diff --git a/internal/cache/conversation_cache.go b/internal/cache/conversation_cache.go
index bfd6999..b8b349d 100644
--- a/internal/cache/conversation_cache.go
+++ b/internal/cache/conversation_cache.go
@@ -606,6 +606,48 @@ func (c *ConversationCache) GetConvMaxSeq(ctx context.Context, convID string) (i
 	return val, nil
 }
 
+// GetConvMaxSeqBatch 批量获取多个会话的 maxSeq（MGet 减少网络往返）
+func (c *ConversationCache) GetConvMaxSeqBatch(ctx context.Context, convIDs []string) (map[string]int64, error) {
+	if len(convIDs) == 0 {
+		return nil, nil
+	}
+
+	redisCache, ok := c.cache.(*RedisCache)
+	if !ok {
+		result := make(map[string]int64, len(convIDs))
+		for _, convID := range convIDs {
+			if seq, err := c.GetConvMaxSeq(ctx, convID); err == nil {
+				result[convID] = seq
+			}
+		}
+		return result, nil
+	}
+
+	rdb := redisCache.GetRedisClient().GetClient()
+	keys := make([]string, len(convIDs))
+	for i, convID := range convIDs {
+		keys[i] = normalizeKey(MessageSeqKey(convID))
+	}
+
+	vals, err := rdb.MGet(ctx, keys...).Result()
+	if err != nil {
+		return nil, err
+	}
+
+	result := make(map[string]int64, len(convIDs))
+	for i, val := range vals {
+		if val == nil {
+			continue
+		}
+		var seq int64
+		fmt.Sscanf(fmt.Sprint(val), "%d", &seq)
+		if seq > 0 {
+			result[convIDs[i]] = seq
+		}
+	}
+	return result, nil
+}
+
 // ComputeUnreadCount 计算单个会话未读数：maxSeq - hasReadSeq
 func (c *ConversationCache) ComputeUnreadCount(ctx context.Context, convID, userID string) (int64, error) {
 	maxSeq, err := c.GetConvMaxSeq(ctx, convID)
@@ -650,128 +692,34 @@ func (c *ConversationCache) ComputeAllUnreadCount(ctx context.Context, userID st
 	return total, nil
 }
 
-// IncrementUnread 递增用户在某会话的未读数（Redis Hash + 总数计数器）
+// IncrementUnread 递增用户在某会话的未读数（已废弃：改用 seq 算术计算）
+// Deprecated: Unread count is now computed via arithmetic (maxSeq - readSeq).
 func (c *ConversationCache) IncrementUnread(ctx context.Context, userID, convID string) error {
-	hashKey := UnreadHashKey(userID)
-	totalKey := UnreadTotalKey(userID)
-
-	_, err := c.cache.HIncrBy(ctx, hashKey, convID, 1)
-	if err != nil {
-		return fmt.Errorf("hincrby unread failed: %w", err)
-	}
-
-	_, err = c.cache.Incr(ctx, totalKey)
-	if err != nil {
-		return fmt.Errorf("incr unread total failed: %w", err)
-	}
-
-	_ = c.cache.Expire(ctx, hashKey, c.settings.UnreadTTL*10)
-	_ = c.cache.Expire(ctx, totalKey, c.settings.UnreadTTL*10)
 	return nil
 }
 
