diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 0778564..d64eab0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -55,7 +55,7 @@ jobs:
       - uses: actions/setup-node@v4
         if: steps.detect.outputs.frontend == 'true'
         with:
-          node-version: 20.20.2
+          node-version: 22
           cache: npm
           cache-dependency-path: frontend/package-lock.json
 
diff --git a/.github/workflows/pr-preview.yml b/.github/workflows/pr-preview.yml
index bfd2897..9db69d0 100644
--- a/.github/workflows/pr-preview.yml
+++ b/.github/workflows/pr-preview.yml
@@ -39,7 +39,7 @@ jobs:
         if: github.event.action != 'closed'
         uses: actions/setup-node@v4
         with:
-          node-version: 20.20.2
+          node-version: 22
           cache: npm
           cache-dependency-path: frontend/package-lock.json
 
diff --git a/README.md b/README.md
index aafa9c8..a2a4ba8 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,35 @@
 # TimeFlow
+
+## Web PR previews (Vercel)
+
+Fork and same-repo pull requests can get an interactive web preview via Vercel.
+
+### One-time setup (org admin)
+
+1. Open [vercel.com](https://vercel.com) and sign in with GitHub.
+2. **Add New Project** → import `1024XEngineer/timeflow`.
+3. Set:
+   - **Root Directory**: `frontend`
+   - **Framework Preset**: Other
+   - **Build Command**: `npx expo export --platform web` (or leave default from `frontend/vercel.json`)
+   - **Output Directory**: `dist`
+   - **Install Command**: `npm ci`
+   - **Node.js Version**: `22.x`
+4. Add **Preview** env vars (do not set these on Production unless you intend a fake demo deploy):
+   - `EXPO_PUBLIC_USE_FAKE_WS=true` — explicit opt-in; required because `expo export` builds with `__DEV__=false`
+   - `EXPO_PUBLIC_WS_URL=` (empty) — leave unset so the preview uses FakeWsServer
+   - Optional: `EXPO_PUBLIC_BAIDU_MAP_AK` if map picker should work in the preview
+5. Approve the Vercel GitHub App for the `1024XEngineer` org if prompted.
+6. Fork PR deployments are gated by Vercel **Git Fork Protection** (Settings → Security):
+   - Default: a Vercel team member must **authorize each fork PR deployment** (especially when the PR changes code or `vercel.json`). Expect a Deployments comment/request, not a fully automatic Preview URL on every external PR.
+   - Optional (higher risk): disable Git Fork Protection only after auditing every Preview environment variable for secrets; then fork PRs can deploy without per-PR approval.
+
+After setup, same-repo PRs get Preview URLs automatically. Fork PRs get a Preview URL after the authorization step above (or after Fork Protection is disabled). The existing GitHub Pages workflow only deploys same-repository branches.
+
+### Local check
+
+```bash
+cd frontend
+npm ci
+EXPO_PUBLIC_USE_FAKE_WS=true EXPO_PUBLIC_WS_URL= npx expo export --platform web
+```
diff --git a/frontend/.env.example b/frontend/.env.example
index 9ecc315..c1c12e3 100644
--- a/frontend/.env.example
+++ b/frontend/.env.example
@@ -13,5 +13,7 @@ EXPO_PUBLIC_BAIDU_MAP_AK=your-baidu-map-browser-ak
 
 EXPO_PUBLIC_WS_URL=
 
-# Force the fake WebSocket even if EXPO_PUBLIC_WS_URL is set (dev only).
+# Explicit fake WebSocket opt-in when EXPO_PUBLIC_WS_URL is empty.
+# Required for hosted web previews (`expo export` sets __DEV__=false).
+# Do not set this on real production deploys.
 # EXPO_PUBLIC_USE_FAKE_WS=true
diff --git a/frontend/__tests__/app/session/sessionEndpoint.test.ts b/frontend/__tests__/app/session/sessionEndpoint.test.ts
index eeeab4c..b89caad 100644
--- a/frontend/__tests__/app/session/sessionEndpoint.test.ts
+++ b/frontend/__tests__/app/session/sessionEndpoint.test.ts
@@ -1,6 +1,10 @@
 import { describe, expect, it } from '@jest/globals';
 
-import { buildSessionWebSocketUrl, resolveSessionUserId } from '@/app/session/sessionEndpoint';
+import {
+  buildSessionWebSocketUrl,
+  resolveAllowFakeWs,
+  resolveSessionUserId,
+} from '@/app/session/sessionEndpoint';
 
