fix(e2e): pick the latest explicit year in the rankings year test

Staging doesn't always carry the full data history, so selecting the
oldest year legitimately returns no rows and fails the promotion gate.
Select the most recent explicit year instead: the default view already
proved it has rows, so an empty table after selecting it can only mean
the year query param was rejected — the regression this test guards.

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

backend/app.py

@@ -834,7 +834,10 @@ async def get_rankings(
     request: Request,
     metric: str = Query("rwm_expected_pct", description="Metric to rank by", max_length=50),
     year: Optional[int] = Query(
-        None, description="Specific year (defaults to most recent)", ge=2000, le=2100
+        None,
+        description="Academic year code, e.g. 201819 (defaults to most recent)",
+        ge=2000,
+        le=210100,
     ),
     limit: int = Query(20, ge=1, le=100, description="Number of schools to return"),
     local_authority: Optional[str] = Query(

e2e/tests/journeys.spec.ts

@@ -73,3 +73,24 @@ test('rankings page loads a populated table', async ({ page }) => {
   await expect(rows.first()).toBeVisible({ timeout: 15_000 });
   expect(await rows.count()).toBeGreaterThan(5);
 });
+
+test('rankings stay populated after picking a specific year', async ({ page }) => {
+  // Years are academic-year codes (e.g. 201819); the API must accept them
+  // as the `year` query param rather than rejecting with a 422.
+  await page.goto('/rankings');
+  const yearSelect = page.locator('#year-select');
+  await expect(yearSelect).toBeVisible({ timeout: 15_000 });
+
+  // Pick the last option — the most recent explicit year. The default view
+  // already proved this year has rows, so an empty table after selecting it
+  // can only mean the year param was rejected. (The oldest year is no good
+  // here: staging doesn't always carry the full data history.)
+  const yearValue = await yearSelect.locator('option').last().getAttribute('value');
+  expect(yearValue).toBeTruthy();
+  await yearSelect.selectOption(yearValue!);
+  await page.waitForURL(/year=/);
+
+  const rows = page.locator('table tbody tr');
+  await expect(rows.first()).toBeVisible({ timeout: 15_000 });
+  expect(await rows.count()).toBeGreaterThan(5);
+});