feat(admissions): surface multi-year admissions trend on school detail

The school detail page only showed the latest admissions year. We store
every year, which is more decision-relevant for parents (the trend and its
consistency matter more than a single noisy year).

Backend now returns the full admissions_history (oldest first) alongside the
existing latest-year object. The primary SchoolDetailView gains a header
toggle ("This year | N-year trend") that swaps the Q&A for an SVG sparkline
of the first-choice offer rate. The toggle only appears when >=2 years carry
an offer rate; otherwise it falls back to the single-year card. Both views
share one CSS-grid cell so switching causes no layout shift.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nextjs-app/components/SchoolDetailView.tsx

@@ -58,6 +58,62 @@ function progressClass(val: number | null | undefined): string {
   return '';
 }
 
+/**
+ * Compact SVG sparkline of the first-choice offer rate across admissions years.
+ * Renders nothing unless at least two years carry an offer-rate value.
+ */
+function OfferRateTrend({ history }: { history: SchoolAdmissions[] }) {
+  const pts = history
+    .filter((h) => h.first_preference_offer_pct != null)
+    .map((h) => ({ year: h.year, v: h.first_preference_offer_pct as number }));
+  if (pts.length < 2) return null;
+
+  const W = 520, H = 118;
+  const padL = 44, padR = 20, padT = 16, padB = 34;
+  const plotW = W - padL - padR, plotH = H - padT - padB;
+
+  const values = pts.map((p) => p.v);
+  let lo = Math.max(0, Math.floor(Math.min(...values) / 10) * 10);
+  let hi = Math.min(100, Math.ceil(Math.max(...values) / 10) * 10);
+  // Guarantee a minimum span so small year-to-year moves aren't exaggerated.
+  if (hi - lo < 30) {
+    hi = Math.min(100, lo + 30);
+    if (hi - lo < 30) lo = Math.max(0, hi - 30);
+  }
+
+  const x = (i: number) => padL + (plotW * i) / (pts.length - 1);
+  const y = (v: number) => padT + plotH * (1 - (v - lo) / (hi - lo));
+  const gridVals = [hi, Math.round((hi + lo) / 2), lo];
+  const polyline = pts.map((p, i) => `${x(i)},${y(p.v)}`).join(' ');
+
+  return (
+    <svg
+      className={styles.admissionsChart}
+      viewBox={`0 0 ${W} ${H}`}
+      role="img"
+      aria-label={`First-choice offer rate from ${formatAcademicYear(pts[0].year)} to ${formatAcademicYear(pts[pts.length - 1].year)}`}
+    >
+      {gridVals.map((gv) => (
+        <g key={gv}>
+          <line x1={padL} y1={y(gv)} x2={W - padR} y2={y(gv)} className={styles.admissionsGrid} />
+          <text x={padL - 8} y={y(gv) + 4} textAnchor="end" className={styles.admissionsAxis}>{gv}%</text>
+        </g>
+      ))}
+      <polyline points={polyline} fill="none" className={styles.admissionsLine} strokeLinecap="round" strokeLinejoin="round" />
+      {pts.map((p, i) => {
+        const isLast = i === pts.length - 1;
+        return (
+          <g key={p.year}>
+            <circle cx={x(i)} cy={y(p.v)} r={isLast ? 6 : 5} className={isLast ? styles.admissionsDotLast : styles.admissionsDot} />
+            <text x={x(i)} y={y(p.v) - 9} textAnchor="middle" className={styles.admissionsPtLabel} data-last={isLast}>{Math.round(p.v)}%</text>
+            <text x={x(i)} y={H - 12} textAnchor="middle" className={styles.admissionsAxis}>{formatAcademicYear(p.year)}</text>
+          </g>
+        );
+      })}
+    </svg>
+  );
+}
+
 interface SchoolDetailViewProps {
   schoolInfo: School;
   yearlyData: SchoolResult[];
@@ -66,6 +122,7 @@ interface SchoolDetailViewProps {
   parentView: OfstedParentView | null;
   census: SchoolCensus | null;
   admissions: SchoolAdmissions | null;
+  admissionsHistory: SchoolAdmissions[];
   senDetail: SenDetail | null;
   phonics: Phonics | null;
   deprivation: SchoolDeprivation | null;
@@ -74,13 +131,17 @@ interface SchoolDetailViewProps {
 
