The controller follows the subject it decodes

The decoder named the forge's merge subject as the fourth thing followed and the
list was three long: every message that fell through to that switch panicked the
control plane (2026-09-28). The entry was written and lost between two attempts
at the same edit. A test now walks the list; the composed grants and the genesis
template carry the subject.

internal/link/receive_nats_test.go

@@ -377,3 +377,17 @@ func TestNatsAReportIsLetGoOnceTheStoreHasBeenGoneTooLong(t *testing.T) {
 
 // A merge announcement is not what these tests are about; taken and forgotten.
 func (t *toldAbout) SourceMoved(context.Context, SourceMoved) error { return nil }
+
+// Every subject the controller follows decodes to a kind, and decoding never reaches past the
+// list: the day the list was three long and the decoder named a fourth, every message panicked
+// the control plane (2026-09-28).
+func TestEverySubjectTheControllerFollowsDecodesToAKind(t *testing.T) {
+	for _, subject := range broker.ControllerFollows {
+		if _, ok := kindOfSubject(subject); !ok {
+			t.Errorf("%s is followed and decodes to nothing", subject)
+		}
+	}
+	if _, ok := kindOfSubject("mesh.mod.nobody.event.nothing"); ok {
+		t.Error("a subject nobody follows decoded to a kind")
+	}
+}