fix(destinations): the table said 'withheld' for a category that just doesn't apply

The Share column keyed off `percentage === null`, which is true for
not_applicable as well as suppressed, so a destination that does not apply
to the school was labelled as one DfE withheld — while the Pupils column
in the same row rendered blank. Two columns, one row, disagreeing about
what the row was, and one of them making a claim about DfE that wasn't
true.

Both columns now derive from `status`, which is the distinction the mart,
the SQLAlchemy model and the serialiser all preserve deliberately:
published shows the figure, suppressed shows the withheld badge,
not_applicable shows an em-dash with a title saying so.

A published count with no published percentage now derives its share from
the cohort rather than falling through to a marker — both halves are
published, so nothing withheld is involved, and it is the same derivation
the bar widths already use.

Verified the new tests fail against the old logic before keeping them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BvdDKvFFSZuMVDH5fEyTob

nextjs-app/components/school/DestinationsView.tsx

@@ -47,6 +47,44 @@ function cellsFor(group: DestinationGroup, card: CardGroup): DestinationCell[] {
   return group.cells.filter(c => wanted.has(c.category));
 }
 
+/**
+ * One cell of the detail table.
+ *
+ * The three statuses are three different statements and the table has to keep
+ * them apart, because the whole pipeline does — the mart, the SQLAlchemy model
+ * and the serialiser all preserve the difference deliberately:
+ *
+ *   published      the figure
+ *   suppressed     DfE withheld it to protect a small number of pupils
+ *   not_applicable this destination does not apply to this school at all
+ *
+ * An earlier version keyed the share column off `percentage === null`, which is
+ * also true for not_applicable, so a category that simply does not apply was
+ * labelled "withheld" — while the pupils column beside it rendered blank. Both
+ * columns now derive from `status`, so they cannot disagree.
+ */
+function cellValue(
+  cell: DestinationCell, cohort: number, kind: 'pupils' | 'share',
+) {
+  if (cell.status === 'suppressed') {
+    return <span className={styles.withheldMark}>withheld</span>;
+  }
+  const notApplicable = (
+    <span className={styles.notApplicable} title="Does not apply to this school">
+      &mdash;
+    </span>
+  );
+
+  if (cell.status !== 'published' || cell.pupils === null) return notApplicable;
+  if (kind === 'pupils') return cell.pupils;
+
+  // Percentages come from the mart, but a published count with no published
+  // percentage is recoverable from the cohort — both halves are published, so
+  // nothing withheld is involved. Same derivation the bar widths use.
+  const share = cell.percentage ?? (cohort > 0 ? (cell.pupils / cohort) * 100 : null);
+  return share === null ? notApplicable : `${Math.round(share)}%`;
+}
+
 export function DestinationsView({
   destinations, phase,
 }: { destinations: DestinationPhase; phase: 'ks4' | 'ks5' }) {
@@ -193,27 +231,19 @@ export function DestinationsView({
               const cell = group.cells.find(c => c.category === category);
               if (!cell) return [];
               const card = cardGroupFor(category);
-              const isWithheld = cell.status === 'suppressed';
               return [(
                 <tr
                   key={category}
                   data-group={card ?? 'none'}
+                  data-status={cell.status}
                   className={dimmed(card) ? styles.dim : ''}
                 >
                   <th scope="row" className={styles.rowName}>
                     <span className={`${styles.swatch} ${styles[category]}`} />
                     {CATEGORY_LABELS[category]}
                   </th>
-                  <td>
-                    {isWithheld
-                      ? <span className={styles.withheldMark}>withheld</span>
-                      : cell.pupils}
-                  </td>
-                  <td>
-                    {isWithheld || cell.percentage === null
-                      ? <span className={styles.withheldMark}>withheld</span>
-                      : `${Math.round(cell.percentage)}%`}
-                  </td>
+                  <td>{cellValue(cell, group.cohort, 'pupils')}</td>
+                  <td>{cellValue(cell, group.cohort, 'share')}</td>
                 </tr>
               )];
             })}