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),
       },
     };