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/deadletters.go

@@ -125,7 +125,7 @@ func actOnDeadLetter(ctx context.Context, on *busHandles, act string, id uint64,
 	}
 	if act == "deliver" {
 		// Refused before it is recorded: an act that cannot be done is not an act.
-		if _, err := link.AgainTo(d); err != nil {
+		if _, err := link.AgainTo(on.js, d); err != nil {
 			return nil, err
 		}
 	}

cmd/mesh-controller/probes.go

@@ -878,6 +878,10 @@ func streamDiffers(want broker.Stream, have nats.StreamConfig) string {
 	if want.MaxBytes > 0 && have.MaxBytes != want.MaxBytes {
 		differs = append(differs, fmt.Sprintf("holds up to %d bytes, defined %d", have.MaxBytes, want.MaxBytes))
 	}
+	if want.DuplicatesSeconds > 0 && have.Duplicates != time.Duration(want.DuplicatesSeconds)*time.Second {
+		differs = append(differs, fmt.Sprintf("keeps one of a message id for %s, defined %s", have.Duplicates,
+			time.Duration(want.DuplicatesSeconds)*time.Second))
+	}
 	if want.DiscardNew && have.Discard != nats.DiscardNew {
 		differs = append(differs, "drops what it holds when full, defined to refuse what comes next")
 	}

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)