diff --git a/llm-fe/src/axiosApi.js b/llm-fe/src/axiosApi.js
index a143e20..2b79527 100644
--- a/llm-fe/src/axiosApi.js
+++ b/llm-fe/src/axiosApi.js
@@ -1,5 +1,6 @@
 import axios from "axios";
-const Cookies = require("js-cookie");
+import Cookies from "js-cookie";
+import { redirectToAppPath } from "./llm-fe/platform/nativePlatform";
 
 const baseURL = process.env.REACT_APP_BACKEND_REST_API_BASE_URL;
 
@@ -46,7 +47,8 @@ axiosInstance.interceptors.response.use(
       error.response.status === 401 &&
       originalRequest.url === baseURL + "/token/refresh/"
     ) {
-      window.location.href = "/signin/";
+      // Hash-safe on Capacitor (#24); plain path on web BrowserRouter.
+      redirectToAppPath("/signin/");
       //console.log('remove the local storage here')
       return Promise.reject(error);
     }
@@ -83,11 +85,11 @@ axiosInstance.interceptors.response.use(
             });
         } else {
           console.log("Refresh token is expired");
-          window.location.href = "/signin/";
+          redirectToAppPath("/signin/");
         }
       } else {
         console.log("Refresh token not available");
-        window.location.href = "/signin/";
+        redirectToAppPath("/signin/");
       }
     }
     return Promise.reject(error);
diff --git a/llm-fe/src/index.tsx b/llm-fe/src/index.tsx
index 1fa274d..55743fa 100644
--- a/llm-fe/src/index.tsx
+++ b/llm-fe/src/index.tsx
@@ -2,7 +2,7 @@ import React from 'react';
 import ReactDOM from 'react-dom/client';
 import './index.css';
 import App from './App';
-import { BrowserRouter } from 'react-router-dom';
+import AppRouter from './llm-fe/platform/AppRouter';
 import { AuthProvider } from './llm-fe/contexts/AuthContext';
 import { AccountProvider } from './llm-fe/contexts/AccountContext';
 import { WebSocketProvider } from './llm-fe/contexts/WebSocketContext';
@@ -16,7 +16,7 @@ const root = ReactDOM.createRoot(
 );
 root.render(
   <React.StrictMode>
-    <BrowserRouter>
+    <AppRouter>
     <script async defer src="https://tianji.aimloperations.com/tracker.js" data-website-id="cm7x7m52m03kbddswbswrt17y"></script>
       <AuthProvider>
         <AccountProvider>
@@ -33,6 +33,6 @@ root.render(
           </WebSocketProvider>
         </AccountProvider>
       </AuthProvider>
-    </BrowserRouter>
+    </AppRouter>
   </React.StrictMode>
 );
diff --git a/llm-fe/src/llm-fe/platform/AppRouter.test.tsx b/llm-fe/src/llm-fe/platform/AppRouter.test.tsx
new file mode 100644
index 0000000..e6e29d3
--- /dev/null
+++ b/llm-fe/src/llm-fe/platform/AppRouter.test.tsx
@@ -0,0 +1,63 @@
+import React from 'react';
+import { render, screen } from '@testing-library/react';
+import { Route, Routes } from 'react-router-dom';
+import AppRouter from './AppRouter';
+import { getAppRouter, isNativePlatform } from './nativePlatform';
+
+describe('AppRouter / getAppRouter (#24)', () => {
+  const originalCapacitor = window.Capacitor;
+
+  afterEach(() => {
+    if (originalCapacitor === undefined) {
+      delete window.Capacitor;
+    } else {
+      window.Capacitor = originalCapacitor;
+    }
+  });
+
+  it('uses BrowserRouter on web', () => {
+    delete window.Capacitor;
+    expect(isNativePlatform()).toBe(false);
+    const Router = getAppRouter();
+    expect(Router.name).toBe('BrowserRouter');
+  });
+
+  it('uses HashRouter on native Capacitor', () => {
+    window.Capacitor = { isNativePlatform: () => true };
+    expect(isNativePlatform()).toBe(true);
+    const Router = getAppRouter();
+    expect(Router.name).toBe('HashRouter');
+  });
+
