test(e2e): cover the detail page server/client boundary

Two journeys for what the split actually changed: the admissions toggle (the
one client island inside an otherwise server-rendered section) and the sticky
nav resolving to server-rendered sections. The nav is client-rendered from a
server-computed list while the sections render on the server, so a mismatch
between the two halves would only show up in a real browser.

Existing journeys already cover all-through and special-school pages.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

e2e/tests/journeys.spec.ts

@@ -556,3 +556,73 @@ test('compare metric-help popover stays within the mobile viewport', async ({ pa
     .evaluate((el) => el.scrollWidth > el.clientWidth + 1);
   expect(bodyOverflowsX).toBe(false);
 });
+
+/**
+ * The following two journeys cover the server/client split of the detail page.
+ * The sections are now React Server Components composed in the route and passed
+ * through a client shell; these assert that the two halves still meet correctly
+ * in a real browser, which no unit test can prove.
+ */
+
+test('admissions year/trend toggle still switches views after the server/client split', async ({ page }) => {
+  // Find a school with at least two years carrying an offer rate — the toggle
+  // only appears then. Data-invariant: uses whatever the environment holds.
+  const res = await page.request.get('/api/schools?search=primary&per_page=50');
+  expect(res.ok()).toBeTruthy();
+  const candidates: number[] = ((await res.json()).schools ?? []).map((s: { urn: number }) => s.urn);
+
+  let target: number | null = null;
+  for (const urn of candidates.slice(0, 12)) {
+    const detail = await page.request.get(`/api/schools/${urn}`);
+    if (!detail.ok()) continue;
+    const history = (await detail.json()).admissions_history ?? [];
+    const withRate = history.filter(
+      (h: { first_preference_offer_pct?: number | null }) => h.first_preference_offer_pct != null,
+    );
+    if (withRate.length >= 2) { target = urn; break; }
+  }
+  test.skip(target === null, 'no school in this environment has 2+ years of admissions offer data');
+
+  await page.goto(`/school/${target}`);
+  await expect(page.locator('#admissions')).toBeVisible({ timeout: 15_000 });
+
+  const yearBtn = page.getByRole('button', { name: 'This year' });
+  const trendBtn = page.getByRole('button', { name: /-year trend$/ });
+  await expect(yearBtn).toHaveAttribute('aria-pressed', 'true');
+
+  // The toggle is the one client island inside an otherwise server-rendered
+  // section: clicking it must swap the two server-rendered views.
+  await trendBtn.click();
+  await expect(trendBtn).toHaveAttribute('aria-pressed', 'true');
+  await expect(yearBtn).toHaveAttribute('aria-pressed', 'false');
+
+  await yearBtn.click();
+  await expect(yearBtn).toHaveAttribute('aria-pressed', 'true');
+});
+
+test('sticky section nav jumps to server-rendered sections', async ({ page }) => {
+  const [urn] = await twoPrimaryUrns(page);
+  await page.goto(`/school/${urn}`);
+  await expect(page.locator('h1').first()).toBeVisible({ timeout: 15_000 });
+
+  // The nav is client-rendered from a server-computed list, while the sections
+  // themselves are server-rendered. Every link must resolve to a real section:
+  // the scroll-spy finds them with document.getElementById, so a mismatch
+  // between the two halves would dead-end here.
+  const navLinks = page.locator('nav a[href^="#"]');
+  const count = await navLinks.count();
+  expect(count).toBeGreaterThan(0);
+
+  for (let i = 0; i < count; i++) {
+    const href = await navLinks.nth(i).getAttribute('href');
+    expect(href).toBeTruthy();
+    await expect(page.locator(href!)).toHaveCount(1);
+  }
+
+  // And following one actually moves the page.
+  const before = await page.evaluate(() => window.scrollY);
+  await navLinks.last().click();
+  await page.waitForTimeout(600);
+  const after = await page.evaluate(() => window.scrollY);
+  expect(after).toBeGreaterThan(before);
+});