feat(web): render durable session titles

packages/client/web/tests/document-title.spec.tsx

@@ -0,0 +1,28 @@
+// @vitest-environment jsdom
+import { afterEach, describe, expect, it } from 'vitest'
+import { cleanup, render } from '@testing-library/react'
+import { DocumentTitle } from '../src/DocumentTitle.tsx'
+
+afterEach(() => {
+  cleanup()
+  document.title = ''
+})
+
+describe('DocumentTitle', () => {
+  it('preserves the product title without a durable title and restores it on unmount', () => {
+    document.title = 'DeepSeek Harness'
+    const mounted = render(<DocumentTitle />)
+    expect(document.title).toBe('DeepSeek Harness')
+
+    mounted.rerender(<DocumentTitle title="First title" />)
+    expect(document.title).toBe('First title — DeepSeek Harness')
+
+    mounted.rerender(<DocumentTitle title="Revised title" />)
+    expect(document.title).toBe('Revised title — DeepSeek Harness')
+
+    mounted.rerender(<DocumentTitle />)
+    expect(document.title).toBe('DeepSeek Harness')
+    mounted.unmount()
+    expect(document.title).toBe('DeepSeek Harness')
+  })
+})