+  it('renders nested routes under HashRouter without blank screen', () => {
+    window.Capacitor = { isNativePlatform: () => true };
+    window.location.hash = '#/account/';
+
+    render(
+      <AppRouter>
+        <Routes>
+          <Route path="/account/" element={<div>Account Page</div>} />
+          <Route path="/" element={<div>Home</div>} />
+        </Routes>
+      </AppRouter>,
+    );
+
+    expect(screen.getByText('Account Page')).toBeInTheDocument();
+  });
+
+  it('renders nested routes under BrowserRouter on web', () => {
+    delete window.Capacitor;
+    window.history.pushState({}, '', '/account/');
+
+    render(
+      <AppRouter>
+        <Routes>
+          <Route path="/account/" element={<div>Account Page</div>} />
+          <Route path="/" element={<div>Home</div>} />
+        </Routes>
+      </AppRouter>,
+    );
+
+    expect(screen.getByText('Account Page')).toBeInTheDocument();
+  });
+});
diff --git a/llm-fe/src/llm-fe/platform/AppRouter.tsx b/llm-fe/src/llm-fe/platform/AppRouter.tsx
new file mode 100644
index 0000000..cdec648
--- /dev/null
+++ b/llm-fe/src/llm-fe/platform/AppRouter.tsx
@@ -0,0 +1,17 @@
+import React, { ReactNode } from 'react';
+import { getAppRouter } from './nativePlatform';
+
+type AppRouterProps = {
+  children: ReactNode;
+};
+
+/**
+ * Single place that chooses BrowserRouter (web) vs HashRouter (Capacitor).
+ * Avoids sprinkling Capacitor.isNativePlatform() through the route tree (#24).
+ */
+const AppRouter = ({ children }: AppRouterProps): JSX.Element => {
+  const Router = getAppRouter();
+  return <Router>{children}</Router>;
+};
+
+export default AppRouter;
diff --git a/llm-fe/src/llm-fe/platform/nativePlatform.js b/llm-fe/src/llm-fe/platform/nativePlatform.js
new file mode 100644
index 0000000..a976e3d
--- /dev/null
+++ b/llm-fe/src/llm-fe/platform/nativePlatform.js
@@ -0,0 +1,65 @@
+/**
+ * Capacitor / WebView platform helpers (#24 / #22).
+ * Prefer window.Capacitor so unit tests and web builds need no Capacitor package.
+ */
+
+/**
+ * @returns {boolean}
+ */
+export function isNativePlatform() {
+  if (typeof window === "undefined") {
+    return false;
+  }
+  const Cap = window.Capacitor;
+  if (!Cap) {
+    return false;
+  }
+  if (typeof Cap.isNativePlatform === "function") {
+    return Cap.isNativePlatform();
+  }
+  return Cap.isNative === true;
+}
+
+/**
+ * Absolute in-app path for full page navigations.
+ * Native Capacitor builds use HashRouter; web keeps BrowserRouter paths.
+ *
+ * @param {string} path e.g. "/signin/"
+ * @returns {string}
+ */
+export function appHref(path) {
+  const normalized = path.startsWith("/") ? path : `/${path}`;
+  if (isNativePlatform()) {
+    return `/#${normalized}`;
+  }
+  return normalized;
+}
+
+/**
+ * Navigate the top-level window to an in-app route (auth failure, forced logout).
+ * @param {string} path
+ */
+export function redirectToAppPath(path) {
+  if (typeof window === "undefined") {
+    return;
+  }
+  if (isNativePlatform()) {
+    const normalized = path.startsWith("/") ? path : `/${path}`;
+    window.location.hash = `#${normalized}`;
+    return;
+  }
+  window.location.href = appHref(path);
+}
+
+/**
+ * Router class for the current runtime.
+ * HashRouter on Capacitor so nested routes reload without a server rewrite.
+ * BrowserRouter on web (nginx already rewrites to index.html).
+ *
+ * @returns {typeof import('react-router-dom').HashRouter | typeof import('react-router-dom').BrowserRouter}
+ */
+export function getAppRouter() {
+  // Lazy require keeps this module usable from axios (no React import cycle in tests).
