fix(terrain): end retries early on a long Retry-After; cover the 429 pause

A Retry-After longer than the 10 s retry budget used to sleep the whole
budget out and then give up, so the proxy's 429 pause started 10 s late
and every new-point poll in that window still went upstream and logged.
The retry loop now stops at once in that case.

Tests: the retry loop no longer sleeps for an unreachable Retry-After;
fully cached points, including stale ones, are served during the pause
with no upstream call; a 503 does not pause; a shorter concurrent
Retry-After never cuts the pause short. CURRENT-STATE now says which
requests are still served and which log.

src/data/terrainHeightsProxy.js

@@ -107,7 +107,10 @@ export function terrainRetryAfterMs(value, nowMs = Date.now()) {
 /**
  * Fetch one upstream chunk with jittered exponential backoff. Network errors,
  * 429, and 5xx retry; other HTTP failures and malformed successes fail fast.
- * Retry sleeps and retry attempts share a 10s budget after attempt one.
+ * Retry sleeps and retry attempts share a 10s budget after attempt one. A
+ * Retry-After longer than the budget left ends the retries at once: sleeping
+ * out the budget cannot reach the time the upstream asked for, and it would
+ * delay the caller's own back-off (the proxy's 429 pause) by up to 10 s.
  *
  * Dependencies are injectable for deterministic offline tests.
  * @param {Array<[number, number]>} points
@@ -168,6 +171,7 @@ export async function fetchTerrainChunkWithRetry(
       if (remaining <= 0) break;
 
       const retryAfterMs = terrainRetryAfterMs(error?.retryAfter, now());
+      if (retryAfterMs != null && retryAfterMs > remaining) break;
       const backoffMs = Math.round(
         350 * 2 ** attempt * (0.75 + random() * 0.5),
       );

src/data/terrainHeightsProxy.test.mjs

@@ -91,6 +91,36 @@ test('429 retry honors Retry-After before the next attempt', async () => {
   assert.equal(results[0].id, 'recovered');
 });
 
+test('a Retry-After longer than the retry budget ends the retries without sleeping', async () => {
+  let clock = 3_000_000;
+  let attempts = 0;
+  const sleeps = [];
+  await assert.rejects(
+    fetchTerrainChunkWithRetry([[1, 1]], {
+      now: () => clock,
+      random: () => 0.5,
+      makeSignal: () => undefined,
+      sleep: async (ms) => {
+        sleeps.push(ms);
+        clock += ms;
+      },
+      fetchImpl: async () => {
+        attempts += 1;
+        return {
+          ok: false,
+          status: 429,
+          headers: {
+            get: (name) => (name.toLowerCase() === 'retry-after' ? '30' : null),
+          },
+        };
+      },
+    }),
+    (error) => error.status === 429 && error.retryAfter === '30',
+  );
+  assert.equal(attempts, 1);
+  assert.deepEqual(sleeps, [], 'no sleep that cannot reach the Retry-After');
+});
+
 test('permanently failing upstream exhausts retries and returns 502 without fake results', async () => {
   let clock = 2_000_000;
   let attempts = 0;