(Resolution{})
+	if _, set := env[RuntimeAgentAccount]; set {
+		t.Errorf("a machine with no account names an agent account: %v", env)
+	}
+	if problems := bundleEnvProblems("x", Artifact{Name: "b", Kind: ArtifactBundle, Loads: []string{"x"},
+		Env: map[string]string{RuntimeAgentAccount: "me"}}); len(problems) == 0 {
+		t.Error("a bundle may tell the runtime whom agents run as")
+	}
+}

go/catalogue/amqp_is_not_a_provision_test.go

@@ -0,0 +1,50 @@
+package catalogue
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/internal/beside"
+)
+
+// **The word does not come back through a manifest** (novox/hq ADR 0131). A module that wants
+// messaging wants the mesh's bus, reached through the sdk and named by the `mesh-broker` seat. Naming
+// the old wire protocol asks for the one server being retired, so both directions are refused at the
+// parser — this is judged from the manifest alone, no store needed.
+
+func TestAManifestProvidingAmqpIsRefused(t *testing.T) {
+	raw := []byte(`{"module":"old-broker","version":"1","provides":[{"name":"amqp","scope":"mesh"}]}`)
+	_, err := ParseManifest(raw)
+	if err == nil || !strings.Contains(err.Error(), `provides "amqp", which is not a provision`) {
+		t.Fatalf("a module providing amqp was not refused, or not for the reason: %v", err)
+	}
+}
+
+func TestAManifestRequiringAmqpIsRefused(t *testing.T) {
+	raw := []byte(`{"module":"forwarder","version":"1","requires":["amqp"]}`)
+	_, err := ParseManifest(raw)
+	if err == nil || !strings.Contains(err.Error(), `requires "amqp", which is not a provision`) {
+		t.Fatalf("a module requiring amqp was not refused, or not for the reason: %v", err)
+	}
+}
+
+// And the catalogue (internal/beside) names it nowhere — the three modules that did are removed under
+// design 28 task 5.4, not converted.
+func TestNoCatalogueManifestNamesAmqp(t *testing.T) {
+	modules, err := filepath.Glob(filepath.Join(beside.Catalogue(t), "*", "module.json"))
+	if err != nil || len(modules) == 0 {
+		t.Fatalf("no manifests in the catalogue, so this proved nothing: %v", err)
+	}
+	for _, path := range modules {
+		raw, err := os.ReadFile(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if strings.Contains(string(raw), `"amqp"`) {
+			t.Errorf("%s names amqp, which is not a provision (novox/hq ADR 0131)",
+				filepath.Base(filepath.Dir(path)))
+		}
+	}
+}

go/catalogue/artifact_store_alias_test.go

@@ -0,0 +1,18 @@
+package catalogue
+
+import "testing"
+
+// A claim written before the rename still holds (novox/hq ADR 0122, ADR 0156): with the store's
+// aliases loaded, the former name resolves to the seat.
+func TestTheArtifactStoresFormerNameResolvesToIt(t *testing.T) {
+	was := aliases
+	t.Cleanup(func() { aliases = was })
+	UseAliases(map[string]string{"the-artifact-store": "mesh-artifact-store"})
+	seat, known := SeatNamed("the-artifact-store")
+	if !known || seat.Name != "mesh-artifact-store" || seat.Delivers != "artifact-store" {
+		t.Fatalf("the former name did not resolve: %+v %v", seat, known)
+	}
+	if _, known := SeatNamed("mesh-artifact-store"); !known {
+		t.Fatal("the seat is not in the set under its name")
+	}
+}

