fix(overpass): read failure phrases from the remark, not element tags

overpassLooksRuntimeError and overpassLooksRateLimited searched the whole
200 body, element tags included. A result containing a place named
"Timed Out Escape Rooms" (or any tag with "runtime error", "out of
memory", "too many requests" or "rate_limited") was refused as an
upstream failure, and the endpoint was put on cooldown for every other
query.

Parse the body once. A data reply (one with an elements array) reports
failure in its remark, so the phrase checks run on the remark. Any other
body, an error page or JSON without elements, is matched whole as
before.

src/overpassProxy.test.mjs

@@ -126,6 +126,32 @@ test('production reader rejects oversized, malformed and runtime-failure bodies'
   }
 });
 
+test('element data that mentions a failure phrase is data, and sets no cooldown', async () => {
+  const names = ['Timed Out Escape Rooms', 'Runtime Error Bar', 'Out of Memory Lane', 'Too Many Requests Cafe', 'rate_limited'];
+  for (const [i, name] of names.entries()) {
+    const body = JSON.stringify({ elements: [{ type: 'node', id: 1, lat: 1, lon: 2, tags: { name } }] });
+    let count = 0;
+    const options = { endpoints: [`https://phrase-${i}.example/`], fetchImpl: async () => {
+      count++; return new Response(body);
+    } };
+    const payload = await fetchOverpassPayload('first', 1024, options);
+    assert.equal(payload.status, 200, name);
+    assert.ok(overpassPayloadIsData(payload), name);
+    assert.ok(payload.body.includes(name), name);
+    await fetchOverpassPayload('different', 1024, options);
+    assert.equal(count, 2, name);
+  }
+  const remark = JSON.stringify({ elements: [], remark: 'runtime error: rate_limited' });
+  const limited = await fetchOverpassPayload('x', 1024, { endpoints: ['https://remark.example/'],
+    fetchImpl: async () => new Response(remark, { headers: { 'Retry-After': '90' } }) });
+  assert.equal(limited.status, 429);
+  assert.equal(limited.retryAfterMs, 90_000);
+  const error = await fetchOverpassPayload('x', 1024, { endpoints: ['https://error.example/'],
+    fetchImpl: async () => new Response('{"error":"rate_limited"}', { headers: { 'Retry-After': '120' } }) });
+  assert.equal(error.status, 429);
+  assert.equal(error.retryAfterMs, 120_000);
+});
+
 function proxyHandler() {
   const plugin = createViteConfig({ mode: 'test' }).plugins.find(p => p.name === 'overpass-proxy');
   const routes = new Map();