Merge branch 'main' into feat/aqhi

Port to current main: main reserved layer-state token 0 for street-level, so
air-quality takes the next free token, 4 (registry, ledger, and the allocation
tests shift by one). Main moved source contracts into sourceComposition.js, so
air-quality registers its getSnapshot contract there. Package boundaries keep
main's lists plus this branch's air-quality modules and packages.

src/app/sourceComposition.js

@@ -0,0 +1,115 @@
+const contract = (layers, methods) =>
+  Object.freeze({
+    layers: Object.freeze(layers),
+    methods: Object.freeze(methods),
+  });
+
+/** Acquisition contracts and their consumers; records remain family-specific. */
+export const CATALOG_SOURCE_CONTRACTS = Object.freeze({
+  directions: contract(['directions'], ['getRoute']),
+  'recent-imagery': contract(
+    ['recent-imagery'],
+    ['searchHls', 'getThumbnail', 'getTileTemplate'],
+  ),
+  flights: contract(['flights'], ['getSnapshot']),
+  military: contract(['military'], ['getSnapshot']),
+  vessels: contract(['ais-live-vessels'], ['getSnapshot']),
+  cctv: contract(
+    ['cctv'],
+    ['getCatalog', 'getHealth', 'getFrameUrl', 'getMediaUrl'],
+  ),
+  radio: contract(['radio'], ['getDirectory', 'recordClick']),
+  traffic: contract(
+    ['traffic'],
+    [
+      'requestRoads',
+      'getStatus',
+      'fetchFlowForBounds',
+      'getFlowSessionStats',
+      'resetFlowTileCache',
+    ],
+  ),
+  bikeshare: contract(['bikeshare'], ['getStations']),
+  installations: contract(
+    ['military-installations'],
+    ['getMappedSites', 'searchNearby'],
+  ),
+  satellites: contract(['satellites'], ['readGroup']),
+  launches: contract(['rocket-launches'], ['getLaunches', 'getActiveTle']),
+  alpr: contract(['alpr-cameras'], ['fetch']),
+  firms: contract(['local-firms'], ['getSnapshot']),
+  wind: contract(['wind'], ['getSnapshot']),
+  weather: contract(
+    ['weather-radar', 'weather-satellite', 'weather-lightning'],
+    ['getSnapshot'],
+  ),
+  cyclones: contract(['weather-cyclones'], ['getSnapshot']),
+  earthquakes: contract(['earthquakes'], ['getSnapshot']),
+  'fire-perimeters': contract(['fire-perimeters'], ['getSnapshot']),
+  'air-quality': contract(['air-quality'], ['getSnapshot']),
+  'gnss-integrity': contract(['gnss-integrity'], ['getSnapshot']),
+  cables: contract(['telegeography-submarine-cables'], ['fetch']),
+  transit: contract(['transit'], ['requestSnapshot', 'getHistory']),
+});
+
+/** An omitted provider is unavailable, never an authoritative empty dataset. */
+export class SourceUnavailableError extends Error {
+  constructor(name) {
+    super(`Data source not configured: ${name}`);
+    this.name = 'SourceUnavailableError';
+    this.code = 'unavailable';
+    this.unavailable = true;
+    this.retryable = false;
+  }
+}
+
+/** Validate supplied contracts and keep omitted sources inert during construction. */
+export function resolveCatalogSources(supplied = {}) {
+  if (!supplied || typeof supplied !== 'object' || Array.isArray(supplied))
+    throw new TypeError('Catalog sources must be an object');
+  const sources = { ...supplied };
+  const missing = new Set();
+  for (const [name, { methods }] of Object.entries(CATALOG_SOURCE_CONTRACTS)) {
+    const source = sources[name];
+    if (source == null) {
+      missing.add(name);
+      const unavailable = () => {
+        throw new SourceUnavailableError(name);
+      };
+      sources[name] = Object.freeze({
+        label: name,
+        ...Object.fromEntries(methods.map((method) => [method, unavailable])),
+      });
+    } else if (methods.some((method) => typeof source[method] !== 'function')) {
+      throw new TypeError(`Invalid catalog source: ${name}`);
+    }
+  }
+  return {
+    sources,
+    isConfigured: (name) => !missing.has(name),
+    createAvailabilityLookup(layers) {
+      const byId = new Map(layers.map((layer) => [layer.id, layer]));
+      const availability = new Map();
+      for (const [name, { layers: ids }] of Object.entries(
+        CATALOG_SOURCE_CONTRACTS,
+      )) {
+        for (const id of ids) {
+          const layer = byId.get(id);
+          if (!layer) throw new Error(`Missing source consumer: ${id}`);
+          availability.set(
+            id,
+            Object.freeze({
+              available: !missing.has(name),
+              source: name,
+              reason: missing.has(name)
+                ? `${layer.name || id}: data source not configured`
+                : null,
+            }),
+          );
+        }
+      }
+      return (id) =>
+        availability.get(id) ?? byId.get(id)?.getSourceAvailability?.();
+    },
+  };
+}