API errors & retries
Mastery: ship checklist
A second person can reproduce 429 + Retry-After:2 → sleep once → 200 with attempts=2 from a clean checkout and name the owner for INC-429-2026-07-11.
1Learn the idea
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Clean-room demo
From a fresh clone/directory, run the commands that prove 429 + Retry-After:2 → sleep once → 200 with attempts=2. A second person plays mobile client waiting on a grounded answer and follows your script without coaching. The demo includes limitations: what resilient TypeScript fetch wrapper around POST /v1/chat still will not do.
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Evidence pack
Bundle: contract snippet, passing tests, metric snapshot for retry_attempts_total{outcome} and p95 wall_ms ≤ 8000, security negative probe, rollback note, owner name. Reference INC-429-2026-07-11 as the drill you rehearsed. If any item is missing, the ship gate fails even if the happy path dazzles.
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Implementation artifact
test("429 once then success", async () => {
const fake = sequence([status(429, { "Retry-After": "1" }), json(200, { answer: "ok" })]);
const r = await retryingFetch("/v1/chat", { method: "POST", body: "{}" }, gate);
expect(r).toMatchObject({ ok: true, attempts: 2 });
});
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Ownership and next review
For API errors & retries, name the human who gets paged, the review date for thresholds, and the condition that triggers reevaluation. Endpoint POST /v1/chat remains the production surface you operate for resilient TypeScript fetch wrapper around POST /v1/chat — not a slide. Keep INC-429-2026-07-11 in the handoff template so the next owner inherits the drill.
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Stage depth
After the peer demo, schedule the next threshold review date. File a short changelog that mentions INC-429-2026-07-11 and the control that addresses it. Archive the evidence pack where your team already stores launch records. Resist rewriting everything “for real production” in one weekend — operate this slice until the metrics bore you, then widen. Final self-check: if telemetry vanished, would you still know to hold? If yes, you learned the operating posture this lane teaches.
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Field notes for `api-error-handling` / `mastery-ship`
Trim the demo script until every command is necessary. Record a peer signature line: name, date UTC, pass/fail. File known limitations as bullets, not apologies. Link the evidence pack from the README. Schedule the next game day on a calendar, even if it is solo. Archive the branch tag or release digest you actually shipped. In this chapter the product is resilient TypeScript fetch wrapper around POST /v1/chat, the human stakeholder is mobile client waiting on a grounded answer, and the incident id you design against is INC-429-2026-07-11. Re-state the oracle in your notes — 429 + Retry-After:2 → sleep once → 200 with attempts=2 — and keep the invariant visible: attempts ≤ 3, wall budget ≤ 8s, non-idempotent POSTs never replay without Idempotency-Key. Track retry_attempts_total{outcome} and p95 wall_ms ≤ 8000 as the scoreboard. Surface under change control: POST /v1/chat. If you only have forty minutes, finish the fixture for 429 storm with missing Retry-After that would amplify to 40 calls before polishing UI. Promotion language stays ternary: promote, hold, or roll back based on evidence, not hope.
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Before you start
Why this matters
Draft a two-minute demo script that proves 429 + Retry-After:2 → sleep once → 200 with attempts=2 from a clean directory. Include the failure rehearsal for 429 storm with missing Retry-After that would amplify to 40 calls and the rollback/owner line. If the script needs tribal knowledge, the lab is not shipped.
In the wild
See how this idea shows up as a product and a company — then come back to the lesson. Skills transfer across vendors.
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