feat: add im group mention flows

server/topic.go

@@ -1052,6 +1052,14 @@ func (t *Topic) saveAndBroadcastMessage(msg *ClientComMessage, asUid types.Uid,
 			return types.ErrPermissionDenied
 		}
 	}
+	if t.cat == types.TopicCatGrp && head != nil && msg.sess != nil && msg.sess.authLvl != auth.LevelRoot {
+		normalized, err := t.validateAndNormalizeMentions(asUid, head)
+		if err != nil {
+			msg.sess.queueOut(ErrPermissionDenied(msg.Id, t.original(asUid), msg.Timestamp))
+			return err
+		}
+		head = normalized
+	}
 	if t.cat == types.TopicCatP2P && msg.sess != nil && msg.sess.authLvl != auth.LevelRoot &&
 		store.Relations != nil && store.Store != nil && store.Store.IsOpen() {
 		peer := t.p2pOtherUser(asUid)
@@ -1196,6 +1204,67 @@ func (t *Topic) handlePubBroadcast(msg *ClientComMessage) {
 	}
 }
 
+func (t *Topic) validateAndNormalizeMentions(asUid types.Uid, head map[string]any) (map[string]any, error) {
+	mentionAll, _ := head["mention_all"].(bool)
+	rawMentions, hasMentions := head["mentions"]
+	if !mentionAll && !hasMentions {
+		return head, nil
+	}
+	pud := t.perUser[asUid]
+	access := pud.modeGiven & pud.modeWant
+	if mentionAll && !access.IsAdmin() {
+		return nil, types.ErrPermissionDenied
+	}
+	validMembers := make(map[string]struct{}, len(t.perUser))
+	for uid, pud := range t.perUser {
+		mode := pud.modeGiven & pud.modeWant
+		if !pud.deleted && mode.IsJoiner() && mode.IsReader() {
+			validMembers[uid.UserId()] = struct{}{}
+		}
+	}
+	normalized := make(map[string]any, len(head))
+	for key, value := range head {
+		normalized[key] = value
+	}
+	if hasMentions {
+		filtered := filterValidMentions(rawMentions, validMembers)
+		if len(filtered) == 0 {
+			delete(normalized, "mentions")
+		} else {
+			normalized["mentions"] = filtered
+		}
+	}
+	return normalized, nil
+}
+
+func filterValidMentions(raw any, validMembers map[string]struct{}) []map[string]any {
+	mentions, ok := raw.([]any)
+	if !ok {
+		if typed, ok := raw.([]map[string]any); ok {
+			mentions = make([]any, 0, len(typed))
+			for _, item := range typed {
+				mentions = append(mentions, item)
+			}
+		}
+	}
+	if len(mentions) == 0 {
+		return nil
+	}
+	filtered := make([]map[string]any, 0, len(mentions))
+	for _, item := range mentions {
+		mention, ok := item.(map[string]any)
+		if !ok {
+			continue
+		}
+		userID, _ := mention["user_id"].(string)
+		if _, ok = validMembers[userID]; !ok {
+			continue
+		}
+		filtered = append(filtered, mention)
+	}
+	return filtered
+}
+
 // handleNoteBroadcast fans out {note} -> {info} messages to recipients in a master topic.
 // This is a NON-proxy broadcast (at master topic).
 func (t *Topic) handleNoteBroadcast(msg *ClientComMessage) {