Say a walk that waits too long, and a delivery's own stalls (hq ADR 0239)

A walk mesh-delivery never lets go waited for ever with nothing open: S16
says it at 30 minutes, urgent at 4 hours, naming plans go. Phase B: probe
D14 reads the delivery owner's stalled and raises delivery.<id>.stalled,
and H2 takes the table's transition through its close.

internal/link/queue.go

@@ -486,3 +486,50 @@ func PausedSaid(js *broker.JetStream, seat string, nodes []string) (map[string]H
 	}
 	return out, nil
 }
+
+// AskMeshSeatTool asks the holder of a mesh-scoped seat one of its verbs, on the seat's flat subject
+// (design 33 §4: a mesh seat's verb carries no machine), and reads its answer (novox/hq ADR 0239: the
+// delivery's owner's `stalled` and `close`).
+func AskMeshSeatTool(ctx context.Context, conn *nats.Conn, seat, verb string, args any, timeout time.Duration) (Answer, error) {
+	body, err := json.Marshal(args)
+	if err != nil {
+		return Answer{}, err
+	}
+	asking, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+	subject := SeatToolSubject(seat, verb)
+	refused, stop := refusalsOf(conn, subject)
+	defer stop()
+	type replied struct {
+		msg *nats.Msg
+		err error
+	}
+	done := make(chan replied, 1)
+	go func() {
+		msg, err := conn.RequestWithContext(asking, subject, body)
+		done <- replied{msg, err}
+	}()
+	var reply *nats.Msg
+	select {
+	case r := <-done:
+		reply, err = r.msg, r.err
+	case why := <-refused:
+		cancel()
+		return Answer{}, fmt.Errorf("the bus refused the controller asking %s.%s — its grants do not name %s: %v",
+			seat, verb, subject, why)
+	}
+	switch {
+	case errors.Is(err, nats.ErrNoResponders):
+		return Answer{}, fmt.Errorf("%w: nothing answers %s.%s — its holder is not running, or is older than the verb",
+			ErrNothingServes, seat, verb)
+	case errors.Is(err, context.DeadlineExceeded), errors.Is(err, nats.ErrTimeout):
+		return Answer{}, fmt.Errorf("%s did not answer %s within %s", seat, verb, timeout)
+	case err != nil:
+		return Answer{}, err
+	}
+	var answer Answer
+	if err := json.Unmarshal(reply.Data, &answer); err != nil {
+		return Answer{}, fmt.Errorf("%s answered %s with something unreadable: %w", seat, verb, err)
+	}
+	return answer, nil
+}