fix(compare): expert should-fixes S1-S4, S6 — banded chips, P8 reason, KS4 gap caption, all-through framing, cohort sizes

S1: first-choice chip banded (More than half / About 1 in 3 / Over 1 in 4
missed out) so a 44%-offered grammar isn't understated by half.
S2: Progress 8 explains its absence for 2024/25+ cohorts (no KS2 baseline,
COVID) instead of a bare 'No data'.
S3: KS4 trend charts get their own honest gap caption (2019/20-2020/21
unpublished; later years not in our dataset yet); y-axis 'Value'→'Score';
buildCompareChart exposes englandOnlyYears.
S4: all-through schools labelled in chips, rail caption says 'N schools ·
<phase> view' for mixed baskets, whole-school roll no longer judged
against the single-phase median, community section carries an all-ages
caveat.
S6 (spec §8.5): disadvantaged attainment shows the cohort behind it
('of ~50 disadvantaged pupils').

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB

nextjs-app/components/ComparisonChart.tsx

@@ -38,13 +38,15 @@ interface ComparisonChartProps {
   /** Official England figure per academic year for this metric — renders a
    * dashed grey reference line when provided. */
   nationalByYear?: Record<number, number | null | undefined>;
+  /** KS4 metrics get a different (honest) gap caption than KS2. */
+  isSecondary?: boolean;
 }
 
 // One shape per basket slot (MAX_SCHOOLS = 5) — secondary encoding so
 // converging lines stay tellable apart without relying on hue alone.
 const POINT_STYLES: PointStyle[] = ['circle', 'triangle', 'rect', 'rectRot', 'star'];
 
-export function ComparisonChart({ comparisonData, schools, metric, metricLabel, nationalByYear }: ComparisonChartProps) {
+export function ComparisonChart({ comparisonData, schools, metric, metricLabel, nationalByYear, isSecondary = false }: ComparisonChartProps) {
   const isMobile = useIsMobile();
   const [focusedUrn, setFocusedUrn] = useState<number | null>(null);
 
@@ -168,7 +170,7 @@ export function ComparisonChart({ comparisonData, schools, metric, metricLabel,
         display: true,
         title: {
           display: !isMobile,
-          text: kind === 'percentage' ? 'Percentage (%)' : kind === 'progress' ? 'Progress Score' : 'Value',
+          text: kind === 'percentage' ? 'Percentage (%)' : kind === 'progress' ? 'Progress Score' : 'Score',
           font: {
             size: 12,
             weight: 'bold',
@@ -240,11 +242,23 @@ export function ComparisonChart({ comparisonData, schools, metric, metricLabel,
       <div className={styles.canvasBox}>
         <Line data={chartData} options={options} aria-label={`${metricLabel} comparison chart`} />
       </div>
-      {built.showUnpublished202122Note && (
+      {isSecondary && built.englandOnlyYears.length > 0 ? (
+        // KS4's honest story differs from KS2's: 2019/20–2020/21 school-level
+        // GCSE results weren't published (COVID grading); later years WERE
+        // published by DfE but aren't in our dataset yet.
         <p className={styles.chartNote}>
-          No national tests were held in 2019/20 and 2020/21 (COVID), and DfE didn&apos;t publish
-          school-level figures for 2021/22 — the England average is shown for that year.
+          School-level GCSE figures for 2019/20 and 2020/21 weren&apos;t published (COVID
+          grading), and more recent years aren&apos;t in our dataset yet where lines break — the
+          England average is shown where available.
         </p>
+      ) : (
+        !isSecondary &&
+        built.showUnpublished202122Note && (
+          <p className={styles.chartNote}>
+            No national tests were held in 2019/20 and 2020/21 (COVID), and DfE didn&apos;t publish
+            school-level figures for 2021/22 — the England average is shown for that year.
+          </p>
+        )
       )}
     </div>
   );