diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main.go
index 2fef5a6..a5d7c6c 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main.go
@@ -7,8 +7,10 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"time"
 
 	stdio "git.novox.be/novox/mesh-sdk/go"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
 
 	"mesh-delivery-checker/internal/check"
 )
@@ -23,6 +25,71 @@ func read(s stdio.KeptState) check.StateRead {
 	}}
 }
 
+// stateStore is a state the tools write: the tries.
+type stateStore struct {
+	check.StateRead
+	create func(key string, value []byte) error
+}
+
+func (s stateStore) Keys() ([]string, error)                 { return s.StateRead.Keys() }
+func (s stateStore) Get(key string) (json.RawMessage, error) { return s.StateRead.Get(key) }
+func (s stateStore) Create(key string, value []byte) error   { return s.create(key, value) }
+
+// Trying is what the try's tools work on: the tries, and the gate's trunk heads.
+type Trying struct {
+	Tries  check.TryStore
+	Trunks func() (map[string]string, error)
+	Now    func() time.Time
+}
+
+// TryTools are the try's two tools (ADR 0501 §5): ask one, read one. mesh-controller's try calls them.
+func TryTools(tr Trying) []stdio.Tool {
+	str := func(args map[string]any, k string) string { s, _ := args[k].(string); return s }
+	return []stdio.Tool{
+		{Name: check.TryTool,
+			Description: "Try a pushed head before its pull request is opened: the checker judges it as it judges a pull request's head, merged onto its trunk's head, " +
+				"its unit and integration levels through the build modules, and owes the forge nothing. Answers the try's id at once; " + check.TryReadTool + " reads " +
+				"where it stands. A try of the same head that waits or runs is the answer to a second ask; at most 4 wait or run at once, mesh-wide. A repository " +
+				"the checker checks no level of (hq, one whose trunk the gate does not name) is refused.",
+			Input: map[string]any{"type": "object", "required": []string{"repository", "head"}, "properties": map[string]any{
+				"repository": map[string]any{"type": "string", "description": "<owner>/<name>"},
+				"head":       map[string]any{"type": "string", "description": "the full commit to try, 40 or 64 hex digits"},
+				"trunk":      map[string]any{"type": "string", "description": "the trunk commit to merge it onto, or the trunk's branch for its head now; the trunk's head when absent"},
+				"tests":      map[string]any{"type": "string", "description": "a go test -run pattern: only those tests run, and nothing is kept"},
+				"level":      map[string]any{"type": "string", "enum": []string{"unit", "integration"}, "description": "only this level; both when absent"}}},
+			Run: func(args map[string]any) (any, error) {
+				if tr.Tries == nil || tr.Trunks == nil {
+					return nil, fmt.Errorf("the tries state cannot be written here")
+				}
+				trunks, err := tr.Trunks()
+				if err != nil {
+					return nil, fmt.Errorf("the trunk heads cannot be read: %w", err)
+				}
+				now := time.Now
+				if tr.Now != nil {
+					now = tr.Now
+				}
+				id, err := check.AskTry(tr.Tries, trunks, check.TryAsk{Repository: str(args, "repository"), Head: str(args, "head"),
+					Trunk: str(args, "trunk"), Tests: str(args, "tests"), Level: str(args, "level")}, now())
+				if err != nil {
+					return nil, err
+				}
+				return map[string]any{"id": id}, nil
+			}},
+		{Name: check.TryReadTool,
+			Description: "Where a try stands, as stored: queued, running, or its end (pass, fail, or error when it could not run), with what was said of it, " +
+				"the head and the trunk commit it was merged onto, the time it took and what failed first. Read-only.",
+			Input: map[string]any{"type": "object", "required": []string{"id"}, "properties": map[string]any{
+				"id": map[string]any{"type": "string", "description": "the try's id, try-<digits>"}}},
+			Run: func(args map[string]any) (any, error) {
+				if tr.Tries == nil {
+					return nil, fmt.Errorf("the tries state cannot be read here")
+				}
+				return check.ReadTry(tr.Tries, str(args, "id"))
+			}},
+	}
+}
+
 // Tools are the read tools over the checker's states.
 func Tools(r check.Reader) []stdio.Tool {
 	return []stdio.Tool{
@@ -59,12 +126,69 @@ func Tools(r check.Reader) []stdio.Tool {
 				kept, err := r.Kept(level, digest)
 				return map[string]any{"kept": kept}, err
 			}},
+		{Name: check.PreviewsReadTool,
+			Description: "The merge previews the checker holds, each as stored under previews.<repository>.<head>.<trunk>: the merge commit, per module directory " +
+				"its tree, manifest digest and lock hashes, or the files in conflict. With a repository, that repository's; with a head (7 or more characters) " +
+				"only that head's. Keys that are no preview key are listed as unreadable. Read-only.",
+			Input: map[string]any{"type": "object", "properties": map[string]any{
+				"repository": map[string]any{"type": "string", "description": "<owner>/<name>"},
+				"head":       map[string]any{"type": "string", "description": "a pull request head commit, or a prefix of at least 7 characters"}}},
+			Run: func(args map[string]any) (any, error) {
+				repository, _ := args["repository"].(string)
+				head, _ := args["head"].(string)
+				if head != "" && len(head) < 7 {
+					return nil, fmt.Errorf("the head %q is too short: give at least 7 characters", head)
+				}
+				ps, bad, err := r.Previews(repository, head)
+				return map[string]any{"previews": ps, "unreadable": bad}, err
+			}},
+		{Name: check.StatusReadTool,
+			Description: "What holds the checker back and what runs: the capacity per node (the setting, the default one step per node), whether the controller's " +
+				"delivery plans in their build phase hold a key (no new check starts while one does), the steps in flight on the build modules by node, and the " +
+				"candidates without a verdict for their heads. The steps the checker holds waiting for a place are in its process, not in a bucket, and the " +
+				"answer says so. Read-only.",
+			Input: map[string]any{"type": "object", "properties": map[string]any{}},
+			Run:   func(map[string]any) (any, error) { return r.Status() }},
 	}
 }
 
+func capacity() (string, error) {
+	path := os.Getenv("MESH_CHECKER_SETTINGS")
+	if path == "" {
+		return os.Getenv("MESH_CHECKER_CAPACITY"), nil
+	}
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		return "", err
+	}
+	var s struct {
+		Capacity string `json:"capacity"`
+	}
+	return s.Capacity, json.Unmarshal(raw, &s)
+}
+
 func main() {
-	r := check.Reader{VerdictState: read(stdio.State("verdicts")), KeptState: read(stdio.State("kept")), CandidateState: read(stdio.State("mesh-delivery-indexer.candidates"))}
-	if err := stdio.Serve("", Tools(r)); err != nil {
+	r := check.Reader{VerdictState: read(stdio.State("verdicts")), KeptState: read(stdio.State("kept")), CandidateState: read(stdio.State("mesh-delivery-indexer.candidates")),
+		PreviewState: read(stdio.State("previews")), PlansState: read(stdio.State("mesh-controller.plans-building")),
+		StepStates: map[string]check.StateRead{"mesh-build-go": read(stdio.State("mesh-build-go.steps")), "mesh-build-node": read(stdio.State("mesh-build-node.steps"))},
+		Capacity:   capacity}
+	tries := stdio.State(check.TriesState)
+	source := stdio.State("mesh-delivery-gate.source")
+	trying := Trying{
+		Tries: stateStore{StateRead: read(tries), create: func(key string, value []byte) error {
+			_, err := tries.Create(key, json.RawMessage(value))
+			return err
+		}},
+		Trunks: func() (map[string]string, error) {
+			e, err := source.Get(delivery.SourceMainKey)
+			if err != nil || e == nil {
+				return nil, err
+			}
+			s, err := delivery.DecodeSource(e.Value)
+			return s.Heads, err
+		},
+	}
+	if err := stdio.Serve("", append(Tools(r), TryTools(trying)...)); err != nil {
 		fmt.Fprintf(os.Stderr, "[mesh-delivery-checker-tools] %v\n", err)
 		os.Exit(1)
 	}
diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main_test.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main_test.go
index 5fec12b..4bafd10 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main_test.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/main_test.go
@@ -1,12 +1,17 @@
 package main
 
 import (
+	"encoding/json"
+	"errors"
+	"slices"
+	"strings"
 	"testing"
+	"time"
 
 	"mesh-delivery-checker/internal/check"
 )
 
-func TestTheToolsServedAreTheThreeReadTools(t *testing.T) {
+func TestTheToolsServedAreTheFiveReadTools(t *testing.T) {
 	var names []string
 	for _, tl := range Tools(check.Reader{}) {
 		names = append(names, tl.Name)
@@ -14,14 +19,63 @@ func TestTheToolsServedAreTheThreeReadTools(t *testing.T) {
 			t.Errorf("%s has no description or no run", tl.Name)
 		}
 	}
-	want := []string{check.VerdictsReadTool, check.PullReadTool, check.KeptReadTool}
-	if len(names) != 3 || names[0] != want[0] || names[1] != want[1] || names[2] != want[2] {
+	want := []string{check.VerdictsReadTool, check.PullReadTool, check.KeptReadTool, check.PreviewsReadTool, check.StatusReadTool}
+	if !slices.Equal(names, want) {
 		t.Errorf("tools = %v, want %v", names, want)
 	}
 	// With nothing to read from a tool says so and changes nothing.
 	for _, tl := range Tools(check.Reader{}) {
+		if tl.Name == check.StatusReadTool {
+			continue // it answers from what it can read, and says what it could not
+		}
 		if _, err := tl.Run(map[string]any{"repository": "novox/x", "number": float64(1)}); err == nil {
 			t.Errorf("%s answered with no state to read", tl.Name)
 		}
 	}
 }
+
+// memStore is a tries state in memory.
+type memStore struct{ vals map[string]json.RawMessage }
+
+func (m *memStore) Keys() ([]string, error) {
+	var out []string
+	for k := range m.vals {
+		out = append(out, k)
+	}
+	return out, nil
+}
+func (m *memStore) Get(key string) (json.RawMessage, error) { return m.vals[key], nil }
+func (m *memStore) Create(key string, value []byte) error {
+	if _, ok := m.vals[key]; ok {
+		return errors.New("exists")
+	}
+	m.vals[key] = value
+	return nil
+}
+
+func TestTheTryToolsAskAndReadATry(t *testing.T) { // ADR 0501 §5, the agreed interface with mesh-controller's try
+	store := &memStore{vals: map[string]json.RawMessage{}}
+	tools := TryTools(Trying{Tries: store, Now: func() time.Time { return time.Unix(1, 5) },
+		Trunks: func() (map[string]string, error) {
+			return map[string]string{"novox/mesh-delivery": strings.Repeat("a", 40)}, nil
+		}})
+	if len(tools) != 2 || tools[0].Name != "checker_try" || tools[1].Name != "checker_try_read" {
+		t.Fatalf("tools = %+v", tools)
+	}
+	out, err := tools[0].Run(map[string]any{"repository": "novox/mesh-delivery", "head": strings.Repeat("1", 40), "trunk": "main"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	id := out.(map[string]any)["id"].(string)
+	if id != "try-1000000005" {
+		t.Errorf("id = %q", id)
+	}
+	raw, err := tools[1].Run(map[string]any{"id": id})
+	if err != nil || !strings.Contains(string(raw.(json.RawMessage)), `"state":"queued"`) {
+		t.Errorf("read = %s, %v", raw, err)
+	}
+	if _, err := tools[0].Run(map[string]any{"repository": "novox/hq", "head": strings.Repeat("1", 40)}); err == nil ||
+		err.Error() != "no level of novox/hq is checked by the checker" {
+		t.Errorf("hq: %v", err)
+	}
+}
diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/mesh-delivery-checker-tools b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/mesh-delivery-checker-tools
new file mode 100755
index 0000000..49d7508
Binary files /dev/null and b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker-tools/mesh-delivery-checker-tools differ
diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/bus.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/bus.go
index e3489c3..6415687 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/bus.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/bus.go
@@ -57,6 +57,9 @@ func (s kvStore) Keys(ctx context.Context) ([]string, error) {
 	return keys, err
 }
 
+// Delete removes a key (an ended try past its keeping).
+func (s kvStore) Delete(ctx context.Context, key string) error { return s.kv.Delete(ctx, key) }
+
 func opOf(e jetstream.KeyValueEntry) bool { return e.Operation() == jetstream.KeyValuePut }
 
 // settle reads the entries a watcher holds now, up to its mark of the last values, and returns the watcher for the
diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge.go
index 31702bf..b3aabfa 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge.go
@@ -3,10 +3,13 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"regexp"
 	"strings"
 
+	"github.com/nats-io/nats.go"
+
 	"mesh-delivery-checker/internal/check"
 )
 
@@ -27,6 +30,16 @@ type forgeReads struct {
 	call func(key string, body any) (json.RawMessage, error)
 }
 
+// ask calls a forge tool; a call that reached nobody (no responders: the forge's tool runner re-serving, or the forge
+// down) is marked Unheard, so the check fails at the forge and is judged again when the nodes change (issue 1624).
+func (f forgeReads) ask(key string, body any) (json.RawMessage, error) {
+	raw, err := f.call(key, body)
+	if errors.Is(err, nats.ErrNoResponders) || errors.Is(err, nats.ErrTimeout) || errors.Is(err, context.DeadlineExceeded) {
+		return nil, &check.Unheard{Err: err}
+	}
+	return raw, err
+}
+
 func ownerRepo(repository string) (string, string) {
 	owner, repo, _ := strings.Cut(repository, "/")
 	return owner, repo
@@ -35,7 +48,7 @@ func ownerRepo(repository string) (string, string) {
 // File is the text of a file of a repository at a ref.
 func (f forgeReads) File(_ context.Context, repository, path, ref string) (string, error) {
 	owner, repo := ownerRepo(repository)
-	raw, err := f.call(getFileTool, map[string]string{"owner": owner, "repo": repo, "path": path, "ref": ref})
+	raw, err := f.ask(getFileTool, map[string]string{"owner": owner, "repo": repo, "path": path, "ref": ref})
 	if err != nil {
 		if notFoundStatus.MatchString(err.Error()) {
 			// The forge answers 404 for a file the ref does not hold (issue 1845). The status is matched in its own place,
@@ -59,7 +72,7 @@ func (f forgeReads) File(_ context.Context, repository, path, ref string) (strin
 // not.
 func (f forgeReads) OnTrunk(_ context.Context, repository, commit string) (bool, error) {
 	owner, repo := ownerRepo(repository)
-	raw, err := f.call(compareTool, map[string]string{"owner": owner, "repo": repo, "base": "main", "head": commit})
+	raw, err := f.ask(compareTool, map[string]string{"owner": owner, "repo": repo, "base": "main", "head": commit})
 	if err != nil {
 		return false, err
 	}
@@ -75,7 +88,7 @@ func (f forgeReads) OnTrunk(_ context.Context, repository, commit string) (bool,
 // FullSHA is the whole sha of a commit named by its first digits: the newest commit of the history at that ref.
 func (f forgeReads) FullSHA(_ context.Context, repository, commit string) (string, error) {
 	owner, repo := ownerRepo(repository)
-	raw, err := f.call(commitsTool, map[string]any{"owner": owner, "repo": repo, "ref": commit, "limit": 1})
+	raw, err := f.ask(commitsTool, map[string]any{"owner": owner, "repo": repo, "ref": commit, "limit": 1})
 	if err != nil {
 		return "", err
 	}
diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge_test.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge_test.go
index e7ecc85..d6487d6 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge_test.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge_test.go
@@ -9,6 +9,8 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/nats-io/nats.go"
+
 	"mesh-delivery-checker/internal/check"
 )
 
@@ -86,3 +88,18 @@ func TestAFileTheRefDoesNotHoldIsNotFoundAndOtherFailuresAreNot(t *testing.T) {
 		t.Errorf("a 500 is %v, want a failure that is not ErrNotFound", err)
 	}
 }
+
+func TestAForgeReadThatReachesNobodyIsUnheard(t *testing.T) { // 1624 C7: "nats: no responders" on mesh-catalog #293
+	f := forgeReads{call: func(string, any) (json.RawMessage, error) { return nil, nats.ErrNoResponders }}
+	_, err := f.File(context.Background(), "novox/mesh-catalog", "checks/agenthome/go.mod", "950e37a46e8d")
+	var u *check.Unheard
+	if !errors.As(err, &u) {
+		t.Errorf("err = %v, want it marked as reaching nobody", err)
+	}
+	if _, err := f.OnTrunk(context.Background(), "novox/mesh-sdk", "abc"); !errors.As(err, &u) {
+		t.Errorf("compare: %v", err)
+	}
+	if _, err := f.FullSHA(context.Background(), "novox/mesh-sdk", "abc"); !errors.As(err, &u) {
+		t.Errorf("commits: %v", err)
+	}
+}
diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/integration_test.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/integration_test.go
index cbf005b..a44507a 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/integration_test.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/integration_test.go
@@ -20,6 +20,8 @@ import (
 	"github.com/nats-io/nats.go/jetstream"
 
 	"git.novox.be/novox/mesh-sdk/go/delivery"
+
+	"mesh-delivery-checker/internal/check"
 )
 
 // busConf is the shape of the composed accounts file (mesh-controller internal/broker): one account with JetStream, the
@@ -267,7 +269,7 @@ func startBed(t *testing.T) *bed {
 	for name, history := range map[string]int{delivery.CheckerVerdictsBucket: delivery.CheckerVerdictsHistory, delivery.CheckerKeptBucket: delivery.CheckerKeptHistory,
 		delivery.CheckerOwedBucket: delivery.CheckerOwedHistory, delivery.PreviewsBucket: delivery.PreviewsHistory, delivery.CandidatesBucket: delivery.CandidatesHistory,
 		delivery.ModulesBucket: delivery.ModulesHistory, delivery.ManifestsBucket: delivery.ManifestsHistory, delivery.SourceBucket: delivery.SourceHistory,
-		delivery.PresenceBucket: delivery.PresenceHistory, delivery.HaveBucket: delivery.HaveHistory} {
+		delivery.PresenceBucket: delivery.PresenceHistory, delivery.HaveBucket: delivery.HaveHistory, check.TriesBucket: 1} {
 		kv, err := js.CreateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: name, History: uint8(history)})
 		if err != nil {
 			t.Fatal(err)
@@ -590,3 +592,62 @@ func TestAMemberNamingAMeshSDKCommitOffTheTrunkFailsNamingTheCommit(t *testing.T
 		t.Errorf("%d test steps ran after a stale pin", n)
 	}
 }
+
+// triesStore is the tries bucket as the tools write it.
+type triesStore struct {
+	kv  jetstream.KeyValue
+	ctx context.Context
+}
+
+func (s triesStore) Keys() ([]string, error) {
+	keys, err := s.kv.Keys(s.ctx)
+	if err == jetstream.ErrNoKeysFound {
+		return nil, nil
+	}
+	return keys, err
+}
+func (s triesStore) Get(key string) (json.RawMessage, error) {
+	e, err := s.kv.Get(s.ctx, key)
+	if err == jetstream.ErrKeyNotFound {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	return e.Value(), nil
+}
+func (s triesStore) Create(key string, value []byte) error {
+	_, err := s.kv.Create(s.ctx, key, value)
+	return err
+}
+
+// TestATryIsJudgedAndItsEndWrittenWithNoStatusOwed: a try written as checker_try writes it is taken by the running checker,
+// judged through the build modules as a pull request's head merged onto its trunk, and ended pass in its key, with no
+// verdict and no status owed (ADR 0501 §5).
+func TestATryIsJudgedAndItsEndWrittenWithNoStatusOwed(t *testing.T) {
+	b := startBed(t)
+	b.start(t, nil)
+	store := triesStore{b.buckets[check.TriesBucket], b.ctx}
+	id, err := check.AskTry(store, map[string]string{repo: trunk}, check.TryAsk{Repository: repo, Head: head1}, time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	var last check.Try
+	for deadline := time.Now().Add(20 * time.Second); time.Now().Before(deadline); time.Sleep(50 * time.Millisecond) {
+		raw, _ := store.Get(id)
+		if last, err = check.DecodeTry(raw); err == nil && last.Over() {
+			break
+		}
+	}
+	if last.State != check.TryPass || last.Trunk != trunk || last.Took == "" {
+		t.Fatalf("try = %+v, want passed on the trunk", last)
+	}
+	if b.fake.count("mesh-build-go.build_go_fetch") == 0 {
+		t.Errorf("the try fetched nothing")
+	}
+	for _, name := range []string{delivery.CheckerOwedBucket, delivery.CheckerVerdictsBucket, delivery.PreviewsBucket} {
+		if keys, _ := b.buckets[name].Keys(b.ctx); len(keys) != 0 {
+			t.Errorf("a try wrote %s: %v", name, keys)
+		}
+	}
+}
diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge.go
index 6dc5381..ed8ff96 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge.go
@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"sort"
+	"strings"
 	"sync"
 