go/catalogue/artifact_store_seat_test.go

@@ -0,0 +1,38 @@
+package catalogue
+
+import (
+	"strings"
+	"testing"
+)
+
+// The artifact store's seat is one per mesh, read from the catalogue beside this checkout.
+//
+// **A second store anywhere is refused by name, not discovered as a consumer failure.** The seat
+// was node-scoped, so a second `distribution` on another machine resolved cleanly there — and a
+// node-scoped requirement with one candidate installs that candidate on the node, so anything that
+// required the store's presence beside it would have raised a fresh, empty store on the wrong
+// machine. Only afterwards did the mesh notice: `artifact-store` offered by two nodes, and every
+// consumer elsewhere refusing to choose. The claim says it first, where the second store is
+// assigned.
+func TestASecondArtifactStoreAnywhereIsRefusedByName(t *testing.T) {
+	store := catalogueManifest(t, "distribution")
+
+	// The first store resolves as it always has.
+	if _, err := Resolve(shelf(store), []string{"distribution"}, workstation(), World{}); err != nil {
+		t.Fatalf("the store alone does not resolve: %v", err)
+	}
+
+	// A second one, on any other machine, is refused — and the refusal names the seat.
+	elsewhere := World{Held: []Held{{Claim: "mesh-artifact-store", Scope: ScopeMesh,
+		Node: "anchor", Module: "distribution"}}}
+	other := workstation()
+	other.Name = "laptop"
+	_, err := Resolve(shelf(store), []string{"distribution"}, other, elsewhere)
+	if err == nil {
+		t.Fatal("a second store was accepted on another machine; it would offer artifact-store a " +
+			"second time and every consumer elsewhere would refuse to choose")
+	}
+	if !strings.Contains(err.Error(), "mesh-artifact-store") || !strings.Contains(err.Error(), "one per mesh") {
+		t.Fatalf("refused without naming the seat: %v", err)
+	}
+}

