feat(layers): add FAA drone restrictions airspace layer

Show US prohibited and restricted special-use airspace from the keyless
FAA SUA FeatureServer as an off-by-default Infrastructure layer, with
share-link token 3 and an informational-only disclaimer.

server/providers/droneAirspace.js

@@ -0,0 +1,135 @@
+import { normalizeDroneAirspaceSnapshot } from '../../src/layers/droneAirspace/records.js';
+import { readResponseJsonCapped, coalesceProxyRequest } from './common/http.js';
+import { makeRateLimiter, clientKey } from './common/rate-limit.js';
+
+// FAA Special Use Airspace (public, keyless). TYPE_CODE P (prohibited) and
+// R (restricted) only — the small, always-in-force slice of the national
+// SUA table. maxAllowableOffset trades ~100 m of boundary fidelity for a
+// payload small enough to refresh (~330 KB for the current P+R set).
+const API_URL =
+  'https://services6.arcgis.com/ssFJjBXIUyZDrSYZ/arcgis/rest/services/' +
+  'Special_Use_Airspace/FeatureServer/0/query?' +
+  new URLSearchParams({
+    where: "TYPE_CODE IN ('P','R')",
+    outFields: [
+      'NAME',
+      'TYPE_CODE',
+      'UPPER_DESC',
+      'LOWER_DESC',
+      'TIMESOFUSE',
+      'CONT_AGENT',
+      'CITY',
+      'STATE',
+      'OBJECTID',
+    ].join(','),
+    maxAllowableOffset: '0.001',
+    outSR: '4326',
+    f: 'geojson',
+  }).toString();
+
+const MAX_PAGES = 5;
+const MIB = 1024 * 1024;
+const SNAPSHOT_TTL_MS = 3_600_000;
+
+const exceededTransferLimit = (payload) =>
+  payload?.exceededTransferLimit === true ||
+  payload?.properties?.exceededTransferLimit === true;
+
+/** Fixed-origin, bounded FAA SUA routes for dev and preview. */
+export function droneAirspaceProxy({
+  fetchImpl = (...args) => globalThis.fetch(...args),
+  now = () => Date.now(),
+} = {}) {
+  const cache = new Map();
+  const inFlight = new Map();
+  const allow = makeRateLimiter({ windowMs: 60_000, max: 60, globalMax: 1200 });
+
+  async function upstream(url, cap, timeout) {
+    const signal = AbortSignal.timeout(timeout);
+    const response = await fetchImpl(url, {
+      signal,
+      redirect: 'error',
+    });
+    if (!response.ok) {
+      await response.body?.cancel();
+      throw new Error('upstream_unavailable');
+    }
+    return readResponseJsonCapped(response, cap, signal);
+  }
+
+  async function fetchZones() {
+    const features = [];
+    for (let page = 0; page < MAX_PAGES; page++) {
+      const url =
+        page === 0 ? API_URL : `${API_URL}&resultOffset=${features.length}`;
+      const payload = await upstream(url, 8 * MIB, 30_000);
+      if (!Array.isArray(payload?.features))
+        throw new Error('invalid_snapshot');
+      features.push(...payload.features);
+      if (!exceededTransferLimit(payload) || !payload.features.length) break;
+    }
+    const rows = normalizeDroneAirspaceSnapshot({ features });
+    if (!rows) throw new Error('invalid_snapshot');
+    return { fetchedAt: now(), rows };
+  }
+
+  async function acquire(key, ttl, load) {
+    const previous = cache.get(key);
+    if (previous && now() - previous.savedAt < ttl)
+      return { value: previous.value, stale: false };
+    if (!inFlight.has(key) && inFlight.size >= 256)
+      throw Object.assign(new Error('busy'), { status: 429 });
+    try {
+      const { promise } = coalesceProxyRequest(inFlight, key, async () => {
+        const value = await load();
+        cache.set(key, { value, savedAt: now() });
+        return value;
+      });
+      return { value: await promise, stale: false };
+    } catch (error) {
+      if (previous) return { value: previous.value, stale: true };
+      throw error;
+    }
+  }
+
+  async function handler(req, res) {
+    const json = (status, value, stale = false) => {
+      if (res.destroyed) return;
+      res.writeHead(status, {
+        'Content-Type': 'application/json',
+        'Cache-Control': 'no-store',
+        ...(status === 405 ? { Allow: 'GET' } : {}),
+        ...(status === 429 ? { 'Retry-After': '60' } : {}),
+        ...(stale ? { 'X-Data-Stale': 'true' } : {}),
+      });
+      res.end(JSON.stringify(value));
+    };
+    if (req.method !== 'GET') return json(405, { error: 'method_not_allowed' });
+    const path = (req.url || '/').split('?')[0];
+    if (path !== '/' && path !== '')
+      return json(404, { error: 'unknown_route' });
+    if (!allow(clientKey(req))) return json(429, { error: 'rate_limited' });
+    try {
+      const { value, stale } = await acquire(
+        'zones',
+        SNAPSHOT_TTL_MS,
+        fetchZones,
+      );
+      json(200, stale ? { ...value, stale: true } : value, stale);
+    } catch (error) {
+      json(error.status === 429 ? 429 : 502, {
+        error: 'drone_airspace_unavailable',
+      });
+    }
+  }
+
+  return {
+    name: 'drone-airspace',
+    configureServer({ middlewares }) {
+      middlewares.use('/api/drone-airspace', handler);
+    },
+    configurePreviewServer({ middlewares }) {
+      middlewares.use('/api/drone-airspace', handler);
+    },
+  };
+}

server/providers/local.js

@@ -24,6 +24,7 @@ import { mapillaryProxy } from './mapillary.js';
 import { keySetupEndpoint } from '../standalone/key-setup.js';
 import { weatherProxy } from './weather.js';
 import { firePerimetersProxy } from './firePerimeters.js';
+import { droneAirspaceProxy } from './droneAirspace.js';
 import { cycloneProxy } from './cyclones.js';
 import { windProxy } from './wind.js';
 
@@ -60,6 +61,7 @@ function localProviderPlugins({ realtime } = {}) {
     cycloneProxy(),
     mapillaryProxy(),
     firePerimetersProxy(),
+    droneAirspaceProxy(),
     keySetupEndpoint(),
   ];
 }