Merge pull request 'Declarations test: the indexer stand-in answers the trunk value at the trunk's commit alone (issue 1945)' (#471) from fix/declarations-test-stand-in into main

The stub answered the trunk for every commit, so since registering on the
fingerprint (666d1b68, #465) mesh-host, registered at an older commit, looked
already at the trunk's fingerprint: the take-in only moved its commit, no build
was recorded, and the fingerprints never named the new node-engine. The real
indexer holds no value at a commit it never indexed.

(cherry picked from commit 779533764b)

cmd/mesh-controller/composed_integration_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/nats-io/nats.go/jetstream"
 
 	"github.com/novox/mesh-controller/internal/broker"
+	"github.com/novox/mesh-controller/internal/builderkeys"
 	"github.com/novox/mesh-controller/internal/identity"
 	"github.com/novox/mesh-controller/internal/link"
 	"github.com/novox/mesh-controller/internal/testbus"
@@ -76,13 +77,18 @@ func aComposingMesh(t *testing.T) *composingMesh {
 	return m
 }
 
-// trunkKeys are a done key and the indexer's trunk value naming it.
+// trunkKeys are a done key and the indexer's trunk value naming it. The indexer holds that value at the trunk's commit
+// alone, as the real one does: answering it for any commit made a module registered at an older commit look already
+// registered at the trunk's fingerprint, so the take-in only moved its commit and recorded no build (issue 1945).
 type trunkKeys struct {
 	keyBuckets
 	trunk sdkdelivery.Module
 }
 
-func (k trunkKeys) ModuleAt(context.Context, string, string) (sdkdelivery.Module, error) {
+func (k trunkKeys) ModuleAt(_ context.Context, _ string, commit string) (sdkdelivery.Module, error) {
+	if commit != "" && !sameCommitID(commit, k.trunk.Commit) {
+		return sdkdelivery.Module{}, builderkeys.ErrNoValue
+	}
 	return k.trunk, nil
 }