 export function SchoolDetailView({
   schoolInfo, yearlyData, absenceData,
-  ofsted, parentView, census, admissions, senDetail, phonics, deprivation, finance,
+  ofsted, parentView, census, admissions, admissionsHistory, senDetail, phonics, deprivation, finance,
 }: SchoolDetailViewProps) {
   const router = useRouter();
   const { addSchool, removeSchool, isSelected } = useComparison();
   const isInComparison = isSelected(schoolInfo.urn);
 
   const [activeSection, setActiveSection] = useState<string>('');
+  const [admissionsView, setAdmissionsView] = useState<'year' | 'trend'>('year');
+  // Trend toggle only appears with ≥2 years carrying an offer rate.
+  const admissionsOfferYears = admissionsHistory.filter((h) => h.first_preference_offer_pct != null).length;
+  const showAdmissionsTrend = admissionsOfferYears >= 2;
   const sectionNavRef = useRef<HTMLElement | null>(null);
   const [sectionNavAtEnd, setSectionNavAtEnd] = useState(false);
 
@@ -880,60 +941,80 @@ export function SchoolDetailView({
       {/* How Hard to Get In */}
       {admissions && (
         <section id="admissions" className={styles.card}>
-          <h2 className={styles.sectionTitle}>How Hard to Get Into This School ({formatAcademicYear(admissions.year)})</h2>
+          <div className={styles.admissionsHeader}>
+            <h2 className={styles.sectionTitle}>
+              How Hard to Get Into This School{!showAdmissionsTrend && ` (${formatAcademicYear(admissions.year)})`}
+            </h2>
+            {showAdmissionsTrend && (
+              <div className={styles.admissionsSeg} role="group" aria-label="Admissions view">
+                <button type="button" aria-pressed={admissionsView === 'year'} onClick={() => setAdmissionsView('year')}>
+                  This year
+                </button>
+                <button type="button" aria-pressed={admissionsView === 'trend'} onClick={() => setAdmissionsView('trend')}>
+                  {admissionsHistory.length}-year trend
+                </button>
+              </div>
+            )}
+          </div>
 
-          {admissions.oversubscribed != null && (
-            <div className={styles.admissionsVerdict}>
-              <div className={styles.admissionsVerdictHeadline}>
-                This school is{' '}
-                <span className={admissions.oversubscribed ? styles.admissionsVerdictOver : styles.admissionsVerdictUnder}>
-                  {admissions.oversubscribed ? 'oversubscribed' : 'not oversubscribed'}
-                </span>
-                .
-              </div>
-              <div className={styles.admissionsVerdictSub}>
-                {admissions.oversubscribed ? 'Demand exceeds capacity.' : 'Supply meets demand.'}
-              </div>
+          <div className={styles.admissionsViewport}>
+            {/* This-year Q&A */}
+            <div className={styles.admissionsViewYear} hidden={showAdmissionsTrend && admissionsView !== 'year'}>
+              <dl className={styles.admissionsQa}>
+                {admissions.places_offered != null && (
+                  <div className={styles.admissionsQaRow}>
+                    <dt className={styles.admissionsQaQuestion}>How many places were offered?</dt>
+                    <dd className={styles.admissionsQaAnswer}>{admissions.places_offered}</dd>
+                  </div>
+                )}
+                {admissions.first_preference_applications != null && (
+                  <div className={styles.admissionsQaRow}>
+                    <dt className={styles.admissionsQaQuestion}>How many families wanted this school first?</dt>
+                    <dd className={styles.admissionsQaAnswer}>{admissions.first_preference_applications}</dd>
+                  </div>
+                )}
+                {admissions.first_preference_offer_pct != null && (
+                  <div className={styles.admissionsQaRow}>
+                    <dt className={styles.admissionsQaQuestion}>How many got their first choice?</dt>
+                    <dd className={styles.admissionsQaAnswer}>
+                      {admissions.first_preference_offers != null && admissions.first_preference_applications != null ? (
+                        <>
+                          {admissions.first_preference_offers}
+                          <span className={styles.admissionsQaAnswerSub}>
+                            of {admissions.first_preference_applications} ({formatPercentage(admissions.first_preference_offer_pct)})
+                          </span>
+                        </>
+                      ) : (
+                        formatPercentage(admissions.first_preference_offer_pct)
+                      )}
+                    </dd>
+                  </div>
+                )}
+                {admissions.total_applications != null && (
+                  <div className={styles.admissionsQaRow}>
+                    <dt className={styles.admissionsQaQuestion}>How many applied in total?</dt>
+                    <dd className={styles.admissionsQaAnswer}>{admissions.total_applications.toLocaleString()}</dd>
+                  </div>
+                )}
+              </dl>
             </div>
-          )}
 
