test(qa): noon sky and stars, surface heights across engines, tile cache

qa-globe-contract checks the noon sky facing the horizon (daylight blue,
no star pixels) and stars at midnight; qa-engine-shell compares
sampleHeight at the Austin startup pose across engines and reports the
wheel floor's lowest frame. QA pages load OSM and keyless terrain tiles
through a disk cache with backoff on 429. Report updated.

src/tooling/tileCache.test.mjs

@@ -0,0 +1,71 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  backoffMs,
+  fetchTile,
+  tileCacheFile,
+} from '../../scripts/qa/tileCache.mjs';
+
+test('only the free tile hosts are cached, per URL and Accept header', () => {
+  const osm = 'https://tile.openstreetmap.org/12/1205/1539.png';
+  const file = tileCacheFile(osm, 'image/png', '/c');
+  assert.match(file, /^\/c\/tile\.openstreetmap\.org-[0-9a-f]{32}$/);
+  assert.equal(tileCacheFile(osm, 'image/png', '/c'), file, 'stable');
+  assert.notEqual(tileCacheFile(osm, 'image/webp', '/c'), file);
+  assert.match(
+    tileCacheFile('https://terrain.reearth.land/1/2/3.terrain', null, '/c'),
+    /^\/c\/terrain\.reearth\.land-/,
+  );
+  for (const url of [
+    'https://tile.googleapis.com/v1/3dtiles/root.json?key=x',
+    'http://tile.openstreetmap.org/1/2/3.png',
+    'not a url',
+  ])
+    assert.equal(tileCacheFile(url, null, '/c'), null, url);
+});
+
+test('429 backs off by Retry-After (at most 30 s) or 1, 2, 4, 8 s', () => {
+  assert.deepEqual(
+    [0, 1, 2, 3].map((attempt) => backoffMs(attempt, null)),
+    [1000, 2000, 4000, 8000],
+  );
+  assert.equal(backoffMs(0, '5'), 5000);
+  assert.equal(backoffMs(0, '600'), 30000);
+});
+
+const response = (status, headers = {}) => ({
+  status,
+  headers: { get: (name) => headers[name] ?? null },
+  arrayBuffer: async () => new Uint8Array([status % 256]).buffer,
+});
+
+test('a tile fetch retries 429s, stops after four retries, keeps Accept', async () => {
+  const waits = [];
+  const seen = [];
+  const replies = [
+    response(429, { 'retry-after': '2' }),
+    response(429),
+    response(200, { 'content-type': 'image/png' }),
+  ];
+  const tile = await fetchTile('u', {
+    accept: 'application/vnd.quantized-mesh',
+    fetchImpl: async (url, init) => (
+      seen.push(init.headers.Accept),
+      replies.shift()
+    ),
+    wait: async (ms) => waits.push(ms),
+  });
+  assert.equal(tile.status, 200);
+  assert.equal(tile.contentType, 'image/png');
+  assert.deepEqual(waits, [2000, 2000]);
+  assert.ok(
+    seen.every((accept) => accept === 'application/vnd.quantized-mesh'),
+  );
+  let calls = 0;
+  const limited = await fetchTile('u', {
+    fetchImpl: async () => (calls++, response(429)),
+    wait: async () => {},
+  });
+  assert.equal(limited.status, 429);
+  assert.equal(calls, 5);
+});