feat(destinations): types and secondary section flags

Destinations are secondary-only, so the flags go on computeSecondaryFlags
rather than computeSchoolFlags. A phase counts as present only when some
pupil group carries categories — an empty block would otherwise open a nav
entry pointing at a section that never renders.

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

nextjs-app/lib/schoolSections.ts

@@ -10,6 +10,7 @@
 import type {
   School, SchoolResult, AbsenceData, SchoolCensus,
   OfstedInspection, SchoolAdmissions, SchoolAdmissionDistance, SchoolDeprivation, SchoolFinance,
+  SchoolDestinations, DestinationPhase,
 } from './types';
 import { isSpecialSchool } from './utils';
 
@@ -20,6 +21,7 @@ export interface SchoolFlagsInput {
   census: SchoolCensus | null;
   deprivation: SchoolDeprivation | null;
   finance: SchoolFinance | null;
+  destinations?: SchoolDestinations | null;
 }
 
 export interface SchoolFlags {
@@ -183,10 +185,22 @@ export interface SecondaryFlags {
   p8Suspended: boolean;
   isSpecial: boolean;
   suppressComparison: boolean;
+  /** Whether a destinations phase has anything to render. A block can exist
+   *  with empty groups when the pipeline has run but the school has no rows,
+   *  and a nav entry for a section that never renders links to nothing. */
+  hasKs4Destinations: boolean;
+  hasKs5Destinations: boolean;
+}
+
+/** A phase is renderable only if some pupil group actually carries categories. */
+function phaseHasContent(phase: DestinationPhase | null | undefined): boolean {
+  if (!phase) return false;
+  return Object.values(phase.groups ?? {})
+    .some(group => (group?.categories?.length ?? 0) > 0);
 }
 
 export function computeSecondaryFlags({
-  schoolInfo, yearlyData, deprivation, finance,
+  schoolInfo, yearlyData, deprivation, finance, destinations,
 }: Omit<SchoolFlagsInput, 'absenceData' | 'census'>): SecondaryFlags {
   const latestResults = yearlyData.length > 0 ? yearlyData[yearlyData.length - 1] : null;
 
@@ -212,6 +226,8 @@ export function computeSecondaryFlags({
   return {
     latestResults, hasSixthForm, hasFinance, hasDeprivation, hasLocation,
     hasWellbeing, hasResults: !!hasResults, p8Suspended, isSpecial, suppressComparison,
+    hasKs4Destinations: phaseHasContent(destinations?.ks4),
+    hasKs5Destinations: phaseHasContent(destinations?.ks5),
   };
 }
 
@@ -228,6 +244,12 @@ export function buildSecondaryNavItems(
   const navItems: NavItem[] = [];
   if (ofsted) navItems.push({ id: 'ofsted', label: 'Ofsted' });
   if (flags.hasResults) navItems.push({ id: 'gcse', label: 'GCSEs' });
+  // Destinations sit straight after attainment: they answer "and then what
+  // happened", which only makes sense once the results are in view.
+  if (flags.hasKs4Destinations) navItems.push({ id: 'destinations', label: 'After Year 11' });
+  if (flags.hasKs5Destinations) {
+    navItems.push({ id: 'post16-destinations', label: 'After sixth form' });
+  }
   if (admissions || admissionDistance) navItems.push({ id: 'admissions', label: 'Admissions' });
   if (admissionDistance?.distance_m != null && hasLocation) {
     navItems.push({ id: 'distance', label: 'Distance' });

nextjs-app/lib/types.ts

@@ -598,3 +598,30 @@ export interface SortConfig {
   key: string;
   direction: SortDirection;
 }
+
+// ── Destination measures ────────────────────────────────────────────────────
+// Shaped by backend/data_loader.py::_destinations_block. `status` is the field
+// that matters: 'suppressed' is DfE withholding a figure it judged disclosive
+// and must render as "withheld"; 'not_applicable' must render as nothing.
+// `pupils` is null for both, so a null check alone loses the difference.
+
+import type { DestinationCell, PupilGroup } from './destinations';
+
+export interface DestinationGroupPayload {
+  cohort: number | null;
+  categories: DestinationCell[];
+  /** Totals DfE published itself. Never computed here — see lib/destinations.ts. */
+  aggregates: Partial<Record<'sustained_education' | 'sustained_all', DestinationCell>>;
+}
+
+export interface DestinationPhase {
+  /** e.g. "2022/23" — the section dates its own cohort, which runs about two
+   *  GCSE years behind the results shown above it. */
+  cohort_year: string | null;
+  groups: Partial<Record<PupilGroup, DestinationGroupPayload>>;
+}
+
+export interface SchoolDestinations {
+  ks4: DestinationPhase | null;
+  ks5: DestinationPhase | null;
+}