fix(perimeters): report a stale WFIGS snapshot as stale, and stop serving it after a day

When WFIGS was unreachable the proxy served its last snapshot, marked stale
(X-Data-Stale, body.stale), with no age limit, and the client source kept
only the rows. The layer then read healthy with a fresh update time and
get_fire_perimeters reported the perimeters as current; three days into an
outage it still said "1 mapped wildfire perimeter in the requested box."
The source now offers getSnapshotDetail ({rows, stale, fetchedAt}); the
layer reports stale with the snapshot's fetch time, the tool adds stale,
retrieved_at and "(data may be stale)", and the proxy serves a stale
snapshot for at most 24 hours, as the GNSS proxy caps its own.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/tools/queries/environment.js

@@ -257,7 +257,14 @@ export const getFirePerimeters = defineTool({
   requires: ['perimeters'],
   async run(args, { services, signal }) {
     const area = await resolveArea(args.area, { services, signal });
-    const rows = (await services.perimeters.getSnapshot({ signal }))
+    const snapshot =
+      typeof services.perimeters.getSnapshotDetail === 'function'
+        ? await services.perimeters.getSnapshotDetail({ signal })
+        : { rows: await services.perimeters.getSnapshot({ signal }) };
+    // The proxy answers from its last snapshot, marked stale, while WFIGS is
+    // unreachable.
+    const stale = snapshot.stale === true;
+    const rows = snapshot.rows
       .filter((fire) => polygonsTouchArea(fire.polygons, area))
       .map((fire) => ({ fire, point: polygonCenter(fire.polygons) }))
       .filter(({ point }) => point)
@@ -279,9 +286,13 @@ export const getFirePerimeters = defineTool({
       }))
       .sort((a, b) => (b.acres ?? 0) - (a.acres ?? 0));
     return {
-      summary: `${countNoun(rows.length, 'mapped wildfire perimeter')} in ${area.label}.`,
+      summary:
+        `${countNoun(rows.length, 'mapped wildfire perimeter')} in ${area.label}` +
+        (stale ? ' (data may be stale).' : '.'),
       data: {
         view: suggestView(services, { area, layers: ['fire-perimeters'] }),
+        stale,
+        retrieved_at: isoTime(snapshot.fetchedAt),
         ...capRows(rows, args.limit),
       },
     };

src/tools/queries/environment.test.mjs

@@ -871,3 +871,39 @@ test('installation names wait for the name pack, briefly', async (t) => {
   assert.equal(slow.data.names_pending, true);
   assert.match(slow.summary, /site names are still loading\)\.$/);
 });
+
+test('stale fire perimeters say so, with when they were fetched', async () => {
+  const fetchedAt = Date.UTC(2026, 9, 22, 6);
+  const ring = [
+    [
+      [-118.5, 35.2],
+      [-118.4, 35.2],
+      [-118.4, 35.3],
+      [-118.5, 35.2],
+    ],
+  ];
+  const perimeters = {
+    getSnapshot: async () => [],
+    getSnapshotDetail: async () => ({
+      rows: [
+        {
+          stableId: 'held',
+          name: 'Held Fire',
+          acres: 300,
+          polygons: [ring],
+        },
+      ],
+      stale: true,
+      fetchedAt,
+    }),
+  };
+  const result = await catalogWith({ perimeters }).call('get_fire_perimeters', {
+    area: { bbox: [-120, 34, -117, 36] },
+  });
+  assert.equal(
+    result.summary,
+    '1 mapped wildfire perimeter in the requested box (data may be stale).',
+  );
+  assert.equal(result.data.stale, true);
+  assert.equal(result.data.retrieved_at, new Date(fetchedAt).toISOString());
+});