// one request per user per 5 minutes
const coeff = 1000 * 60 * 5
const t = new Date(Math.round(new Date().getTime() / coeff) * coeff).toISOString()
const unique = await isUnique('UPLOAD_REQUEST', t + '#' + userHash)
if (!unique)
  return { statusCode: 429, body: JSON.stringify({ err: 'Only one upload request per user per ~5 minutes.' }) }