-          <dl className={styles.admissionsQa}>
-            {admissions.places_offered != null && (
-              <div className={styles.admissionsQaRow}>
-                <dt className={styles.admissionsQaQuestion}>How many places were offered?</dt>
-                <dd className={styles.admissionsQaAnswer}>{admissions.places_offered}</dd>
-              </div>
-            )}
-            {admissions.first_preference_applications != null && (
-              <div className={styles.admissionsQaRow}>
-                <dt className={styles.admissionsQaQuestion}>How many families wanted this school first?</dt>
-                <dd className={styles.admissionsQaAnswer}>{admissions.first_preference_applications}</dd>
-              </div>
-            )}
-            {admissions.first_preference_offer_pct != null && (
-              <div className={styles.admissionsQaRow}>
-                <dt className={styles.admissionsQaQuestion}>How many got their first choice?</dt>
-                <dd className={styles.admissionsQaAnswer}>
-                  {admissions.first_preference_offers != null && admissions.first_preference_applications != null ? (
-                    <>
-                      {admissions.first_preference_offers}
-                      <span className={styles.admissionsQaAnswerSub}>
-                        of {admissions.first_preference_applications} ({formatPercentage(admissions.first_preference_offer_pct)})
-                      </span>
-                    </>
-                  ) : (
-                    formatPercentage(admissions.first_preference_offer_pct)
+            {/* Multi-year trend */}
+            {showAdmissionsTrend && (
+              <div className={styles.admissionsViewTrend} hidden={admissionsView !== 'trend'}>
+                <div className={styles.admissionsChartCap}>First-choice offer rate</div>
+                <OfferRateTrend history={admissionsHistory} />
+                <p className={styles.admissionsTrendSummary}>
+                  This year ({formatAcademicYear(admissions.year)}),{' '}
+                  {admissions.first_preference_applications != null && (
+                    <><strong>{admissions.first_preference_applications}</strong> families put it first for </>
                   )}
-                </dd>
+                  {admissions.places_offered != null && <><strong>{admissions.places_offered}</strong> places</>}
+                  {admissions.total_applications != null && ` — ${admissions.total_applications.toLocaleString()} applications in total`}.
+                </p>
               </div>
             )}
-            {admissions.total_applications != null && (
-              <div className={styles.admissionsQaRow}>
-                <dt className={styles.admissionsQaQuestion}>How many applied in total?</dt>
-                <dd className={styles.admissionsQaAnswer}>{admissions.total_applications.toLocaleString()}</dd>
-              </div>
-            )}
-          </dl>
+          </div>
         </section>
       )}