Retry 429 with backoff + pool

const sleep = (ms) => new Promise((r) => setTimeout(r, ms))

export function createPool(size) {
  let active = 0
  const waiting = []
  const next = () => {
    if (active >= size || waiting.length === 0) return
    active++
    const { task, resolve, reject } = waiting.shift()
    task()
      .then(resolve, reject)
      .finally(() => {
        active--
        next()
      })
  }
  return (task) =>
    new Promise((resolve, reject) => {
      waiting.push({ task, resolve, reject })
      next()
    })
}

const RETRYABLE = new Set([429, 502, 503, 504])

export async function withRetry(doRequest, { maxAttempts = 6, baseMs = 500, capMs = 30_000 } = {}) {
  for (let attempt = 1; ; attempt++) {
    let res
    try {
      res = await doRequest()
    } catch (networkError) {
      if (attempt >= maxAttempts) throw networkError
    }
    if (res && !RETRYABLE.has(res.status)) return res
    if (res && attempt >= maxAttempts) return res

    const retryAfter = Number(res?.headers.get('retry-after')) * 1000
    const ceiling = Math.min(capMs, baseMs * 2 ** attempt)
    await sleep(retryAfter || Math.random() * ceiling)
  }
}

const pool = createPool(4)
const results = await Promise.all(
  ids.map((id) => pool(() => withRetry(() => fetch(urlFor(id), { headers: authHeaders() }))))
)