fix(web): SSE 连接添加指数退避重连策略

useAlertSSE hook 和 message store 的 connectSSE 均改为手动重连：
1s→2s→4s→8s→16s→30s(cap)，最大重试 10 次，随机 jitter 0.5-1.0x。
替代浏览器原生 EventSource 固定 ~3s 重连，避免服务端压力。

apps/web/src/hooks/useAlertSSE.ts

@@ -24,49 +24,51 @@ export interface VitalUpdateSSEEvent {
   occurred_at?: string;
 }
 
+type ConnectionState = 'connecting' | 'connected' | 'disconnected';
+
 interface UseAlertSSEOptions {
-  /** 是否启用 SSE 连接（默认 true） */
   enabled?: boolean;
-  /** 收到 alert 事件的回调 */
   onAlert?: (data: AlertSSEEvent) => void;
-  /** 收到 vital_update 事件的回调 */
   onVitalUpdate?: (data: VitalUpdateSSEEvent) => void;
 }
 
 interface UseAlertSSEReturn {
-  /** 连接状态 */
   connected: boolean;
-  /** 最近收到的 alert 事件列表（最多保留 100 条） */
+  connectionState: ConnectionState;
   recentAlerts: AlertSSEEvent[];
-  /** 手动重连 */
   reconnect: () => void;
 }
 
 const MAX_RECENT_ALERTS = 100;
+const INITIAL_DELAY_MS = 1000;
+const MAX_DELAY_MS = 30_000;
+const MAX_RETRIES = 10;
 
-/**
- * SSE 实时告警订阅 Hook。
- *
- * 封装 EventSource 连接管理，支持：
- * - 自动重连（EventSource 内置）
- * - 事件分发（alert / vital_update）
- * - 连接状态追踪
- * - 最近告警缓存
- */
 export function useAlertSSE(options: UseAlertSSEOptions = {}): UseAlertSSEReturn {
   const { enabled = true, onAlert, onVitalUpdate } = options;
   const eventSourceRef = useRef<EventSource | null>(null);
+  const reconnectTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+  const retryCountRef = useRef(0);
   const reconnectKeyRef = useRef(0);
   const [connected, setConnected] = useState(false);
+  const [connectionState, setConnectionState] = useState<ConnectionState>('disconnected');
   const [recentAlerts, setRecentAlerts] = useState<AlertSSEEvent[]>([]);
 
+  const clearReconnectTimer = useCallback(() => {
+    if (reconnectTimerRef.current) {
+      clearTimeout(reconnectTimerRef.current);
+      reconnectTimerRef.current = null;
+    }
+  }, []);
+
   const connect = useCallback(() => {
-    // 关闭旧连接
     if (eventSourceRef.current) {
       eventSourceRef.current.close();
       eventSourceRef.current = null;
     }
+    clearReconnectTimer();
     setConnected(false);
+    setConnectionState('disconnected');
 
     if (!enabled) return;
 
@@ -75,11 +77,14 @@ export function useAlertSSE(options: UseAlertSSEOptions = {}): UseAlertSSEReturn
 
     const baseUrl = import.meta.env.VITE_API_BASE_URL || '/api/v1';
     const url = `${baseUrl}/messages/stream?token=${encodeURIComponent(token)}`;
+    setConnectionState('connecting');
     const es = new EventSource(url);
     eventSourceRef.current = es;
 
     es.onopen = () => {
+      retryCountRef.current = 0;
       setConnected(true);
+      setConnectionState('connected');
     };
 
     es.addEventListener('alert', (e: MessageEvent) => {
@@ -90,25 +95,41 @@ export function useAlertSSE(options: UseAlertSSEOptions = {}): UseAlertSSEReturn
           const next = [data, ...prev];
           return next.length > MAX_RECENT_ALERTS ? next.slice(0, MAX_RECENT_ALERTS) : next;
         });
-      } catch {
-        // 忽略解析失败的事件
-      }
+      } catch { /* ignore parse errors */ }
     });
 
     es.addEventListener('vital_update', (e: MessageEvent) => {
       try {
         const data = JSON.parse(e.data) as VitalUpdateSSEEvent;
         onVitalUpdate?.(data);
-      } catch {
-        // 忽略解析失败的事件
-      }
+      } catch { /* ignore parse errors */ }
     });
 
     es.onerror = () => {
       setConnected(false);
-      // EventSource 会自动重连，无需手动处理
+      setConnectionState('disconnected');
+      es.close();
+      eventSourceRef.current = null;
+
+      retryCountRef.current += 1;
+      if (retryCountRef.current > MAX_RETRIES) {
+        return;
+      }
+
+      const delay = Math.min(
+        INITIAL_DELAY_MS * Math.pow(2, retryCountRef.current - 1),
+        MAX_DELAY_MS,
+      );
+      const jitter = delay * (0.5 + Math.random() * 0.5);
+
+      reconnectTimerRef.current = setTimeout(() => {
+        reconnectTimerRef.current = null;
+        const tokenNow = localStorage.getItem('access_token');
+        if (!tokenNow || !enabled) return;
+        connect();
+      }, jitter);
     };
-  }, [enabled, onAlert, onVitalUpdate]);
+  }, [enabled, onAlert, onVitalUpdate, clearReconnectTimer]);
 
   useEffect(() => {
     connect();
@@ -117,13 +138,16 @@ export function useAlertSSE(options: UseAlertSSEOptions = {}): UseAlertSSEReturn
         eventSourceRef.current.close();
         eventSourceRef.current = null;
       }
+      clearReconnectTimer();
       setConnected(false);
+      setConnectionState('disconnected');
     };
   }, [connect, reconnectKeyRef.current]);
 
   const reconnect = useCallback(() => {
+    retryCountRef.current = 0;
     reconnectKeyRef.current += 1;
   }, []);
 
-  return { connected, recentAlerts, reconnect };
+  return { connected, connectionState, recentAlerts, reconnect };
 }