 	"git.novox.be/novox/mesh-sdk/go/catalogue"
@@ -31,7 +32,7 @@ type judgeDeps struct {
 
 func newJudge(d judgeDeps) check.Judge {
 	return &check.Examiner{Steps: d.runner, Toolchains: d.tools, Presence: d.presence, Health: d.have, Places: d.places,
-		Kept: check.Kept{Store: d.kept}, Previews: d.previews, Modules: d.repos, Forge: d.forge, Runs: d.repos, Builds: d.builds, Announce: d.announce, Trunks: d.trunks, Logf: d.logf}
+		Kept: check.Kept{Store: d.kept}, Previews: d.previews, Modules: d.repos, Packages: d.repos, Forge: d.forge, Runs: d.repos, Builds: d.builds, Announce: d.announce, Trunks: d.trunks, Logf: d.logf}
 }
 
 // manifestKV reads a manifest by its digest.
@@ -47,10 +48,13 @@ type repoModules struct {
 	logf      func(format string, args ...any)
 
 	mu     sync.Mutex
-	langs  map[string]map[string]bool // by manifest digest: the languages of its artifacts
-	repoOf map[string]string          // by module: its repository
-	commit map[string]string          // by module: the commit its record was computed at (the commit the mesh runs)
-	typed  map[string]string          // by module: its manifest digest
+	langs  map[string]map[string]bool     // by manifest digest: the languages of its artifacts
+	tsPkgs map[string][]string            // by manifest digest: the names of its TypeScript package artifacts
+	path   map[string]string              // by module: its directory in its repository
+	named  map[string]map[string][]string // by module: each artifact's named paths, as the indexer keeps them
+	repoOf map[string]string              // by module: its repository
+	commit map[string]string              // by module: the commit its record was computed at (the commit the mesh runs)
+	typed  map[string]string              // by module: its manifest digest
 }
 
 // Put takes a change of the indexer's modules bucket in: a module's repository and the languages its manifest names.
@@ -58,11 +62,14 @@ func (r *repoModules) Put(ctx context.Context, key string, value []byte, deleted
 	r.mu.Lock()
 	if r.repoOf == nil {
 		r.repoOf, r.typed, r.langs, r.commit = map[string]string{}, map[string]string{}, map[string]map[string]bool{}, map[string]string{}
+		r.tsPkgs, r.path, r.named = map[string][]string{}, map[string]string{}, map[string]map[string][]string{}
 	}
 	if deleted {
 		delete(r.repoOf, key)
 		delete(r.typed, key)
 		delete(r.commit, key)
+		delete(r.path, key)
+		delete(r.named, key)
 		r.mu.Unlock()
 		return
 	}
@@ -75,12 +82,15 @@ func (r *repoModules) Put(ctx context.Context, key string, value []byte, deleted
 	r.repoOf[key] = m.Repository
 	r.typed[key] = m.Manifest
 	r.commit[key] = m.Commit
+	r.path[key] = m.Path
+	r.named[key] = m.ArtifactPaths
 	_, known := r.langs[m.Manifest]
 	r.mu.Unlock()
 	if m.Manifest == "" || known {
 		return
 	}
 	set := map[string]bool{}
+	var pkgs []string
 	if mk, err := delivery.ManifestsKey(m.Manifest); err == nil {
 		if raw, _, found, err := r.manifests.Get(ctx, mk); err == nil && found {
 			if kept, err := delivery.DecodeManifest(raw); err == nil {
@@ -89,6 +99,9 @@ func (r *repoModules) Put(ctx context.Context, key string, value []byte, deleted
 						if a.Language != "" {
 							set[a.Language] = true
 						}
+						if a.Kind == "package" && a.Language == "typescript" {
+							pkgs = append(pkgs, a.Name)
+						}
 					}
 				} else if err != nil && r.logf != nil {
 					r.logf("the manifest %s cannot be read, so its module counts as no TypeScript: %v", m.Manifest, err)
@@ -98,9 +111,37 @@ func (r *repoModules) Put(ctx context.Context, key string, value []byte, deleted
 	}
 	r.mu.Lock()
 	r.langs[m.Manifest] = set
+	r.tsPkgs[m.Manifest] = pkgs
 	r.mu.Unlock()
 }
 
+// PackagePaths are the paths, relative to the repository, that the TypeScript package artifacts of a repository's modules
+// are built from, sorted: the named paths the indexer keeps in each module's value (delivery.Module.ArtifactPaths; only the
+// indexer reads them from a manifest, the lead's decision L8), under the module's directory. None for a module whose value
+// holds no paths.
+func (r *repoModules) PackagePaths(repository string) []string {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	var out []string
+	for module, repo := range r.repoOf {
+		if repo != repository {
+			continue
+		}
+		dir := strings.Trim(r.path[module], "/")
+		for _, name := range r.tsPkgs[r.typed[module]] {
+			for _, p := range r.named[module][name] {
+				p = strings.Trim(strings.TrimPrefix(p, "./"), "/")
+				if dir != "" && dir != delivery.RootPath {
+					p = dir + "/" + p
+				}
+				out = append(out, p)
+			}
+		}
+	}
+	sort.Strings(out)
+	return out
+}
+
 // BuildModules are the build modules that judge a repository, sorted.
 func (r *repoModules) BuildModules(repository string) []string {
 	out := []string{buildrun.GoBuildModule}
diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge_test.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge_test.go
index 28329bf..8afa3c1 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge_test.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/judge_test.go
@@ -73,3 +73,40 @@ func TestARepositoryWithATypeScriptModuleIsJudgedByTheNodeBuildModuleToo(t *test
 		t.Errorf("a repository with no module: %v, want the Go build module", got)
 	}
 }
+
+// sdkManifest is mesh-sdk's own manifest (its module.json at feat/r4e-sdk): one TypeScript package naming its paths.
+const sdkManifest = `{"module":"mesh-sdk","version":"1","slug":"sdk","build":{"artifacts":[{"name":"lib","kind":"package","language":"typescript",` +
+	`"paths":["src","test","package.json","package-lock.json","tsconfig.json"]}]},"resources":[]}`
+
+func TestTheTypeScriptPackagesPathsComeFromTheIndexersModulesNotTheManifest(t *testing.T) { // ADR 0500 §5 with lead decision L8
+	store := memManifests{}
+	data, err := delivery.EncodeManifest(delivery.Manifest{Module: "mesh-sdk", JSON: sdkManifest})
+	if err != nil {
+		t.Fatal(err)
+	}
+	store[delivery.ManifestDigest([]byte(sdkManifest))] = data
+	r := &repoModules{manifests: store}
+	put := func(path string, paths map[string][]string) {
+		v, err := delivery.EncodeModule(delivery.Module{Repository: "novox/mesh-sdk", Commit: strings.Repeat("a", 40), FP: "src1:" + strings.Repeat("a", 64),
+			Manifest: delivery.ManifestDigest([]byte(sdkManifest)), Path: path, ArtifactPaths: paths})
+		if err != nil {
+			t.Fatal(err)
+		}
+		r.Put(context.Background(), "mesh-sdk", v, false)
+	}
+	put(".", map[string][]string{"lib": {"src", "package.json"}}) // the indexer's word, not the manifest's five paths
+	if got := strings.Join(r.PackagePaths("novox/mesh-sdk"), ","); got != "package.json,src" {
+		t.Errorf("paths = %q, want the indexer's, at the repository's root", got)
+	}
+	put("ts", map[string][]string{"lib": {"src"}})
+	if got := strings.Join(r.PackagePaths("novox/mesh-sdk"), ","); got != "ts/src" {
+		t.Errorf("paths = %q, want them under the module's directory", got)
+	}
+	put(".", nil) // a value written before the indexer kept paths: nothing to serve by
+	if got := r.PackagePaths("novox/mesh-sdk"); len(got) != 0 {
+		t.Errorf("paths = %v, want none", got)
+	}
+	if got := r.PackagePaths("novox/mesh-delivery"); len(got) != 0 {
+		t.Errorf("another repository: %v", got)
+	}
+}
diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/main.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/main.go
index 40ed0d7..3320df7 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/main.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/main.go
@@ -151,7 +151,7 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	}
 	buckets := map[string]jetstream.KeyValue{}
 	for _, name := range []string{delivery.CheckerVerdictsBucket, delivery.CheckerKeptBucket, delivery.CheckerOwedBucket, delivery.PreviewsBucket,
-		delivery.CandidatesBucket, delivery.ModulesBucket, delivery.ManifestsBucket} {
+		delivery.CandidatesBucket, delivery.ModulesBucket, delivery.ManifestsBucket, check.TriesBucket} {
 		if buckets[name], err = bucket(name); err != nil {
 			return err
 		}
@@ -209,8 +209,11 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	default:
 		builds = buildReader{kvStore{kv}}
 	}
-	holds := newHoldWatch(ctx, js, ch.Reconsider, logger)
+	// The tries (ADR 0501 §5) are judged by the same judge, held by the same deliveries.
+	tryer := &check.Tryer{Tries: kvStore{buckets[check.TriesBucket]}, Bound: checkBound, Logf: logger.Printf}
+	holds := newHoldWatch(ctx, js, func(ctx context.Context) { ch.Reconsider(ctx); tryer.Reconsider(ctx) }, logger)
 	ch.Hold = holds.Held
+	tryer.Hold = holds.Held
 	announce := func(ctx context.Context, event, key string) {
 		body, _ := json.Marshal(map[string]string{"key": key})
 		if _, err := js.Publish(ctx, eventSubject(event), body); err != nil {
@@ -225,6 +228,7 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 		announce: announce,
 	})
 	ch.Announce = announce
+	tryer.Judge = ch.Judge
 
 	// The toolchains first, so a check that starts from the first candidate finds the nodes.
 	watch := newToolchainWatch(ctx, js, tools, ch.NodesChanged, logger)
@@ -308,7 +312,7 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 		go func() {
 			errs <- follow(ctx, sw, func(e jetstream.KeyValueEntry) {
 				if e.Key() == delivery.SourceMainKey && trunks.Put(e.Value(), !opOf(e)) {
-					ch.Reconsider(ctx) // the trunk moved: a verdict for the old trunk is judged again
+					ch.TrunkMoved(ctx) // the trunk moved: its statuses go pending, and a verdict for the old trunk is judged again
 				}
 			})
 		}()
@@ -336,11 +340,25 @@ func run(ctx context.Context, getenv func(string) string, logOut io.Writer) erro
 	if err := ch.Sweep(ctx); err != nil {
 		return err
 	}
+	// The tries: a queued one starts, one left running is taken over, an ended one past its keeping is removed.
+	tw, err := settle(ctx, buckets[check.TriesBucket], func(jetstream.KeyValueEntry) {})
+	if err != nil {
+		return err
+	}
+	tryer.Reconsider(ctx)
+	go func() {
+		errs <- follow(ctx, tw, func(e jetstream.KeyValueEntry) {
+			if opOf(e) {
+				tryer.Put(ctx, e.Key(), e.Value())
+			}
+		})
+	}()
 	logger.Printf("started on %s", cred.Node)
 	go func() { errs <- follow(ctx, w, each) }()
 	select {
 	case <-ctx.Done():
 		ch.Wait()
+		tryer.Wait()
 		return nil
 	case err := <-errs:
 		return err
diff --git a/modules/mesh-delivery-checker/go.mod b/modules/mesh-delivery-checker/go.mod
index 9c911a8..8f008d1 100644
--- a/modules/mesh-delivery-checker/go.mod
+++ b/modules/mesh-delivery-checker/go.mod
@@ -3,7 +3,7 @@ module mesh-delivery-checker
 go 1.26.0
 
 require (
-	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261021192148-78364e318bdc
+	git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261022160024-9cb4d59093a7
 	github.com/nats-io/nats-server/v2 v2.11.17
 	github.com/nats-io/nats.go v1.54.0
 )
diff --git a/modules/mesh-delivery-checker/go.sum b/modules/mesh-delivery-checker/go.sum
index 3515fb8..bb52af2 100644
--- a/modules/mesh-delivery-checker/go.sum
+++ b/modules/mesh-delivery-checker/go.sum
@@ -1,5 +1,7 @@
 git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261021192148-78364e318bdc h1:ZJScJSnF6LgFl55/VJ9RT/lNroVWun469sXtx0nlVYw=
 git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261021192148-78364e318bdc/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261022160024-9cb4d59093a7 h1:wK9O1CgNk7mo3IdJqW/CCx/hebg+1F0rkvW8CvJfnRM=
+git.novox.be/novox/mesh-sdk/go v0.1.14-0.20261022160024-9cb4d59093a7/go.mod h1:ouERNpZizzwZ0HLEtAypsY9FR20FyUgUYRni6J7kVCY=
 github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op h1:Z/MZK75wC/NSrkgqeNIa7jexam9uWzhLmFTSCPI/kn0=
 github.com/antithesishq/antithesis-sdk-go v0.7.0-default-no-op/go.mod h1:FQyySiasQQM8735Ddel3MRojmy4dA1IqCeyJ5jmPMbI=
 github.com/google/go-tpm v0.9.8 h1:slArAR9Ft+1ybZu0lBwpSmpwhRXaa85hWtMinMyRAWo=
diff --git a/modules/mesh-delivery-checker/internal/check/case.go b/modules/mesh-delivery-checker/internal/check/case.go
index 24cb19e..4240ed4 100644
--- a/modules/mesh-delivery-checker/internal/check/case.go
+++ b/modules/mesh-delivery-checker/internal/check/case.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"maps"
 	"sort"
+	"strings"
 	"sync"
 	"time"
 
@@ -35,13 +36,17 @@ type Case struct {
 	Key       string
 	Group     string
 	HeadsHash string
-	Pulls     []Pull
+	// Heads is the heads hash the gate matches an Approve's members by (GateHeads): a verdict carries it.
+	Heads string
+	Pulls []Pull
 	// Trunk is the trunk head of each repository of Pulls.
 	Trunk map[string]string
 	// Left says why pull requests of the candidate are not judged (hq's, a repository with no known trunk); empty when all are.
 	Left []string
 	// Queued is when the checker took the case up, for the time of its queue.
 	Queued time.Time
+	// Try narrows a try's check (its level, its tests); nil for a pull request's.
+	Try *TryOptions
 	// Progress says what the check is doing, so a check that ran past its bound names the step it was stuck at.
 	Progress *Progress
 }
@@ -75,7 +80,7 @@ func CaseOf(c delivery.Candidate, trunk map[string]string) *Case {
 	if err != nil {
 		return nil
 	}
-	cs := &Case{Key: key, Group: c.Group, HeadsHash: c.HeadsHash, Trunk: map[string]string{}, Progress: &Progress{}}
+	cs := &Case{Key: key, Group: c.Group, HeadsHash: c.HeadsHash, Heads: GateHeads(c), Trunk: map[string]string{}, Progress: &Progress{}}
 	for _, p := range c.Pulls {
 		switch head, known := trunk[p.Repository]; {
 		case p.Repository == HQRepository:
@@ -99,6 +104,22 @@ func CaseOf(c delivery.Candidate, trunk map[string]string) *Case {
 	return cs
 }
 
+// GateHeads is the hash the gate matches the members an Approve covers by (mesh-catalog mesh-delivery-gate onestatus.go
+// headsOf): delivery.HeadsHash over every pull request of the candidate, hq's included, as
+// `<owner/name lowercase>#<number>=<full head sha lowercase>`. A lone pull request is a group of one. Empty for a candidate
+// with no pull request.
+func GateHeads(c delivery.Candidate) string {
+	heads := make([]delivery.Head, 0, len(c.Pulls))
+	for _, p := range c.Pulls {
+		heads = append(heads, delivery.Head{Repository: strings.ToLower(p.Repository), Number: p.Number, Head: strings.ToLower(p.Head.Head)})
+	}
+	hash, err := delivery.HeadsHash(heads)
+	if err != nil {
+		return ""
+	}
+	return hash
+}
+
 // sameTrunk says whether two verdicts' trunk heads are the same.
 func sameTrunk(a, b map[string]string) bool { return maps.Equal(a, b) }
 
diff --git a/modules/mesh-delivery-checker/internal/check/checker.go b/modules/mesh-delivery-checker/internal/check/checker.go
index 84753ed..1236af4 100644
--- a/modules/mesh-delivery-checker/internal/check/checker.go
+++ b/modules/mesh-delivery-checker/internal/check/checker.go
@@ -18,6 +18,10 @@ const DefaultBound = 30 * time.Minute
 // is judged again when the nodes change, by a watch and never a timer (ADR 0437 §8).
 const NodesWords = "build node qualifies"
 
+// UnheardWords end the Words of a failure because a part of the mesh the check reads was not heard (the forge, issue 1624):
+// like a failure of the nodes, it is not the change's, and is judged again when the nodes change.
+const UnheardWords = "not heard; judged again when the nodes change"
+
 // The events the checker says on its stream checks (module.json): a preview or a status was written, so a part that reads
 // the bucket, which is made when the checker is assigned and may not exist when that part starts, finds it (ADR 0437 §8: no
 // timer). The body is {"key": ...}.
@@ -234,7 +238,7 @@ type claimed struct{ rev uint64 }
 //   - a pass or a failure for the trunk heads the case has stands; one for other trunk heads (the trunk moved) is taken
 //     again by compare-and-set on the same key, and so is a failure of the nodes after the nodes changed.
 func (ch *Checker) claim(ctx context.Context, cs *Case, first bool, epoch uint64) (*claimed, error) {
-	running := delivery.Verdict{Group: cs.Group, Heads: cs.HeadsHash, Trunk: cs.Trunk, State: delivery.VerdictRunning}
+	running := delivery.Verdict{Group: cs.Group, Heads: cs.Heads, Trunk: cs.Trunk, State: delivery.VerdictRunning}
 	data, err := delivery.EncodeVerdict(running)
 	if err != nil {
 		return nil, err
@@ -287,7 +291,7 @@ func (ch *Checker) claim(ctx context.Context, cs *Case, first bool, epoch uint64
 
