feat(frontend): Implement silent refresh logic

frontend/src/App.tsx

@@ -10,6 +10,7 @@ import { type Conversation } from "./components/layout/HistorySidebar"
 import { registerUnauthorizedCallback } from "./services/api"
 import { Button } from "./components/ui/button"
 import { ThemeProvider, useTheme } from "./components/theme-provider"
+import { useSilentRefresh } from "./hooks/use-silent-refresh"
 
 // --- Auth Context ---
 interface AuthContextType {
@@ -52,6 +53,8 @@ function AppContent() {
   const { setThemeLocal } = useTheme()
   const { isAuthenticated, setIsAuthenticated, user, setUser } = useAuth()
   
+  useSilentRefresh(isAuthenticated)
+  
   const [authMode, setAuthMode] = useState<"login" | "register">("login")
   const [isLoading, setIsLoading] = useState(true)
   const [selectedThreadId, setSelectedThreadId] = useState<string | null>(null)

frontend/src/hooks/use-silent-refresh.ts

@@ -0,0 +1,33 @@
+import { useEffect, useCallback } from 'react'
+import { AuthService } from '@/services/auth'
+
+/**
+ * Hook to handle silent token refresh in the background.
+ * It proactively refreshes the session to prevent expiration while the user is active.
+ */
+export function useSilentRefresh(isAuthenticated: boolean) {
+  const refresh = useCallback(async () => {
+    try {
+      console.log('Proactively refreshing session...')
+      await AuthService.refreshSession()
+    } catch (error) {
+      console.error('Silent refresh failed:', error)
+      // If refresh fails, we don't necessarily logout here, 
+      // as the reactive interceptor will handle 401s if the session is truly dead.
+    }
+  }, [])
+
+  useEffect(() => {
+    if (!isAuthenticated) return
+
+    // Refresh every 25 minutes (access token defaults to 30 mins)
+    const REFRESH_INTERVAL = 25 * 60 * 1000 
+    
+    const intervalId = setInterval(refresh, REFRESH_INTERVAL)
+
+    // Also refresh immediately on mount/auth if we want to ensure we have a fresh start
+    // refresh()
+
+    return () => clearInterval(intervalId)
+  }, [isAuthenticated, refresh])
+}

frontend/src/services/auth.ts

@@ -52,6 +52,11 @@ export const AuthService = {
     await api.post("/auth/logout")
   },
 
+  async refreshSession(): Promise<AuthResponse> {
+    const response = await api.post<AuthResponse>("/auth/refresh")
+    return response.data
+  },
+
   async updateTheme(theme: Theme): Promise<UserResponse> {
     const response = await api.patch<UserResponse>("/auth/theme", { theme })
     return response.data