export function transientServiceUnavailableDetail(
  error: unknown,
): string | null {
  const detail = error instanceof Error ? error.message : String(error);
  // The Convex HTTP client surfaces socket/DNS interruptions as the native
  // Undici `TypeError: fetch failed`, without an HTTP envelope. Callers only
  // use this classifier where replay is explicitly safe (for example, reads).
  if (error instanceof TypeError && /^fetch failed$/i.test(detail.trim())) {
    return detail;
  }
  // Convex uses explicit ServiceUnavailable and ExpiredInQueue responses, as
  // well as this generic InternalServerError envelope for short control-plane
  // outages. The latter text is intentionally exact: application exceptions
  // must not become retryable merely because they mention an internal-server
  // error.
  return /ServiceUnavailable|Service temporarily unavailable|temporarily unavailable \(Code:\s*\d+\)|"code"\s*:\s*"ExpiredInQueue"|"code"\s*:\s*"InternalServerError"[\s\S]*(?:Your request couldn't be completed\. Try again later\.|Your request timed out performing too many system operations\.)/i.test(
    detail,
  )
    ? detail
    : null;
}