test(examples-chat): add url-routing e2e for knob query params

Four scenarios:
1. Deep-link /embed/<thread-id> loads the thread without resending.
2. /embed?model=gpt-5-nano sets the model picker via URL hydration.
3. Mode switch preserves both /embed/<id> path and ?model= query.
4. Ephemeral hydration: /embed?theme=material-dark does NOT write
   theme to localStorage (URL hydrates signal but not storage).

Author: blove

examples/chat/angular/e2e/url-routing.spec.ts

@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: MIT
+import { test, expect } from '@playwright/test';
+import {
+  activeThreadIdFromUrl,
+  messageInput,
+  openDemo,
+  sendButton,
+  waitForFinalAssistant,
+} from './test-helpers';
+
+test('url routing: deep-link with thread id loads that thread', async ({ page }) => {
+  // Bootstrap: create a thread by sending one message.
+  await openDemo(page, '/embed');
+  await messageInput(page).fill('say hi briefly');
+  await sendButton(page).click();
+  await waitForFinalAssistant(page);
+
+  await expect(page).toHaveURL(/\/embed\/[A-Za-z0-9-]+$/);
+  const threadId = await activeThreadIdFromUrl(page);
+  expect(threadId).toBeTruthy();
+
+  // Reload via direct navigation to /embed/<id> — assert the existing
+  // assistant message renders without resending the prompt.
+  await page.goto(`/embed/${threadId}`);
+  await expect(page.locator('chat-message[data-role="assistant"]')).toContainText(/hi/i, {
+    timeout: 30_000,
+  });
+});
+
+test('url routing: deep-link with knob param sets the picker', async ({ page }) => {
+  await openDemo(page, '/embed?model=gpt-5-nano');
+
+  // The model toolbar trigger surfaces the current model. Confirm the URL
+  // value won, not the default.
+  const modelTrigger = page.locator('.demo-shell__field[data-field="model"] .chat-select__trigger');
+  await expect(modelTrigger).toContainText('gpt-5-nano');
+});
+
+test('url routing: mode switch preserves thread + knob params', async ({ page }) => {
+  // Bootstrap: thread + non-default knob.
+  await openDemo(page, '/embed');
+  await messageInput(page).fill('say hi briefly');
+  await sendButton(page).click();
+  await waitForFinalAssistant(page);
+  const threadId = await activeThreadIdFromUrl(page);
+  expect(threadId).toBeTruthy();
+
+  // Set a non-default model via the toolbar.
+  const modelTrigger = page.locator('.demo-shell__field[data-field="model"] .chat-select__trigger');
+  await modelTrigger.click();
+  await page.locator('.chat-select__option', { hasText: 'gpt-5-nano' }).first().click();
+  await expect(page).toHaveURL(/[?&]model=gpt-5-nano/);
+
+  // Click Popup mode in the segmented control.
+  await page.locator('.demo-shell__segmented-button', { hasText: 'Popup' }).click();
+
+  // URL holds both thread + knob param.
+  await expect(page).toHaveURL(new RegExp(`/popup/${threadId}(\\?|\\?.*&)model=gpt-5-nano`));
+});
+
+test('url routing: ephemeral hydration does not write to localStorage', async ({ page }) => {
+  // Visit with a non-default theme in the URL.
+  await openDemo(page, '/embed?theme=material-dark');
+
+  // openDemo clears localStorage before the test starts; assert it's
+  // still clean (no `theme: 'material-dark'` written by hydration).
+  const stored = await page.evaluate(() => {
+    const raw = localStorage.getItem('ngaf-chat-demo:palette');
+    return raw ? (JSON.parse(raw) as { theme?: string }).theme : null;
+  });
+  expect(stored).toBeNull();
+});