Render Cron Transactional Email with Rovela (2026): Env Secrets + Idempotency-Key per Window
Run a Render Cron Job that exits cleanly, load ROVELA_API_KEY from Render env vars or environment groups, and POST /emails with Idempotency-Key scoped to the UTC schedule window. Distinct from Railway cron, Vercel Cron routes, and GitHub Actions.