 // IsNodesFailure says whether a verdict failed because no build node could take the check.
 func IsNodesFailure(v delivery.Verdict) bool {
-	return v.State == delivery.VerdictFail && strings.Contains(v.Failed.Words, NodesWords)
+	return v.State == delivery.VerdictFail && (strings.Contains(v.Failed.Words, NodesWords) || strings.Contains(v.Failed.Words, UnheardWords))
 }
 
 // try claims the check, judges it within its bound and writes the verdict and the owed statuses. A check that ends
@@ -313,14 +317,14 @@ func (ch *Checker) try(ctx context.Context, key string, cs *Case) {
 		return
 	}
 	v := out.Verdict
-	v.Group, v.Heads, v.Trunk = cs.Group, cs.HeadsHash, cs.Trunk
+	v.Group, v.Heads, v.Trunk = cs.Group, cs.Heads, cs.Trunk
 	if v.Took.Queue == 0 && !cs.Queued.IsZero() && began.After(cs.Queued) {
 		v.Took.Queue = began.Sub(cs.Queued).Milliseconds()
 	}
 	data, err := delivery.EncodeVerdict(v)
 	if err != nil {
 		ch.logf("%s: the verdict cannot be written: %v", cs.Key, err)
-		v = delivery.Verdict{Group: cs.Group, Heads: cs.HeadsHash, Trunk: cs.Trunk, State: delivery.VerdictFail,
+		v = delivery.Verdict{Group: cs.Group, Heads: cs.Heads, Trunk: cs.Trunk, State: delivery.VerdictFail,
 			Failed: delivery.FailedFirst{Machine: "checker", Words: "the verdict could not be written: " + err.Error()}}
 		if data, err = delivery.EncodeVerdict(v); err != nil {
 			return
@@ -335,6 +339,13 @@ func (ch *Checker) try(ctx context.Context, key string, cs *Case) {
 		ch.nodesFail[cs.Key] = epoch
 		ch.mu.Unlock()
 	}
+	if ch.movedSince(cs) {
+		// Judged on a trunk that moved while it ran: the verdict is kept as judged, and the status stays pending until the
+		// check of the new trunk, which Reconsider starts, ends.
+		ch.writeOwed(ctx, cs, delivery.Verdict{State: delivery.VerdictRunning}, nil, nil)
+		ch.logf("%s: %s on a trunk that moved while it ran; the status stays pending", cs.Key, v.State)
+		return
+	}
 	ch.writeOwed(ctx, cs, v, out.Builds, out.Slowest)
 	ch.logf("%s: %s", cs.Key, v.State)
 }
@@ -342,25 +353,7 @@ func (ch *Checker) try(ctx context.Context, key string, cs *Case) {
 // judge runs the case within the bound. A judge that fails to judge, and a check that ran past its bound, are verdicts of
 // failure naming the machine and the step.
 func (ch *Checker) judge(ctx context.Context, cs *Case) Outcome {
-	bound := ch.bound()
-	run, cancel := context.WithTimeoutCause(ctx, bound, errBound)
-	defer cancel()
-	out, err := ch.Judge.Judge(run, cs)
-	stage, node := cs.Progress.Now()
-	if node == "" {
-		node = "checker"
-	}
-	switch {
-	case ctx.Err() != nil:
-		return Outcome{}
-	case context.Cause(run) == errBound:
-		if stage == "" {
-			stage = "starting"
-		}
-		return Outcome{Verdict: failure(node, fmt.Sprintf("the check ran past its bound of %s, stuck at: %s", bound, stage))}
-	case err != nil:
-		return Outcome{Verdict: failure(node, err.Error())}
-	}
+	out, _ := judgeWithin(ctx, ch.Judge, cs, ch.bound())
 	return out
 }
 
@@ -467,3 +460,44 @@ func (ch *Checker) Sweep(ctx context.Context) error {
 	}
 	return nil
 }
+
+// TrunkMoved is Reconsider after a move of a trunk, which first owes mesh/check pending on every open pull request of a
+// candidate whose verdict was judged on other trunk heads, every member's for a group (the lead's decision L4, the checker's
+// part of issue 1302): the forge's success of the old trunk never stands while the check waits for a place or for a delivery
+// that holds it, so the gate never reads it as the head's.
+func (ch *Checker) TrunkMoved(ctx context.Context) {
+	ch.init()
+	ch.mu.Lock()
+	known := make(map[string]delivery.Candidate, len(ch.known))
+	for k, c := range ch.known {
+		known[k] = c
+	}
+	ch.mu.Unlock()
+	heads := ch.heads()
+	for _, c := range known {
+		cs := CaseOf(c, heads)
+		if cs == nil {
+			continue
+		}
+		value, _, found, err := ch.Verdicts.Get(ctx, cs.Key)
+		if err != nil || !found {
+			continue // never judged: no status to put out of date
+		}
+		if v, err := delivery.DecodeVerdict(value); err == nil && sameTrunk(v.Trunk, cs.Trunk) {
+			continue
+		}
+		ch.writeOwed(ctx, cs, delivery.Verdict{State: delivery.VerdictRunning}, nil, nil)
+	}
+	ch.Reconsider(ctx)
+}
+
+// movedSince says whether a trunk the case was judged on is no longer the trunk's head.
+func (ch *Checker) movedSince(cs *Case) bool {
+	now := ch.heads()
+	for repo, head := range cs.Trunk {
+		if now[repo] != head {
+			return true
+		}
+	}
+	return false
+}
diff --git a/modules/mesh-delivery-checker/internal/check/checker_test.go b/modules/mesh-delivery-checker/internal/check/checker_test.go
index f57ed71..295a9ff 100644
--- a/modules/mesh-delivery-checker/internal/check/checker_test.go
+++ b/modules/mesh-delivery-checker/internal/check/checker_test.go
@@ -19,6 +19,7 @@ const (
 	trunkA  = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
 	trunkA2 = "abababababababababababababababababababab"
 	trunkS  = "5555555555555555555555555555555555555555"
+	trunkS2 = "5656565656565656565656565656565656565656"
 )
 
 // candidateOf is a candidate of a group with the given pull requests, as the indexer writes one.
diff --git a/modules/mesh-delivery-checker/internal/check/examiner_test.go b/modules/mesh-delivery-checker/internal/check/examiner_test.go
index 66edd34..1864f55 100644
--- a/modules/mesh-delivery-checker/internal/check/examiner_test.go
+++ b/modules/mesh-delivery-checker/internal/check/examiner_test.go
@@ -2,10 +2,14 @@ package check
 
 import (
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"os"
 	"path/filepath"
+	"reflect"
+	"sort"
 	"strings"
 	"sync"
 	"testing"
@@ -565,7 +569,7 @@ func trunksOf(t *testing.T, heads map[string]string) *Trunks {
 	return tr
 }
 
-func TestNothingIsKeptForAWorkspaceGivenSiblingsBeside(t *testing.T) { // review D1, ADR 0444, issue 1287
+func TestNothingIsKeptForAWorkspaceGivenSiblingsWhenTheDigestDoesNotSayItCoversThem(t *testing.T) { // review D1, ADR 0444, issue 1287
 	b := newBench(t)
 	b.ex.Trunks = trunksOf(t, map[string]string{repoSDK: trunkS, "novox/mesh-catalog": trunkA})
 	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
@@ -573,7 +577,7 @@ func TestNothingIsKeptForAWorkspaceGivenSiblingsBeside(t *testing.T) { // review
 		t.Fatalf("the fetch was not given siblings: %+v", b.steps.tool("fetch"))
 	}
 	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 0 {
-		t.Errorf("kept %v for a package whose tests may read a sibling the digest does not cover", keys)
+		t.Errorf("kept %v for a package whose digest does not say it covers the siblings", keys)
 	}
 	// And a kept verdict of the same digest from elsewhere is not taken for it: everything runs.
 	if _, err := (Kept{Store: b.kept}).Keep(context.Background(), "unit", digA, keptValue("fixture/slow", 2)); err != nil {
@@ -585,3 +589,137 @@ func TestNothingIsKeptForAWorkspaceGivenSiblingsBeside(t *testing.T) { // review
 		t.Errorf("%d test steps, want both levels run whole", n)
 	}
 }
+
+// besideDigest stands for the Go build module's digest over a workspace with siblings (DigestVersion 3, lead decision L5):
+// each package's digest folds the siblings' commits in, and the answer echoes the lines it folded.
+func besideDigest(b *bench) func(c stepCall) (any, error) {
+	return func(c stepCall) (any, error) {
+		level := c.args["level"].(string)
+		var lines []string
+		for _, f := range b.steps.tool("fetch") {
+			refs, _ := f.args["beside"].([]BesideRef)
+			for _, r := range refs {
+				lines = append(lines, r.Repository+" "+r.Commit)
+			}
+		}
+		sort.Strings(lines)
+		sum := sha256.Sum256([]byte(level + "\n" + strings.Join(lines, "\n")))
+		return Digested{Level: level, Packages: map[string]string{"fixture/slow": hex.EncodeToString(sum[:])}, Beside: lines}, nil
+	}
+}
+
+func TestACoreRepositorysPassingPackageIsKeptUnderADigestCoveringItsSiblings(t *testing.T) { // 1287 AC1-AC3, AC7 with L5
+	b := newBench(t)
+	b.steps.handlers["build_go_digest"] = besideDigest(b)
+	b.ex.Trunks = trunksOf(t, map[string]string{repoSDK: trunkS, "novox/mesh-catalog": trunkA})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	keys, _ := b.kept.Keys(context.Background())
+	if len(keys) != 2 {
+		t.Fatalf("kept %v, want the passing package at both levels", keys)
+	}
+	// The same siblings again: everything is taken, nothing runs.
+	b.steps.calls = nil
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if n := len(b.steps.tool("test")); n != 0 || v.Levels[delivery.LevelUnit].Run != 0 || v.Levels[delivery.LevelUnit].Kept == 0 {
+		t.Fatalf("%d test steps, unit %+v, want none run and the kept verdict taken", n, v.Levels[delivery.LevelUnit])
+	}
+	// A sibling's commit moves: a new digest, so the package runs again and is kept under it.
+	b.ex.Trunks = trunksOf(t, map[string]string{repoSDK: trunkS2, "novox/mesh-catalog": trunkA})
+	b.steps.calls = nil
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if n := len(b.steps.tool("test")); n != 2 {
+		t.Errorf("%d test steps after a sibling moved, want both levels run", n)
+	}
+	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 4 {
+		t.Errorf("kept %v, want a second key per level under the new digest", keys)
+	}
+}
+
+func TestADigestThatEchoesOtherSiblingsKeepsNothing(t *testing.T) { // 1287 with L5: an echo that differs is not trusted
+	b := newBench(t)
+	inner := besideDigest(b)
+	b.steps.handlers["build_go_digest"] = func(c stepCall) (any, error) {
+		v, err := inner(c)
+		d := v.(Digested)
+		d.Beside = d.Beside[:len(d.Beside)-1]
+		return d, err
+	}
+	b.ex.Trunks = trunksOf(t, map[string]string{repoSDK: trunkS, "novox/mesh-catalog": trunkA})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if keys, _ := b.kept.Keys(context.Background()); len(keys) != 0 {
+		t.Errorf("kept %v under a digest that does not cover every sibling", keys)
+	}
+}
+
+type pkgPaths map[string][]string
+
+func (p pkgPaths) PackagePaths(repository string) []string { return p[repository] }
+
+// groupPackageBench is a group of a TypeScript member (mesh-delivery) and the mesh-sdk member, whose merge changes sdkChanged.
+func groupPackageBench(t *testing.T, sdkChanged []string) *bench {
+	b := newBench(t)
+	b.ex.Modules = langs{repoA: {buildrun.GoBuildModule, buildrun.NodeBuildModule}, repoSDK: {buildrun.GoBuildModule, buildrun.NodeBuildModule}}
+	b.ex.Packages = pkgPaths{repoSDK: {"src", "test", "package.json", "package-lock.json", "tsconfig.json"}}
+	fetch := func(c stepCall) (any, error) {
+		f := b.fetch
+		if c.args["repository"] == repoSDK {
+			f.Changed = sdkChanged
+		}
+		return f, nil
+	}
+	b.steps.handlers["build_go_fetch"], b.steps.handlers["build_node_fetch"] = fetch, fetch
+	return b
+}
+
+func nodeFetchOf(b *bench, repo string) stepCall {
+	for _, c := range b.steps.tool("fetch") {
+		if c.module == buildrun.NodeBuildModule && c.args["repository"] == repo {
+			return c
+		}
+	}
+	return stepCall{}
+}
+
+func TestATypeScriptMemberTakesTheGroupsPackageWhenTheSDKMemberChangesItsPaths(t *testing.T) { // ADR 0500 §5, C11b
+	b := groupPackageBench(t, []string{"go/delivery/x.go", "src/state.ts"})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2)))
+	want := map[string]any{"repository": repoSDK, "commit": head2, "ref": "refs/pull/12/head"}
+	if got := nodeFetchOf(b, repoA).args["package"]; !reflect.DeepEqual(got, want) {
+		t.Errorf("mesh-delivery's Node fetch was given the package %v, want %v", got, want)
+	}
+	if got := nodeFetchOf(b, repoSDK).args["package"]; got != nil {
+		t.Errorf("the mesh-sdk member's own fetch was given %v: it builds its package itself", got)
+	}
+}
+
+func TestATypeScriptMemberResolvesTheRegistryWhenTheSDKMemberLeavesItsPaths(t *testing.T) { // ADR 0500 §5: the manifest alone, or Go alone
+	for _, changed := range [][]string{{"go/delivery/x.go"}, {"module.json"}, {"srcx/a.ts"}} {
+		b := groupPackageBench(t, changed)
+		b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2)))
+		if got := nodeFetchOf(b, repoA).args["package"]; got != nil {
+			t.Errorf("%v: the Node fetch was given %v, want the registry", changed, got)
+		}
+	}
+	// A lone TypeScript pull request: no group package either.
+	b := groupPackageBench(t, []string{"src/state.ts"})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1)))
+	if got := nodeFetchOf(b, repoA).args["package"]; got != nil {
+		t.Errorf("a lone pull request's Node fetch was given %v", got)
+	}
+}
+
+func TestNoStepOfACheckCarriesPublish(t *testing.T) { // ADR 0500 §4, 1309 (the checker's half): only the builder's trunk build publishes
+	b := groupPackageBench(t, []string{"src/state.ts"})
+	b.judge(t, caseOf(t, pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2)))
+	if len(b.steps.calls) == 0 {
+		t.Fatal("no step ran")
+	}
+	for _, c := range b.steps.calls {
+		if _, ok := c.args["publish"]; ok {
+			t.Errorf("%s was given publish: %v", c.tool, c.args)
+		}
+		if strings.HasSuffix(c.tool, "_build") || strings.HasSuffix(c.tool, "_pack") {
+			t.Errorf("the checker asked %s: a check builds no artifact of its own", c.tool)
+		}
+	}
+}
diff --git a/modules/mesh-delivery-checker/internal/check/gate_test.go b/modules/mesh-delivery-checker/internal/check/gate_test.go
new file mode 100644
index 0000000..6c709e0
--- /dev/null
+++ b/modules/mesh-delivery-checker/internal/check/gate_test.go
@@ -0,0 +1,106 @@
+package check
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// What the gate reads of the checker (R4e, lead's interface with dev-r4e-gate): the verdict's heads are the gate's hash over
+// `<owner/name lowercase>#<number>=<full head sha>`, a lone pull request is a group of one, and a move of a trunk marks
+// mesh/check pending on every open pull request into it, every member's for a group, before any check starts.
+
+func owedState(t testing.TB, r *rig, repo string, number int, head string) string {
+	t.Helper()
+	key, err := delivery.CheckerOwedKey(repo, number, head)
+	if err != nil {
+		t.Fatal(err)
+	}
+	raw, _, found, _ := r.owed.Get(context.Background(), key)
+	if !found {
+		return ""
+	}
+	o, err := delivery.DecodeCheckerOwed(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return o.State
+}
+
+func TestTheVerdictsHeadsAreTheGatesHashOverLowercaseHeads(t *testing.T) { // gate (b), (c)
+	ctx := context.Background()
+	r := newRig(t, passJudge())
+	upper := strings.ToUpper(head1[:20]) + head1[20:]
+	r.setTrunks(t, map[string]string{"Novox/Mesh-Delivery": trunkA, repoA: trunkA, repoSDK: trunkS})
+	cand := candidateOf(t, "feat/x", pullOf("Novox/Mesh-Delivery", 7, upper))
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	want, _ := delivery.HeadsHash([]delivery.Head{{Repository: repoA, Number: 7, Head: head1}})
+	if v := r.verdict(t, keyOf(t, "feat/x", cand)); v.Heads != want {
+		t.Errorf("heads = %q, want the gate's hash of the lone pull request, a group of one, %q", v.Heads, want)
+	}
+}
+
+func TestAGroupsVerdictHeadsCoverEveryMember(t *testing.T) { // gate (b): hq's member too, as the gate's ask covers it
+	ctx := context.Background()
+	r := newRig(t, passJudge())
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2), pullOf(HQRepository, 3, head2))
+	r.ch.Candidate(ctx, "feat%2Fx", cand)
+	r.ch.Wait()
+	want, _ := delivery.HeadsHash([]delivery.Head{{Repository: repoA, Number: 7, Head: head1}, {Repository: repoSDK, Number: 12, Head: head2},
+		{Repository: HQRepository, Number: 3, Head: head2}})
+	if v := r.verdict(t, keyOf(t, "feat/x", cand)); v.Heads != want {
+		t.Errorf("heads = %q, want %q", v.Heads, want)
+	}
+}
+
+func TestATrunkMoveMarksEveryOpenPullRequestIntoItPendingAtOnce(t *testing.T) { // gate (a), lead decision L4 (1302's checker part)
+	ctx := context.Background()
+	r := newRig(t, passJudge())
+	r.ch.Candidate(ctx, "feat%2Fg", candidateOf(t, "feat/g", pullOf(repoA, 7, head1), pullOf(repoSDK, 12, head2)))
+	r.ch.Candidate(ctx, "feat%2Fs", candidateOf(t, "feat/s", pullOf(repoSDK, 13, head1)))
+	r.ch.Wait()
+	for _, p := range []struct {
+		repo string
+		n    int
+		head string
+	}{{repoA, 7, head1}, {repoSDK, 12, head2}, {repoSDK, 13, head1}} {
+		if s := owedState(t, r, p.repo, p.n, p.head); s != "success" {
+			t.Fatalf("%s#%d is %q before the move", p.repo, p.n, s)
+		}
+	}
+	// A delivery builds, so no check starts; mesh-delivery's trunk moves.
+	r.ch.Hold = func() bool { return true }
+	r.setTrunks(t, map[string]string{repoA: trunkA2, repoSDK: trunkS})
+	r.ch.TrunkMoved(ctx)
+	r.ch.Wait()
+	if s := owedState(t, r, repoA, 7, head1); s != "pending" {
+		t.Errorf("mesh-delivery#7, into the moved trunk, is %q, want pending", s)
+	}
+	if s := owedState(t, r, repoSDK, 12, head2); s != "pending" {
+		t.Errorf("mesh-sdk#12, a member of the same group, is %q, want pending", s)
+	}
+	if s := owedState(t, r, repoSDK, 13, head1); s != "success" {
+		t.Errorf("mesh-sdk#13, alone into a trunk that did not move, is %q, want its success to stand", s)
+	}
+}
+
+func TestACheckThatEndsAfterItsTrunkMovedOwesPendingNotItsVerdict(t *testing.T) { // gate (a): a pass on an old trunk is never shown
+	ctx := context.Background()
+	var r *rig
+	j := &judgeFunc{f: func(ctx context.Context, c *Case, call int) (Outcome, error) {
+		if call == 1 {
+			r.setTrunks(t, map[string]string{repoA: trunkA2, repoSDK: trunkS}) // the trunk moves while it runs
+			r.ch.Hold = func() bool { return true }                            // and a delivery holds the next check
+		}
+		return Outcome{Verdict: passing()}, nil
+	}}
+	r = newRig(t, j)
+	r.ch.Candidate(ctx, "feat%2Fx", candidateOf(t, "feat/x", pullOf(repoA, 7, head1)))
+	r.ch.Wait()
+	if s := owedState(t, r, repoA, 7, head1); s != "pending" {
+		t.Errorf("the status is %q, want pending: the pass was judged on a trunk that moved", s)
+	}
+}
diff --git a/modules/mesh-delivery-checker/internal/check/judge.go b/modules/mesh-delivery-checker/internal/check/judge.go
index df003a4..5593b58 100644
--- a/modules/mesh-delivery-checker/internal/check/judge.go
+++ b/modules/mesh-delivery-checker/internal/check/judge.go
@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"path"
+	"slices"
 	"sort"
 	"strings"
 	"time"
@@ -68,6 +69,11 @@ type Examiner struct {
 	Builds BuildStates
 	// Announce says a preview was written under the key (EventPreviewWritten); nil says nothing.
 	Announce Announcer
+	// Packages names, of a repository, the paths (repository-relative) its TypeScript package artifacts are built from, from
+	// the indexer's modules (delivery.Module.ArtifactPaths, lead decision L8); nil serves no group package.
+	Packages interface {
+		PackagePaths(repository string) []string
+	}
 	// Trunks are the trunk heads of every repository, for the siblings a repository's tests read.
 	Trunks interface{ Heads() map[string]string }
 	Now    func() time.Time
@@ -87,6 +93,16 @@ func (j *Examiner) logf(format string, args ...any) {
 	}
 }
 
