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fix(engine): widen 429 backoff budget, correct the rate-limit explanation

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Measured directly against the live forge: nginx never sends a
Retry-After header on its 429s (the branch handling it is dead code
in practice), the limit is a leaky bucket rather than a fixed ban (a
20-25 request burst took up to ~15s to drain), it is IP-based rather
than token-quota-based (a valid FORGEJO_TOKEN made no difference to a
reproduced burst), and it triggers well below "13 calls in a loop" —
20 concurrent anonymous requests reproduced it directly. The old
default (retries: 3, ~7s worst case) was tuned for a hard ban that
doesn't exist. fetchWithRetry now defaults to retries: 5 with a
maxDelayMs: 8000 cap (23s worst case), covering the measured drain
time without one attempt blocking for a full uncapped exponential
step. CLAUDE.md's explanation is corrected to match; test count in
README/CLAUDE.md updated for the two new tests (111 -> 113).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01W1ZJFViVYpr8cvf4fs91j1
This commit is contained in:
Kjell Tore Guttormsen 2026-08-04 22:09:21 +02:00
commit e6b0f04021
4 changed files with 61 additions and 9 deletions
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25
scripts/repo-standard-check.test.mjs
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@ -1102,6 +1102,31 @@ test('no Retry-After header falls back to exponential backoff from baseDelayMs',
assert.deepEqual(calls, [1000, 2000]);
});
test('exponential backoff is capped, so a long retry budget does not wait minutes between attempts', async () => {
// Measured 2026-08-04 against the live forge: 20 parallel requests from one
// IP produced 429 with NO Retry-After header at all (nginx never sends one
// here) — the exponential fallback is the only path that ever runs in
// practice. Recovery was gradual, not a fixed-duration ban: a burst that
// size took up to ~15s to fully drain, and a 20s manual pause cleared it.
// Uncapped doubling would reach 32s on a single attempt; capping at 8s and
// extending the retry budget covers the measured recovery window without
// one attempt blocking for excessive time.
const calls = [];
const responses = [
fakeResponse(429),
fakeResponse(429),
fakeResponse(429),
fakeResponse(429),
fakeResponse(429),
fakeResponse(200),
];
const fetchImpl = async () => responses.shift();
const sleep = async (ms) => calls.push(ms);
await fetchWithRetry('https://x', {}, { fetchImpl, sleep, baseDelayMs: 1000, maxDelayMs: 8000, retries: 5 });
// Uncapped, the 5th delay would be 1000 * 2**4 = 16000.
assert.deepEqual(calls, [1000, 2000, 4000, 8000, 8000]);
});
test('retries are bounded — a persistent 429 returns the 429, not an infinite loop', async () => {
let calls = 0;
const fetchImpl = async () => fakeResponse(429);