fix(places): submit and link the phase variants

/schools/[place]/[phase] shipped as routes but reached nothing. The sitemap
emitted one URL per registry entry and the registry had no phase dimension, so
~950 pages were absent from every sitemap — and PlaceView did not link them
either, leaving them reachable by nothing at all.

That is the query shape the baseline actually showed: 'primary schools in
beccles', 'secondary schools in brentwood'. Publishing the routes without a
path in meant building for the demand and then hiding from it.

Place now carries phase_urns so the per-phase threshold can be applied without
re-querying, the sitemap emits a variant wherever a phase clears the threshold
on its own, and the API exposes the qualifying phases so the place page links
only variants that exist. Outcodes are excluded: nobody searches 'primary
schools in SW11' and those routes do not exist.

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

nextjs-app/__tests__/components/PlaceView.test.tsx

@@ -4,7 +4,7 @@ import type { PlaceDetail } from '@/lib/places';
 
 const detail: PlaceDetail = {
   place: { kind: 'town', slug: 'brentwood', name: 'Brentwood', count: 29,
-           parent_authority: 'Essex' },
+           parent_authority: 'Essex', phases: ['primary'] },
   schools: [
     { urn: 1, school_name: 'Alpha Primary', rwm_expected_pct: 82,
       ofsted_grade: 1 } as never,
@@ -91,3 +91,24 @@ describe('PlaceView structured data', () => {
     }
   });
 });
+
+describe('PlaceView phase variants', () => {
+  it('links the phase variants that exist', () => {
+    render(<PlaceView detail={detail} englandAverage={61} neighbours={[]} />);
+    expect(screen.getByRole('link', { name: /Primary schools in Brentwood/i }))
+      .toHaveAttribute('href', '/schools/brentwood/primary');
+  });
+
+  it('links no variant for a phase below its own threshold', () => {
+    render(<PlaceView detail={detail} englandAverage={61} neighbours={[]} />);
+    expect(screen.queryByRole('link', { name: /Secondary schools in Brentwood/i }))
+      .not.toBeInTheDocument();
+  });
+
+  it('does not link sideways from a variant page to itself', () => {
+    render(<PlaceView detail={detail} phase="primary" englandAverage={61}
+      neighbours={[]} />);
+    expect(screen.queryByRole('link', { name: /Primary schools in Brentwood/i }))
+      .not.toBeInTheDocument();
+  });
+});

nextjs-app/components/places/PlaceView.module.css

@@ -106,3 +106,13 @@
   padding: 0;
   margin: 0;
 }
+
+/* Phase variants are separate indexable pages, so the bare place page has to
+   link them — a sitemap entry alone leaves them with no internal path in. */
+.phaseLinks {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.5rem 1rem;
+  margin: 0 0 1.25rem;
+  font-size: 0.9375rem;
+}

nextjs-app/components/places/PlaceView.tsx

@@ -89,6 +89,16 @@ export function PlaceView({ detail, phase, englandAverage, neighbours }: Props)
         </p>
       </header>
 
+      {!phase && (place.phases ?? []).length > 0 && (
+        <nav className={styles.phaseLinks} aria-label="By phase">
+          {(place.phases ?? []).map((ph) => (
+            <Link key={ph} href={`/schools/${place.slug}/${ph}`}>
+              {ph === 'secondary' ? 'Secondary schools' : 'Primary schools'} in {place.name}
+            </Link>
+          ))}
+        </nav>
+      )}
+
       {local != null && englandAverage != null && (
         <p className={styles.compare} data-testid="local-vs-england">
           {place.name} averages <strong>{Math.round(local)}</strong> against{' '}

nextjs-app/lib/places.ts

@@ -13,6 +13,9 @@ export interface PlaceSummary {
   slug: string;
   name: string;
   count: number;
+  /** Phases that clear the threshold on their own, so the page links
+   *  variants that exist rather than 404s. Absent on the registry listing. */
+  phases?: string[];
 }
 
 export interface PlaceDetail {