经得起 App 审核的离线模式和错误状态：面向 WebViewGold 应用的 Codex 工作流程

## Network and error states (every screen)
- All HTTP calls go through src/lib/request.ts: request(path, { timeoutMs = 10000 }).
  It uses AbortSignal.timeout, retries idempotent GETs once with backoff, and throws
  typed errors (OfflineError, TimeoutError, HttpError with status) that carry a
  user-facing message. Components never call fetch directly.
- Every data view renders exactly one of: loading (skeleton, ends after 10 s at the
  latest), content, empty (helpful text and a next action), error (message and a
  "Try again" button).
- No raw error text in the UI: no "TypeError", no stack traces, no JSON.
- Offline banner: listen to the online and offline events and render
  <div role="status">You are offline. Changes will sync when you are back.</div>
  Do not rely on navigator.onLine alone; a failed request also counts as offline.
- Forms keep their input when a submit fails. Submit buttons show progress and
  re-enable on error. Never send the same mutation twice without an idempotency key.
- Firestore: initializeFirestore with persistentLocalCache. Show "Last updated"
  when snapshot.metadata.fromCache is true.
- Express: error middleware returns JSON { error, message } with the right status,
  never an HTML error page. GET /healthz answers 200 without touching the database.
- No service worker for offline inside the native app. WebViewGold's offline screen
  and the bundled fallback page handle "no network at launch".

## Review guidelines
- P1: fetch() or axios outside src/lib/request.ts, or any request without a timeout.
- P1: a catch block that swallows an error without showing an error state.
- P1: a loading state with no exit (no timeout, no error branch).

// tests/offline.spec.js (Playwright)
import { test, expect } from "@playwright/test";

test("failed API shows a retry, not a white screen", async ({ page }) => {
  await page.route("**/api/**", (route) => route.abort("internetdisconnected"));
  await page.goto("/dashboard");
  await expect(page.getByRole("button", { name: /try again/i })).toBeVisible({ timeout: 12000 });
  await expect(page.getByText(/TypeError|Failed to fetch/)).toHaveCount(0);
});

test("hanging API never leaves an endless spinner", async ({ page }) => {
  await page.route("**/api/**", () => { /* never answer: a server that hangs */ });
  await page.goto("/dashboard");
  await expect(page.getByRole("button", { name: /try again/i })).toBeVisible({ timeout: 12000 });
});

test("offline banner appears and clears", async ({ page, context }) => {
  await page.goto("/dashboard");
  await context.setOffline(true);
  await expect(page.getByRole("status")).toContainText(/offline/i);
  await context.setOffline(false);
  await expect(page.getByRole("status")).toHaveCount(0);
});