go/catalogue/artifacts.go

@@ -0,0 +1,145 @@
+package catalogue
+
+import (
+	"fmt"
+	"strings"
+)
+
+// What the mesh built, named by what it is rather than by where it was pushed.
+//
+// **An image is recorded by its digest and its path; the registry's address is a route to it**
+// (novox/hq 04-ISSUES/102). A build used to be recorded as `<registry>:<port>/<module>/<artifact>@sha256:…`
+// — the reference the builder pushed to, kept whole — and every declaration carried that literal.
+// Move the registry's port, or the registry, and every fresh pull of a mesh image fails: a new
+// node, a recreate after eviction. The digest is the identity; the address is the node's setting
+// for the module that serves the artifact store, and it is read from there when a reference is
+// composed, never written into a record.
+//
+// So a kept reference has a scheme of the mesh's own, named after the provision that answers it:
+//
+//	artifact-store://<module>/<artifact>@sha256:<hex>            an image
+//	artifact-store://<module>/<artifact>/blobs/sha256:<hex>      an archive
+//
+// No runtime knows the scheme. That is the point of it being one: a reference that leaks to a
+// machine uncomposed is refused by the runtime as malformed, in front of whoever sent it, rather
+// than pulled from a public registry that happens to have a repository by that name — which is
+// what an address-less `<module>/<artifact>@sha256:…` would be.
+
+// ArtifactStoreScheme marks a reference to something in the mesh's artifact store, kept without
+// the store's address.
+const ArtifactStoreScheme = ArtifactStoreProvision + "://"
+
+// Recorded is a reference as the mesh records it: the artifact store's address, if the builder wrote
+// one, taken off.
+//
+// For a reference the builder announced — one it pushed to the store — which is the only kind
+// this is called on. An image the builder named `<host>/<path>@sha256:…` is kept as its path; an
+// archive it named `http://<host>/v2/<path>/blobs/<digest>` likewise. A reference with no address
+// in it — an image id from a genesis build that had nowhere to publish, a package version — is
+// what it was.
+func Recorded(reference string) string {
+	if strings.HasPrefix(reference, ArtifactStoreScheme) {
+		return reference
+	}
+	if rest, isURL := strings.CutPrefix(reference, "http://"); isURL {
+		if _, path, ok := strings.Cut(rest, "/v2/"); ok && strings.Contains(path, "/blobs/") {
+			return ArtifactStoreScheme + path
+		}
+		return reference
+	}
+	host, path, ok := strings.Cut(reference, "/")
+	if !ok || !isRegistryHost(host) || !strings.Contains(path, "@sha256:") {
+		return reference
+	}
+	return ArtifactStoreScheme + path
+}
+
+// isRegistryHost is the runtime's own rule for reading the first component of a reference as a
+// registry rather than as a namespace: it has a dot or a port in it, or it is localhost.
+func isRegistryHost(component string) bool {
+	return component == "localhost" || strings.ContainsAny(component, ".:")
+}
+
+// InArtifactStore reports whether a reference is a kept one, and what it names there.
+func InArtifactStore(reference string) (path string, kept bool) {
+	return strings.CutPrefix(reference, ArtifactStoreScheme)
+}
+
+// Routed is a kept reference as a machine fetches it, through the artifact store at `address`
+// (host:port). A reference that is not a kept one is what it was.
+func Routed(reference, address string) string {
+	path, kept := InArtifactStore(reference)
+	if !kept {
+		return reference
+	}
+	if strings.Contains(path, "/blobs/") {
+		return "http://" + address + "/v2/" + path
+	}
+	return address + "/" + path
+}
+
+// Rerouted is a reference the mesh recorded, whichever way it was recorded, as a machine fetches
+// it now: a kept one composed with the store's address, and one recorded before references were
+// kept without their address — the builder's own `<host>/<path>@sha256:…` — re-routed to where
+// the store is now. Only for references that are the mesh's own: everything a build record
+// holds is, by construction.
+func Rerouted(reference, address string) string {
+	return Routed(Recorded(reference), address)
+}
+
+// artifactsInto composes the artifact store's address into a resource's `image` and `source`.
+//
+// **Composed here, at the last moment before a machine, and stored nowhere.** A kept reference is
+// routed through the store as this network reaches it now. A reference recorded with an address
+// before references were kept without one is re-routed the same way — but only when the mesh
+// built it (`with.Built` names every `<module>/<artifact>` it has), because a module may run an
+// image from a public registry under its own name and that one is exactly where it says.
+//
+// A kept reference with no store to route it through is refused: sent as it is, the runtime would
+// refuse the scheme on the machine, one push away from the reason.
+//
+// **What this does not reach: the images genesis pinned.** The installer builds the control plane
+// and the builder before the mesh exists, pushes them itself and pins their manifests to
+// `<registry>:<port>/mesh-controller@…` and `<registry>:<port>/mesh-builder@…` — single-segment
+// repositories with no build record, so `with.Built` does not name them and they are left as
+// written until each is rebuilt through the mesh, which records it by digest and path. Until then
+// a registry that moves strands exactly those two on a recreate, and the control plane's is the
+// one that cannot be repaired through the mesh. Rebuild both through `build` before moving the
+// store (novox/hq 04-ISSUES/102, finding F4).
+func artifactsInto(resource map[string]any, module string, with Rendering) error {
+	for _, key := range []string{"image", "source"} {
+		written, ok := resource[key].(string)
+		if !ok {
+			continue
+		}
+		if _, kept := InArtifactStore(written); kept {
+			if with.ArtifactStore == "" {
+				return fmt.Errorf(
+					"%s's %v names %s, which is in the mesh's artifact store, and this mesh has no "+
+						"artifact store on its network to fetch it from — nothing assigned offers "+
+						"%s, or the machine offering it is not on the private network",
+					module, resource["id"], written, ArtifactStoreProvision)
+			}
+			resource[key] = Routed(written, with.ArtifactStore)
+			continue
+		}
+		if with.ArtifactStore == "" {
+			continue
+		}
+		recorded := Recorded(written)
+		if recorded == written {
+			continue
+		}
+		path, _ := InArtifactStore(recorded)
+		repository := path
+		if at := strings.IndexAny(path, "@"); at >= 0 {
+			repository = path[:at]
+		} else if blobs := strings.Index(path, "/blobs/"); blobs >= 0 {
+			repository = path[:blobs]
+		}
+		if with.Built[repository] {
+			resource[key] = Routed(recorded, with.ArtifactStore)
+		}
+	}
+	return nil
+}