+  const { BrowserRouter, HashRouter } = require("react-router-dom");
+  return isNativePlatform() ? HashRouter : BrowserRouter;
+}
diff --git a/llm-fe/src/llm-fe/platform/nativePlatform.test.js b/llm-fe/src/llm-fe/platform/nativePlatform.test.js
new file mode 100644
index 0000000..80ebe68
--- /dev/null
+++ b/llm-fe/src/llm-fe/platform/nativePlatform.test.js
@@ -0,0 +1,92 @@
+import {
+  appHref,
+  isNativePlatform,
+  redirectToAppPath,
+} from './nativePlatform';
+
+describe('nativePlatform', () => {
+  const originalCapacitor = window.Capacitor;
+  const originalLocation = window.location;
+
+  afterEach(() => {
+    if (originalCapacitor === undefined) {
+      delete window.Capacitor;
+    } else {
+      window.Capacitor = originalCapacitor;
+    }
+    Object.defineProperty(window, 'location', {
+      configurable: true,
+      value: originalLocation,
+    });
+  });
+
+  describe('isNativePlatform', () => {
+    it('returns false when Capacitor missing', () => {
+      delete window.Capacitor;
+      expect(isNativePlatform()).toBe(false);
+    });
+
+    it('uses Capacitor.isNativePlatform when present', () => {
+      window.Capacitor = {
+        isNativePlatform: () => true,
+      };
+      expect(isNativePlatform()).toBe(true);
+    });
+
+    it('falls back to Capacitor.isNative', () => {
+      window.Capacitor = { isNative: true };
+      expect(isNativePlatform()).toBe(true);
+    });
+  });
+
+  describe('appHref', () => {
+    it('returns plain path on web', () => {
+      delete window.Capacitor;
+      expect(appHref('/signin/')).toBe('/signin/');
+    });
+
+    it('returns hash path on native', () => {
+      window.Capacitor = { isNativePlatform: () => true };
+      expect(appHref('/signin/')).toBe('/#/signin/');
+    });
+  });
+
+  describe('redirectToAppPath', () => {
+    it('sets location.href on web', () => {
+      delete window.Capacitor;
+      const hrefSetter = jest.fn();
+      Object.defineProperty(window, 'location', {
+        configurable: true,
+        value: {
+          ...originalLocation,
+          set href(v) {
+            hrefSetter(v);
+          },
+          get href() {
+            return '';
+          },
+        },
+      });
+      redirectToAppPath('/signin/');
+      expect(hrefSetter).toHaveBeenCalledWith('/signin/');
+    });
+
+    it('sets location.hash on native', () => {
+      window.Capacitor = { isNativePlatform: () => true };
+      let hashValue = '';
+      Object.defineProperty(window, 'location', {
+        configurable: true,
+        value: {
+          get hash() {
+            return hashValue;
+          },
+          set hash(v) {
+            hashValue = v;
+          },
+        },
+      });
+      redirectToAppPath('/signin/');
+      expect(hashValue).toBe('#/signin/');
+    });
+  });
+});
diff --git a/llm-fe/src/react-app-env.d.ts b/llm-fe/src/react-app-env.d.ts
index 6431bc5..2e4afca 100644
--- a/llm-fe/src/react-app-env.d.ts
+++ b/llm-fe/src/react-app-env.d.ts
@@ -1 +1,19 @@
 /// <reference types="react-scripts" />
+
+interface CapacitorBridge {
+  isNativePlatform?: () => boolean;
+  isNative?: boolean;
+  Plugins?: {
+    App?: { addListener?: (...args: unknown[]) => unknown };
+    Network?: { addListener?: (...args: unknown[]) => unknown };
+    Preferences?: {
+      get?: (options: { key: string }) => Promise<{ value?: string | null }>;
+      set?: (options: { key: string; value: string }) => Promise<void>;
+      remove?: (options: { key: string }) => Promise<void>;
+    };
+  };
+}
+
+interface Window {
+  Capacitor?: CapacitorBridge;
+}