 describe('session endpoint compatibility', () => {
   it('adds the persisted device id to the backend WebSocket URL', () => {
@@ -33,4 +37,12 @@ describe('session endpoint compatibility', () => {
     expect(resolveSessionUserId(undefined)).toBe('default_user');
     expect(resolveSessionUserId(' user_1 ')).toBe('user_1');
   });
+
+  it('allows an explicit fake-ws opt-in outside __DEV__ for hosted previews', () => {
+    expect(resolveAllowFakeWs('true', false)).toBe(true);
+    expect(resolveAllowFakeWs('1', false)).toBe(true);
+    expect(resolveAllowFakeWs('false', false)).toBe(false);
+    expect(resolveAllowFakeWs(undefined, false)).toBe(false);
+    expect(resolveAllowFakeWs(undefined, true)).toBe(true);
+  });
 });
diff --git a/frontend/package.json b/frontend/package.json
index bb4965c..b932870 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -3,7 +3,7 @@
   "version": "1.0.0",
   "main": "index.ts",
   "engines": {
-    "node": ">=20.20.2 <21",
+    "node": ">=22 <23",
     "npm": ">=10.8.2 <11"
   },
   "packageManager": "npm@10.8.2",
diff --git a/frontend/src/app/session/SessionProvider.tsx b/frontend/src/app/session/SessionProvider.tsx
index 027ed40..f2cdd34 100644
--- a/frontend/src/app/session/SessionProvider.tsx
+++ b/frontend/src/app/session/SessionProvider.tsx
@@ -14,7 +14,11 @@ import { FakeWsServer } from '@/dev/fakes/FakeWsServer';
 import { getOrCreateDeviceId, type DeviceIdStore } from '@/infrastructure/storage/deviceIdStore';
 import { WsClient } from '@/infrastructure/ws/WsClient';
 
-import { buildSessionWebSocketUrl, resolveSessionUserId } from './sessionEndpoint';
+import {
+  buildSessionWebSocketUrl,
+  resolveAllowFakeWs,
+  resolveSessionUserId,
+} from './sessionEndpoint';
 
 export type SessionTransportMode = 'remote' | 'fake' | 'unavailable';
 
@@ -38,21 +42,11 @@ function resolveWsUrl(): string | null {
   return fromEnv || null;
 }
 
-function resolveAllowFake(): boolean {
-  const flag =
-    typeof process !== 'undefined' ? process.env.EXPO_PUBLIC_USE_FAKE_WS?.trim() : undefined;
-  const isDevBuild = typeof __DEV__ !== 'undefined' && __DEV__;
-  // Fake 只能进入开发/调试构建；release 即使误带变量也必须拒绝。
-  if (!isDevBuild) return false;
-  if (flag === '0' || flag === 'false') return false;
-  return flag === '1' || flag === 'true' || flag == null;
-}
-
 const RECONNECT_BASE_MS = 1000;
 const RECONNECT_MAX_MS = 30_000;
 const SESSION_READY_TIMEOUT_MS = 10_000;
 const UNAVAILABLE_CONNECTION_ERROR =
-  '缺少 EXPO_PUBLIC_WS_URL。开发环境可设置 EXPO_PUBLIC_USE_FAKE_WS=true 使用进程内 Fake。';
+  '缺少 EXPO_PUBLIC_WS_URL。可设置 EXPO_PUBLIC_USE_FAKE_WS=true 使用进程内 Fake（含托管预览）。';
 
 function isSessionReady(message: WsJsonMessage, deviceId: string): message is SessionReady {
   return (
@@ -78,7 +72,13 @@ export function SessionProvider({
   const [connectionError, setConnectionError] = useState<string | null>(null);
 
   const url = useMemo(() => resolveWsUrl(), []);
-  const allowFake = useMemo(() => resolveAllowFake(), []);
+  const allowFake = useMemo(
+    () =>
+      resolveAllowFakeWs(
+        typeof process !== 'undefined' ? process.env.EXPO_PUBLIC_USE_FAKE_WS : undefined,
+      ),
+    [],
+  );
   const transportMode: SessionTransportMode = url ? 'remote' : allowFake ? 'fake' : 'unavailable';
 
   const remoteEndpoint = useMemo(() => {
diff --git a/frontend/src/app/session/sessionEndpoint.ts b/frontend/src/app/session/sessionEndpoint.ts
index 23a7dee..9084b79 100644
--- a/frontend/src/app/session/sessionEndpoint.ts
+++ b/frontend/src/app/session/sessionEndpoint.ts
@@ -4,6 +4,23 @@ function isDevelopmentBuild(): boolean {
   return typeof __DEV__ !== 'undefined' && __DEV__;
 }
 
+/**
+ * Decide whether the in-process FakeWsServer may be used when EXPO_PUBLIC_WS_URL is empty.
+ *
+ * - Explicit `true`/`1`: deliberate opt-in for any build (hosted web previews).
+ * - Explicit `false`/`0`: always disabled.
+ * - Unset: allowed only in `__DEV__` builds so store/production releases stay remote-only.
+ */
+export function resolveAllowFakeWs(
+  flag: string | undefined,
+  isDevBuild: boolean = isDevelopmentBuild(),
+): boolean {
+  const normalized = flag?.trim();
+  if (normalized === '0' || normalized === 'false') return false;
+  if (normalized === '1' || normalized === 'true') return true;
+  return isDevBuild;
+}
+
 export function buildSessionWebSocketUrl(
   baseUrl: string,
   deviceId: string,
diff --git a/frontend/vercel.json b/frontend/vercel.json
new file mode 100644
index 0000000..13cf064
--- /dev/null
+++ b/frontend/vercel.json
@@ -0,0 +1,12 @@
+{
+  "buildCommand": "npx expo export --platform web",
+  "outputDirectory": "dist",
+  "installCommand": "npm ci",
+  "framework": null,
+  "rewrites": [
+    {
+      "source": "/:path*",
+      "destination": "/"
+    }
+  ]
+}