+// besideLines are the siblings as the digest step echoes them: `<owner/repo> <commit>`, sorted.
+func besideLines(refs []BesideRef) []string {
+	out := make([]string, 0, len(refs))
+	for _, r := range refs {
+		out = append(out, r.Repository+" "+r.Commit)
+	}
+	sort.Strings(out)
+	return out
+}
+
 // target is a pull request on one build module: the node chosen, the workspace its fetch made and what it said.
 type target struct {
 	pull      Pull
@@ -98,8 +114,9 @@ type target struct {
 	fetchArgs map[string]any
 	// priority are the Go packages (import paths) or the Node module directories whose test files the merge changes.
 	changed []string
-	// beside says the workspace was given siblings: its tests may read what the digest does not cover, so nothing is kept for it.
-	beside bool
+	// beside are the lines `<owner/repo> <commit>` of the siblings the workspace was given, sorted: its tests may read them,
+	// so a verdict is kept or taken only under a digest that says it folded exactly these in (lead decision L5).
+	beside []string
 	plans  map[string]*goPlan // by level
 }
 
@@ -142,6 +159,9 @@ func (j *Examiner) Judge(ctx context.Context, c *Case) (Outcome, error) {
 		return st.finish(ctx, *v), nil
 	}
 	for _, level := range []string{delivery.LevelUnit, delivery.LevelIntegration} {
+		if c.Try != nil && c.Try.Level != "" && c.Try.Level != level {
+			continue // a try of one level runs that level alone
+		}
 		for _, priority := range []bool{true, false} {
 			for _, t := range st.targets {
 				if v := st.runTarget(ctx, t, level, priority); v != nil {
@@ -254,7 +274,20 @@ func (st *state) choose(bm string) (node, toolchain string, err error) {
 func (st *state) fetchAll(ctx context.Context) *delivery.Verdict {
 	began := st.j.now()
 	defer func() { st.clone = st.j.now().Sub(began) }()
-	for _, p := range st.c.Pulls {
+	// The mesh-sdk member first: whether its merge changes the TypeScript package's paths decides whether the other members'
+	// Node fetches take the group's package (ADR 0500 §5).
+	pulls := slices.Clone(st.c.Pulls)
+	slices.SortStableFunc(pulls, func(a, b Pull) int {
+		if (a.Repository == SDKRepository) != (b.Repository == SDKRepository) {
+			if a.Repository == SDKRepository {
+				return -1
+			}
+			return 1
+		}
+		return 0
+	})
+	var groupPackage map[string]any
+	for _, p := range pulls {
 		var merged []Fetched
 		for _, bm := range st.j.Modules.BuildModules(p.Repository) {
 			node, tc, err := st.choose(bm)
@@ -265,14 +298,17 @@ func (st *state) fetchAll(ctx context.Context) *delivery.Verdict {
 			st.nodes[node] = true
 			args := map[string]any{"repository": p.Repository, "commit": p.Head, "ref": refOf(p.Number), "base": p.Trunk}
 			t.fetchArgs = args
+			if bm == buildrun.NodeBuildModule && groupPackage != nil && p.Repository != SDKRepository {
+				args["package"] = groupPackage
+			}
 			if bm == buildrun.GoBuildModule {
 				beside, err := st.j.besideFor(ctx, st.c, p)
 				if err != nil {
-					return fail(node, err.Error())
+					return fail(forgeMachine(err, node), err.Error()+unheardWords(err))
 				}
 				if len(beside) > 0 {
 					args["beside"] = beside
-					t.beside = true
+					t.beside = besideLines(beside)
 				}
 			}
 			raw, err := st.step(ctx, t, "fetch", fmt.Sprintf("fetch %s#%d on %s", p.Repository, p.Number, node), args)
@@ -284,18 +320,45 @@ func (st *state) fetchAll(ctx context.Context) *delivery.Verdict {
 				return fail(node, fmt.Sprintf("the fetch of %s#%d answered no workspace: %s", p.Repository, p.Number, raw))
 			}
 			if len(t.fetched.Conflicts) > 0 {
-				st.j.writePreview(ctx, p, append(merged, t.fetched))
+				if st.c.Try == nil {
+					st.j.writePreview(ctx, p, append(merged, t.fetched))
+				}
 				return fail(node, fmt.Sprintf("%s#%d does not merge into the trunk: files in conflict: %s", p.Repository, p.Number, strings.Join(t.fetched.Conflicts, ", ")))
 			}
 			t.changed = t.fetched.Changed
 			merged = append(merged, t.fetched)
 			st.targets = append(st.targets, t)
 		}
-		st.j.writePreview(ctx, p, merged)
+		if st.c.Try == nil { // a try owes the indexer no preview: no pull request holds its head
+			st.j.writePreview(ctx, p, merged)
+		}
+		if p.Repository == SDKRepository && len(st.c.Pulls) > 1 && st.j.changesPackage(p, merged) {
+			groupPackage = map[string]any{"repository": p.Repository, "commit": p.Head, "ref": refOf(p.Number)}
+		}
 	}
 	return nil
 }
 
+// changesPackage says whether the merge of a pull request changes a file inside the named paths of one of its repository's
+// TypeScript packages: a change of the manifest alone, or of files outside those paths, does not (ADR 0500 §5).
+func (j *Examiner) changesPackage(p Pull, merged []Fetched) bool {
+	if j.Packages == nil {
+		return false
+	}
+	paths := j.Packages.PackagePaths(p.Repository)
+	for _, f := range merged {
+		for _, changed := range f.Changed {
+			for _, named := range paths {
+				named = strings.TrimSuffix(strings.TrimPrefix(named, "./"), "/")
+				if changed == named || strings.HasPrefix(changed, named+"/") {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
 // isTestFile says whether a repository-relative path is a test file of the languages the checker judges: Go's _test.go and
 // the TypeScript module's .test. and .spec. files and test directories.
 func isTestFile(p string) bool {
@@ -398,9 +461,8 @@ func (st *state) planGo(ctx context.Context, t *target, level string) *delivery.
 	}
 	plan := &goPlan{digests: map[string]string{}}
 	t.plans[level] = plan
-	if t.beside {
-		// The digest covers the package's own files, the toolchain and the header, not the siblings placed beside the tree: a
-		// package whose tests read one must never be kept, nor taken from a verdict kept for other inputs (ADR 0444).
+	if st.c.Try != nil && st.c.Try.Run != "" {
+		// A try of some tests runs them alone: a partial run proves no package, so nothing is taken or kept.
 		plan.all = true
 		return nil
 	}
@@ -421,6 +483,13 @@ func (st *state) planGo(ctx context.Context, t *target, level string) *delivery.
 		plan.all = true
 		return nil
 	}
+	if !slices.Equal(d.Beside, t.beside) {
+		// The siblings the tests read are not all in the digest (a build module before DigestVersion 3, or another set): a
+		// package whose tests read one is never kept, nor taken from a verdict kept for other inputs (ADR 0444, L5).
+		st.j.logf("%s#%d: the %s level's digest covers the siblings %v, not %v, so it runs whole and keeps nothing", t.pull.Repository, t.pull.Number, level, d.Beside, t.beside)
+		plan.all = true
+		return nil
+	}
 	plan.digests = d.Packages
 	a := st.levels[level]
 	pkgs := make([]string, 0, len(d.Packages))
@@ -467,6 +536,9 @@ func (st *state) runGo(ctx context.Context, t *target, level string, priority bo
 	if run != nil {
 		args["packages"] = run
 	}
+	if st.c.Try != nil && st.c.Try.Run != "" {
+		args["run"] = st.c.Try.Run // build_go_test's go test -run pattern
+	}
 	raw, err := st.step(ctx, t, "test", fmt.Sprintf("test the %s level of %s#%d on %s", level, t.pull.Repository, t.pull.Number, t.node), args)
 	if err != nil {
 		return fail(t.node, fmt.Sprintf("the %s level of %s#%d: %v", level, t.pull.Repository, t.pull.Number, err))
diff --git a/modules/mesh-delivery-checker/internal/check/line.go b/modules/mesh-delivery-checker/internal/check/line.go
index 0882cf1..cedef15 100644
--- a/modules/mesh-delivery-checker/internal/check/line.go
+++ b/modules/mesh-delivery-checker/internal/check/line.go
@@ -2,6 +2,7 @@ package check
 
 import (
 	"fmt"
+	"slices"
 	"strings"
 	"unicode/utf8"
 
@@ -50,7 +51,7 @@ func firstFailed(v delivery.Verdict) string {
 
 // pieces are the parts of a line, from the most to the least needed.
 type pieces struct {
-	head, commits, counts, shortCounts, times, shortTimes, over, builds, composition, group string
+	head, commits, counts, shortCounts, times, shortTimes, over, builds, composition, shortComposition, group string
 }
 
 func (p pieces) join(drop int) string {
@@ -70,7 +71,10 @@ func (p pieces) join(drop int) string {
 	if drop < 2 && p.group != "" {
 		parts = append(parts, p.group)
 	}
-	if p.composition != "" {
+	switch {
+	case drop >= 3 && p.shortComposition != "":
+		parts = append(parts, p.shortComposition)
+	case p.composition != "":
 		parts = append(parts, p.composition)
 	}
 	out := make([]string, 0, len(parts))
@@ -90,14 +94,37 @@ func levelWords(name string, r delivery.LevelResult) string {
 	return s
 }
 
-func compositionWords(c *delivery.Composition) string {
-	switch {
-	case c == nil, c.State == delivery.CompositionNotRun:
+// compositionWords says the composition: not yet run, or once the assigner's check reports it (issue 1297) passed or
+// failed, with the time it took and the machines it composed (issue 1300).
+func compositionWords(c *delivery.Composition, took int64) string { return composition(c, took, false) }
+
+// composition is compositionWords; short counts the machines and leaves the SDK commit to the report.
+func composition(c *delivery.Composition, took int64, short bool) string {
+	if c == nil || c.State == delivery.CompositionNotRun {
 		return "composition not yet run"
-	case c.State == delivery.CompositionPass:
-		return "composition passed with " + short12(c.SDK)
 	}
-	return "composition failed: " + c.Words
+	in := ""
+	if took > 0 {
+		in = " in " + seconds(took)
+	}
+	on := ""
+	if len(c.Machines) > 0 {
+		machines := slices.Sorted(slices.Values(c.Machines))
+		on = " on " + strings.Join(machines, ", ")
+		switch {
+		case len(machines) > 1 && short:
+			on = fmt.Sprintf(" on %d machines", len(machines))
+		case len(machines) > 1:
+			on = fmt.Sprintf(" on %d machines: %s", len(machines), strings.Join(machines, ", "))
+		}
+	}
+	switch {
+	case c.State == delivery.CompositionPass && short:
+		return "composition passed" + in + on // the SDK it composed with is in the report
+	case c.State == delivery.CompositionPass:
+		return "composition passed" + in + " with " + short12(c.SDK) + on
+	}
+	return "composition failed" + in + on + ": " + c.Words
 }
 
 func buildWords(builds []BuildNote) string {
@@ -149,7 +176,7 @@ func parts(v delivery.Verdict, cs *Case, p Pull, builds []BuildNote, slowest []s
 		for _, x := range []struct {
 			name string
 			ms   int64
-		}{{"queue", t.Queue}, {"clone", t.Clone}, {"unit", t.Unit}, {"int setup", t.IntegrationSetup}, {"int run", t.IntegrationRun}, {"composition", t.Composition}} {
+		}{{"queue", t.Queue}, {"clone", t.Clone}, {"unit", t.Unit}, {"int setup", t.IntegrationSetup}, {"int run", t.IntegrationRun}} {
 			if x.ms > 0 {
 				times = append(times, x.name+" "+seconds(x.ms))
 			}
@@ -181,7 +208,8 @@ func parts(v delivery.Verdict, cs *Case, p Pull, builds []BuildNote, slowest []s
 	}
 	pc.builds = buildWords(builds)
 	if v.State != delivery.VerdictRunning {
-		pc.composition = compositionWords(v.Composition)
+		pc.composition = compositionWords(v.Composition, v.Took.Composition)
+		pc.shortComposition = composition(v.Composition, v.Took.Composition, true)
 	}
 	if cs != nil && len(cs.Pulls) > 1 {
 		pc.group = fmt.Sprintf("group %s of %d pull requests", cs.Group, len(cs.Pulls))
diff --git a/modules/mesh-delivery-checker/internal/check/line_test.go b/modules/mesh-delivery-checker/internal/check/line_test.go
index 6ea2499..662db1d 100644
--- a/modules/mesh-delivery-checker/internal/check/line_test.go
+++ b/modules/mesh-delivery-checker/internal/check/line_test.go
@@ -133,3 +133,24 @@ func TestThePassedCompositionIsSaidOnlyWhenItWasRun(t *testing.T) { // ADR 0484
 		t.Errorf("a verdict with no composition: %q", r)
 	}
 }
+
+func TestTheCompositionsTimeAndMachinesAreSaidOnceTheAssignerReportsThem(t *testing.T) { // 1300 (C10), the assigner's verdict (issue 1297)
+	cs, p := lineCase(t, pullOf(repoA, 7, head1))
+	v := passVerdict()
+	v.Took.Composition = 2400
+	v.Composition = &delivery.Composition{State: delivery.CompositionPass, SDK: "afbe371003a570f088be4a394d83aa7a9458f7ab", Machines: []string{"g14", "ace", "novox", "shanks"}}
+	r := Report(v, cs, p, nil, nil)
+	for _, want := range []string{"composition passed in 2.4s with afbe371003a5 on 4 machines: ace, g14, novox, shanks"} {
+		if !strings.Contains(r, want) {
+			t.Errorf("report %q lacks %q", r, want)
+		}
+	}
+	if l := Line(v, cs, p, nil, nil); !strings.Contains(l, "composition passed in 2.4s") || !strings.Contains(l, "on 4 machines") || utf8.RuneCountInString(l) > MaxLine {
+		t.Errorf("line = %q", l)
+	}
+	v.State, v.Failed = delivery.VerdictFail, delivery.FailedFirst{Machine: "novox", Words: "composition refused"}
+	v.Composition = &delivery.Composition{State: delivery.CompositionFail, Words: "novox: two seats claim dns", Machines: []string{"novox"}}
+	if r := Report(v, cs, p, nil, nil); !strings.Contains(r, "composition failed in 2.4s on novox: novox: two seats claim dns") {
+		t.Errorf("failed composition report = %q", r)
+	}
+}
diff --git a/modules/mesh-delivery-checker/internal/check/pins.go b/modules/mesh-delivery-checker/internal/check/pins.go
index 326d606..f1e2937 100644
--- a/modules/mesh-delivery-checker/internal/check/pins.go
+++ b/modules/mesh-delivery-checker/internal/check/pins.go
@@ -77,7 +77,7 @@ func (st *state) checkPins(ctx context.Context) verdictPtr {
 				text, err = st.j.Forge.File(ctx, t.pull.Repository, file, t.pull.Trunk)
 			}
 			if err != nil {
-				return failed(forgeMachine(err, t.node), fmt.Sprintf("%s#%d: %s cannot be read to check its mesh-sdk pin: %v", t.pull.Repository, t.pull.Number, file, err))
+				return failed(forgeMachine(err, t.node), fmt.Sprintf("%s#%d: %s cannot be read to check its mesh-sdk pin: %v%s", t.pull.Repository, t.pull.Number, file, err, unheardWords(err)))
 			}
 			pin, ok := SDKPin(text)
 			if !ok {
@@ -88,7 +88,7 @@ func (st *state) checkPins(ctx context.Context) verdictPtr {
 			}
 			onTrunk, err := st.j.Forge.OnTrunk(ctx, SDKRepository, pin)
 			if err != nil {
-				return failed(forgeMachine(err, t.node), fmt.Sprintf("%s#%d: whether mesh-sdk %s is on its trunk cannot be told: %v", t.pull.Repository, t.pull.Number, pin, err))
+				return failed(forgeMachine(err, t.node), fmt.Sprintf("%s#%d: whether mesh-sdk %s is on its trunk cannot be told: %v%s", t.pull.Repository, t.pull.Number, pin, err, unheardWords(err)))
 			}
 			if onTrunk {
 				continue
@@ -115,6 +115,14 @@ func pinHint(c *Case, fetchError string) string {
 	return " (a pin to the head of the group's mesh-sdk pull request names a commit only that head carries, which go mod download cannot resolve; " + Issue1148 + ")"
 }
 
