fix: move group push work off topic loop

server/topic.go

@@ -650,6 +650,14 @@ func (t *Topic) runLocal(hub *Hub) {
 
 // handleClientMsg is the top-level handler of messages received by the topic from sessions.
 func (t *Topic) handleClientMsg(msg *ClientComMessage) {
+	kind := "other"
+	if t.cat == types.TopicCatP2P {
+		kind = "p2p"
+	} else if t.cat == types.TopicCatGrp {
+		kind = "group"
+	}
+	immetrics.ObserveTopicQueueWait(kind, msg.queuedAt)
+	msg.queuedAt = time.Time{}
 	if msg.TenantID.IsZero() {
 		msg.TenantID = t.tenantID
 	} else if msg.TenantID != t.tenantID {
@@ -1464,9 +1472,13 @@ func (t *Topic) saveAndBroadcastMessage(msg *ClientComMessage, asUid types.Uid,
 	publishRealtimeTopicMessage(t.name, data)
 	immetrics.ObserveMessagePublishStage(kind, "realtime_fanout", fanoutStarted, nil)
 
-	// sendPush will update unread message count and send push notification.
-	if pushRcpt := t.pushForData(asUid, data.Data, markedReadBySender); pushRcpt != nil {
-		sendPush(pushRcpt)
+	// Push preparation copies immutable topic state. Presence resolution, cluster
+	// recipient partitioning and unread updates run outside the topic loop.
+	pushStarted := time.Now()
+	pushRcpt := t.pushForData(asUid, data.Data, markedReadBySender)
+	immetrics.ObserveMessagePublishStage(kind, "push_prepare", pushStarted, nil)
+	if pushRcpt != nil {
+		dispatchPushAsync(pushRcpt, true)
 	}
 	return nil
 }