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/__tests__/components/DestinationsSection.test.tsx

@@ -89,3 +89,61 @@ describe('DestinationsSection', () => {
     expect(container.firstChild).toBeNull();
   });
 });
+
+describe('the detail table keeps the three statuses apart', () => {
+  // 'suppressed' and 'not_applicable' are different claims, and the mart, the
+  // SQLAlchemy model and the serialiser all preserve the difference. The table
+  // used to key its Share column off `percentage === null`, which is true for
+  // both, so a category that simply does not apply was labelled "withheld" —
+  // while the Pupils column beside it rendered blank.
+  const mixedPhase: DestinationPhase = {
+    cohort_year: '2022/23',
+    groups: {
+      all: {
+        cohort: 180,
+        categories: [
+          cell('school_sixth_form', 75),
+          cell('sixth_form_college', null, 'suppressed'),
+          cell('further_education', null, 'suppressed'),
+          cell('apprenticeship', null, 'not_applicable'),
+        ],
+      },
+    },
+  };
+
+  const rowFor = (container: HTMLElement, category: string) =>
+    Array.from(container.querySelectorAll('tbody tr'))
+      .find(tr => tr.textContent?.includes(category));
+
+  it('never labels a not-applicable category as withheld', () => {
+    const { container } = render(<DestinationsSection destinations={mixedPhase} />);
+    const row = rowFor(container, 'Apprenticeship');
+    expect(row).toBeTruthy();
+    expect(row!.textContent).not.toMatch(/withheld/i);
+  });
+
+  it('labels a genuinely suppressed category as withheld in both columns', () => {
+    const { container } = render(<DestinationsSection destinations={mixedPhase} />);
+    const row = rowFor(container, 'Sixth-form college');
+    expect(row).toBeTruthy();
+    expect(row!.querySelectorAll('td')).toHaveLength(2);
+    Array.from(row!.querySelectorAll('td')).forEach(td =>
+      expect(td.textContent).toMatch(/withheld/i));
+  });
+
+  it('the two columns of a row never disagree about what the row is', () => {
+    const { container } = render(<DestinationsSection destinations={mixedPhase} />);
+    Array.from(container.querySelectorAll('tbody tr')).forEach(tr => {
+      const cells = Array.from(tr.querySelectorAll('td'))
+        .map(td => /withheld/i.test(td.textContent ?? ''));
+      expect(new Set(cells).size).toBe(1);
+    });
+  });
+
+  it('shows a published category its real figures', () => {
+    const { container } = render(<DestinationsSection destinations={mixedPhase} />);
+    const row = rowFor(container, 'State-funded school sixth form');
+    expect(row!.textContent).toMatch(/75/);
+    expect(row!.textContent).toMatch(/42%/);
+  });
+});