fix(places): phase links must stay in their own namespace

Every place page built its phase links as /schools/[slug]/[phase], the
shape that belongs to towns alone.

On an authority page that pointed into the town namespace. For 87 of the
151 authorities the target does not exist and the link 404s; for the
other 64 it resolves to the town of the same name — a different set of
schools, which is precisely the near-duplicate the two namespaces were
introduced to prevent. On an outcode page it 404s outright.

Two causes behind it, both a rule written twice and inherited by only
one of the places that needed it.

The authority phase route was in the spec and dropped by the plan, which
built the three bare routes and no fourth. The sitemap is generated from
the place registry, which was right about them all along, so 302
authority phase URLs have been submitted to Google and every one 404s.
Adding the route makes the sitemap true and serves a real query —
admissions are authority-run, so "primary schools in Kent" is how a
parent searches before they have settled on a town.

The outcode variants were the opposite: the registry computed phases for
outcodes although the spec gives them no route, and the sitemap knew to
skip them while the API did not. The registry now decides alone, and the
sitemap's duplicate of that rule is gone.

Also: an authority under the five-school threshold has no page, so the
API sends a null slug for it and the page names it without linking.
Two English authorities are in that position. It was unreachable in
today's data — verified across the EC and TR outcodes — but the thin
place redirect would have sent a reader to a 404 the year it isn't.

The e2e journey now walks every /schools link a page of each family
emits and requires a 200, which is the check that was missing.

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

nextjs-app/app/schools/[place]/page.tsx

@@ -74,9 +74,14 @@ export default async function PlacePage({ params }: Props) {
   // defers to its authority rather than publishing a thin page.
   if (detail.averages.rwm_expected_pct == null
       && detail.averages.attainment_8_score == null) {
-    if (detail.place.parent_authority) {
-      redirect(`/schools/authority/${authoritySlug(detail.place.parent_authority)}`);
-    }
+    // The API's own slug, which is null when that authority is itself under
+    // the threshold and has no page. Re-slugifying the name here would send
+    // the reader to a 404 instead of telling them the place has no page.
+    const target = detail.place.authorities?.[0]?.slug
+      ?? (detail.place.parent_authority
+        ? authoritySlug(detail.place.parent_authority)
+        : null);
+    if (target) redirect(`/schools/authority/${target}`);
     notFound();
   }
 

nextjs-app/app/schools/authority/[la]/[phase]/page.tsx

@@ -0,0 +1,65 @@
+/**
+ * Phase variants of an authority page.
+ *
+ * The spec called for these; the plan built the bare authority route and
+ * dropped them. Nothing caught it, because the sitemap is written from the
+ * place registry — which was right about them all along — while the routes
+ * were written by hand. 302 authority phase URLs were submitted to Google and
+ * every one 404'd, and every authority page linked to a phase page in the
+ * *town* namespace, which is a different set of schools entirely.
+ *
+ * "Primary schools in Kent" is the query these serve, and it is a real one:
+ * admissions are authority-run, so the authority is the unit a parent thinks
+ * in when they have not settled on a town.
+ */
+import { notFound } from 'next/navigation';
+import type { Metadata } from 'next';
+import { fetchPlace } from '@/lib/places';
+import { fetchNationalAverages } from '@/lib/api';
+import { PlaceView } from '@/components/places/PlaceView';
+import { absoluteUrl } from '@/lib/site';
+
+interface Props { params: Promise<{ la: string; phase: string }> }
+
+export const revalidate = 604800;
+export const dynamicParams = true;
+
+const PHASES = ['primary', 'secondary'] as const;
+type Phase = (typeof PHASES)[number];
+
+const isPhase = (v: string): v is Phase => (PHASES as readonly string[]).includes(v);
+
+export async function generateMetadata({ params }: Props): Promise<Metadata> {
+  const { la, phase } = await params;
+  if (!isPhase(phase)) return { title: 'Place Not Found' };
+  const detail = await fetchPlace('authority', la, phase);
+  if (!detail || detail.schools.length === 0) return { title: 'Place Not Found' };
+
+  const word = phase === 'secondary' ? 'Secondary' : 'Primary';
+  const { name } = detail.place;
+  return {
+    // "Local Authority" stays in the title for the same reason it is on the
+    // bare authority page: 67 town names collide with an authority name, and
+    // a reader landing on both needs to know which set each covers.
+    title: { absolute: `${word} Schools in ${name} — Local Authority | schoolcompare` },
+    description:
+      `Every ${phase} school in the ${name} local authority, with results, Ofsted `
+      + `grades and the authority average against England.`,
+    alternates: { canonical: absoluteUrl(`/schools/authority/${la}/${phase}`) },
+  };
+}
+
+export default async function AuthorityPhasePage({ params }: Props) {
+  const { la, phase } = await params;
+  if (!isPhase(phase)) notFound();
+  const detail = await fetchPlace('authority', la, phase);
+  if (!detail || detail.schools.length === 0) notFound();
+
+  const national = await fetchNationalAverages().catch(() => null);
+  const englandAverage = phase === 'secondary'
+    ? national?.secondary?.attainment_8_score ?? null
+    : national?.primary?.rwm_expected_pct ?? null;
+
+  return <PlaceView detail={detail} phase={phase}
+    englandAverage={englandAverage} neighbours={[]} />;
+}