test(e2e): make the distance journeys fail loudly, not skip quietly

The existing distance journeys all skip when no school has a published
figure, which is right when the feature is off — and wrong when it is
supposed to be on and is silently broken, because that shows up as a
green run full of skips. The new gate fails in exactly that case.

Feature state is read from the data, not from /api/flags: the public
proxy denies that path on purpose, since it names unreleased features.
Presence of the admission_distance key is the observable effect.

Verified against staging, where the feature is currently on: the on-gate
passes, the off-gate skips, the existing eight distance journeys are
unaffected.

One honest caveat — the /api/flags check passes on staging today because
that image predates the endpoint, not because the denylist works. The
denylist itself is covered by the jest unit test; this is defence in
depth and becomes a real assertion once deployed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015mWQnpye9F299NVRCCSRvj

e2e/tests/journeys.spec.ts

@@ -1226,6 +1226,27 @@ const CUTOFF_CANDIDATE_URNS = [
   101099, 100553, 102574, 100769,                 // mixed
 ];
 
+/**
+ * Whether the last-distance-offered feature is switched on here.
+ *
+ * Read from the data rather than from /api/flags, which the public proxy
+ * denies on purpose — the endpoint names unreleased features. The observable
+ * effect is the field's presence: the flag is off iff no candidate school
+ * carries an `admission_distance` key at all.
+ *
+ * The distinction that matters: `admission_distance: null` means this school
+ * has no published cut-off, and the key being ABSENT means cut-offs are not
+ * being published at all.
+ */
+async function distanceFeatureIsOn(page: Page): Promise<boolean> {
+  for (const urn of CUTOFF_CANDIDATE_URNS) {
+    const res = await page.request.get(`/api/schools/${urn}`);
+    if (!res.ok()) continue;
+    if ('admission_distance' in (await res.json())) return true;
+  }
+  return false;
+}
+
 async function schoolWithCutoff(page: Page) {
   for (const urn of CUTOFF_CANDIDATE_URNS) {
     const res = await page.request.get(`/api/schools/${urn}`);
@@ -1237,6 +1258,59 @@ async function schoolWithCutoff(page: Page) {
   return null;
 }
 
+test('when the distance feature is on, a school with a cut-off is findable', async ({ page }) => {
+  /*
+   * The gate that stops the other distance journeys passing vacuously.
+   *
+   * They all skip when schoolWithCutoff() finds nothing, which is right when
+   * the feature is off — but it means a feature that is *supposed* to be on
+   * and is silently broken shows up as a green run full of skips. This test
+   * fails in that case.
+   */
+  test.skip(!(await distanceFeatureIsOn(page)),
+    'the admission_distance flag is off in this environment');
+
+  expect(await schoolWithCutoff(page),
+    'the distance feature is on, but no candidate school has a cut-off — '
+    + 'the flag is on and the data or the query behind it is broken')
+    .not.toBeNull();
+});
+
+test('with the distance feature off, the section is absent rather than empty', async ({ page }) => {
+  // Shipping dark means the page renders as it did before the feature existed,
+  // not as a feature with its content removed.
+  test.skip(await distanceFeatureIsOn(page),
+    'the admission_distance flag is on in this environment');
+
+  // A school that exists, found rather than hardcoded — a 404 page would
+  // satisfy the absent-heading assertion without proving anything.
+  //
+  // A plain loop, not Array.find: find's predicate is synchronous, so an async
+  // one returns a Promise, every Promise is truthy, and it would always hand
+  // back the first URN whether or not that school exists.
+  let urn: number | null = null;
+  for (const candidate of CUTOFF_CANDIDATE_URNS) {
+    if ((await page.request.get(`/api/schools/${candidate}`)).ok()) {
+      urn = candidate;
+      break;
+    }
+  }
+  expect(urn, 'no candidate school resolves in this environment').not.toBeNull();
+
+  await page.goto(`/school/${urn}`);
+  await expect(page.locator('h1')).toBeVisible();
+
+  await expect(page.getByRole('heading', { name: /How far away are you\?/ }))
+    .toHaveCount(0);
+});
+
+test('/api/flags is not reachable from the public internet', async ({ page }) => {
+  // It names every unreleased feature and whether it is on. Next reads it
+  // server-side over the Docker network; the public proxy must deny it.
+  const res = await page.request.get('/api/flags');
+  expect(res.status()).toBe(404);
+});
+
 test('a published cut-off distance is shown with the year it belongs to', async ({ page }) => {
   const found = await schoolWithCutoff(page);
   test.skip(found === null, 'no school in the sample has a published cut-off distance yet');