-// ClearUnread 清零用户在某会话的未读数（原子操作，防止与 IncrementUnread 竞态）
+// ClearUnread 清零用户在某会话的未读数（已废弃：改用 seq 算术计算）
+// Deprecated: No longer needed. Unread is computed from seq arithmetic.
 func (c *ConversationCache) ClearUnread(ctx context.Context, userID, convID string) error {
-	hashKey := UnreadHashKey(userID)
-	totalKey := UnreadTotalKey(userID)
-
-	redisCache, ok := c.cache.(*RedisCache)
-	if !ok {
-		// miniredis/内存模式：保持原逻辑（非原子，但无并发竞态风险）
-		currentStr, err := c.cache.HGet(ctx, hashKey, convID)
-		if err != nil {
-			currentStr = "0"
-		}
-		current := int64(0)
-		if v, parseErr := fmt.Sscanf(currentStr, "%d", &current); parseErr != nil || v != 1 {
-			current = 0
-		}
-		if err := c.cache.HSet(ctx, hashKey, convID, "0"); err != nil {
-			return fmt.Errorf("hset clear unread failed: %w", err)
-		}
-		if current > 0 {
-			c.cache.IncrBySeq(ctx, totalKey, -current)
-		}
-		return nil
-	}
-
-	rdb := redisCache.GetRedisClient().GetClient()
-	nHashKey := normalizeKey(hashKey)
-	nTotalKey := normalizeKey(totalKey)
-
-	script := redis.NewScript(`
-		local current = tonumber(redis.call('HGET', KEYS[1], ARGV[1]))
-		if current == nil or current <= 0 then
-			return 0
-		end
-		redis.call('HSET', KEYS[1], ARGV[1], '0')
-		local newTotal = tonumber(redis.call('INCRBY', KEYS[2], -current))
-		if newTotal < 0 then
-			redis.call('SET', KEYS[2], '0')
-		end
-		return current
-	`)
-	_, err := script.Run(ctx, rdb, []string{nHashKey, nTotalKey}, convID).Result()
-	if err != nil {
-		return fmt.Errorf("lua clear unread failed: %w", err)
-	}
 	return nil
 }
 
-// GetUnreadCountFromHash 从 Redis Hash 获取单个会话未读数
+// GetUnreadCountFromHash 从 Redis Hash 获取单个会话未读数（已废弃）
+// Deprecated: Use ComputeUnreadCount instead.
 func (c *ConversationCache) GetUnreadCountFromHash(ctx context.Context, userID, convID string) (int64, error) {
-	hashKey := UnreadHashKey(userID)
-	val, err := c.cache.HGet(ctx, hashKey, convID)
-	if err != nil {
-		return 0, err
-	}
-	var count int64
-	fmt.Sscanf(val, "%d", &count)
-	return count, nil
+	return 0, ErrKeyNotFound
 }
 
-// GetAllUnreadCounts 从 Redis Hash 获取用户所有会话的未读数
+// GetAllUnreadCounts 从 Redis Hash 获取用户所有会话的未读数（已废弃）
+// Deprecated: Use ComputeAllUnreadCount instead.
 func (c *ConversationCache) GetAllUnreadCounts(ctx context.Context, userID string) (map[string]int64, error) {
-	hashKey := UnreadHashKey(userID)
-	all, err := c.cache.HGetAll(ctx, hashKey)
-	if err != nil {
-		return nil, err
-	}
-	result := make(map[string]int64, len(all))
-	for k, v := range all {
-		var count int64
-		fmt.Sscanf(v, "%d", &count)
-		result[k] = count
-	}
-	return result, nil
+	return nil, ErrKeyNotFound
 }
 
-// GetTotalUnread 从 Redis 获取用户总未读数
+// GetTotalUnread 从 Redis 获取用户总未读数（已废弃）
+// Deprecated: Use ComputeAllUnreadCount instead.
 func (c *ConversationCache) GetTotalUnread(ctx context.Context, userID string) (int64, error) {
-	totalKey := UnreadTotalKey(userID)
-
-	redisCache, ok := c.cache.(*RedisCache)
-	if ok {
-		val, err := redisCache.GetRedisClient().GetClient().Get(ctx, normalizeKey(totalKey)).Int64()
-		if err != nil {
-			return 0, nil
-		}
-		return val, nil
-	}
-
-	raw, ok := c.cache.Get(totalKey)
-	if !ok {
-		return 0, nil
-	}
-	switch v := raw.(type) {
-	case int64:
-		return v, nil
-	case string:
-		var n int64
-		fmt.Sscanf(v, "%d", &n)
-		return n, nil
-	}
-	return 0, nil
+	return 0, ErrKeyNotFound
 }
 
 // GetNextSeq 获取会话的下一个 seq 值（原子递增）
diff --git a/internal/dto/dto.go b/internal/dto/dto.go
index 06adc47..9e60901 100644
--- a/internal/dto/dto.go
+++ b/internal/dto/dto.go
@@ -437,6 +437,23 @@ type MarkReadRequest struct {
 	LastReadSeq int64 `json:"last_read_seq" binding:"required"` // 已读到的seq位置
 }
 
