Deliver a dead letter again only where it is received, and never stop serving for the notices

A dead letter was let go as delivered even when its consumer did not filter
its again subject; seat asks needed a grant over every seat's queue and left
the original stuck; a notices bind failure stopped the controller (review).

cmd/mesh-controller/watchdogs.go

@@ -688,6 +688,8 @@ func watchTheMesh(ctx context.Context, open *stores, server *link.Server, bus li
 	return func() {
 		stop()
 		stopHearing()
+		// No longer serving: the verb answers that it does not read DEAD_LETTERS here (novox/hq issue 330).
+		deadLettersOn.Store(nil)
 		flushing, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 		defer cancel()
 		keeper.Close(flushing)