Verify physical reading stability through background completion (U5)

Why: Retained React nodes alone did not prove actual browser scrolling was preserved.

Evidence: The settled Chromium case failed on the previous bundle, then all 11 browser cases passed with exact material, scroll and focus assertions.

Impact: Browser regression coverage only; fixture transport stays outside the production bundle.

Refs: UI10, ce-code-review UI finding #3, work-companion-ui

e2e/work-companion.playwright.ts

@@ -125,6 +125,41 @@ test('keeps one expanded ordinary summary when the desktop work pane opens', asy
   expect(state.errors).toEqual([])
 })
 
+test('preserves the selected material, physical scroll and focus when background work finishes', async ({ page }) => {
+  await page.setViewportSize({ width: 1440, height: 960 })
+  const tabbed = work('work1', 'active', { body: [...progress.body!, {
+    type: 'tabs', id: 'materials', tabs: { tabs: [
+      { id: 'first', label: '第一份材料', nodes: [{ type: 'markdown', markdown: '第一份材料的范围' }] },
+      { id: 'second', label: '第二份材料', nodes: [{ type: 'markdown', markdown: Array.from({ length: 70 }, (_, i) => `待核对事项 ${i + 1}`).join('\n\n') }] },
+    ] },
+  }] })
+  const state = await fixture(page, [tabbed, work('peer', 'active', { body: [] })])
+  await page.getByRole('button', { name: '打开工作', exact: true }).click()
+  const card = page.locator('.right-panel [data-card-id="work1"]')
+  await card.getByRole('button', { name: '查看依据与范围', exact: true }).click()
+  const tab = card.getByRole('tab', { name: '第二份材料', exact: true })
+  await tab.click()
+  await tab.focus()
+  const details = card.locator('.acard-detail-body')
+  await expect.poll(() => details.evaluate(element => element.clientHeight)).toBe(420)
+  const physical = await details.evaluate(element => {
+    Object.assign(window, { __workReading: element })
+    element.scrollTop = 137
+    return { height: element.clientHeight, scrollHeight: element.scrollHeight, top: element.scrollTop }
+  })
+  expect(physical.scrollHeight).toBeGreaterThan(physical.height)
+  expect(physical.top).toBe(137)
+  await state.emit('card.status', { cardId: 'work1', status: 'done' }, 12)
+  await expect(card.locator('.acard-status')).toHaveText('已完成')
+  await expect(tab).toHaveAttribute('aria-selected', 'true')
+  expect(await details.evaluate(element => ({
+    retained: (window as typeof window & { __workReading: Element }).__workReading === element,
+    top: element.scrollTop,
+  }))).toEqual({ retained: true, top: 137 })
+  expect(await tab.evaluate(element => document.activeElement === element)).toBe(true)
+  expect(state.errors).toEqual([])
+})
+
 test('shares submitting feedback between conversation and work confirmations', async ({ page }) => {
   const state = await fixture(page, [confirmation])
   await page.getByRole('button', { name: '打开工作', exact: true }).click()