fix(terrain): pause upstream calls after a 429

A rate-limited upstream got asked again by every page request for new
points (about once a second while the camera moves), each with its own
retries, which kept the limit in force and logged "refresh incomplete" each
time. After a 429 the proxy now leaves the upstream alone for its
Retry-After (at most 10 minutes), or 60 s when it sends none, serving
cached points meanwhile. The warning that starts the pause says
"(HTTP 429; pausing upstream for N s)"; requests refused during the pause
don't log.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

server/providers/terrain.js

@@ -6,6 +6,7 @@ import {
   parseTerrainPoints,
   resolveTerrainHeightRequest,
   terrainPointKey,
+  terrainRetryAfterMs,
   validTerrainResult,
 } from '../../src/data/terrainHeightsProxy.js';
 import { makeRateLimiter, clientKey } from './common/rate-limit.js';
@@ -55,6 +56,15 @@ export function terrainHeightsProxy(options = {}) {
   // 2026-08-21). 64 points costs 5.6-12 s, inside the timeout at both ends of
   // that range.
   const UPSTREAM_CHUNK = 64;
+  // After a 429 the upstream is left alone for its Retry-After (at most
+  // RATE_LIMIT_PAUSE_MAX_MS, so a far-off date can't stop terrain until a
+  // restart), or RATE_LIMIT_PAUSE_MS when it gives none. Every page poll for
+  // new points (about once a second while the camera moves) otherwise asks
+  // again with its own retries, which keeps the limit in force and logs each
+  // time.
+  const RATE_LIMIT_PAUSE_MS = 60_000;
+  const RATE_LIMIT_PAUSE_MAX_MS = 10 * 60_000;
+  let rateLimitedUntil = 0;
   const MAX_POINTS = UPSTREAM_CHUNK;
   /**
    * Entry ceiling for the point cache, and with it the file written from it.
@@ -211,15 +221,31 @@ export function terrainHeightsProxy(options = {}) {
    * @returns {Promise<Array<object>>}
    */
   async function fetchUpstreamAll(points) {
+    if (Date.now() < rateLimitedUntil) {
+      // Rate-limited: asking again only extends the limit. Cached points are
+      // still served; the rest resolve on the page through its geoid.
+      const error = new Error('HTTP 429');
+      error.coolingDown = true;
+      throw error;
+    }
     const results = [];
     let firstError = null;
     for (let i = 0; i < points.length; i += UPSTREAM_CHUNK) {
       const chunk = points.slice(i, i + UPSTREAM_CHUNK);
       let chunkResults = [];
-      try {
+      if (Date.now() >= rateLimitedUntil) {
-        chunkResults = await fetchTerrainChunkWithRetry(chunk);
+        try {
-      } catch (error) {
+          chunkResults = await fetchTerrainChunkWithRetry(chunk);
-        firstError = firstError || error;
+        } catch (error) {
+          firstError = firstError || error;
+          if (error?.message === 'HTTP 429')
+            rateLimitedUntil =
+              Date.now() +
+              Math.min(
+                terrainRetryAfterMs(error.retryAfter) ?? RATE_LIMIT_PAUSE_MS,
+                RATE_LIMIT_PAUSE_MAX_MS,
+              );
+        }
       }
       // Keep later chunks aligned even if a malformed upstream response omits
       // trailing positions. The resolver will reject each null individually.
@@ -292,9 +318,17 @@ export function terrainHeightsProxy(options = {}) {
           evictOverflow();
           diskDirty = true;
         }
-        if (outcome.upstreamError) {
+        if (outcome.upstreamError?.coolingDown) {
+          // Logged once, when the pause began.
+        } else if (outcome.upstreamError) {
+          const pause =
+            outcome.upstreamError.message === 'HTTP 429' &&
+            Date.now() < rateLimitedUntil
+              ? ` (HTTP 429; pausing upstream for ${Math.ceil((rateLimitedUntil - Date.now()) / 1000)} s)`
+              : '';
           console.warn(
             '[terrain-heights-proxy] refresh incomplete' +
+              pause +
               ' — serving stale points when available',
           );
         } else if (outcome.absentPoints > 0) {

src/tooling/environmentProviders.test.mjs

@@ -411,3 +411,55 @@ test('terrain middleware retains successful chunks around a failure and retries
   );
   assert.equal(requests.length, 4);
 });
+
+test('after a 429 the terrain proxy leaves the upstream alone and logs once', async (t) => {
+  isolate(t);
+  const warnings = [];
+  t.mock.method(console, 'warn', (...args) => warnings.push(args.join(' ')));
+  let calls = 0;
+  t.mock.method(globalThis, 'fetch', async () => {
+    calls += 1;
+    return new Response('', { status: 429 });
+  });
+  const request = install(terrainHeightsProxy());
+  await request('/?points=1,2');
+  const afterFirst = calls;
+  assert.ok(afterFirst >= 1);
+  assert.equal(warnings.length, 1);
+  assert.match(warnings[0], /HTTP 429; pausing upstream for 60 s/);
+  // New points during the pause: no upstream call, no new log line.
+  const paused = await request('/?points=3,4');
+  assert.equal(calls, afterFirst);
+  assert.equal(paused.status, 502);
+  assert.equal(warnings.length, 1);
+});
+
+test('a far-off Retry-After pauses the terrain upstream for at most 10 minutes', async (t) => {
+  isolate(t);
+  t.mock.method(console, 'warn', () => {});
+  t.mock.timers.enable({ apis: ['Date', 'setTimeout'], now: 1_000_000 });
+  let limited = true;
+  t.mock.method(globalThis, 'fetch', async () =>
+    limited
+      ? new Response('', { status: 429, headers: { 'retry-after': '86400' } })
+      : Response.json({ results: [{ ellipsoid: 100 }] }),
+  );
+  const request = install(terrainHeightsProxy());
+  // The first request spends its retry budget on 429s, then the pause begins.
+  let settled = false;
+  const first = request('/?points=1,2').then((res) => {
+    settled = true;
+    return res;
+  });
+  while (!settled) {
+    await new Promise((resolve) => setImmediate(resolve));
+    t.mock.timers.tick(1_000);
+  }
+  assert.equal((await first).status, 502);
+  limited = false;
+  const pausedAt = Date.now();
+  t.mock.timers.setTime(pausedAt + 9 * 60_000);
+  assert.equal((await request('/?points=3,4')).status, 502, 'still paused');
+  t.mock.timers.setTime(pausedAt + 10 * 60_000 + 1);
+  assert.equal((await request('/?points=3,4')).status, 200, 'pause over');
+});