+// BatchMarkReadItem 批量标记已读单项
+type BatchMarkReadItem struct {
+	ConversationID string `json:"conversation_id" binding:"required"`
+	LastReadSeq    int64  `json:"last_read_seq" binding:"required"`
+}
+
+// BatchMarkReadRequest 批量标记已读请求
+type BatchMarkReadRequest struct {
+	Conversations []BatchMarkReadItem `json:"conversations" binding:"required"`
+}
+
+// BatchMarkReadResponse 批量标记已读响应
+type BatchMarkReadResponse struct {
+	SuccessCount int `json:"success_count"`
+	TotalCount   int `json:"total_count"`
+}
+
 // SetConversationPinnedRequest 设置会话置顶请求
 type SetConversationPinnedRequest struct {
 	ConversationID string `json:"conversation_id" binding:"required"`
@@ -481,6 +498,18 @@ type ConversationUnreadCountResponse struct {
 	UnreadCount    int64  `json:"unread_count"`
 }
 
+// SyncDataItem 同步数据单项（轻量级，仅包含 seq 和时间）
+type SyncDataItem struct {
+	ConversationID string `json:"id"`
+	MaxSeq         int64  `json:"max_seq"`
+	LastMessageAt  string `json:"last_message_at"`
+}
+
+// SyncDataResponse 同步数据响应
+type SyncDataResponse struct {
+	Conversations []SyncDataItem `json:"conversations"`
+}
+
 // MessageListResponse 消息列表响应
 type MessageListResponse struct {
 	Messages []*MessageResponse `json:"messages"`
diff --git a/internal/handler/message_handler.go b/internal/handler/message_handler.go
index d309a4d..6c37558 100644
--- a/internal/handler/message_handler.go
+++ b/internal/handler/message_handler.go
@@ -565,6 +565,26 @@ func (h *MessageHandler) GetUnreadCount(c *gin.Context) {
 	})
 }
 
+// HandleGetSyncData 获取同步元数据（轻量级 seq + 时间）
+// GET /api/v1/conversations/sync-data
+func (h *MessageHandler) HandleGetSyncData(c *gin.Context) {
+	userID := c.GetString("user_id")
+	if userID == "" {
+		response.Unauthorized(c, "")
+		return
+	}
+
+	items, err := h.chatService.GetSyncData(c.Request.Context(), userID)
+	if err != nil {
+		response.InternalServerError(c, "failed to get sync data")
+		return
+	}
+
+	response.Success(c, &dto.SyncDataResponse{
+		Conversations: items,
+	})
+}
+
 // GetConversationUnreadCount 获取单个会话的未读数
 // GET /api/conversations/:id/unread/count
 func (h *MessageHandler) GetConversationUnreadCount(c *gin.Context) {
@@ -900,6 +920,33 @@ func (h *MessageHandler) HandleMarkRead(c *gin.Context) {
 	response.SuccessWithMessage(c, "marked as read", nil)
 }
 
+// HandleMarkReadAll 批量标记所有会话已读
+// POST /api/v1/conversations/read-all
+func (h *MessageHandler) HandleMarkReadAll(c *gin.Context) {
+	userID := c.GetString("user_id")
+	if userID == "" {
+		response.Unauthorized(c, "")
+		return
+	}
+
+	var req dto.BatchMarkReadRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, err.Error())
+		return
+	}
+
+	successCount, err := h.chatService.MarkAsReadBatch(c.Request.Context(), userID, req.Conversations)
+	if err != nil {
+		response.InternalServerError(c, "failed to mark all as read")
+		return
+	}
+
+	response.Success(c, &dto.BatchMarkReadResponse{
+		SuccessCount: successCount,
+		TotalCount:   len(req.Conversations),
+	})
+}
+
 // HandleSetConversationPinned 设置会话置顶
 // PUT /api/v1/conversations/:id/pinned
 func (h *MessageHandler) HandleSetConversationPinned(c *gin.Context) {
diff --git a/internal/router/router.go b/internal/router/router.go
index 4421c3c..dad91c3 100644
--- a/internal/router/router.go
+++ b/internal/router/router.go
@@ -426,9 +426,11 @@ func (r *Router) setupRoutes() {
 			conversations.GET("/:id/messages/cursor", r.messageHandler.GetMessagesByCursor)                                 // 消息列表游标分页
 			conversations.POST("/:id/messages", middleware.RequireVerified(r.userRepo), r.messageHandler.HandleSendMessage) // 发送消息
 			conversations.POST("/:id/read", r.messageHandler.HandleMarkRead)                                                // 标记已读
+				conversations.POST("/read-all", r.messageHandler.HandleMarkReadAll)                                                 // 批量标记已读
 			conversations.PUT("/:id/pinned", r.messageHandler.HandleSetConversationPinned)                                  // 置顶设置
 			conversations.PUT("/:id/notification_muted", r.messageHandler.HandleSetConversationNotificationMuted)          // 免打扰设置
 			conversations.GET("/unread/count", r.messageHandler.GetUnreadCount)                                             // 未读数
+				conversations.GET("/sync-data", r.messageHandler.HandleGetSyncData)                                                    // 同步元数据
 			conversations.POST("/:id/typing", r.messageHandler.HandleTyping)                                                // 输入状态
 			conversations.DELETE("/:id/self", r.messageHandler.HandleDeleteConversationForSelf)                             // 删除会话(仅自己)
 
