feat(ws): implement sync_required event and message acknowledgement

Add support for a new `sync_required` WebSocket message type to trigger
incremental synchronization of conversations, unread counts, and active
messages. Also implement an `ack` mechanism to acknowledge received
messages.

src/stores/message/services/WSMessageHandler.ts

@@ -155,7 +155,7 @@ export class WSMessageHandler implements IWSMessageHandler {
       if (now - this.lastReconnectSyncAt > 1500) {
         this.lastReconnectSyncAt = now;
         const activeConversation = useMessageStore.getState().getActiveConversation();
-        
+
         if (!activeConversation) {
           this.fetchConversationsCallback(true, 'sse-reconnect').catch(error => {
             console.error('[WSMessageHandler] 连接后同步会话失败:', error);
@@ -165,7 +165,7 @@ export class WSMessageHandler implements IWSMessageHandler {
             console.error('[WSMessageHandler] 连接后同步未读数失败:', error);
           });
         }
-        
+
         if (activeConversation) {
           this.fetchMessagesCallback(activeConversation).catch(error => {
             console.error('[WSMessageHandler] 连接后同步当前会话消息失败:', error);
@@ -174,6 +174,25 @@ export class WSMessageHandler implements IWSMessageHandler {
       }
     });
 
+    // 监听 sync_required 事件，触发增量同步
+    wsService.on('sync_required', () => {
+      console.log('[WSMessageHandler] 收到 sync_required，开始增量同步');
+      const activeConversation = useMessageStore.getState().getActiveConversation();
+
+      this.fetchConversationsCallback(true, 'sync_required').catch(error => {
+        console.error('[WSMessageHandler] sync_required 同步会话失败:', error);
+      });
+      this.fetchUnreadCountCallback().catch(error => {
+        console.error('[WSMessageHandler] sync_required 同步未读数失败:', error);
+      });
+
+      if (activeConversation) {
+        this.fetchMessagesCallback(activeConversation).catch(error => {
+          console.error('[WSMessageHandler] sync_required 同步消息失败:', error);
+        });
+      }
+    });
+
     wsService.onDisconnect(() => {
       useMessageStore.getState().setSSEConnected(false);
     });
@@ -263,6 +282,9 @@ export class WSMessageHandler implements IWSMessageHandler {
     }
     this.deduplication.markMessageAsProcessed(id);
 
+    // 发送 ACK 确认
+    wsService.sendAck(id);
+
     // 对于群聊消息，获取发送者信息
     if (message.type === 'group_message' && sender_id && sender_id !== currentUserId && sender_id !== '10000') {
       this.userCacheService.getSenderInfo(sender_id).then(user => {