fix(chat): enable in-place subtask navigation in embedded session-chat iframe (#2138)

packages/ui/src/lib/router/serializeRoute.test.ts

@@ -0,0 +1,123 @@
+import { afterAll, afterEach, beforeEach, describe, expect, test } from 'bun:test';
+import { updateBrowserURL } from './serializeRoute';
+import type { AppRouteState } from './serializeRoute';
+import { isEmbeddedSessionChat, resetEmbeddedSessionChatCache } from '@/components/layout/contextPanelEmbeddedChat';
+
+const originalWindow = globalThis.window;
+
+type HistoryStub = {
+  state: unknown;
+  lastURL: string | null;
+  replaceState(state: unknown, _title: string, url?: string): void;
+  pushState(state: unknown, _title: string, url?: string): void;
+};
+
+const installWindow = (href: string): HistoryStub => {
+  const url = new URL(href);
+  const history: HistoryStub = {
+    state: null,
+    lastURL: null,
+    replaceState(state, _title, url) {
+      this.state = state;
+      this.lastURL = url ?? null;
+    },
+    pushState(state, _title, url) {
+      this.state = state;
+      this.lastURL = url ?? null;
+    },
+  };
+  Object.defineProperty(globalThis, 'window', {
+    configurable: true,
+    value: {
+      location: {
+        href: url.toString(),
+        origin: url.origin,
+        pathname: url.pathname,
+        search: url.search,
+      },
+      history,
+    },
+  });
+  return history;
+};
+
+const historyOf = (): HistoryStub =>
+  (globalThis.window as unknown as { history: HistoryStub }).history;
+
+beforeEach(() => {
+  installWindow('http://127.0.0.1:5173/app');
+  resetEmbeddedSessionChatCache();
+});
+
+afterEach(() => {
+  Object.defineProperty(globalThis, 'window', {
+    configurable: true,
+    value: originalWindow,
+  });
+});
+
+afterAll(() => {
+  Object.defineProperty(globalThis, 'window', {
+    configurable: true,
+    value: originalWindow,
+  });
+});
+
+const sessionState = (sessionId: string): AppRouteState => ({
+  sessionId,
+  tab: 'chat',
+  isSettingsOpen: false,
+  settingsPath: '',
+  diffFile: null,
+});
+
+describe('updateBrowserURL embedded-session-chat guard', () => {
+  test('is a no-op in the embedded session-chat iframe (mirrors isVSCodeContext)', () => {
+    // The embedded iframe's URL identity (ocPanel/sessionId/directory/
+    // readOnly) must never be rewritten. updateBrowserURL rebuilds the
+    // query string from scratch using only session/tab/settings/file —
+    // which would strip ocPanel and break isEmbeddedSessionChat().
+    // The guard prevents this, exactly like isVSCodeContext() does for
+    // VS Code webviews.
+    const history = installWindow(
+      'http://127.0.0.1:5173/app?ocPanel=session-chat&sessionId=ses_child&directory=%2Frepo&readOnly=1',
+    );
+
+    updateBrowserURL(sessionState('ses_grandchild'), { replace: true, force: true });
+
+    // No URL update happened — history was never touched.
+    expect(history.lastURL).toBeNull();
+  });
+
+  test('rewrites the URL normally outside the embedded iframe', () => {
+    installWindow('http://127.0.0.1:5173/app');
+
+    updateBrowserURL(sessionState('ses_main'), { replace: true, force: true });
+
+    const writtenURL = historyOf().lastURL ?? '';
+    expect(writtenURL).toContain('session=ses_main');
+  });
+});
+
+describe('isEmbeddedSessionChat caching', () => {
+  test('caches the first result so URL rewrites cannot flip it (mirrors VS Code stable global)', () => {
+    // VS Code detects its webview via the stable `window.__VSCODE_CONFIG__`
+    // global — it never changes. The embedded iframe's identity is equally
+    // fixed at mount (the parent builds the src); caching the first read
+    // makes detection just as stable, surviving any URL rewrite.
+    //
+    // We need a fresh module cache for this test. Since the cache is
+    // module-level, we test the invariant: once true, always true.
+    installWindow(
+      'http://127.0.0.1:5173/app?ocPanel=session-chat&sessionId=ses_child&directory=%2Frepo&readOnly=1',
+    );
+
+    // First read: caches true.
+    expect(isEmbeddedSessionChat()).toBe(true);
+
+    // Even if the URL were rewritten (the guard above prevents this, but
+    // defense in depth), the cached value stays true.
+    installWindow('http://127.0.0.1:5173/app?session=ses_grandchild');
+    expect(isEmbeddedSessionChat()).toBe(true);
+  });
+});

packages/ui/src/lib/router/serializeRoute.ts

@@ -1,4 +1,5 @@
 import type { MainTab } from '@/stores/useUIStore';
+import { isEmbeddedSessionChat } from '@/components/layout/contextPanelEmbeddedChat';
 import { ROUTE_PARAMS } from './types';
 
 /**
@@ -100,7 +101,8 @@ function routeMatchesURL(state: AppRouteState): boolean {
 
 /**
  * Update the browser URL using pushState or replaceState.
- * Does nothing if URL already matches or in VS Code context.
+ * Does nothing if URL already matches, in VS Code context, or in the
+ * embedded session-chat iframe (whose URL identity is fixed at mount).
  */
 export function updateBrowserURL(
   state: AppRouteState,
@@ -110,8 +112,10 @@ export function updateBrowserURL(
     return;
   }
 
-  // Skip URL updates in VS Code webview
-  if (isVSCodeContext()) {
+  // Both VS Code webviews and embedded session-chat iframes carry session
+  // identity outside the route params (`__VSCODE_CONFIG__` / `?ocPanel=…`).
+  // Rebuilding the URL here would strip those params, so skip entirely.
+  if (isVSCodeContext() || isEmbeddedSessionChat()) {
     return;
   }