fix: reject unrouted messages without seq

server/hub.go

@@ -255,14 +255,17 @@ func (h *Hub) run() {
 				}
 			} else if msg.Note == nil {
 				// Topic is unknown or offline.
-				// Note is silently ignored, all other messages are reported as accepted to prevent
-				// clients from guessing valid topic names.
+				// Note is silently ignored. Other client messages cannot be accepted here
+				// because they are not routed to a live topic and therefore cannot reserve a
+				// message seq or be persisted.
 
 				// TODO(gene): validate topic name, discarding invalid topics.
 
 				logs.Info.Printf("Hub. Topic[%s] is unknown or offline", msg.RcptTo)
 
-				msg.sess.queueOut(NoErrAcceptedExplicitTs(msg.Id, msg.RcptTo, types.TimeNow(), msg.Timestamp))
+				if msg.sess != nil {
+					msg.sess.queueOut(ErrAttachFirst(msg, types.TimeNow()))
+				}
 			}
 		case msg := <-h.routeSrv:
 			// This is a server message from a connection not subscribed to topic