diff --git a/internal/service/chat_service.go b/internal/service/chat_service.go
index 4500b21..ff86d43 100644
--- a/internal/service/chat_service.go
+++ b/internal/service/chat_service.go
@@ -41,9 +41,13 @@ type ChatService interface {
 
 	// 已读管理
 	MarkAsRead(ctx context.Context, conversationID string, userID string, seq int64) error
+		MarkAsReadBatch(ctx context.Context, userID string, items []dto.BatchMarkReadItem) (int, error)
 	GetUnreadCount(ctx context.Context, conversationID string, userID string) (int64, error)
 	GetAllUnreadCount(ctx context.Context, userID string) (int64, error)
 
+	// 消息同步
+	GetSyncData(ctx context.Context, userID string) ([]dto.SyncDataItem, error)
+
 	// 消息扩展功能
 	RecallMessage(ctx context.Context, messageID string, userID string) error
 	DeleteMessage(ctx context.Context, messageID string, userID string) error
@@ -388,20 +392,8 @@ func (s *chatServiceImpl) SendMessage(ctx context.Context, senderID string, conv
 	participants, err := s.getParticipants(ctx, conversationID)
 	if err == nil {
 		// 先更新未读计数器，再推送 WS 事件，确保事件中的 total_unread 已包含新消息
+		// 注意：已移除 IncrementUnread，未读数完全由 maxSeq - readSeq 算术计算
 		if s.conversationCache != nil {
-			for _, p := range participants {
-				if p.UserID == senderID {
-					continue
-				}
-				if incrErr := s.conversationCache.IncrementUnread(context.Background(), p.UserID, conversationID); incrErr != nil {
-					zap.L().Warn("increment unread from redis hash failed",
-						zap.String("userID", p.UserID),
-						zap.String("convID", conversationID),
-						zap.Error(incrErr),
-					)
-				}
-			}
-
 			keys := make([]string, 0, len(participants)*2)
 			for _, p := range participants {
 				keys = append(keys,
@@ -602,15 +594,7 @@ func (s *chatServiceImpl) MarkAsRead(ctx context.Context, conversationID string,
 	// 2. 更新 Redis hasReadSeq 缓存（防回退）
 	if s.conversationCache != nil {
 		_ = s.conversationCache.SetUserReadSeq(ctx, conversationID, userID, seq)
-		// 清除旧式 Hash 未读数缓存
-		if clearErr := s.conversationCache.ClearUnread(ctx, userID, conversationID); clearErr != nil {
-			zap.L().Warn("clear unread from redis hash failed",
-				zap.String("userID", userID),
-				zap.String("convID", conversationID),
-				zap.Error(clearErr),
-			)
-		}
-		// 失效参与者缓存，下次读取时会从 DB 加载最新数据
+		// 清除旧// 失效参与者缓存
 		s.conversationCache.InvalidateParticipant(conversationID, userID)
 		// 失效未读数缓存（旧 cache-aside 键）
 		s.conversationCache.InvalidateUnreadCount(userID, conversationID)
@@ -656,9 +640,66 @@ func (s *chatServiceImpl) MarkAsRead(ctx context.Context, conversationID string,
 	return nil
 }
 