go/catalogue/artifacts_test.go

@@ -0,0 +1,137 @@
+package catalogue
+
+import (
+	"strings"
+	"testing"
+)
+
+// A build is recorded by what it is; where it is pushed is composed where it is used (novox/hq
+// 04-ISSUES/102).
+
+var digest = "sha256:" + strings.Repeat("d", 64)
+
+func TestAReferenceIsRecordedWithoutTheStoresAddress(t *testing.T) {
+	cases := map[string]string{
+		"anchor.internal:5100/gitea/server@" + digest:                 ArtifactStoreScheme + "gitea/server@" + digest,
+		"localhost:5000/gitea/server@" + digest:                       ArtifactStoreScheme + "gitea/server@" + digest,
+		"http://anchor.internal:5100/v2/gitea/config/blobs/" + digest: ArtifactStoreScheme + "gitea/config/blobs/" + digest,
+		ArtifactStoreScheme + "gitea/server@" + digest:                ArtifactStoreScheme + "gitea/server@" + digest,
+		digest:                  digest,
+		"@novox/sdk@1.2.3":      "@novox/sdk@1.2.3",
+		"gitea/gitea@" + digest: "gitea/gitea@" + digest,
+		"https://registry.example/v2/gitea/config/blobs/" + digest: "https://registry.example/v2/gitea/config/blobs/" + digest,
+	}
+	for announced, want := range cases {
+		if got := Recorded(announced); got != want {
+			t.Errorf("Recorded(%q) = %q, want %q", announced, got, want)
+		}
+	}
+}
+
+func TestARecordedReferenceIsRoutedThroughTheStoreAsItIsNow(t *testing.T) {
+	if got := Routed(ArtifactStoreScheme+"gitea/server@"+digest, "anchor.internal:5101"); got != "anchor.internal:5101/gitea/server@"+digest {
+		t.Errorf("an image is fetched as %q", got)
+	}
+	if got := Routed(ArtifactStoreScheme+"gitea/config/blobs/"+digest, "anchor.internal:5101"); got != "http://anchor.internal:5101/v2/gitea/config/blobs/"+digest {
+		t.Errorf("an archive is fetched as %q", got)
+	}
+	if got := Routed("gitea/gitea@"+digest, "anchor.internal:5101"); got != "gitea/gitea@"+digest {
+		t.Errorf("a reference that is not the store's was routed: %q", got)
+	}
+	// One recorded before references were kept without their address follows the store too.
+	if got := Rerouted("anchor.internal:5100/gitea/server@"+digest, "anchor.internal:5101"); got != "anchor.internal:5101/gitea/server@"+digest {
+		t.Errorf("a reference recorded with the old address stays there: %q", got)
+	}
+}
+
+// **The address is composed into a declaration, and the record never carries it.**
+func TestAnImageTheMeshBuiltIsRoutedThroughTheStoreWhenDeclared(t *testing.T) {
+	m := Manifest{Module: "gitea", Version: "1", Resources: []map[string]any{
+		{"id": "server", "type": "container", "name": "mesh-gitea", "artifact": "server"},
+		{"id": "config", "type": "archive", "path": "/etc/gitea", "artifact": "config"},
+		{"id": "cache", "type": "container", "name": "mesh-gitea-cache", "image": "valkey/valkey@" + digest},
+	}, Build: &Build{Artifacts: []Artifact{
+		{Name: "server", Kind: ArtifactImage, From: "Dockerfile"},
+		{Name: "config", Kind: ArtifactArchive, From: "config"},
+	}}}
+	resolved, err := m.Resolve([]Built{
+		{Name: "server", Kind: ArtifactImage, Reference: ArtifactStoreScheme + "gitea/server@" + digest},
+		{Name: "config", Kind: ArtifactArchive, Reference: ArtifactStoreScheme + "gitea/config/blobs/" + digest, Digest: digest},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	r := Resolution{Node: "anchor", Modules: []Manifest{resolved}}
+
+	out, err := r.Declaration(Rendering{ArtifactStore: "anchor.internal:5101"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := fileNamed(out, "gitea.server")["image"]; got != "anchor.internal:5101/gitea/server@"+digest {
