修复 Step 5 导航交棒后的完成收尾

tests/background-step5-post-completion-validation.test.js

@@ -201,3 +201,59 @@ return {
     true
   );
 });
+
+test('step 5 recovers from bfcache transport close when tab already reached chatgpt', async () => {
+  const api = new Function(`
+const logs = [];
+let waitCalls = 0;
+
+async function getTabId(source) {
+  return source === 'openai-auth' ? 42 : null;
+}
+
+async function waitForTabStableComplete(tabId) {
+  waitCalls += 1;
+  if (tabId !== 42) throw new Error('unexpected tab id');
+  return { url: 'https://chatgpt.com/' };
+}
+
+async function addLog(message, level, meta) {
+  logs.push({ message, level, meta });
+}
+
+function getErrorMessage(error) {
+  return String(error?.message || error || '');
+}
+
+${extractFunction('parseUrlSafely')}
+${extractFunction('isSignupEntryHost')}
+${extractFunction('isLikelyLoggedInChatgptHomeUrl')}
+${extractFunction('isStep5CompletionChatgptUrl')}
+${extractFunction('completeStep5FromTabUrlAfterTransportError')}
+
+return {
+  async run() {
+    return completeStep5FromTabUrlAfterTransportError(new Error('The page keeping the extension port is moved into back/forward cache, so the message channel is closed.'));
+  },
+  snapshot() {
+    return { logs, waitCalls };
+  },
+};
+`)();
+
+  const result = await api.run();
+  const snapshot = api.snapshot();
+
+  assert.deepStrictEqual(result, {
+    profileSubmitted: true,
+    postSubmitChecked: true,
+    outcome: 'logged_in_home',
+    url: 'https://chatgpt.com/',
+    recoveredFromTransportError: true,
+  });
+  assert.equal(snapshot.waitCalls, 1);
+  assert.equal(
+    snapshot.logs.some(({ message }) => /通信中断，但后台确认标签页已进入 chatgpt\.com/.test(message)),
+    true
+  );
+});