-// GetUnreadCount 获取指定会话的未读消息数（带缓存）
+// MarkAsReadBatch 批量标记多个会话已读
+func (s *chatServiceImpl) MarkAsReadBatch(ctx context.Context, userID string, items []dto.BatchMarkReadItem) (int, error) {
+	successCount := 0
+
+	for _, item := range items {
+		_, err := s.getParticipant(ctx, item.ConversationID, userID)
+		if err != nil {
+			continue
+		}
+
+		if err := s.repo.UpdateLastReadSeq(item.ConversationID, userID, item.LastReadSeq); err != nil {
+			continue
+		}
+
+		if s.conversationCache != nil {
+			_ = s.conversationCache.SetUserReadSeq(ctx, item.ConversationID, userID, item.LastReadSeq)
+			s.conversationCache.InvalidateParticipant(item.ConversationID, userID)
+			s.conversationCache.InvalidateUnreadCount(userID, item.ConversationID)
+		}
+
+		successCount++
+	}
+
+	if s.conversationCache != nil {
+		s.conversationCache.InvalidateConversationList(userID)
+	}
+
+	// 为每个成功的会话发送 read 通知
+	for i := 0; i < successCount && i < len(items); i++ {
+		item := items[i]
+		participants, pErr := s.getParticipants(ctx, item.ConversationID)
+		if pErr == nil {
+			conv, _ := s.getConversation(ctx, item.ConversationID)
+			readTargets := []string{userID}
+			if conv != nil && conv.Type == model.ConversationTypePrivate {
+				readTargets = make([]string, 0, len(participants))
+				for _, p := range participants {
+					readTargets = append(readTargets, p.UserID)
+				}
+			}
+			s.publishToUsers(readTargets, "message_read", map[string]any{
+				"conversation_id": item.ConversationID,
+				"user_id":         userID,
+				"seq":             item.LastReadSeq,
+			})
+		}
+	}
+
+	// 发送总未读数通知
+	if totalUnread, uErr := s.GetAllUnreadCount(ctx, userID); uErr == nil {
+		s.publishToUsers([]string{userID}, "conversation_unread", map[string]any{
+			"total_unread": totalUnread,
+		})
+	}
+
+	return successCount, nil
+}
+
+// GetUnreadCount 获取指定会话的未读消息数（纯算术：maxSeq - readSeq）
 func (s *chatServiceImpl) GetUnreadCount(ctx context.Context, conversationID string, userID string) (int64, error) {
-	// 验证用户是否是会话参与者
 	_, err := s.getParticipant(ctx, conversationID, userID)
 	if err != nil {
 		if errors.Is(err, gorm.ErrRecordNotFound) {
@@ -667,45 +708,29 @@ func (s *chatServiceImpl) GetUnreadCount(ctx context.Context, conversationID str
 		return 0, fmt.Errorf("failed to get participant: %w", err)
 	}
 
-	// 优先算术计算：maxSeq - hasReadSeq（OpenIM 风格，O(1) 无 DB）
 	if s.conversationCache != nil {
 		if count, err := s.conversationCache.ComputeUnreadCount(ctx, conversationID, userID); err == nil {
 			return count, nil
 		}
-		// 降级到 Redis Hash
-		if count, err := s.conversationCache.GetUnreadCountFromHash(ctx, userID, conversationID); err == nil {
-			return count, nil
-		}
-		return s.conversationCache.GetUnreadCount(ctx, userID, conversationID)
 	}
-
 	return s.repo.GetUnreadCount(conversationID, userID)
 }
 
-// GetAllUnreadCount 获取所有会话的未读消息总数
+// GetAllUnreadCount 获取所有会话的未读消息总数（批量 MGet maxSeq，纯算术）
 func (s *chatServiceImpl) GetAllUnreadCount(ctx context.Context, userID string) (int64, error) {
-	// 优先算术计算：sum(maxSeq - hasReadSeq)（OpenIM 风格）
 	if s.conversationCache != nil {
 		if convs, _, err := s.GetConversationList(ctx, userID, 1, 200); err == nil && len(convs) > 0 {
 			convIDs := make([]string, len(convs))
-			maxSeqs := make(map[string]int64, len(convs))
 			for i, conv := range convs {
 				convIDs[i] = conv.ID
-				if maxSeq, err := s.conversationCache.GetConvMaxSeq(ctx, conv.ID); err == nil {
-					maxSeqs[conv.ID] = maxSeq
-				}
 			}
-			// 只有全部会话的 msg_seq 都命中时才用算术结果，避免部分缺失导致低估
-			if len(maxSeqs) == len(convIDs) {
+			maxSeqs, err := s.conversationCache.GetConvMaxSeqBatch(ctx, convIDs)
+			if err == nil && len(maxSeqs) == len(convIDs) {
 				if total, err := s.conversationCache.ComputeAllUnreadCount(ctx, userID, convIDs, maxSeqs); err == nil {
 					return total, nil
 				}
 			}
 		}
-		// 降级到 Redis Hash
-		if total, err := s.conversationCache.GetTotalUnread(ctx, userID); err == nil {
-			return total, nil
-		}
 	}
 	return s.repo.GetAllUnreadCount(userID)
 }
@@ -920,23 +945,18 @@ func (s *chatServiceImpl) SaveMessage(ctx context.Context, senderID string, conv
 	return message, nil
 }
 
