Resend has no quota alert; transactional sends just 429 when over

Resend's free plan caps at 100 emails/day and 3,000/month (sent and received both count), and its docs describe no email alert to the account owner near or at the limit: sends simply fail with 429 (e.g. daily_quota_exceeded), with usage only visible on the dashboard Usage page. If sign-in codes go through Resend, a launch-day spike silently breaks email login, so upgrade or log/alert on 429s yourself. Also note: an API key labeled send-only may actually be full access; test it with GET /domains.