Delete the declarations' stream once every node runs the new node-engine, and assert it no more (issue 1945, B13)

A node away during the switch finds its last declaration on the stream; once every node's have names the
node-engine registered, no node reads one, so the stream and the nodes' consumers on it go, said once, and a raise
leaves them out (ADR 0539 clause 11).

cmd/mesh-controller/composed_integration_test.go

@@ -154,7 +154,9 @@ type trunkKeys struct {
 	trunk sdkdelivery.Module
 }
 
-func (k trunkKeys) ModuleAt(context.Context, string, string) (sdkdelivery.Module, error) { return k.trunk, nil }
+func (k trunkKeys) ModuleAt(context.Context, string, string) (sdkdelivery.Module, error) {
+	return k.trunk, nil
+}
 
 // 1945/AC3 (and AC1, AC2's half for a new fingerprint): a done key of a new fingerprint of an assigned module is taken
 // in, its composition is written on the node it is assigned to, signed by the controller's key, with its digest beside
@@ -315,3 +317,59 @@ func TestAFreshStartComposesEveryNodeAndDeletesThePlansBucketsOnce(t *testing.T)
 	}
 	m.noDeclarationSent(t)
 }
+
+// 1945/AC14: the declarations' stream stays while one node's have names another node-engine than the one registered,
+// and goes, said once, when every node's names it (ADR 0539 clause 11).
+func TestTheDeclarationsStreamGoesOnceEveryNodeRunsTheNewEngine(t *testing.T) {
+	m := aComposingMesh(t)
+	ctx := t.Context()
+	legacy, err := m.conn.JetStream()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := legacy.AddStream(&nats.StreamConfig{Name: broker.DeclarationsStream, Subjects: []string{"mesh.node.*.declare"},
+		MaxMsgsPerSubject: 1}); err != nil {
+		t.Fatal(err)
+	}
+	// The new node-engine registered at its fingerprint, from its done key.
+	n6 := fpOf('6')
+	keys, trunk := aKeyFor("mesh-host", "6", n6, "novox/mesh-host", "", "f00d0123456789ab")
+	if _, err := liveDoneKeySteps(m.open, trunkKeys{keyBuckets: keys, trunk: trunk}).take(ctx, "mesh-host"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := m.js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{Bucket: sdkdelivery.HaveBucket, History: sdkdelivery.HaveHistory}); err != nil {
+		t.Fatal(err)
+	}
+	haves, err := m.js.KeyValue(ctx, sdkdelivery.HaveBucket)
+	if err != nil {
+		t.Fatal(err)
+	}
+	have := func(node, fp string) {
+		key, _ := sdkdelivery.HaveKey(node, "mesh-host")
+		raw, _ := sdkdelivery.EncodeHave(sdkdelivery.Have{FP: fp, Phase: sdkdelivery.PhaseRunning, Health: sdkdelivery.HealthOK})
+		if _, err := haves.Put(ctx, key, raw); err != nil {
+			t.Fatal(err)
+		}
+	}
+	have("anchor", n6)
+	have("laptop", fpOf('5'))
+	if done, err := retireDeclarations(ctx, m.open); err != nil || done {
+		t.Fatalf("with laptop on the old node-engine: done %v (%v)", done, err)
+	}
+	if _, err := m.js.Stream(ctx, broker.DeclarationsStream); err != nil {
+		t.Fatalf("the stream went while laptop runs the old node-engine: %v", err)
+	}
+	have("laptop", n6)
+	if done, err := retireDeclarations(ctx, m.open); err != nil || !done {
+		t.Fatalf("with every node on the new node-engine: done %v (%v)", done, err)
+	}
+	if _, err := m.js.Stream(ctx, broker.DeclarationsStream); !errors.Is(err, jetstream.ErrStreamNotFound) {
+		t.Errorf("the stream is still there: %v", err)
+	}
+	if done, err := retireDeclarations(ctx, m.open); err != nil || !done {
+		t.Errorf("a second look: done %v (%v)", done, err)
+	}
+	if !declarationsRetiredNow(ctx, m.open.inventory) {
+		t.Errorf("a raise after the retirement would assert the stream again")
+	}
+}