fix(search): stop replaying a failed LA-averages request forever

The search page fetched LA averages with cache: 'force-cache', which serves
any stored response, however old, without asking the server. One failed
request (a staging deploy restart; the July proxy outage) was stored and
replayed on every later visit, and the error was swallowed, so the
"vs LA avg" delta silently vanished from every secondary row in that
browser. A Playwright profile still held a 500 dated 5 July.

The default cache mode honours the API's Cache-Control (five minutes), so
a good answer is still reused and an error never is. Browsers holding a
stored failure recover on their next visit.

A journey now checks that a mainstream secondary's row shows the
comparison: nothing did, which is how it could go missing unnoticed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

e2e/tests/journeys.spec.ts

@@ -410,6 +410,29 @@ test('search and the school page agree on how many pupils a secondary has', asyn
   expect(school.total_pupils).toBe(detail.school_info.total_pupils);
 });
 
+test('a secondary search row compares its Attainment 8 with the LA average', async ({ page }) => {
+  // The comparison vanished unnoticed: the averages were fetched with
+  // force-cache, so one stored failure hid it in that browser for good.
+  // Playwright disables the HTTP cache when it intercepts requests, so this
+  // guards the comparison itself; the unit test pins the cache mode.
+  const la = await (await page.request.get('/api/la-averages')).json();
+  const averages: Record<string, number> = la.secondary?.attainment_8_by_la ?? {};
+  const res = await page.request.get('/api/schools?search=school&phase=secondary&page_size=50');
+  expect(res.ok()).toBeTruthy();
+  const school = ((await res.json()).schools ?? []).find(
+    (s: { attainment_8_score?: number | null; local_authority?: string; school_type?: string }) =>
+      s.attainment_8_score != null && s.local_authority != null && averages[s.local_authority] != null
+      && !/special|pupil referral|alternative provision/i.test(s.school_type ?? ''));
+  test.skip(!school, 'no mainstream secondary with an LA average here');
+
+  await searchByName(page, school.school_name);
+  const link = page.locator(`a[href^="/school/${school.urn}-"]`).first();
+  await expect(link).toBeVisible({ timeout: 15_000 });
+  const stats = link.locator('xpath=ancestor::div[contains(@class, "__rowContent")][1]')
+    .locator('[class*="__line3"]');
+  await expect(stats.getByText(/vs LA avg/)).toBeVisible();
+});
+
 test('a phase outside primary/secondary filters to that phase, not to everything', async ({ page }) => {
   // The search page offers every GIAS phase, but the API only knew the grouped
   // ones and silently dropped the rest — so "Nursery" returned primaries.