-// GetUnreadCountBatch 批量获取用户在多个会话中的未读数
+// GetUnreadCountBatch 批量获取用户在多个会话中的未读数（批量 MGet）
 func (s *chatServiceImpl) GetUnreadCountBatch(ctx context.Context, userID string, convIDs []string) (map[string]int64, error) {
-	// 优先算术计算：maxSeq - hasReadSeq（OpenIM 风格）
 	if s.conversationCache != nil && len(convIDs) > 0 {
-		maxSeqs := make(map[string]int64, len(convIDs))
-		for _, convID := range convIDs {
-			if maxSeq, err := s.conversationCache.GetConvMaxSeq(ctx, convID); err == nil {
-				maxSeqs[convID] = maxSeq
-			}
-		}
-		if len(maxSeqs) > 0 {
+		maxSeqs, err := s.conversationCache.GetConvMaxSeqBatch(ctx, convIDs)
+		if err == nil && len(maxSeqs) > 0 {
 			readSeqs, err := s.conversationCache.GetUserReadSeqs(ctx, userID, convIDs)
 			if err == nil {
 				result := make(map[string]int64, len(convIDs))
 				for _, convID := range convIDs {
 					maxSeq, ok := maxSeqs[convID]
 					if !ok {
+						result[convID] = 0
 						continue
 					}
 					readSeq, hasRead := readSeqs[convID]
@@ -950,27 +970,12 @@ func (s *chatServiceImpl) GetUnreadCountBatch(ctx context.Context, userID string
 						result[convID] = unread
 					}
 				}
-				// 补齐缺失的会话（未命中缓存时归零）
-				for _, convID := range convIDs {
-					if _, exists := result[convID]; !exists {
-						result[convID] = 0
-					}
-				}
-				// 只有全部会话都算出来了才回返回，否则降级
-				allComputed := true
-				for _, convID := range convIDs {
-					if _, exists := maxSeqs[convID]; !exists {
-						allComputed = false
-						break
-					}
-				}
-				if allComputed {
+				if len(maxSeqs) == len(convIDs) {
 					return result, nil
 				}
 			}
 		}
 	}
-	// 降级到 DB
 	return s.repo.GetUnreadCountBatch(ctx, userID, convIDs)
 }
 
@@ -993,3 +998,33 @@ func (s *chatServiceImpl) GetUserReadSeq(ctx context.Context, conversationID str
 	}
 	return participant.LastReadSeq, nil
 }
+
+// GetSyncData 获取用户所有会话的同步元数据（seq + 时间，轻量级）
+func (s *chatServiceImpl) GetSyncData(ctx context.Context, userID string) ([]dto.SyncDataItem, error) {
+	convs, _, err := s.GetConversationList(ctx, userID, 1, 200)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get conversation list: %w", err)
+	}
+
+	if len(convs) == 0 {
+		return nil, nil
+	}
+
+	convIDs := make([]string, len(convs))
+	for i, conv := range convs {
+		convIDs[i] = conv.ID
+	}
+
+	maxSeqs, _ := s.conversationCache.GetConvMaxSeqBatch(ctx, convIDs)
+
+	items := make([]dto.SyncDataItem, 0, len(convs))
+	for _, conv := range convs {
+		item := dto.SyncDataItem{
+			ConversationID: conv.ID,
+			MaxSeq:         maxSeqs[conv.ID],
+			LastMessageAt:  conv.UpdatedAt.Format(time.RFC3339),
+		}
+		items = append(items, item)
+	}
+	return items, nil
+}