feat(core): optimize performance and reliability through batching and redis-backed unread counts

This commit introduces several significant architectural improvements to enhance system performance, scalability, and reliability:

- **Performance Optimization (N+1 Problem Resolution)**: Implemented batching mechanisms across `MessageHandler`, `ChatService`, `GroupService`, `MessageService`, and `UserService`. This replaces multiple individual database/cache queries with single batch operations for fetching unread counts, last messages, participants, and user information.
- **Enhanced Unread Count Management**: Migrated unread count tracking to a Redis Hash-based approach (`unread#️⃣{userID}`). This allows for atomic increments/decrements and efficient retrieval of both individual conversation unread counts and total unread counts for a user.
- **Improved Message Sequencing**: Integrated Redis-based sequence (`seq`) pre-allocation for messages to ensure strict ordering and reduce database contention during high-concurrency message creation.
- **Push Service Reliability**: Refactored the push notification system to include persistent `PushRecord` tracking. Added a recovery mechanism (`recoverPendingPushes`) to reload pending notifications from the database upon service startup, ensuring better delivery guarantees.
- **WebSocket Reliability**: Updated the WebSocket hub to move away from in-memory history replay in favor of a client-driven synchronization model (`sync_required` event and `ack` handling), reducing memory overhead and improving connection stability.
- **Cache Layer Enhancements**: Added `HIncrBy` and `IncrBySeq` to the `Cache` interface and its implementations (`RedisCache`, `LayeredCache`) to support the new unread and sequence management logic.

internal/cache/conversation_cache.go

@@ -74,19 +74,23 @@ type ConversationCacheSettings struct {
 	MessageListTTL   time.Duration // 消息分页列表缓存 (5min)
 	MessageIndexTTL  time.Duration // 消息索引缓存 (30min)
 	MessageCountTTL  time.Duration // 消息计数缓存 (30min)
+
+	// Seq 缓存配置
+	SeqTTL time.Duration // Seq 计数器缓存 (24h)
 }
 
 // DefaultConversationCacheSettings 返回默认配置
 func DefaultConversationCacheSettings() *ConversationCacheSettings {
 	return &ConversationCacheSettings{
-		DetailTTL:        5 * time.Minute,
-		ListTTL:          60 * time.Second,
-		ParticipantTTL:   5 * time.Minute,
+		DetailTTL:        15 * time.Minute,
+		ListTTL:          120 * time.Second,
+		ParticipantTTL:   15 * time.Minute,
 		UnreadTTL:        30 * time.Second,
 		MessageDetailTTL: 30 * time.Minute,
 		MessageListTTL:   5 * time.Minute,
 		MessageIndexTTL:  30 * time.Minute,
 		MessageCountTTL:  30 * time.Minute,
+		SeqTTL:           24 * time.Hour,
 	}
 }
 
@@ -480,6 +484,142 @@ func (c *ConversationCache) InvalidateUnreadCount(userID, convID string) {
 	c.cache.Delete(UnreadDetailKey(userID, convID))
 }
 
+// IncrementUnread 递增用户在某会话的未读数（Redis Hash + 总数计数器）
+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
+func (c *ConversationCache) ClearUnread(ctx context.Context, userID, convID string) error {
+	hashKey := UnreadHashKey(userID)
+	totalKey := UnreadTotalKey(userID)
+
+	// 读取当前未读数
+	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
+	}
+
+	// 清零该会话未读数
+	if err := c.cache.HSet(ctx, hashKey, convID, "0"); err != nil {
+		return fmt.Errorf("hset clear unread failed: %w", err)
+	}
+
+	// 减少总未读数
+	if current > 0 {
+		c.cache.IncrBySeq(ctx, totalKey, -current)
+	}
+
+	return nil
+}
+
+// GetUnreadCountFromHash 从 Redis Hash 获取单个会话未读数
+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
+}
+
+// GetAllUnreadCounts 从 Redis Hash 获取用户所有会话的未读数
+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
+}
+
+// GetTotalUnread 从 Redis 获取用户总未读数
+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
+}
+
+// GetNextSeq 获取会话的下一个 seq 值（原子递增）
+// 使用 Redis INCR 实现，首次调用时从 DB 初始化并补齐差值
+func (c *ConversationCache) GetNextSeq(ctx context.Context, convID string) (int64, error) {
+	seqKey := MessageSeqKey(convID)
+
+	newSeq, err := c.cache.Incr(ctx, seqKey)
+	if err != nil {
+		return 0, fmt.Errorf("redis incr seq failed: %w", err)
+	}
+
+	// 首次调用时 Redis key 不存在，INCR 从 0 返回 1
+	if newSeq == 1 && c.repo != nil {
+		conv, err := c.repo.GetConversationByID(convID)
+		if err != nil {
+			return 0, fmt.Errorf("failed to load conversation for seq init: %w", err)
+		}
+
+		if conv.LastSeq > 0 {
+			// INCR 已返回 1，需要补齐 delta 使总值为 last_seq + 1
+			alignedSeq, err := c.cache.IncrBySeq(ctx, seqKey, conv.LastSeq)
+			if err != nil {
+				return conv.LastSeq + 1, nil // 降级返回 DB 值
+			}
+			newSeq = alignedSeq
+		}
+
+		_ = c.cache.Expire(ctx, seqKey, c.settings.SeqTTL)
+	}
+
+	return newSeq, nil
+}
+
 // ============================================================
 // 消息缓存方法
 // ============================================================