+// unheardWords ends the words of a failed read of the forge that reached nobody: the forge was not heard (UnheardWords).
+func unheardWords(err error) string {
+	if isUnheard(err) {
+		return " (the forge was " + UnheardWords + ")"
+	}
+	return ""
+}
+
 // forgeMachine is the machine a failed read of the forge is put at: the forge when nobody answered it (no build node is to
 // blame, issue 1820), the build node whose workspace was read otherwise.
 func forgeMachine(err error, node string) string {
diff --git a/modules/mesh-delivery-checker/internal/check/pins_test.go b/modules/mesh-delivery-checker/internal/check/pins_test.go
index 9198b17..703a11b 100644
--- a/modules/mesh-delivery-checker/internal/check/pins_test.go
+++ b/modules/mesh-delivery-checker/internal/check/pins_test.go
@@ -253,3 +253,15 @@ func TestThePinOfTheControllerThatCannotBeReadFailsTheCheck(t *testing.T) { // r
 		t.Errorf("verdict = %+v", v)
 	}
 }
+
+func TestAForgeThatIsNotHeardFailsAtTheForgeAndIsJudgedAgainWhenTheNodesChange(t *testing.T) { // 1624 C7
+	b := newBench(t)
+	b.ex.Forge = &fakeForge{err: &Unheard{Err: fmt.Errorf("nats: no responders available for request")}}
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict
+	if v.State != delivery.VerdictFail || v.Failed.Machine != "forge" {
+		t.Fatalf("verdict = %+v, want failed at the forge", v)
+	}
+	if !IsNodesFailure(v) {
+		t.Errorf("a forge that was not heard is not the change's failure: %+v is not judged again when the nodes change", v.Failed)
+	}
+}
diff --git a/modules/mesh-delivery-checker/internal/check/read.go b/modules/mesh-delivery-checker/internal/check/read.go
index 874e99b..e4eebd3 100644
--- a/modules/mesh-delivery-checker/internal/check/read.go
+++ b/modules/mesh-delivery-checker/internal/check/read.go
@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"git.novox.be/novox/mesh-sdk/go/delivery"
+	"git.novox.be/novox/mesh-sdk/go/delivery/buildrun"
 )
 
 // The read tools (novox/hq ADR 0484 clauses 8 and 13, issue 1686): what the checker stored, as stored, with the line of the
@@ -17,6 +18,9 @@ const (
 	VerdictsReadTool = "checker_verdicts"
 	PullReadTool     = "checker_pull"
 	KeptReadTool     = "checker_kept"
+	// PreviewsReadTool reads the previews state (issue 1680); StatusReadTool reads what the checker is held by and what it runs (issue 1685).
+	PreviewsReadTool = "checker_previews"
+	StatusReadTool   = "checker_status"
 )
 
 // StateRead reads one state: its keys and a key's stored value (nil for a key with none).
@@ -26,7 +30,14 @@ type StateRead struct {
 }
 
 // Reader answers the read tools from the checker's verdicts and kept states and the indexer's candidates.
-type Reader struct{ VerdictState, KeptState, CandidateState StateRead }
+type Reader struct {
+	VerdictState, KeptState, CandidateState StateRead
+
+	PreviewState StateRead              // the checker's merge previews
+	PlansState   StateRead              // the controller's delivery plans in their build phase; zero where the bucket is absent
+	StepStates   map[string]StateRead   // the build modules' steps states, by module
+	Capacity     func() (string, error) // the capacity setting as written, `node=steps,...`
+}
 
 // VerdictRead is a verdict as stored with the full report of the status of each pull request it judged (Report), when the
 // candidate still holds those heads; without it the report is that of the verdict alone.
@@ -57,7 +68,7 @@ func (r Reader) read(key string, raw json.RawMessage) (VerdictRead, error) {
 		return out, fmt.Errorf("%s holds what is not a verdict: %w", key, err)
 	}
 	c, ok := r.candidate(v.Group)
-	if !ok || c.HeadsHash != v.Heads {
+	if !ok || (c.HeadsHash != v.Heads && GateHeads(c) != v.Heads) {
 		out.Note = "the candidate no longer holds these heads"
 		return out, nil
 	}
@@ -191,3 +202,153 @@ func (r Reader) Kept(level, digest string) (map[string]json.RawMessage, error) {
 	}
 	return out, nil
 }
+
+// PreviewRead is one preview as stored, with the parts of its key.
+type PreviewRead struct {
+	Key        string          `json:"key"`
+	Repository string          `json:"repository"`
+	Head       string          `json:"head"`
+	Trunk      string          `json:"trunk"`
+	Preview    json.RawMessage `json:"preview"`
+}
+
+// Previews are the previews the checker holds, each as stored. With a repository only that repository's; with a head (a
+// prefix of at least 7 characters is enough) only previews of that head. A key that is no preview key is listed as unreadable.
+func (r Reader) Previews(repository, head string) ([]PreviewRead, []string, error) {
+	if r.PreviewState.Keys == nil || r.PreviewState.Get == nil {
+		return nil, nil, fmt.Errorf("the previews state cannot be read here")
+	}
+	keys, err := r.PreviewState.Keys()
+	if err != nil {
+		return nil, nil, err
+	}
+	sort.Strings(keys)
+	out := []PreviewRead{}
+	var bad []string
+	for _, k := range keys {
+		repo, h, trunk, err := delivery.ParsePreviewKey(k)
+		if err != nil {
+			bad = append(bad, k)
+			continue
+		}
+		if (repository != "" && repo != repository) || (head != "" && !strings.HasPrefix(h, head)) {
+			continue
+		}
+		raw, err := r.PreviewState.Get(k)
+		if err != nil {
+			return nil, nil, err
+		}
+		if len(raw) > 0 {
+			out = append(out, PreviewRead{Key: k, Repository: repo, Head: h, Trunk: trunk, Preview: raw})
+		}
+	}
+	return out, bad, nil
+}
+
+// RunningStep is a step in flight on a build module.
+type RunningStep struct {
+	Module string `json:"module"`
+	Node   string `json:"node"`
+	ID     string `json:"id"`
+	Tool   string `json:"tool"`
+	Since  string `json:"since,omitempty"`
+}
+
+// Status is what holds the checker back and what runs now, read from the buckets: the checker's held and running steps live in
+// its process, so they are shown as what the buckets say (the steps in flight on the build modules, the candidates without a
+// verdict for their heads, and the delivery plans in their build phase), not as the process's own counters.
+type Status struct {
+	Capacity       map[string]int `json:"capacity"`
+	CapacityNote   string         `json:"capacity_note,omitempty"`
+	DefaultPerNode int            `json:"default_per_node"`
+	PlansBuilding  struct {
+		Readable bool     `json:"readable"`
+		Keys     []string `json:"keys"`
+		Holds    bool     `json:"holds"`
+	} `json:"plans_building"`
+	Running       []RunningStep  `json:"running_steps"`
+	RunningByNode map[string]int `json:"running_by_node"`
+	Unjudged      []string       `json:"unjudged_candidates"`
+	Notes         []string       `json:"notes,omitempty"`
+}
+
+// Status reads the capacity, the plan bucket, the build modules' steps and the candidates against their verdicts.
+func (r Reader) Status() (Status, error) {
+	st := Status{DefaultPerNode: buildrun.DefaultCapacity, Capacity: map[string]int{}, RunningByNode: map[string]int{}}
+	if r.Capacity == nil {
+		st.CapacityNote = "the capacity setting cannot be read from here"
+	} else if setting, err := r.Capacity(); err != nil {
+		st.CapacityNote = "the capacity setting cannot be read: " + err.Error()
+	} else if st.Capacity, err = buildrun.ParseCapacity(setting); err != nil {
+		st.Capacity, st.CapacityNote = map[string]int{}, "the capacity setting is not valid: "+err.Error()
+	}
+	if r.PlansState.Keys == nil {
+		st.Notes = append(st.Notes, PlansBuildingBucket+" is not readable here (absent), so it is read as empty: no delivery holds the checker")
+	} else if keys, err := r.PlansState.Keys(); err != nil {
+		st.Notes = append(st.Notes, PlansBuildingBucket+" cannot be listed, so it is read as empty: "+err.Error())
+	} else {
+		sort.Strings(keys)
+		st.PlansBuilding.Readable, st.PlansBuilding.Keys, st.PlansBuilding.Holds = true, keys, len(keys) > 0
+	}
+	mods := make([]string, 0, len(r.StepStates))
+	for m := range r.StepStates {
+		mods = append(mods, m)
+	}
+	sort.Strings(mods)
+	st.Running = []RunningStep{}
+	for _, m := range mods {
+		sr := r.StepStates[m]
+		if sr.Keys == nil || sr.Get == nil {
+			continue
+		}
+		keys, err := sr.Keys()
+		if err != nil {
+			st.Notes = append(st.Notes, "the steps of "+m+" cannot be listed: "+err.Error())
+			continue
+		}
+		sort.Strings(keys)
+		for _, k := range keys {
+			raw, err := sr.Get(k)
+			if err != nil || len(raw) == 0 {
+				continue
+			}
+			step, err := delivery.DecodeStep(raw)
+			if err != nil || step.State != delivery.StepRunning {
+				continue
+			}
+			rs := RunningStep{Module: m, Node: step.Node, ID: step.ID, Tool: step.Tool}
+			if !step.Started.IsZero() {
+				rs.Since = step.Started.UTC().Format("2006-01-02T15:04:05Z")
+			}
+			st.Running = append(st.Running, rs)
+			st.RunningByNode[step.Node]++
+		}
+	}
+	st.Unjudged = []string{}
+	if r.CandidateState.Keys != nil && r.CandidateState.Get != nil && r.VerdictState.Get != nil {
+		keys, err := r.CandidateState.Keys()
+		if err != nil {
+			return st, err
+		}
+		sort.Strings(keys)
+		for _, k := range keys {
+			raw, err := r.CandidateState.Get(k)
+			if err != nil || len(raw) == 0 {
+				continue
+			}
+			c, err := delivery.DecodeCandidate(raw)
+			if err != nil {
+				continue
+			}
+			vkey, err := delivery.CheckerVerdictKey(c.Group, c.HeadsHash)
+			if err != nil {
+				continue
+			}
+			if v, err := r.VerdictState.Get(vkey); err == nil && len(v) == 0 {
+				st.Unjudged = append(st.Unjudged, c.Group)
+			}
+		}
+	}
+	st.Notes = append(st.Notes, "the steps the checker holds waiting for a place are in its process and in no bucket: a candidate without a verdict while a plan key exists, or while its node runs as many steps as its capacity, is held")
+	return st, nil
+}
diff --git a/modules/mesh-delivery-checker/internal/check/read_test.go b/modules/mesh-delivery-checker/internal/check/read_test.go
index 1d1c8fb..de12542 100644
--- a/modules/mesh-delivery-checker/internal/check/read_test.go
+++ b/modules/mesh-delivery-checker/internal/check/read_test.go
@@ -3,8 +3,10 @@ package check
 import (
 	"context"
 	"encoding/json"
+	"os"
 	"strings"
 	"testing"
+	"time"
 
