HTTP 429 Too Many Requests

Fix checklist

• →Honor the Retry-After header exactly — don't invent your own delay when one is given.
• →Implement exponential backoff with jitter for the no-header case.
• →Spread bursty workloads with a client-side token bucket.
• →Request a tier upgrade if you hit limits at steady state.
• →Cache repeated prompt prefixes to cut token throughput.

async function fetchWithRetry(url: string, init: RequestInit, maxRetries = 5) {
  for (let attempt = 0; ; attempt++) {
    const res = await fetch(url, init);
    // 429 is retryable — back off and try again.
    if (res.status !== 429 || attempt >= maxRetries) return res;
    const retryAfter = Number(res.headers.get("retry-after"));
    const delay = Number.isFinite(retryAfter) && retryAfter > 0
      ? retryAfter * 1000
      : Math.min(60_000, 1000 * 2 ** attempt) * (0.5 + Math.random()); // expo backoff + jitter
    await new Promise((r) => setTimeout(r, delay));
  }
}