fix: resolve WebSocket connection issues and API errors

- Fix React StrictMode double-mount causing WebSocket connection loops
  - Add isMountedRef to Tasks.tsx and NotificationContext.tsx
  - Delay WebSocket connection by 100ms to avoid race conditions
  - Check mounted state before reconnection attempts

- Fix React Router v7 deprecation warnings
  - Add future flags: v7_startTransition, v7_relativeSplatPath

- Fix CalendarView 422 API error
  - Send full ISO 8601 datetime format instead of date-only
  - Add URL encoding for query parameters

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/components/CalendarView.tsx

@@ -119,12 +119,12 @@ export function CalendarView({
   const loadTasks = async (start: Date, end: Date) => {
     setLoading(true)
     try {
-      // Format dates for API
-      const dueAfter = start.toISOString().split('T')[0]
-      const dueBefore = end.toISOString().split('T')[0]
+      // Format dates for API (backend expects ISO 8601 datetime)
+      const dueAfter = start.toISOString()
+      const dueBefore = end.toISOString()
 
       const response = await api.get(
-        `/projects/${projectId}/tasks?due_after=${dueAfter}&due_before=${dueBefore}`
+        `/projects/${projectId}/tasks?due_after=${encodeURIComponent(dueAfter)}&due_before=${encodeURIComponent(dueBefore)}`
       )
       const tasks: Task[] = response.data.tasks
 

frontend/src/contexts/NotificationContext.tsx

@@ -25,6 +25,7 @@ export function NotificationProvider({ children }: { children: ReactNode }) {
   const wsRef = useRef<WebSocket | null>(null)
   const pingIntervalRef = useRef<ReturnType<typeof setInterval> | null>(null)
   const reconnectTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null)
+  const isMountedRef = useRef(true)
 
   const refreshUnreadCount = useCallback(async () => {
     try {
@@ -168,11 +169,15 @@ export function NotificationProvider({ children }: { children: ReactNode }) {
           pingIntervalRef.current = null
         }
 
-        // Attempt to reconnect after delay
+        // Only attempt to reconnect if component is still mounted
+        if (isMountedRef.current) {
           reconnectTimeoutRef.current = setTimeout(() => {
+            if (isMountedRef.current) {
               connectWebSocket()
+            }
           }, WS_RECONNECT_DELAY)
         }
+      }
 
       ws.onerror = (err) => {
         console.error('WebSocket error:', err)
@@ -184,13 +189,20 @@ export function NotificationProvider({ children }: { children: ReactNode }) {
 
   // Initial fetch and WebSocket connection
   useEffect(() => {
+    isMountedRef.current = true
     const token = localStorage.getItem('token')
     if (token) {
       refreshUnreadCount()
+      // Delay WebSocket connection to avoid StrictMode race condition
+      const connectTimeout = setTimeout(() => {
+        if (isMountedRef.current) {
           connectWebSocket()
         }
+      }, 100)
 
       return () => {
+        clearTimeout(connectTimeout)
+        isMountedRef.current = false
         // Cleanup on unmount
         if (wsRef.current) {
           wsRef.current.close()
@@ -202,6 +214,11 @@ export function NotificationProvider({ children }: { children: ReactNode }) {
           clearTimeout(reconnectTimeoutRef.current)
         }
       }
+    }
+
+    return () => {
+      isMountedRef.current = false
+    }
   }, [refreshUnreadCount, connectWebSocket])
 
   return (

frontend/src/contexts/ProjectSyncContext.tsx

@@ -1,5 +1,4 @@
 import React, { createContext, useContext, useEffect, useRef, useState, useCallback } from 'react'
-import { useAuth } from './AuthContext'
 
 interface TaskEvent {
   type: 'task_created' | 'task_updated' | 'task_status_changed' | 'task_deleted' | 'task_assigned'
@@ -62,7 +61,6 @@ const devError = (...args: unknown[]) => {
 }
 
 export function ProjectSyncProvider({ children }: { children: React.ReactNode }) {
-  const { user } = useAuth()
   const [isConnected, setIsConnected] = useState(false)
   const [currentProjectId, setCurrentProjectId] = useState<string | null>(null)
   const wsRef = useRef<WebSocket | null>(null)
@@ -212,7 +210,7 @@ export function ProjectSyncProvider({ children }: { children: React.ReactNode })
     } catch (err) {
       devError('Failed to create WebSocket:', err)
     }
-  }, [user?.id, cleanup])
+  }, [cleanup])
 
   const unsubscribeFromProject = useCallback(() => {
     targetProjectIdRef.current = null

frontend/src/main.tsx

@@ -10,7 +10,7 @@ import './index.css'
 
 ReactDOM.createRoot(document.getElementById('root')!).render(
   <React.StrictMode>
-    <BrowserRouter>
+    <BrowserRouter future={{ v7_startTransition: true, v7_relativeSplatPath: true }}>
       <AuthProvider>
         <ToastProvider>
           <NotificationProvider>

frontend/src/pages/Tasks.tsx

@@ -122,14 +122,28 @@ export default function Tasks() {
   }
 
   // Subscribe to project WebSocket when project changes
+  // Use isMounted ref to handle React StrictMode's double-mount behavior
+  const isMountedRef = useRef(true)
   useEffect(() => {
+    isMountedRef.current = true
     if (projectId) {
+      // Small delay to avoid race conditions with StrictMode's rapid mount/unmount
+      const timeoutId = setTimeout(() => {
+        if (isMountedRef.current) {
           subscribeToProject(projectId)
         }
+      }, 100)
       return () => {
+        clearTimeout(timeoutId)
+        isMountedRef.current = false
         unsubscribeFromProject()
       }
-  }, [projectId, subscribeToProject, unsubscribeFromProject])
+    }
+    return () => {
+      isMountedRef.current = false
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [projectId])
 
   // Handle real-time task events from WebSocket
   const handleTaskEvent = useCallback((event: TaskEvent) => {