 	"git.novox.be/novox/mesh-sdk/go/delivery"
 )
@@ -102,3 +104,64 @@ func TestTheKeptToolAnswersTheKeysAsStoredByLevelAndByDigest(t *testing.T) { //
 		t.Error("a digest nothing kept was answered")
 	}
 }
+
+// 1680 live acceptance: checker_previews shows the preview key of an open pull request, as stored, narrowed by repository and head.
+func TestThePreviewsToolShowsTheStoredPreviewOfAPullRequest(t *testing.T) {
+	pv := delivery.Preview{Repository: repoA, Head: head1, Trunk: head2, Merge: "m1", Modules: map[string]delivery.PreviewModule{}}
+	data, err := delivery.EncodePreview(pv)
+	if err != nil {
+		t.Fatal(err)
+	}
+	key, _ := delivery.PreviewKey(repoA, head1, head2)
+	rd := Reader{PreviewState: fakeState{key: data, "junk": []byte("{}")}.read()}
+	got, bad, err := rd.Previews(repoA, head1[:8])
+	if err != nil || len(got) != 1 || got[0].Key != key || got[0].Head != head1 || got[0].Trunk != head2 || string(got[0].Preview) != string(data) {
+		t.Fatalf("previews = %+v, %v", got, err)
+	}
+	if len(bad) != 1 || bad[0] != "junk" {
+		t.Errorf("unreadable = %v", bad)
+	}
+	if got, _, _ := rd.Previews("novox/other", ""); len(got) != 0 {
+		t.Errorf("another repository's = %+v", got)
+	}
+	if _, _, err := (Reader{}).Previews("", ""); err == nil {
+		t.Error("answered with no state to read")
+	}
+}
+
+// 1685 live acceptance: checker_status reads the capacity, whether a plan key holds the checker, the steps in flight by node and
+// the candidates without a verdict.
+func TestTheStatusToolReadsCapacityHoldsAndRunningSteps(t *testing.T) {
+	running, _ := delivery.EncodeStep(delivery.Step{ID: "abc1", Tool: "build_go_test", Node: "shanks", State: delivery.StepRunning, Started: time.Date(2026, 10, 22, 15, 0, 0, 0, time.UTC)})
+	passed, _ := delivery.EncodeStep(delivery.Step{ID: "abc2", Tool: "build_go_test", Node: "ace", State: delivery.StepPassed})
+	cand := candidateOf(t, "feat/x", pullOf(repoA, 7, head1))
+	ckey, _ := delivery.CandidatesKey("feat/x")
+	rd := Reader{
+		Capacity:       func() (string, error) { return "shanks=2,ace=0", nil },
+		PlansState:     fakeState{"p1": []byte("{}")}.read(),
+		StepStates:     map[string]StateRead{"mesh-build-go": fakeState{"shanks.abc1": running, "ace.abc2": passed}.read()},
+		CandidateState: fakeState{ckey: cand}.read(),
+		VerdictState:   fakeState{}.read(),
+	}
+	st, err := rd.Status()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if st.Capacity["shanks"] != 2 || st.Capacity["ace"] != 0 || st.DefaultPerNode != 1 {
+		t.Errorf("capacity = %v default %d", st.Capacity, st.DefaultPerNode)
+	}
+	if !st.PlansBuilding.Holds || len(st.PlansBuilding.Keys) != 1 {
+		t.Errorf("plans = %+v", st.PlansBuilding)
+	}
+	if len(st.Running) != 1 || st.Running[0].Node != "shanks" || st.RunningByNode["shanks"] != 1 || st.RunningByNode["ace"] != 0 {
+		t.Errorf("running = %+v %v", st.Running, st.RunningByNode)
+	}
+	if len(st.Unjudged) != 1 || st.Unjudged[0] != "feat/x" {
+		t.Errorf("unjudged = %v", st.Unjudged)
+	}
+	// An absent plan bucket is read as empty and said; an unreadable capacity is said, not guessed.
+	st, err = Reader{Capacity: func() (string, error) { return "", os.ErrNotExist }}.Status()
+	if err != nil || st.PlansBuilding.Holds || st.CapacityNote == "" || len(st.Notes) == 0 {
+		t.Errorf("empty status = %+v, %v", st, err)
+	}
+}
diff --git a/modules/mesh-delivery-checker/internal/check/results.go b/modules/mesh-delivery-checker/internal/check/results.go
index 5583592..355185d 100644
--- a/modules/mesh-delivery-checker/internal/check/results.go
+++ b/modules/mesh-delivery-checker/internal/check/results.go
@@ -89,6 +89,9 @@ type Tested struct {
 // Digested is the answer of the Go build module's digest step: one digest per package that has tests at the level, by import
 // path.
 type Digested struct {
+	// Beside are the lines `<owner/repo> <commit>` of the siblings the digest folded in (DigestVersion 3, lead decision L5),
+	// sorted; absent when the workspace has none or the build module folds none in.
+	Beside       []string          `json:"beside,omitempty"`
 	Level        string            `json:"level"`
 	Packages     map[string]string `json:"packages"`
 	WithoutTests []string          `json:"without_tests,omitempty"`
diff --git a/modules/mesh-delivery-checker/internal/check/try.go b/modules/mesh-delivery-checker/internal/check/try.go
new file mode 100644
index 0000000..ac5c6db
--- /dev/null
+++ b/modules/mesh-delivery-checker/internal/check/try.go
@@ -0,0 +1,389 @@
+package check
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// A try is a pushed head judged by the checker as a pull request's head is, before its pull request is opened (ADR 0501
+// §5; issue 686's `mesh-controller.try`, which calls these tools from R4e): the head merged onto its trunk, the unit and the
+// integration level through the build modules. It owes the forge nothing (no status, no preview) and writes no verdict; its
+// state is the value of its key in the checker's state tries.
+
+// The try's tools and state.
+const (
+	TryTool     = "checker_try"
+	TryReadTool = "checker_try_read"
+	// TriesState is the checker's state of tries: the bucket mesh-delivery-checker_tries, keys try-<unix nanoseconds>.
+	TriesState  = "tries"
+	TriesBucket = delivery.CheckerModule + "_" + TriesState
+	// MaxTries is how many tries may wait or run at once, mesh-wide: each holds a build node for minutes.
+	MaxTries = 4
+	// TryKeep is how long an ended try's key is kept before the checker removes it.
+	TryKeep = 7 * 24 * time.Hour
+)
+
+// The states of a try: asked and waiting, running, and its end.
+const (
+	TryQueued  = "queued"
+	TryRunning = "running"
+	TryPass    = "pass"
+	TryFail    = "fail"
+	TryError   = "error"
+)
+
+var (
+	tryKeyOK   = regexp.MustCompile(`^try-[0-9]{1,20}$`)
+	tryHeadOK  = regexp.MustCompile(`^([0-9a-f]{40}|[0-9a-f]{64})$`)
+	tryTestsOK = regexp.MustCompile(`^[A-Za-z0-9_^$|().*+?/\[\]-]+$`)
+	tryRepoOK  = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]*/[A-Za-z0-9][A-Za-z0-9._-]*$`)
+	tryTrunkOK = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._/-]*$`)
+)
+
+// Try is the value of a tries key.
+type Try struct {
+	V          int    `json:"v"`
+	ID         string `json:"id"`
+	Repository string `json:"repository"`
+	// Head is the commit tried; Trunk the trunk commit it is merged onto, and Branch the trunk's branch when it was asked by name.
+	Head   string `json:"head"`
+	Trunk  string `json:"trunk"`
+	Branch string `json:"branch,omitempty"`
+	// Tests is a go test -run pattern: only those tests run, and nothing is kept. Level is unit or integration: only that
+	// level runs. Empty is every test of both levels.
+	Tests string `json:"tests,omitempty"`
+	Level string `json:"level,omitempty"`
+	State string `json:"state"`
+	// Said is the try's report in words: what failed first, the tests run, kept and skipped per level, the time of each part.
+	Said string `json:"said,omitempty"`
+	// Took is the time from its start to its end, as Go writes a duration.
+	Took     string                          `json:"took,omitempty"`
+	Failed   []string                        `json:"failed,omitempty"`
+	Levels   map[string]delivery.LevelResult `json:"levels,omitempty"`
+	Machines []string                        `json:"machines,omitempty"`
+	Asked    time.Time                       `json:"asked"`
+	Started  time.Time                       `json:"started,omitzero"`
+	Ended    time.Time                       `json:"ended,omitzero"`
+}
+
+// Over says whether the try came to its end.
+func (t Try) Over() bool { return t.State == TryPass || t.State == TryFail || t.State == TryError }
+
+// DecodeTry reads a tries value.
+func DecodeTry(raw []byte) (Try, error) {
+	var t Try
+	if err := json.Unmarshal(raw, &t); err != nil {
+		return Try{}, fmt.Errorf("not a try: %w", err)
+	}
+	if !tryKeyOK.MatchString(t.ID) || t.Repository == "" || t.Head == "" || t.Trunk == "" {
+		return Try{}, errors.New("not a try: it names no id, repository, head or trunk")
+	}
+	return t, nil
+}
+
+func encodeTry(t Try) ([]byte, error) {
+	t.V = delivery.Version
+	return json.Marshal(t)
+}
+
+// TryAsk is what checker_try is given.
+type TryAsk struct {
+	Repository, Head, Trunk, Tests, Level string
+}
+
+// TryStore is the tries state as the tools see it.
+type TryStore interface {
+	Keys() ([]string, error)
+	Get(key string) (json.RawMessage, error)
+	Create(key string, value []byte) error
+}
+
+// NotChecked is the error of a try of a repository the checker judges no level of: hq, judged by merge-check.sh (ADR 0484
+// clause 8), and a repository whose trunk the gate's source does not name.
+func NotChecked(repository string) error {
+	return fmt.Errorf("no level of %s is checked by the checker", repository)
+}
+
+// AskTry writes a new try, queued, and answers its id: a try of the same head that waits or runs is the answer to a second
+// ask, and at most MaxTries wait or run at once. trunks are the gate's trunk heads of every repository (source.main): a
+// repository with none, and hq, are no repository the checker checks. A trunk asked by name is its trunk head now.
+func AskTry(store TryStore, trunks map[string]string, a TryAsk, now time.Time) (string, error) {
+	repo := strings.ToLower(strings.TrimSuffix(strings.TrimSpace(a.Repository), ".git"))
+	head := strings.ToLower(strings.TrimSpace(a.Head))
+	switch {
+	case !tryRepoOK.MatchString(repo) || strings.Contains(repo, ".."):
+		return "", fmt.Errorf("%q is not a repository, <owner>/<name>", a.Repository)
+	case !tryHeadOK.MatchString(head):
+		return "", fmt.Errorf("the head %q is not a full commit, 40 or 64 hex digits", a.Head)
+	case a.Level != "" && a.Level != delivery.LevelUnit && a.Level != delivery.LevelIntegration:
+		return "", fmt.Errorf("the level %q is neither unit nor integration", a.Level)
+	case a.Tests != "" && !tryTestsOK.MatchString(a.Tests):
+		return "", fmt.Errorf("the tests %q are not a go test -run pattern", a.Tests)
+	}
+	trunkHead := ""
+	for r, h := range trunks {
+		if strings.EqualFold(r, repo) {
+			trunkHead = h
+		}
+	}
+	if repo == HQRepository || trunkHead == "" {
+		return "", NotChecked(repo)
+	}
+	t := Try{Repository: repo, Head: head, Tests: a.Tests, Level: a.Level, State: TryQueued, Asked: now.UTC()}
+	switch trunk := strings.TrimSpace(a.Trunk); {
+	case trunk == "":
+		t.Trunk = trunkHead
+	case tryHeadOK.MatchString(strings.ToLower(trunk)):
+		t.Trunk = strings.ToLower(trunk)
+	case tryTrunkOK.MatchString(trunk) && !strings.Contains(trunk, ".."):
+		// The checker judges pull requests into the trunk alone (ADR 0484 clause 11): a branch named is the trunk's head now.
+		t.Trunk, t.Branch = trunkHead, trunk
+	default:
+		return "", fmt.Errorf("the trunk %q is neither a full commit nor a branch", a.Trunk)
+	}
+	keys, err := store.Keys()
+	if err != nil {
+		return "", fmt.Errorf("the tries cannot be listed: %w", err)
+	}
+	sort.Strings(keys)
+	var open []string
+	for _, k := range keys {
+		raw, err := store.Get(k)
+		if err != nil || len(raw) == 0 {
+			continue
+		}
+		cur, err := DecodeTry(raw)
+		if err != nil || cur.Over() {
+			continue
+		}
+		if cur.Repository == t.Repository && cur.Head == t.Head && cur.Trunk == t.Trunk && cur.Tests == t.Tests && cur.Level == t.Level {
+			return cur.ID, nil
+		}
+		open = append(open, fmt.Sprintf("%s (%s@%.12s, %s)", cur.ID, cur.Repository, cur.Head, cur.State))
+	}
+	if len(open) >= MaxTries {
+		return "", fmt.Errorf("%d tries wait or run, the most at once: %s; ask again when one ends", len(open), strings.Join(open, ", "))
+	}
+	t.ID = "try-" + strconv.FormatInt(now.UnixNano(), 10)
+	data, err := encodeTry(t)
+	if err != nil {
+		return "", err
+	}
+	if err := store.Create(t.ID, data); err != nil {
+		return "", fmt.Errorf("the try %s cannot be written: %w", t.ID, err)
+	}
+	return t.ID, nil
+}
+
+// ReadTry is a try's value, as stored.
+func ReadTry(store TryStore, id string) (json.RawMessage, error) {
+	if !tryKeyOK.MatchString(id) {
+		return nil, fmt.Errorf("%q is not a try's id, try-<digits>", id)
+	}
+	raw, err := store.Get(id)
+	if err != nil {
+		return nil, err
+	}
+	if len(raw) == 0 {
+		return nil, fmt.Errorf("no try %s: it was never asked, or it ended more than %s ago and was removed", id, TryKeep)
+	}
+	return raw, nil
+}
+
+// TryOptions narrow what a try runs; a pull request's check has none.
+type TryOptions struct {
+	Level string
+	Run   string
+}
+
+// Tryer runs the tries: it takes a queued try, judges it through the same Judge as a pull request's check, and writes its
+// end. It holds no timer: a try starts when its key is written, or when a delivery that held it ends (Reconsider).
+type Tryer struct {
+	Tries KV
+	Judge Judge
+	// Hold says whether a delivery builds, so no try starts (ADR 0484 clause 12); nil never holds.
+	Hold  func() bool
+	Bound time.Duration
+	Now   func() time.Time
+	Logf  func(format string, args ...any)
+
+	mu       sync.Mutex
+	wg       sync.WaitGroup
+	inflight map[string]bool
+	seen     map[string]bool // looked at since this process started: a try left running is taken over the first time
+}
+
+func (tr *Tryer) now() time.Time {
+	if tr.Now != nil {
+		return tr.Now()
+	}
+	return time.Now()
+}
+
+func (tr *Tryer) logf(format string, args ...any) {
+	if tr.Logf != nil {
+		tr.Logf(format, args...)
+	}
+}
+
+// Wait returns when every try started so far has ended.
+func (tr *Tryer) Wait() { tr.wg.Wait() }
+
+// Put takes a value of the tries state in: a queued try is started, and a try left running is taken over the first time
+// this process sees it (the checker that ran it stopped; there is one checker).
+func (tr *Tryer) Put(ctx context.Context, key string, value []byte) {
+	t, err := DecodeTry(value)
+	if err != nil {
+		tr.logf("tries.%s holds what is not a try, left: %v", key, err)
+		return
+	}
+	if t.Over() {
+		return
+	}
+	held := tr.Hold != nil && tr.Hold()
+	tr.mu.Lock()
+	if tr.inflight == nil {
+		tr.inflight, tr.seen = map[string]bool{}, map[string]bool{}
+	}
+	if tr.inflight[key] || (t.State == TryRunning && tr.seen[key]) {
+		tr.mu.Unlock()
+		return
+	}
+	if held {
+		tr.mu.Unlock() // not seen yet: a try left running is still taken over when the hold ends
+		tr.logf("%s: not started, a delivery builds", key)
+		return
+	}
+	tr.seen[key] = true
+	tr.inflight[key] = true
+	tr.mu.Unlock()
+	tr.wg.Add(1)
+	go func() {
+		defer tr.wg.Done()
+		defer func() { tr.mu.Lock(); delete(tr.inflight, key); tr.mu.Unlock() }()
+		tr.run(ctx, key)
+	}()
+}
+
+// Reconsider looks at every try again (a delivery that held them ended), and removes the ended tries older than TryKeep.
+func (tr *Tryer) Reconsider(ctx context.Context) {
+	keys, err := tr.Tries.Keys(ctx)
+	if err != nil {
+		tr.logf("the tries cannot be listed: %v", err)
+		return
+	}
+	for _, k := range keys {
+		raw, _, found, err := tr.Tries.Get(ctx, k)
+		if err != nil || !found {
+			continue
+		}
+		if t, err := DecodeTry(raw); err == nil && t.Over() && tr.now().Sub(t.Ended) > TryKeep {
+			if d, ok := tr.Tries.(interface {
+				Delete(ctx context.Context, key string) error
+			}); ok {
+				if err := d.Delete(ctx, k); err != nil {
+					tr.logf("%s ended %s ago and could not be removed: %v", k, tr.now().Sub(t.Ended).Round(time.Hour), err)
+				}
+			}
+			continue
+		}
+		tr.Put(ctx, k, raw)
+	}
+}
+
+// run claims the try by compare-and-set, judges it within its bound and writes its end.
+func (tr *Tryer) run(ctx context.Context, key string) {
+	raw, rev, found, err := tr.Tries.Get(ctx, key)
+	if err != nil || !found {
+		return
+	}
+	t, err := DecodeTry(raw)
+	if err != nil || t.Over() {
+		return
+	}
+	t.State, t.Started = TryRunning, tr.now().UTC()
+	data, err := encodeTry(t)
+	if err != nil {
+		return
+	}
+	if rev, err = tr.Tries.Update(ctx, key, data, rev); err != nil {
+		if !errors.Is(err, ErrConflict) {
+			tr.logf("%s: %v", key, err)
+		}
+		return
+	}
+	cs := &Case{Key: key, Group: key,
+		Pulls:    []Pull{{Repository: t.Repository, Head: t.Head, Trunk: t.Trunk}},
+		Trunk:    map[string]string{t.Repository: t.Trunk},
+		Queued:   t.Asked,
+		Progress: &Progress{},
+		Try:      &TryOptions{Level: t.Level, Run: t.Tests}}
+	out, judged := judgeWithin(ctx, tr.Judge, cs, tr.Bound)
+	if ctx.Err() != nil {
+		return // left running: the checker takes it over when it starts
+	}
+	v := out.Verdict
+	t.Ended = tr.now().UTC()
+	t.Took = t.Ended.Sub(t.Started).Round(time.Second).String()
+	t.Levels, t.Machines = v.Levels, v.Machines
+	t.Said = Report(v, cs, cs.Pulls[0], out.Builds, out.Slowest)
+	switch {
+	case !judged || IsNodesFailure(v):
+		t.State = TryError
+	case v.State == delivery.VerdictPass:
+		t.State = TryPass
+	default:
+		t.State = TryFail
+		if f := firstFailed(v); f != "" {
+			t.Failed = []string{f}
+		}
+	}
+	if t.Tests != "" {
+		t.Said += " | only the tests " + t.Tests + " (Go); nothing kept"
+	}
+	if data, err = encodeTry(t); err == nil {
+		_, err = tr.Tries.Update(ctx, key, data, rev)
+	}
+	if err != nil {
+		tr.logf("%s: its end could not be written: %v", key, err)
+		return
+	}
+	tr.logf("%s: %s", key, t.State)
+}
+
+// judgeWithin runs a case within the bound (DefaultBound when 0). A judge that fails to judge, and a check that ran past its
+// bound, are verdicts of failure naming the machine and the step, and judged says false for them.
+func judgeWithin(ctx context.Context, j Judge, cs *Case, bound time.Duration) (Outcome, bool) {
+	if bound <= 0 {
+		bound = DefaultBound
+	}
+	run, cancel := context.WithTimeoutCause(ctx, bound, errBound)
+	defer cancel()
+	out, err := j.Judge(run, cs)
+	stage, node := cs.Progress.Now()
+	if node == "" {
+		node = "checker"
+	}
+	switch {
+	case ctx.Err() != nil:
+		return Outcome{}, false
+	case context.Cause(run) == errBound:
+		if stage == "" {
+			stage = "starting"
+		}
+		return Outcome{Verdict: failure(node, fmt.Sprintf("the check ran past its bound of %s, stuck at: %s", bound, stage))}, false
+	case err != nil:
+		return Outcome{Verdict: failure(node, err.Error())}, false
+	}
+	return out, true
+}
diff --git a/modules/mesh-delivery-checker/internal/check/try_test.go b/modules/mesh-delivery-checker/internal/check/try_test.go
new file mode 100644
index 0000000..65b89b5
--- /dev/null
+++ b/modules/mesh-delivery-checker/internal/check/try_test.go
@@ -0,0 +1,196 @@
+package check
+
+import (
+	"context"
+	"encoding/json"
+	"strings"
+	"testing"
+	"time"
+
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// memTries is the tries state as the tools see it, over a memKV.
+type memTries struct{ kv *memKV }
+
+func (m memTries) Keys() ([]string, error) { return m.kv.Keys(context.Background()) }
+func (m memTries) Get(key string) (json.RawMessage, error) {
+	v, _, _, err := m.kv.Get(context.Background(), key)
+	return v, err
+}
+func (m memTries) Create(key string, value []byte) error {
+	_, err := m.kv.Create(context.Background(), key, value)
+	return err
+}
+
+var tryTrunks = map[string]string{repoA: trunkA, repoSDK: trunkS, HQRepository: trunkA}
+
+func readTry(t testing.TB, kv *memKV, id string) Try {
+	t.Helper()
+	raw, _, found, _ := kv.Get(context.Background(), id)
+	if !found {
+		t.Fatalf("no try %s", id)
+	}
+	tr, err := DecodeTry(raw)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return tr
+}
+
+func TestATryIsAskedQueuedOncePerHeadAndAtMostFourAtOnce(t *testing.T) { // ADR 0501 §5
+	kv := newMemKV()
+	store := memTries{kv}
+	at := time.Date(2026, 10, 22, 18, 0, 0, 0, time.UTC)
+	id, err := AskTry(store, tryTrunks, TryAsk{Repository: repoA, Head: head1, Trunk: "main"}, at)
+	if err != nil || !strings.HasPrefix(id, "try-") {
+		t.Fatalf("id %q, %v", id, err)
+	}
+	tr := readTry(t, kv, id)
+	if tr.State != TryQueued || tr.Trunk != trunkA || tr.Branch != "main" || tr.Head != head1 || tr.Repository != repoA {
+		t.Errorf("try = %+v, want queued on the trunk's head", tr)
+	}
+	again, err := AskTry(store, tryTrunks, TryAsk{Repository: repoA, Head: head1, Trunk: "main"}, at.Add(time.Second))
+	if err != nil || again != id {
+		t.Errorf("a second ask of the same head answered %q, %v, want %q", again, err, id)
+	}
+	heads := []string{head2, trunkA2, trunkS2}
+	for i, h := range heads {
+		if _, err := AskTry(store, tryTrunks, TryAsk{Repository: repoA, Head: h, Trunk: trunkA}, at.Add(time.Duration(i+2)*time.Second)); err != nil {
+			t.Fatalf("try %d: %v", i+2, err)
+		}
+	}
+	if _, err := AskTry(store, tryTrunks, TryAsk{Repository: repoSDK, Head: head1}, at.Add(time.Minute)); err == nil || !strings.Contains(err.Error(), "4 tries wait or run") {
+		t.Errorf("a fifth try answered %v, want refused naming the four", err)
+	}
+}
+
+func TestATryOfARepositoryWithNoCheckedLevelIsRefused(t *testing.T) { // the agreed error of the try
+	store := memTries{newMemKV()}
+	for _, repo := range []string{HQRepository, "novox/mesh-lab"} {
+		_, err := AskTry(store, tryTrunks, TryAsk{Repository: repo, Head: head1, Trunk: "main"}, time.Now())
+		if err == nil || err.Error() != "no level of "+repo+" is checked by the checker" {
+			t.Errorf("%s: %v", repo, err)
+		}
+	}
+	for _, bad := range []TryAsk{{Repository: repoA, Head: "abc"}, {Repository: repoA, Head: head1, Level: "e2e"},
+		{Repository: repoA, Head: head1, Tests: "a b"}, {Repository: "x", Head: head1}, {Repository: repoA, Head: head1, Trunk: "-x"}} {
+		if _, err := AskTry(store, tryTrunks, bad, time.Now()); err == nil {
+			t.Errorf("%+v was taken", bad)
+		}
+	}
+}
+
+func TestATryIsJudgedAsAPullRequestsHeadAndOwesTheForgeNothing(t *testing.T) { // ADR 0501 §5
+	ctx := context.Background()
+	kv := newMemKV()
+	id, err := AskTry(memTries{kv}, tryTrunks, TryAsk{Repository: repoA, Head: head1, Trunk: trunkA}, time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	b := newBench(t)
+	tr := &Tryer{Tries: kv, Judge: b.ex}
+	raw, _, _, _ := kv.Get(ctx, id)
+	tr.Put(ctx, id, raw)
+	tr.Wait()
+	got := readTry(t, kv, id)
+	if got.State != TryPass || got.Took == "" || got.Head != head1 || got.Trunk != trunkA || got.Said == "" || got.Levels[delivery.LevelUnit].Run != 2 {
+		t.Fatalf("try = %+v", got)
+	}
+	fetch := b.steps.tool("fetch")
+	if len(fetch) != 1 || fetch[0].args["commit"] != head1 || fetch[0].args["base"] != trunkA || fetch[0].args["ref"] != "" {
+		t.Errorf("fetch = %+v, want the head merged onto the trunk, with no pull request's ref", fetch)
+	}
+	if keys, _ := b.prev.Keys(ctx); len(keys) != 0 {
+		t.Errorf("a try wrote the previews %v", keys)
+	}
+	// An ended try is not run again.
+	raw, _, _, _ = kv.Get(ctx, id)
+	tr.Put(ctx, id, raw)
+	tr.Wait()
+	if n := len(b.steps.tool("fetch")); n != 1 {
+		t.Errorf("an ended try was fetched again: %d fetches", n)
+	}
+}
+
+func TestATryOfOneLevelAndSomeTestsRunsThemAloneAndKeepsNothing(t *testing.T) {
+	ctx := context.Background()
+	kv := newMemKV()
+	id, err := AskTry(memTries{kv}, tryTrunks, TryAsk{Repository: repoA, Head: head1, Level: delivery.LevelIntegration, Tests: "TestBus|TestStore"}, time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	b := newBench(t)
+	tr := &Tryer{Tries: kv, Judge: b.ex}
+	raw, _, _, _ := kv.Get(ctx, id)
+	tr.Put(ctx, id, raw)
+	tr.Wait()
+	tests := b.steps.tool("test")
+	if len(tests) != 1 || tests[0].args["level"] != delivery.LevelIntegration || tests[0].args["run"] != "TestBus|TestStore" {
+		t.Fatalf("tests = %+v, want the integration level alone with the run pattern", tests)
+	}
+	if n := len(b.steps.tool("digest")); n != 0 {
+		t.Errorf("%d digests for a try of some tests", n)
+	}
+	if keys, _ := b.kept.Keys(ctx); len(keys) != 0 {
+		t.Errorf("kept %v from a try of some tests", keys)
+	}
+	if got := readTry(t, kv, id); got.State != TryPass || !strings.Contains(got.Said, "only the tests TestBus|TestStore") {
+		t.Errorf("try = %+v", got)
+	}
+}
+
+func TestAFailingTryNamesWhatFailedAndAStepThatCannotRunIsAnError(t *testing.T) {
+	ctx := context.Background()
+	kv := newMemKV()
+	b := newBench(t)
+	b.test = func(c stepCall) (any, error) { return captured[Tested](t, "go-test-failing"), nil }
+	id, _ := AskTry(memTries{kv}, tryTrunks, TryAsk{Repository: repoA, Head: head1}, time.Now())
+	tr := &Tryer{Tries: kv, Judge: b.ex}
+	raw, _, _, _ := kv.Get(ctx, id)
+	tr.Put(ctx, id, raw)
+	tr.Wait()
+	if got := readTry(t, kv, id); got.State != TryFail || len(got.Failed) != 1 || !strings.Contains(got.Failed[0], "TestThreeIsFour") {
+		t.Errorf("try = %+v", got)
+	}
+	// No build node: the try could not run, which is an error, not a failure of the change.
+	kv2 := newMemKV()
+	b2 := newBench(t)
+	b2.ex.Toolchains = entries{}
+	id2, _ := AskTry(memTries{kv2}, tryTrunks, TryAsk{Repository: repoA, Head: head1}, time.Now())
+	tr2 := &Tryer{Tries: kv2, Judge: b2.ex}
+	raw, _, _, _ = kv2.Get(ctx, id2)
+	tr2.Put(ctx, id2, raw)
+	tr2.Wait()
+	if got := readTry(t, kv2, id2); got.State != TryError {
+		t.Errorf("try with no node = %+v, want error", got)
+	}
+}
+
+func TestATryWaitsWhileADeliveryBuildsAndATryLeftRunningIsTakenOver(t *testing.T) {
+	ctx := context.Background()
+	kv := newMemKV()
+	id, _ := AskTry(memTries{kv}, tryTrunks, TryAsk{Repository: repoA, Head: head1}, time.Now())
+	// Left running by a checker that stopped.
+	raw, rev, _, _ := kv.Get(ctx, id)
+	cur, _ := DecodeTry(raw)
+	cur.State = TryRunning
+	data, _ := encodeTry(cur)
+	if _, err := kv.Update(ctx, id, data, rev); err != nil {
+		t.Fatal(err)
+	}
+	b := newBench(t)
+	held := true
+	tr := &Tryer{Tries: kv, Judge: b.ex, Hold: func() bool { return held }}
+	tr.Reconsider(ctx)
+	tr.Wait()
+	if n := len(b.steps.tool("fetch")); n != 0 {
+		t.Fatalf("a try ran while a delivery builds")
+	}
+	held = false
+	tr.Reconsider(ctx)
+	tr.Wait()
+	if got := readTry(t, kv, id); got.State != TryPass {
+		t.Errorf("the try left running = %+v, want taken over and passed", got)
+	}
+}
diff --git a/modules/mesh-delivery-checker/manifest_test.go b/modules/mesh-delivery-checker/manifest_test.go
index c3d4592..a4b5442 100644
--- a/modules/mesh-delivery-checker/manifest_test.go
+++ b/modules/mesh-delivery-checker/manifest_test.go
@@ -92,7 +92,7 @@ func TestManifestDeclarations(t *testing.T) { // 1678/AC1
 		t.Errorf("module = %q", m.Module)
 	}
 	// delivery.CheckerKeptHistory, CheckerOwedHistory, PreviewsHistory, CheckerVerdictsHistory; the names follow the SDK's buckets.
-	if want := []state{{Name: "kept", History: 1}, {Name: "owed", History: 5}, {Name: "previews", History: 5}, {Name: "verdicts", History: 5}}; !reflect.DeepEqual(m.State, want) {
+	if want := []state{{Name: "kept", History: 1}, {Name: "owed", History: 5}, {Name: "previews", History: 5}, {Name: "tries", History: 1}, {Name: "verdicts", History: 5}}; !reflect.DeepEqual(m.State, want) {
 		t.Errorf("state = %+v, want %+v", m.State, want)
 	}
 	if want := []string{"mesh-build-go.steps", "mesh-build-go.toolchains", "mesh-build-node.steps", "mesh-build-node.toolchains",
@@ -118,7 +118,8 @@ func TestManifestDeclarations(t *testing.T) { // 1678/AC1
 		t.Errorf("streams = %+v, want %+v", m.Streams, want)
 	}
 	// The read tools (issue 1686) are served by the tools bundle, not by the checker's process.
-	if want := []string{"checker_kept", "checker_pull", "checker_verdicts"}; !reflect.DeepEqual(sorted(m.Tools), want) {
+	// The try's two tools (ADR 0501 §5) beside them: mesh-controller's try calls them.
+	if want := []string{"checker_kept", "checker_previews", "checker_pull", "checker_status", "checker_try", "checker_try_read", "checker_verdicts"}; !reflect.DeepEqual(sorted(m.Tools), want) {
 		t.Errorf("tools = %v, want %v", m.Tools, want)
 	}
 	for _, k := range []string{"logs", "emits", "claims", "provides", "requires", "uses", "defines-seats", "seat", "seats", "bus"} {
diff --git a/modules/mesh-delivery-checker/module.json b/modules/mesh-delivery-checker/module.json
index 87c1005..2c22576 100644
--- a/modules/mesh-delivery-checker/module.json
+++ b/modules/mesh-delivery-checker/module.json
@@ -13,6 +13,7 @@
     { "name": "kept", "history": 1 },
     { "name": "owed", "history": 5 },
     { "name": "previews", "history": 5 },
+    { "name": "tries", "history": 1 },
     { "name": "verdicts", "history": 5 }
   ],
   "reads": [
@@ -31,7 +32,11 @@
   ],
   "tools": [
     "checker_kept",
+    "checker_previews",
     "checker_pull",
+    "checker_status",
+    "checker_try",
+    "checker_try_read",
     "checker_verdicts"
   ],
   "invokes": [
diff --git a/modules/mesh-delivery-forge-bridge/cmd/mesh-delivery-forge-bridge/gate_test.go b/modules/mesh-delivery-forge-bridge/cmd/mesh-delivery-forge-bridge/gate_test.go
index 2a7b64b..92982c4 100644
--- a/modules/mesh-delivery-forge-bridge/cmd/mesh-delivery-forge-bridge/gate_test.go
+++ b/modules/mesh-delivery-forge-bridge/cmd/mesh-delivery-forge-bridge/gate_test.go
@@ -229,7 +229,7 @@ func TestTheCheckersStatusIsSetOncePerRevisionAndAKeyOfTheGateIsNotItsKey(t *tes
 	key, v := checkerOwed(t, 12, "success", "pass aaaaaaaaaaaa on bbbbbbbbbbbb")
 	p.checkOwed(context.Background(), key, 3, v)
 	p.checkOwed(context.Background(), key, 3, v)
-	if len(f.calls) != 1 || f.calls[0].key != "gitea.gitea_commit_status" ||
+	if len(f.calls) != 1 || f.calls[0].key != "gitea.gitea_check_status" ||
 		f.calls[0].body != `{"context":"mesh/check","description":"pass aaaaaaaaaaaa on bbbbbbbbbbbb","owner":"novox","repo":"mesh-delivery","sha":"`+headA+`","state":"success","target_url":"https://view.example/checks/g.0123456789ab"}` {
 		t.Fatalf("calls = %+v", f.calls)
 	}
diff --git a/modules/mesh-delivery-forge-bridge/cmd/mesh-delivery-forge-bridge/integration_test.go b/modules/mesh-delivery-forge-bridge/cmd/mesh-delivery-forge-bridge/integration_test.go
index 679a8ae..64d90c1 100644
--- a/modules/mesh-delivery-forge-bridge/cmd/mesh-delivery-forge-bridge/integration_test.go
+++ b/modules/mesh-delivery-forge-bridge/cmd/mesh-delivery-forge-bridge/integration_test.go
@@ -95,6 +95,10 @@ accounts {
             "mesh.mod.gitea.call.gitea_commit_status.n1~mesh-delivery-forge-bridge"
             "mesh.mod.gitea.tool.gitea_commit_status"
             "mesh.mod.gitea.tool.gitea_commit_status.*"
+            "mesh.mod.gitea.call.gitea_check_status.*.n1~mesh-delivery-forge-bridge"
+            "mesh.mod.gitea.call.gitea_check_status.n1~mesh-delivery-forge-bridge"
+            "mesh.mod.gitea.tool.gitea_check_status"
+            "mesh.mod.gitea.tool.gitea_check_status.*"
             "mesh.mod.gitea.call.gitea_delivery_view.*.n1~mesh-delivery-forge-bridge"
             "mesh.mod.gitea.call.gitea_delivery_view.n1~mesh-delivery-forge-bridge"
             "mesh.mod.gitea.tool.gitea_delivery_view"
@@ -735,7 +739,7 @@ func sha256Sum(b []byte) []byte { s := sha256.Sum256(b); return s[:] }
 func TestBridgePerformsTheCheckersStatusOncePerRevisionOfItsOwedKey(t *testing.T) { // 1683/AC5, ADR 0484 §2
 	b := startBed(t, `{"result":{"pulls":[]}}`, nil)
 	calls := make(chan string, 8)
-	sub, err := b.ctl.Subscribe("mesh.mod.gitea.tool.gitea_commit_status", func(m *nats.Msg) {
+	sub, err := b.ctl.Subscribe("mesh.mod.gitea.tool.gitea_check_status", func(m *nats.Msg) {
 		calls <- string(m.Data)
 		_ = m.Respond([]byte(`{"result":{},"node":"n0"}`))
 	})
diff --git a/modules/mesh-delivery-forge-bridge/internal/bridge/acts.go b/modules/mesh-delivery-forge-bridge/internal/bridge/acts.go
index f844717..6073dc3 100644
--- a/modules/mesh-delivery-forge-bridge/internal/bridge/acts.go
+++ b/modules/mesh-delivery-forge-bridge/internal/bridge/acts.go
@@ -31,6 +31,9 @@ type Act struct {
 // number, body), merge.ts gitea_merge_pull_request (owner, repo, number, head, approved_heads).
 const (
 	commitStatusTool = "gitea.gitea_commit_status"
+	// checkStatusTool is the one tool that writes mesh/check (R4e, issue 1301's option A): gitea_commit_status refuses that
+	// context, and only this bridge invokes it. Its arguments: owner, repo, sha, state, description, target_url, context.
+	checkStatusTool  = "gitea.gitea_check_status"
 	deliveryViewTool = "gitea.gitea_delivery_view"
 	noteAppendTool   = "gitea.gitea_note_append"
 	addCommentTool   = "gitea.gitea_add_comment"
@@ -77,7 +80,11 @@ func OwedAct(key string, value []byte) (Act, error) {
 		if o.Context != context {
 			return Act{}, fmt.Errorf("the owed status %s says the context %q, not the %q its key names", key, o.Context, context)
 		}
-		a.Call = Call{Tool: commitStatusTool, Args: map[string]any{"owner": owner, "repo": repo, "sha": head, "context": o.Context,
+		tool := commitStatusTool
+		if o.Context == delivery.StatusContextCheck {
+			tool = checkStatusTool
+		}
+		a.Call = Call{Tool: tool, Args: map[string]any{"owner": owner, "repo": repo, "sha": head, "context": o.Context,
 			"state": o.State, "description": o.Text, "target_url": o.Target}}
 	case delivery.OwedView:
 		if err := needsPull(); err != nil {
diff --git a/modules/mesh-delivery-forge-bridge/internal/bridge/acts_test.go b/modules/mesh-delivery-forge-bridge/internal/bridge/acts_test.go
index 5b555b8..d3a1d90 100644
--- a/modules/mesh-delivery-forge-bridge/internal/bridge/acts_test.go
+++ b/modules/mesh-delivery-forge-bridge/internal/bridge/acts_test.go
@@ -43,6 +43,26 @@ func TestOwedStatusIsACommitStatusCall(t *testing.T) { // 1341/AC1
 	}
 }
 
