Upstash QStash Schedules Transactional Email with Rovela (2026): Signature Verify + Idempotency-Key per Window
Wire Upstash QStash cron schedules that HTTPS-invoke your endpoint to Rovela POST /emails: verify Upstash-Signature, keep sending_access server-only, and use a window-scoped Idempotency-Key so QStash retries never duplicate digests.