diff --git a/docs/APP_REFACTORING_DESIGN.md b/docs/APP_REFACTORING_DESIGN.md
index d2ce23e..89406b9 100644
--- a/docs/APP_REFACTORING_DESIGN.md
+++ b/docs/APP_REFACTORING_DESIGN.md
@@ -103,7 +103,7 @@ We will gradually eliminate React state variables in `src/app.tsx` and derive th
 *   [x] **Step 4.1:** Create `src/hooks/use_google_auth.ts` to manage Google Drive authentication token updates. Remove `hasGoogleToken` state from `src/app.tsx`.
 *   [x] **Step 4.2:** Create `src/pages/view_page.tsx` containing layout rendering (`renderMainArea`), asynchronous data loaders, view state management, `revokeObjectUrls` cleanups, and `<GoogleAuthModal>` error fallback state and rendering.
 *   [x] **Step 4.3:** Create `src/pages/intro_page.tsx` rendering the landing screen and its own local header.
-*   [ ] **Step 4.4:** Refactor `src/app.tsx` to serve as a pure routing switch routing to `<IntroPage />` or `<ViewPage />`. In `App`, handle Google Drive redirection synchronously during the render pass by returning a `<Navigate replace />` element (preventing render flashing), and ensure the redirection parser checks both the router `location.search` and the external `window.location.search` to handle HashRouter query structure robustly. Once external parameters (like `state` or `authcode`) are detected, they must be stripped from `window.location.search` using `window.history.replaceState` to prevent redirection loops on page refresh. Remove all layout state logic from the root file, including moving the `useWebMcpBridge` hook invocation into `<ViewPage />`. Run final verification scripts (`npm run check:all`).
+*   [x] **Step 4.4:** Refactor `src/app.tsx` to serve as a pure routing switch routing to `<IntroPage />` or `<ViewPage />`. In `App`, handle Google Drive redirection synchronously during the render pass by returning a `<Navigate replace />` element (preventing render flashing), and ensure the redirection parser checks both the router `location.search` and the external `window.location.search` to handle HashRouter query structure robustly. Once external parameters (like `state` or `authcode`) are detected, they must be stripped from `window.location.search` using `window.history.replaceState` to prevent redirection loops on page refresh. Remove all layout state logic from the root file, including moving the `useWebMcpBridge` hook invocation into `<ViewPage />`. Run final verification scripts (`npm run check:all`).
 
 ## Future Considerations
 
diff --git a/src/app.tsx b/src/app.tsx
index 47edb4d..fcebd74 100644
--- a/src/app.tsx
+++ b/src/app.tsx
@@ -1,6 +1,6 @@
 import queryString from 'query-string';
-import {useEffect, useRef} from 'react';
-import {Navigate, Route, Routes, useLocation, useNavigate} from 'react-router';
+import {useMemo} from 'react';
+import {Navigate, Route, Routes, useLocation} from 'react-router';
 import {IntroPage} from './pages/intro_page';
 import {ViewPage} from './pages/view_page';
 import {getStaticUrl} from './util/url_args';
@@ -9,20 +9,27 @@ const staticUrl = getStaticUrl();
 
 /**
  * Root App component that orchestrates top-level routing, Google Drive "Open with"
- * payload interception and redirection.
+ * payload interception, and WikiTree auth code redirection.
  */
 export function App() {
-  const navigate = useNavigate();
   const location = useLocation();
 
-  /** Prevents the Google Drive "Open with" state from being processed more than once. */
-  const stateProcessed = useRef(false);
+  // Synchronously parse and evaluate redirect query parameters from both external window and router searches.
+  const redirectTarget = useMemo(() => {
+    if (typeof window === 'undefined') {
+      return null;
+    }
 
-  // Google Drive "Open with" flow state checking.
-  useEffect(() => {
-    const search = queryString.parse(location.search);
-    const stateParam = search.state;
-    if (typeof stateParam === 'string' && !stateProcessed.current) {
+    const windowSearch = queryString.parse(window.location.search);
+    const routerSearch = queryString.parse(location.search);
+
+    let redirectPath: string | null = null;
+    const mergedParams = {...routerSearch, ...windowSearch};
+    let paramsModified = false;
+
+    // 1. Handle Google Drive "Open with" action
+    const stateParam = mergedParams.state;
+    if (typeof stateParam === 'string') {
       try {
         const parsedState = JSON.parse(stateParam);
         if (
@@ -31,29 +38,58 @@ export function App() {
           Array.isArray(parsedState.ids) &&
           parsedState.ids.length > 0
         ) {
-          stateProcessed.current = true;
           const fileId = parsedState.ids[0];
-          // Soft redirect to view file
-          navigate(
-            {
-              pathname: '/view',
-              search: queryString.stringify({
-                source: 'google-drive',
-                fileId,
-              }),
-            },
-            {replace: true},
-          );
+          redirectPath = '/view';
+          mergedParams.source = 'google-drive';
+          mergedParams.fileId = fileId;
+          delete mergedParams.state;
+          paramsModified = true;
         }
       } catch (err) {
-        // Silently catch JSON parsing errors for state parameters not meant for us (e.g. from other auth tools)
+        // Silently catch JSON parsing errors for state parameters not meant for us
         console.warn(
           'Google Drive state query parameter JSON parsing failed or action mismatch:',
           err,
         );
       }
     }
-  }, [navigate, location.search]);
+
+    // 2. Handle WikiTree authcode presence
+    if (windowSearch.authcode) {
+      redirectPath = redirectPath || location.pathname;
+      paramsModified = true;
+    }
+
+    if (paramsModified || windowSearch.state || windowSearch.authcode) {
+      // Strip external state / authcode parameters from window.location.search to prevent redirect loops.
+      const cleanWindowSearch = {...windowSearch};
+      delete cleanWindowSearch.state;
+      delete cleanWindowSearch.authcode;
+
+      const cleanWindowSearchStr = queryString.stringify(cleanWindowSearch);
+      const newUrl =
+        window.location.origin +
+        window.location.pathname +
+        (cleanWindowSearchStr ? '?' + cleanWindowSearchStr : '') +
+        window.location.hash;
+      window.history.replaceState(null, '', newUrl);
+
+      return {
+        pathname: redirectPath || location.pathname,
+        search: queryString.stringify(mergedParams),
+      };
+    }
+
+    return null;
+  }, [location.pathname, location.search]);
+
+  if (redirectTarget) {
+    return (
+      <Routes>
+        <Route path="*" element={<Navigate to={redirectTarget} replace />} />
+      </Routes>
+    );
+  }
 
   const isViewPage = location.pathname === '/view';