+func TestOwedMeshCheckGoesThroughTheCheckStatusToolAlone(t *testing.T) { // R4e 1301-S4 option A: only gitea_check_status writes mesh/check
+	key, err := delivery.CheckerOwedKey("novox/mesh-delivery", 12, headA)
+	if err != nil {
+		t.Fatal(err)
+	}
+	v, err := delivery.EncodeCheckerOwed(delivery.Owed{Act: delivery.OwedStatus, Context: delivery.StatusContextCheck, State: "success", Text: "pass", Target: "https://view.example/checks/g.1"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	a, err := OwedAct(key, v)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := Call{Tool: "gitea.gitea_check_status", Args: map[string]any{"owner": "novox", "repo": "mesh-delivery", "sha": headA,
+		"context": "mesh/check", "state": "success", "description": "pass", "target_url": "https://view.example/checks/g.1"}}
+	if !reflect.DeepEqual(a.Call, want) {
+		t.Errorf("call = %+v, want %+v", a.Call, want)
+	}
+}
+
 func TestOwedViewNoteAndCommentCalls(t *testing.T) { // 1341/AC2
 	cases := []struct {
 		act  string
diff --git a/modules/mesh-delivery-forge-bridge/manifest_test.go b/modules/mesh-delivery-forge-bridge/manifest_test.go
index 40fb8a8..2653931 100644
--- a/modules/mesh-delivery-forge-bridge/manifest_test.go
+++ b/modules/mesh-delivery-forge-bridge/manifest_test.go
@@ -92,7 +92,7 @@ func TestManifestDeclarations(t *testing.T) { // 1235/AC1
 	if want := []string{"mesh-delivery-checker.owed", "mesh-delivery-gate.merges", "mesh-delivery-gate.owed"}; !reflect.DeepEqual(sorted(m.Reads), want) {
 		t.Errorf("reads = %v, want %v", m.Reads, want)
 	}
-	if want := []string{"gitea.gitea_add_comment", "gitea.gitea_commit_status", "gitea.gitea_commit_trees", "gitea.gitea_delivery_view",
+	if want := []string{"gitea.gitea_add_comment", "gitea.gitea_check_status", "gitea.gitea_commit_status", "gitea.gitea_commit_trees", "gitea.gitea_delivery_view",
 		"gitea.gitea_get_file", "gitea.gitea_merge_pull_request", "gitea.gitea_note_append", "gitea.gitea_open_pulls"}; !reflect.DeepEqual(sorted(m.Invokes), want) {
 		t.Errorf("invokes = %v, want %v", m.Invokes, want)
 	}
diff --git a/modules/mesh-delivery-forge-bridge/module.json b/modules/mesh-delivery-forge-bridge/module.json
index d411e5f..895944a 100644
--- a/modules/mesh-delivery-forge-bridge/module.json
+++ b/modules/mesh-delivery-forge-bridge/module.json
@@ -23,6 +23,7 @@
   "invokes": [
     "gitea.gitea_merge_pull_request",
     "gitea.gitea_commit_status",
+    "gitea.gitea_check_status",
     "gitea.gitea_delivery_view",
     "gitea.gitea_note_append",
     "gitea.gitea_add_comment",
diff --git a/modules/mesh-delivery-view/cmd/mesh-delivery-view-tools/main.go b/modules/mesh-delivery-view/cmd/mesh-delivery-view-tools/main.go
index b6079de..645c726 100644
--- a/modules/mesh-delivery-view/cmd/mesh-delivery-view-tools/main.go
+++ b/modules/mesh-delivery-view/cmd/mesh-delivery-view-tools/main.go
@@ -35,18 +35,39 @@ func Tools(r view.Reader) []stdio.Tool {
 				mods, err := r.Modules(only)
 				return map[string]any{"modules": mods}, err
 			}},
+		{Name: view.CandidateReadTool,
+			Description: "What the indexer stored for one candidate (the open pull requests of a branch) under candidates.<group>, as stored: " +
+				"the pull requests and heads, the base, and per pull request the touched modules with their new-form fingerprint (fp2) or why " +
+				"they have none (none2). Read-only.",
+			Input: map[string]any{"type": "object", "required": []string{"group"}, "properties": map[string]any{
+				"group": map[string]any{"type": "string", "description": "the candidate's group, the branch name its pull requests share"}}},
+			Run: func(args map[string]any) (any, error) {
+				group, _ := args["group"].(string)
+				return r.Candidate(group)
+			}},
+		{Name: view.CandidatesReadTool,
+			Description: "Every candidate the indexer holds, by group, each as stored under candidates.<group>; with module, only those with a " +
+				"pull request touching that module. Keys that cannot be read are listed as unreadable. Read-only.",
+			Input: map[string]any{"type": "object", "properties": map[string]any{
+				"module": map[string]any{"type": "string", "description": "only candidates touching this module"}}},
+			Run: func(args map[string]any) (any, error) {
+				module, _ := args["module"].(string)
+				c, bad, err := r.Candidates(module)
+				return map[string]any{"candidates": c, "unreadable": bad}, err
+			}},
 		{Name: view.BuilderBuildsReadTool,
 			Description: "The builder's build keys, each as stored in mesh-delivery-builder_builds: key, module, fingerprint (src2) and build " +
 				"(state, by, step with the nodes it was built on, manifest, artifacts with their digests, toolchains, error). Narrow by module " +
-				"or state (queued, building, done, failed). Read-only.",
+				"or state (queued, building, done, failed); at most limit builds (default 50), newest revision first for a module, and the answer says when it was cut and lists keys that are no build key (unreadable). Without a module, give one to get its newest. Read-only.",
 			Input: map[string]any{"type": "object", "properties": map[string]any{
 				"module": map[string]any{"type": "string", "description": "only this module's builds"},
-				"state":  map[string]any{"type": "string", "description": "only builds in this state"}}},
+				"state":  map[string]any{"type": "string", "description": "only builds in this state"},
+				"limit":  map[string]any{"type": "integer", "description": "at most this many builds (default 50), newest revision first"}}},
 			Run: func(args map[string]any) (any, error) {
 				module, _ := args["module"].(string)
 				state, _ := args["state"].(string)
-				rows, err := r.BuilderBuilds(module, state)
-				return map[string]any{"builds": rows}, err
+				limit, _ := args["limit"].(float64)
+				return r.BuilderBuilds(module, state, int(limit))
 			}},
 		{Name: view.BuilderBuildReadTool,
 			Description: "One build of the builder as stored. Give the module and its fingerprint (fp2, src2:...), or the module alone for the build " +
@@ -65,7 +86,13 @@ func Tools(r view.Reader) []stdio.Tool {
 }
 
 func read(state stdio.KeptState) view.StateRead {
-	return view.StateRead{Keys: state.Keys, Get: func(key string) (json.RawMessage, error) {
+	return view.StateRead{Keys: state.Keys, GetEntry: func(key string) (json.RawMessage, uint64, error) {
+		e, err := state.Get(key)
+		if err != nil || e == nil {
+			return nil, 0, err
+		}
+		return e.Value, e.Revision, nil
+	}, Get: func(key string) (json.RawMessage, error) {
 		e, err := state.Get(key)
 		if err != nil || e == nil {
 			return nil, err
@@ -75,7 +102,7 @@ func read(state stdio.KeptState) view.StateRead {
 }
 
 func main() {
-	r := view.Reader{State: read(stdio.State("mesh-delivery-indexer.modules")), Builds: read(stdio.State("mesh-delivery-builder.builds"))}
+	r := view.Reader{State: read(stdio.State("mesh-delivery-indexer.modules")), Builds: read(stdio.State("mesh-delivery-builder.builds")), CandidatesState: read(stdio.State("mesh-delivery-indexer.candidates"))}
 	if err := stdio.Serve("", Tools(r)); err != nil {
 		fmt.Fprintf(os.Stderr, "[mesh-delivery-view-tools] %v\n", err)
 		os.Exit(1)
diff --git a/modules/mesh-delivery-view/cmd/mesh-delivery-view-tools/main_test.go b/modules/mesh-delivery-view/cmd/mesh-delivery-view-tools/main_test.go
index a5e2193..0c13bdf 100644
--- a/modules/mesh-delivery-view/cmd/mesh-delivery-view-tools/main_test.go
+++ b/modules/mesh-delivery-view/cmd/mesh-delivery-view-tools/main_test.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/json"
+	"fmt"
 	"strings"
 	"testing"
 
