fix: sync public channel preview updates

internal/store/memory/channel_members.go

@@ -892,6 +892,42 @@ func (s *ChannelStore) FilterActiveChannelMemberIDs(_ context.Context, channelID
 	return out, nil
 }
 
+func (s *ChannelStore) FilterChannelMessageAudienceIDs(_ context.Context, channelID int64, userIDs []int64) ([]int64, error) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	if channelID == 0 || len(userIDs) == 0 {
+		return nil, nil
+	}
+	channel, ok := s.channels[channelID]
+	if !ok || channel.Deleted {
+		return nil, nil
+	}
+	public := publicPreviewableChannel(channel)
+	members := s.members[channelID]
+	out := make([]int64, 0, len(userIDs))
+	seen := make(map[int64]struct{}, len(userIDs))
+	for _, userID := range userIDs {
+		if userID == 0 {
+			continue
+		}
+		if _, ok := seen[userID]; ok {
+			continue
+		}
+		seen[userID] = struct{}{}
+		member, found := members[userID]
+		if member.BannedRights.ViewMessages ||
+			member.Status == domain.ChannelMemberKicked ||
+			member.Status == domain.ChannelMemberBanned {
+			continue
+		}
+		if member.Status == domain.ChannelMemberActive || public && (!found || member.Status == domain.ChannelMemberLeft) {
+			out = append(out, userID)
+		}
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i] < out[j] })
+	return out, nil
+}
+
 func (s *ChannelStore) ListActiveChannelMembers(_ context.Context, viewerUserID, channelID int64, limit int) (domain.Channel, domain.ChannelMember, []domain.ChannelMember, error) {
 	s.mu.RLock()
 	defer s.mu.RUnlock()

internal/store/memory/channel_updates.go

@@ -31,16 +31,6 @@ func (s *ChannelStore) ListChannelDifference(_ context.Context, req domain.Chann
 	if preview {
 		dialog = previewChannelDialog(req.UserID, channel, member)
 	}
-	if preview && member.Status != domain.ChannelMemberActive {
-		return domain.ChannelDifference{
-			Channel: channel,
-			Self:    member,
-			Pts:     channel.Pts,
-			Final:   true,
-			Timeout: 30,
-			Dialog:  dialog,
-		}, nil
-	}
 	checkpoint := s.channelUpdateCheckpointLocked(req.ChannelID, channel)
 	if req.Pts < checkpoint.RetainedThroughPts || channel.Pts-req.Pts > limit {
 		messages := make([]domain.ChannelMessage, 0, domain.MaxChannelDifferenceTooLongMessages)
@@ -81,10 +71,15 @@ func (s *ChannelStore) ListChannelDifference(_ context.Context, req domain.Chann
 			}
 		}
 	}
+	scanned := 0
 	for _, event := range s.events[req.ChannelID] {
 		if event.Pts <= req.Pts {
 			continue
 		}
+		if scanned >= limit {
+			break
+		}
+		scanned++
 		lastPts = event.Pts
 		visible, ok := domain.FilterChannelUpdateEventForAvailableMinID(cloneChannelEvent(event), member.AvailableMinID)
 		if !ok {
@@ -106,7 +101,7 @@ func (s *ChannelStore) ListChannelDifference(_ context.Context, req domain.Chann
 			Channel: channel,
 			Self:    member,
 			Pts:     maxInt(lastPts, req.Pts),
-			Final:   true,
+			Final:   lastPts >= channel.Pts,
 			Timeout: 30,
 			Dialog:  dialog,
 		}, nil