fix(wildlife): treat a valid empty Acartia snapshot as a fresh success

A quiet or fully filtered feed raised invalid_snapshot, so the proxy
answered 502 with a 15 s cooldown and re-polled about four times a
minute. Only a non-array payload is malformed now; an empty projection
caches for the normal ten minutes and clears earlier rows.

docs/CURRENT-STATE.md

@@ -123,7 +123,10 @@ known `Retry-After`. Failures keep filters and drawn rows, reporting DEGRADED
 with retry timing; logs exclude request URLs and upstream exception text.
 
 `/api/acartia/sightings` adds Salish Sea marine mammals within 45.5–50.5° N,
-126–121° W, cached ten minutes and stale for at most 24 h. WHALES accepts only
+126–121° W, cached ten minutes and stale for at most 24 h. A valid empty
+snapshot, including one whose rows all fall outside coverage or the species
+checks, is a fresh success that clears earlier rows; only a malformed or failed
+upstream reply serves stale and starts a retry cooldown. WHALES accepts only
 recognized cetaceans; other identified marine mammals appear under ALL or
 MAMMALS. Sensitive iNaturalist locations remain 0.2° privacy cells; Acartia
 positions are rounded to 0.01° on the server. Acartia comments are never retained.

server/providers/acartia.js

@@ -100,7 +100,9 @@ export function acartiaProxy({
         signal,
       );
       const rows = normalizeAcartiaSightings(payload, now());
-      if (!rows?.length) throw new Error('invalid_snapshot');
+      // Only a non-array is malformed. A quiet feed, or one whose rows all fall
+      // outside coverage or the species checks, is a valid empty snapshot.
+      if (!rows) throw new Error('invalid_snapshot');
       return { fetchedAt: now(), rows };
     } catch (error) {
       if (error.status !== 429) coolDown(502, FAILURE_COOLDOWN_MS);

server/providers/acartia.test.mjs

@@ -221,43 +221,81 @@ test('one global snapshot single-flights and stays fresh for ten minutes', async
   assert.equal(calls, 2);
 });
 
-test('empty, unprojectable and invented wrapped snapshots never replace the cache', async () => {
-  for (const bad of [
+test('a valid empty or fully filtered snapshot is a fresh success that clears old rows', async () => {
+  for (const quiet of [
     [],
     [null],
     [{ ...sighting(), data_source_name: '' }],
-    { results: [sighting()] },
+    [{ ...sighting(), latitude: 37.8 }],
+    [{ ...sighting(), type: 'Unknown' }],
   ]) {
     let at = NOW;
-    let fail = false;
+    let calls = 0;
+    let empty = false;
     const cache = new Map();
     const request = install({
       cache,
       now: () => at,
-      fetchImpl: async () => Response.json(fail ? bad : [sighting()]),
+      fetchImpl: async () => {
+        calls += 1;
+        return Response.json(empty ? quiet : [sighting()]);
+      },
     });
-    const fresh = await request();
-    const retained = cache.get('sightings');
-    fail = true;
+    assert.equal((await request()).body.rows.length, 1);
+    empty = true;
     at += 600_001;
-    const stale = await request();
-    assert.equal(stale.status, 200);
-    assert.equal(stale.headers['X-Data-Stale'], 'true');
-    assert.equal(stale.body.stale, true);
-    assert.equal(stale.body.fetchedAt, fresh.body.fetchedAt);
-    assert.equal(cache.get('sightings'), retained);
-    const coldCache = new Map();
-    const cold = install({
-      cache: coldCache,
-      fetchImpl: async () => Response.json(bad),
-    });
-    const result = await cold();
-    assert.equal(result.status, 502);
-    assert.equal(result.body.error, 'acartia_unavailable');
-    assert.equal(coldCache.size, 0);
+    const result = await request();
+    assert.equal(result.status, 200);
+    assert.deepEqual(result.body, { fetchedAt: at, rows: [] });
+    assert.equal(result.headers['X-Data-Stale'], undefined);
+    assert.equal(result.headers['Retry-After'], undefined);
+    assert.deepEqual(cache.get('sightings').value.rows, []);
+    // The quiet feed keeps the normal ten-minute cadence, not a failure retry.
+    at += 599_999;
+    assert.equal((await request()).status, 200);
+    assert.equal(calls, 2);
+    at += 1;
+    await request();
+    assert.equal(calls, 3);
+    const cold = install({ fetchImpl: async () => Response.json(quiet) });
+    const coldResult = await cold();
+    assert.equal(coldResult.status, 200);
+    assert.deepEqual(coldResult.body, { fetchedAt: NOW, rows: [] });
   }
 });
 
+test('an invented wrapped snapshot never replaces the cache', async () => {
+  const bad = { results: [sighting()] };
+  let at = NOW;
+  let fail = false;
+  const cache = new Map();
+  const request = install({
+    cache,
+    now: () => at,
+    fetchImpl: async () => Response.json(fail ? bad : [sighting()]),
+  });
+  const fresh = await request();
+  const retained = cache.get('sightings');
+  fail = true;
+  at += 600_001;
+  const stale = await request();
+  assert.equal(stale.status, 200);
+  assert.equal(stale.headers['X-Data-Stale'], 'true');
+  assert.equal(stale.body.stale, true);
+  assert.equal(stale.body.fetchedAt, fresh.body.fetchedAt);
+  assert.equal(cache.get('sightings'), retained);
+  const coldCache = new Map();
+  const cold = install({
+    cache: coldCache,
+    fetchImpl: async () => Response.json(bad),
+  });
+  const result = await cold();
+  assert.equal(result.status, 502);
+  assert.equal(result.body.error, 'acartia_unavailable');
+  assert.equal(result.headers['Retry-After'], '15');
+  assert.equal(coldCache.size, 0);
+});
+
 test('failure serves stale for at most 24 hours and never reports a cold success', async () => {
   let at = NOW;
   let fail = false;