@@ -117,13 +118,16 @@ func TestBuilderBuildsListsKeysAsStored(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	rows := out.(map[string]any)["builds"].([]view.BuilderRow)
+	rows := out.(view.BuildsAnswer).Builds
+	if u := out.(view.BuildsAnswer).Unreadable; len(u) != 1 || u[0] != "junk" {
+		t.Errorf("unreadable = %v, want [junk] (issue 1818)", u)
+	}
 	if len(rows) != 2 || rows[0].Key != keyA || rows[0].Module != "netcheck" || rows[0].Fingerprint != fp2A || string(rows[0].Build) != doneBuild || string(rows[1].Build) != failBuild {
 		t.Errorf("rows = %+v", rows)
 	}
 	for args, want := range map[string]string{"state": keyB, "module": keyA} {
 		out, _ := run(t, r, view.BuilderBuildsReadTool, map[string]any{args: map[string]string{keyB: "failed", keyA: "netcheck"}[want]})
-		got := out.(map[string]any)["builds"].([]view.BuilderRow)
+		got := out.(view.BuildsAnswer).Builds
 		if len(got) != 1 || got[0].Key != want {
 			t.Errorf("%s filter = %+v, want %s", args, got, want)
 		}
@@ -156,3 +160,107 @@ func TestBuilderBuildJoinsTheIndexersFingerprint(t *testing.T) {
 		t.Errorf("an unbuilt fingerprint: %v", err)
 	}
 }
+
+// bigBuilds is a bucket of n keys over 100 modules that counts the values read.
+type bigBuilds struct {
+	fake  fake
+	reads *int
+}
+
+func newBig(n int) bigBuilds {
+	f := fake{}
+	for i := 0; i < n; i++ {
+		f[fmt.Sprintf("mod%02d.%064x", i%100, i)] = doneBuild
+	}
+	return bigBuilds{fake: f, reads: new(int)}
+}
+
+func (b bigBuilds) reader() view.Reader {
+	r := b.fake.reader()
+	get := r.State.Get
+	r.Builds = view.StateRead{Keys: r.State.Keys, Get: func(k string) (json.RawMessage, error) { *b.reads++; return get(k) },
+		GetEntry: func(k string) (json.RawMessage, uint64, error) {
+			*b.reads++
+			raw, err := get(k)
+			var rev uint64
+			fmt.Sscanf(k[strings.Index(k, ".")+1:], "%x", &rev) // the fake's revision is the key's number
+			return raw, rev + 1, err
+		}}
+	return r
+}
+
+// 1827/AC1: with 2,000 keys, a module's builds are found by key prefix, so only that module's values are read (20, not 2,000),
+// newest revision first, within the limit, and the answer says it was cut.
+func TestBuilderBuildsFiltersByPrefixBeforeAnyGet(t *testing.T) {
+	b := newBig(2000)
+	out, err := run(t, b.reader(), view.BuilderBuildsReadTool, map[string]any{"module": "mod07", "limit": float64(5)})
+	if err != nil {
+		t.Fatal(err)
+	}
+	a := out.(view.BuildsAnswer)
+	if *b.reads != 20 {
+		t.Errorf("read %d values for a module of 20 keys, want 20", *b.reads)
+	}
+	if len(a.Builds) != 5 || !a.Cut || !strings.Contains(a.Note, "5") {
+		t.Errorf("answer = %d rows, cut %v, note %q", len(a.Builds), a.Cut, a.Note)
+	}
+	for i := 1; i < len(a.Builds); i++ {
+		if a.Builds[i-1].Revision < a.Builds[i].Revision {
+			t.Errorf("not newest first: %d before %d", a.Builds[i-1].Revision, a.Builds[i].Revision)
+		}
+	}
+	if a.Builds[0].Revision != 1908 {
+		t.Errorf("newest revision = %d, want 1908", a.Builds[0].Revision)
+	}
+}
+
+// 1827/AC2: with no module the answer reads at most the limit's worth in key order (default 50), never the 2,000.
+func TestBuilderBuildsWithoutAModuleIsBounded(t *testing.T) {
+	b := newBig(2000)
+	out, err := run(t, b.reader(), view.BuilderBuildsReadTool, map[string]any{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	a := out.(view.BuildsAnswer)
+	if len(a.Builds) != view.DefaultBuildsLimit || !a.Cut || *b.reads > view.DefaultBuildsLimit {
+		t.Errorf("%d rows, cut %v, %d reads", len(a.Builds), a.Cut, *b.reads)
+	}
+	b = newBig(2000)
+	out, _ = run(t, b.reader(), view.BuilderBuildsReadTool, map[string]any{"state": "failed"})
+	if a := out.(view.BuildsAnswer); *b.reads != view.MaxBuildReads || !a.Cut || len(a.Builds) != 0 {
+		t.Errorf("a state matching nothing: %d reads (want the bound %d), cut %v", *b.reads, view.MaxBuildReads, a.Cut)
+	}
+}
+
+// 1818: fp2 together with commit is refused, naming both.
+func TestBuilderBuildRefusesFP2WithCommit(t *testing.T) {
+	r := both(fake{keyA: doneBuild}, fake{"netcheck": `{"v":3,"fp2":"` + fp2A + `","commit":"c1","path":"."}`})
+	_, err := run(t, r, view.BuilderBuildReadTool, map[string]any{"module": "netcheck", "fp2": fp2A, "commit": "c1"})
+	if err == nil || !strings.Contains(err.Error(), "fp2") || !strings.Contains(err.Error(), "commit") || !strings.Contains(err.Error(), "not both") {
+		t.Errorf("err = %v", err)
+	}
+}
+
+// 1681: indexer_candidates and indexer_candidate answer the stored value; a pull request's fp2 per touched module shows.
+func TestCandidateToolsAnswerTheStoredValue(t *testing.T) {
+	cand := `{"v":1,"group":"feat/x","base":3,"heads":"h","pulls":[{"modules":["zsh"],"fps":{"zsh":{"fp2":"` + fp2B + `","manifest":"m"}}}]}`
+	other := `{"v":1,"group":"fix","base":3,"heads":"h","pulls":[{"modules":["netcheck"]}]}`
+	r := fake{"feat/x": cand, "fix": other, "bad": "{"}.reader()
+	r.CandidatesState = r.State
+	out, err := run(t, r, view.CandidateReadTool, map[string]any{"group": "feat/x"})
+	if err != nil || string(out.(json.RawMessage)) != cand || !strings.Contains(string(out.(json.RawMessage)), fp2B) {
+		t.Fatalf("candidate = %v, %v", out, err)
+	}
+	if _, err := run(t, r, view.CandidateReadTool, map[string]any{"group": "gone"}); err == nil || !strings.Contains(err.Error(), "no candidate gone") {
+		t.Errorf("err = %v", err)
+	}
+	out, err = run(t, r, view.CandidatesReadTool, map[string]any{})
+	m := out.(map[string]any)
+	if err != nil || len(m["candidates"].(map[string]json.RawMessage)) != 2 || len(m["unreadable"].([]string)) != 1 {
+		t.Errorf("all = %v, %v", m, err)
+	}
+	out, _ = run(t, r, view.CandidatesReadTool, map[string]any{"module": "zsh"})
+	if c := out.(map[string]any)["candidates"].(map[string]json.RawMessage); len(c) != 1 || c["feat/x"] == nil {
+		t.Errorf("by module = %v", c)
+	}
+}
diff --git a/modules/mesh-delivery-view/internal/view/read.go b/modules/mesh-delivery-view/internal/view/read.go
index e99a327..8f1546a 100644
--- a/modules/mesh-delivery-view/internal/view/read.go
+++ b/modules/mesh-delivery-view/internal/view/read.go
@@ -7,6 +7,7 @@ package view
 import (
 	"encoding/json"
 	"fmt"
+	"slices"
 	"sort"
 	"strings"
 
@@ -23,12 +24,16 @@ const (
 type StateRead struct {
 	Keys func() ([]string, error)
 	Get  func(key string) (json.RawMessage, error)
+	// GetEntry, when set, also gives the revision of the value; builder_builds orders by it.
+	GetEntry func(key string) (json.RawMessage, uint64, error)
 }
 
 // Reader answers the read tools from a modules state.
 type Reader struct {
 	State  StateRead // the indexer's modules
 	Builds StateRead // the builder's builds
+
+	CandidatesState StateRead // the indexer's candidates
 }
 
 // Module is the stored value of modules.<module>, exactly as the indexer wrote it.
@@ -84,6 +89,67 @@ func (r Reader) Modules(none2 bool) (map[string]json.RawMessage, error) {
 	return out, nil
 }
 
+// The read tools of the indexer's candidates (issue 1681): what the indexer stored under candidates.<group>, as stored, so the
+// new-form fingerprint of each touched module of an open pull request (pulls[].fps) can be read live.
+const (
+	CandidateReadTool  = "indexer_candidate"
+	CandidatesReadTool = "indexer_candidates"
+)
+
+// Candidate is the stored value of the candidates key of a group, exactly as the indexer wrote it.
+func (r Reader) Candidate(group string) (json.RawMessage, error) {
+	key, err := delivery.CandidatesKey(strings.TrimSpace(group))
+	if err != nil {
+		return nil, err
+	}
+	if r.CandidatesState.Get == nil {
+		return nil, fmt.Errorf("the candidates state cannot be read here")
+	}
+	raw, err := r.CandidatesState.Get(key)
+	if err != nil {
+		return nil, err
+	}
+	if len(raw) == 0 {
+		return nil, fmt.Errorf("no candidate %s in the candidates state", group)
+	}
+	return raw, nil
+}
+
+// Candidates is every candidate, by group, each as stored; with a module only the candidates with a pull request touching it.
+// A value that is not readable is listed under unreadable with its key, not skipped.
+func (r Reader) Candidates(module string) (map[string]json.RawMessage, []string, error) {
+	if r.CandidatesState.Keys == nil || r.CandidatesState.Get == nil {
+		return nil, nil, fmt.Errorf("the candidates state cannot be read here")
+	}
+	keys, err := r.CandidatesState.Keys()
+	if err != nil {
+		return nil, nil, err
+	}
+	sort.Strings(keys)
+	out := map[string]json.RawMessage{}
+	var unreadable []string
+	for _, k := range keys {
+		raw, err := r.CandidatesState.Get(k)
+		if err != nil {
+			return nil, nil, err
+		}
+		if len(raw) == 0 {
+			continue
+		}
+		group, perr := delivery.ParseCandidatesKey(k)
+		var c delivery.Candidate
+		if perr != nil || json.Unmarshal(raw, &c) != nil {
+			unreadable = append(unreadable, k)
+			continue
+		}
+		if module != "" && !slices.ContainsFunc(c.Pulls, func(p delivery.CandidatePull) bool { return slices.Contains(p.Modules, module) }) {
+			continue
+		}
+		out[group] = raw
+	}
+	return out, unreadable, nil
+}
+
 // The read tools of the builder's builds (novox/hq issue 1723): what the builder stored under `<module>.<fingerprint hex>`
 // in mesh-delivery-builder_builds, answered as stored, so its states, nodes (in the step) and digests can be checked live.
 const (
@@ -91,48 +157,100 @@ const (
 	BuilderBuildsReadTool = "builder_builds"
 )
 
-// BuilderRow is one key of the builder's builds: the key, the module and the fingerprint it parses to, and the stored value
-// as the builder wrote it (state, by, step, manifest, artifacts with digests, toolchains, error).
+// BuilderRow is one key of the builder's builds: the key, the module and the fingerprint it parses to, the revision of its
+// stored value (when the read gives one) and the stored value as the builder wrote it.
 type BuilderRow struct {
 	Key         string          `json:"key"`
 	Module      string          `json:"module"`
 	Fingerprint string          `json:"fingerprint"`
+	Revision    uint64          `json:"revision,omitempty"`
 	Build       json.RawMessage `json:"build"`
 }
 
+// The bounds of builder_builds (issue 1827): the rows it returns when no limit is given, and the values it reads in one call.
+// Reading a value is a bus round trip, so the answer must not read the whole bucket (it timed out at 30 s on the live one).
+const (
+	DefaultBuildsLimit = 50
+	MaxBuildReads      = 200
+)
+
+// BuildsAnswer is the answer of builder_builds: the rows, newest revision first, whether the answer was cut and why, and
+// the keys that are no build key (Unreadable), which are listed rather than silently skipped (issue 1818).
+type BuildsAnswer struct {
+	Builds     []BuilderRow `json:"builds"`
+	Cut        bool         `json:"cut,omitempty"`
+	Note       string       `json:"note,omitempty"`
+	Unreadable []string     `json:"unreadable,omitempty"`
+}
+
+func (r Reader) get(key string) (json.RawMessage, uint64, error) {
+	if r.Builds.GetEntry != nil {
+		return r.Builds.GetEntry(key)
+	}
+	raw, err := r.Builds.Get(key)
+	return raw, 0, err
+}
+
 func (r Reader) builderRow(key string) (BuilderRow, bool, error) {
 	module, fp, err := delivery.ParseBuilderBuildKey(key)
 	if err != nil {
 		return BuilderRow{}, false, nil // a key that is no build key is not a build
 	}
-	raw, err := r.Builds.Get(key)
+	raw, rev, err := r.get(key)
 	if err != nil {
 		return BuilderRow{}, false, err
 	}
 	if len(raw) == 0 {
 		return BuilderRow{}, false, nil
 	}
-	return BuilderRow{Key: key, Module: module, Fingerprint: fp, Build: raw}, true, nil
+	return BuilderRow{Key: key, Module: module, Fingerprint: fp, Revision: rev, Build: raw}, true, nil
 }
 
-// BuilderBuilds lists the builder's keys, each as stored, sorted by key; module and state, when given, keep only the builds
-// of that module or in that state.
-func (r Reader) BuilderBuilds(module, state string) ([]BuilderRow, error) {
+// BuilderBuilds lists the builder's keys, each as stored, newest revision first. With a module it considers only the keys
+// that begin `<module>.`, before any value is read; with a state it keeps the builds in that state. It returns at most limit
+// rows (DefaultBuildsLimit when limit is not above zero) and reads at most MaxBuildReads values, and says when it cut the
+// answer. Keys that are no build key are listed as unreadable. Without a module the keys are walked in key order, so the
+// answer is the first rows found, not the newest of the bucket: give a module to get its newest.
+func (r Reader) BuilderBuilds(module, state string, limit int) (BuildsAnswer, error) {
 	if r.Builds.Keys == nil || r.Builds.Get == nil {
-		return nil, fmt.Errorf("the builder's builds cannot be read here")
+		return BuildsAnswer{}, fmt.Errorf("the builder's builds cannot be read here")
+	}
+	if limit <= 0 {
+		limit = DefaultBuildsLimit
 	}
 	keys, err := r.Builds.Keys()
 	if err != nil {
-		return nil, err
+		return BuildsAnswer{}, err
 	}
 	sort.Strings(keys)
-	rows := []BuilderRow{}
+	prefix := ""
+	if module = strings.TrimSpace(module); module != "" {
+		prefix = module + "."
+	}
+	out := BuildsAnswer{Builds: []BuilderRow{}}
+	var candidates []string
 	for _, k := range keys {
+		if prefix != "" && !strings.HasPrefix(k, prefix) {
+			continue
+		}
+		if _, _, err := delivery.ParseBuilderBuildKey(k); err != nil {
+			out.Unreadable = append(out.Unreadable, k)
+			continue
+		}
+		candidates = append(candidates, k)
+	}
+	reads := 0
+	for _, k := range candidates {
+		if reads >= MaxBuildReads {
+			out.Cut, out.Note = true, fmt.Sprintf("read %d values and stopped; give a module (and a state) to narrow the answer", MaxBuildReads)
+			break
+		}
+		reads++
 		row, ok, err := r.builderRow(k)
 		if err != nil {
-			return nil, err
+			return BuildsAnswer{}, err
 		}
-		if !ok || (module != "" && row.Module != module) {
+		if !ok {
 			continue
 		}
 		if state != "" {
@@ -143,9 +261,26 @@ func (r Reader) BuilderBuilds(module, state string) ([]BuilderRow, error) {
 				continue
 			}
 		}
-		rows = append(rows, row)
+		out.Builds = append(out.Builds, row)
+		// Without a module the walk is in key order and stops at the limit; with one, all its (few) keys are read to order them.
+		if prefix == "" && len(out.Builds) >= limit {
+			if reads < len(candidates) {
+				out.Cut, out.Note = true, fmt.Sprintf("stopped at the limit of %d builds in key order, not newest first; give a module for its newest", limit)
+			}
+			break
+		}
 	}
-	return rows, nil
+	sort.SliceStable(out.Builds, func(i, j int) bool {
+		if out.Builds[i].Revision != out.Builds[j].Revision {
+			return out.Builds[i].Revision > out.Builds[j].Revision
+		}
+		return out.Builds[i].Key < out.Builds[j].Key
+	})
+	if len(out.Builds) > limit {
+		out.Builds = out.Builds[:limit]
+		out.Cut, out.Note = true, fmt.Sprintf("cut to the newest %d builds of %s", limit, module)
+	}
+	return out, nil
 }
 
 // BuilderBuild is the build of module at the new-form fingerprint fp2; with an empty fp2 it is the build at the fingerprint
@@ -156,6 +291,9 @@ func (r Reader) BuilderBuild(module, fp2, commit string) (BuilderRow, error) {
 	if r.Builds.Get == nil {
 		return BuilderRow{}, fmt.Errorf("the builder's builds cannot be read here")
 	}
+	if fp2 != "" && commit != "" {
+		return BuilderRow{}, fmt.Errorf("give fp2 or commit, not both: fp2 %s names a build directly, commit %s asks for the build at the indexer's fingerprint of that commit", fp2, commit)
+	}
 	if fp2 == "" {
 		raw, err := r.Module(module)
 		if err != nil {
diff --git a/modules/mesh-delivery-view/manifest_test.go b/modules/mesh-delivery-view/manifest_test.go
index 0e185a2..b3c0e1c 100644
--- a/modules/mesh-delivery-view/manifest_test.go
+++ b/modules/mesh-delivery-view/manifest_test.go
@@ -95,7 +95,7 @@ func TestManifestIsTakenAndReadsOnly(t *testing.T) { // 1134/AC7
 	}
 	// The two read tools of the indexer's modules (issue 1562), carried by a bundle the runtime launches; the indexer
 	// itself serves no tool (ADR 0437 §4). Carrying them gives the tool runner read access to every bucket the view reads.
-	if want := []string{"indexer_module", "indexer_modules", "builder_build", "builder_builds"}; !reflect.DeepEqual(m.Tools, want) {
+	if want := []string{"indexer_module", "indexer_modules", "indexer_candidate", "indexer_candidates", "builder_build", "builder_builds"}; !reflect.DeepEqual(m.Tools, want) {
 		t.Errorf("tools = %v, want %v", m.Tools, want)
 	}
 	for _, a := range m.Build.Artifacts {
diff --git a/modules/mesh-delivery-view/module.json b/modules/mesh-delivery-view/module.json
index 89bf62c..09cd55b 100644
--- a/modules/mesh-delivery-view/module.json
+++ b/modules/mesh-delivery-view/module.json
@@ -6,6 +6,8 @@
   "tools": [
     "indexer_module",
     "indexer_modules",
+    "indexer_candidate",
+    "indexer_candidates",
     "builder_build",
     "builder_builds"
   ],