+		t.Errorf("the image the mesh built is fetched as %v", got)
+	}
+	if got := fileNamed(out, "gitea.config")["source"]; got != "http://anchor.internal:5101/v2/gitea/config/blobs/"+digest {
+		t.Errorf("the archive the mesh built is fetched from %v", got)
+	}
+	if got := fileNamed(out, "gitea.cache")["image"]; got != "valkey/valkey@"+digest {
+		t.Errorf("an image from a public registry was routed through the store: %v", got)
+	}
+	// The manifest the mesh holds still says what it is, not where it was fetched from.
+	if got := resolved.Resources[0]["image"]; got != ArtifactStoreScheme+"gitea/server@"+digest {
+		t.Errorf("composing wrote the address into the catalogue's copy: %v", got)
+	}
+
+	// And the store moves: the same record, another address, without a rebuild.
+	out, err = r.Declaration(Rendering{ArtifactStore: "laptop.internal:5000"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := fileNamed(out, "gitea.server")["image"]; got != "laptop.internal:5000/gitea/server@"+digest {
+		t.Errorf("after the store moved, the image is still fetched as %v", got)
+	}
+}
+
+func TestAnImageInTheStoreWithNoStoreToFetchItFromIsRefused(t *testing.T) {
+	m := Manifest{Module: "gitea", Version: "1", Resources: []map[string]any{
+		{"id": "server", "type": "container", "name": "mesh-gitea",
+			"image": ArtifactStoreScheme + "gitea/server@" + digest},
+	}}
+	_, err := Resolution{Node: "anchor", Modules: []Manifest{m}}.Declaration(Rendering{})
+	if err == nil || !strings.Contains(err.Error(), "no artifact store") {
+		t.Fatalf("a reference nothing can fetch was sent to a machine: %v", err)
+	}
+}
+
+// **A reference recorded with an address before this follows the store too** — when the mesh
+// built it. A module running an image straight from a public registry under its own name is left
+// exactly where it says: `quay.io/keycloak/keycloak` is not the mesh's, whatever it is called.
+func TestAReferenceRecordedWithAnAddressFollowsTheStoreWhenTheMeshBuiltIt(t *testing.T) {
+	m := Manifest{Module: "keycloak", Version: "1", Resources: []map[string]any{
+		{"id": "server", "type": "container", "name": "mesh-keycloak",
+			"image": "anchor.internal:5100/keycloak/server@" + digest},
+		{"id": "upstream", "type": "container", "name": "mesh-keycloak-upstream",
+			"image": "quay.io/keycloak/keycloak@" + digest},
+	}}
+	r := Resolution{Node: "anchor", Modules: []Manifest{m}}
+	out, err := r.Declaration(Rendering{
+		ArtifactStore: "anchor.internal:5101",
+		Built:         map[string]bool{"keycloak/server": true},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := fileNamed(out, "keycloak.server")["image"]; got != "anchor.internal:5101/keycloak/server@"+digest {
+		t.Errorf("an image the mesh built, recorded with the old address, is fetched as %v", got)
+	}
+	if got := fileNamed(out, "keycloak.upstream")["image"]; got != "quay.io/keycloak/keycloak@"+digest {
+		t.Errorf("a public image was re-routed through the store: %v", got)
+	}
+	// Nothing known to be built: nothing re-routed, nothing refused.
+	out, err = r.Declaration(Rendering{ArtifactStore: "anchor.internal:5101"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := fileNamed(out, "keycloak.server")["image"]; got != "anchor.internal:5100/keycloak/server@"+digest {
+		t.Errorf("with no build record, a reference was rewritten: %v", got)
+	}
+}