internal/link/builds.go

@@ -27,6 +27,14 @@ const TheBuildMachine = "mesh-build-machine"
 func BuildWork() string    { return "mesh.seat." + TheBuildMachine + ".accept.build" }
 func BuildOutcome() string { return "mesh.seat." + TheBuildMachine + ".event.built" }
 
+// KeyRoleBuilt is the build outcome under the role's name, on the bus the mesh runs on today.
+//
+// The same event as KeyModuleBuilt and published beside it, because a catalogue installed before this
+// change listens for the module's name and one installed after listens for the role's. Both, until
+// this bus retires: a rename needs publisher and subscriber to change together, and a deployment
+// cannot promise which arrives first.
+const KeyRoleBuilt = "built"
+
 // Builders is how work reaches a build machine and how the outcome comes back.
 type Builders interface {
 	// Submit asks for one build and waits for its outcome.

internal/link/builds_current.go

@@ -161,8 +161,26 @@ func (b *currentBuild) Announce(ctx context.Context, result BuildResult) error {
 	if result.Failed != "" || result.Commit == "" {
 		return nil
 	}
-	return EmitEvent(ctx, OverCurrent{Channel: b.channel}, KeyModuleBuilt, "builder", b.on,
-		announcementOf(result))
+
+	// **Announced under both names on this bus, for exactly as long as this bus lives.**
+	//
+	// A build's outcome belongs to the role now (novox/hq ADR 0121), so a catalogue built from the
+	// current manifests listens for the role's name. A catalogue that is *already running* listens for
+	// the module's, because that is what it was told when it was installed. A rename on a live bus
+	// needs the publisher and the subscriber to change together, and a merge cannot promise that: one
+	// of them is deployed first, and in that window the graph silently stops being updated — which is
+	// the failure this whole change was cleaning up after.
+	//
+	// So both, and the order stops mattering. The module's own name goes with the bus, in step 5's
+	// retirement list; nothing has ever run on the bus being built, so there is no legacy name there
+	// and this doubling has no counterpart.
+	announced := announcementOf(result)
+	if err := EmitEvent(ctx, OverCurrent{Channel: b.channel}, KeyModuleBuilt, "builder", b.on,
+		announced); err != nil {
+		return err
+	}
+	return EmitEvent(ctx, OverCurrent{Channel: b.channel}, KeyRoleBuilt, TheBuildMachine, b.on,
+		announced)
 }
 
 func (b *currentBuild) Done() error { return b.delivery.Ack(false) }

internal/link/builds_current_test.go

@@ -0,0 +1,36 @@
+package link
+
+import (
+	"strings"
+	"testing"
+)
+
+// **The old bus announces a build under both names, and that is not belt-and-braces.**
+//
+// A build's outcome belongs to the role now, so a catalogue built from the current manifests listens
+// for the role's name — and a catalogue already running listens for the module's, because that is what
+// it was told when it was installed. A rename on a live bus needs publisher and subscriber to change
+// together, which a deployment cannot promise: one arrives first, and in that window the module graph
+// silently stops being updated.
+//
+// Caught by asking what merging this would do to the mesh that is actually running, which is the only
+// place the question could have been asked — the tests were green and both buses were self-consistent.
+func TestTheOldBusAnnouncesABuildUnderBothNames(t *testing.T) {
+	// The routing key a catalogue installed before the change is bound to.
+	if KeyModuleBuilt != "module.builder.built" {
+		t.Fatalf("the module's own name is %q; a catalogue already running is bound to the old one",
+			KeyModuleBuilt)
+	}
+	// And the local name a catalogue built from the current manifests declares, which the old bus's
+	// client turns into `module.<role>.built`.
+	if KeyRoleBuilt != "built" {
+		t.Fatalf("the role's event is %q, and a holder emits its verbs bare", KeyRoleBuilt)
+	}
+	if TheBuildMachine != "mesh-build-machine" {
+		t.Fatalf("the role is %q", TheBuildMachine)
+	}
+	// The two must differ, or one publish would serve both and this doubling would be pointless.
+	if strings.HasSuffix(KeyModuleBuilt, "."+TheBuildMachine+"."+KeyRoleBuilt) {
+		t.Fatal("the two names are the same, so nothing was renamed and this is dead weight")
+	}
+}