Fix bugs found in full security and stability audit.

Harden artifact paths and fusion uploads, repair pool reconnect and login ID tracking, fix agent/fusion/frontend regressions, and refresh PROBLEMS.md with the full findings list.

server/web/src/hooks/useWebSocket.ts

@@ -35,6 +35,16 @@ export function useWebSocket(): UseWebSocketReturn {
   const connect = useCallback(() => {
     if (unmounted.current) return;
 
+    if (reconnectTimer.current) {
+      clearTimeout(reconnectTimer.current);
+      reconnectTimer.current = null;
+    }
+
+    const existing = wsRef.current;
+    if (existing && (existing.readyState === WebSocket.OPEN || existing.readyState === WebSocket.CONNECTING)) {
+      existing.close();
+    }
+
     const protocol = window.location.protocol === 'https:' ? 'wss:' : 'ws:';
     const wsUrl = `${protocol}//${window.location.host}/ws/dashboard`;
 
@@ -48,6 +58,7 @@ export function useWebSocket(): UseWebSocketReturn {
     ws.onclose = () => {
       if (unmounted.current) return;
       setIsConnected(false);
+      if (reconnectTimer.current) clearTimeout(reconnectTimer.current);
       reconnectTimer.current = setTimeout(connect, 3000);
     };