frontend/src/App.tsx

@@ -365,17 +365,24 @@ function App() {
   const [showAddVehicle, setShowAddVehicle] = useState(false);
 
   // Sync browser URL to Zustand screen state on mount (enables direct URL navigation on mobile)
+  // Skip on auth routes -- their query params must survive until Auth0 SDK processes them
   useEffect(() => {
-    const screen = routeToScreen[window.location.pathname];
+    const path = window.location.pathname;
+    if (path === '/callback' || path === '/signup' || path === '/verify-email') return;
+    const screen = routeToScreen[path];
     if (screen && screen !== activeScreen) {
       navigateToScreen(screen, { source: 'url-sync' });
     }
   }, []); // eslint-disable-line react-hooks/exhaustive-deps -- intentionally runs once on mount
 
   // Sync Zustand screen changes back to browser URL (enables bookmarks and URL sharing)
+  // Skip on auth routes -- replaceState would strip ?code= and &state= params that
+  // Auth0 SDK needs for handleRedirectCallback (child effects fire before parent effects)
   useEffect(() => {
+    const path = window.location.pathname;
+    if (path === '/callback' || path === '/signup' || path === '/verify-email') return;
     const targetPath = screenToRoute[activeScreen];
-    if (targetPath && window.location.pathname !== targetPath) {
+    if (targetPath && path !== targetPath) {
       window.history.replaceState(null, '', targetPath);
     }
   }, [activeScreen]);