Email & Notifications

Two independent notification systems exist in this ecosystem, for two independent purposes — worth documenting together specifically so they don't get confused with each other.

Playground Outage/Recovery Emails (Resend)

The playground's "Notify me" flow (shown when the backend is offline) uses Resend to send a "the playground is back" email once the host genuinely recovers.

• From address: on the jaysynclab.com apex, domain-verified (SPF/DKIM/DMARC) — migrated from an anujajay.com address once jaysynclab.com's own domain verification completed.
• Queue: a Redis SET (Vercel KV / Upstash Redis) holding every email address that signed up during the current outage. Additive only during an outage; fully cleared after every recovery send, so a later, separate outage always starts from an empty list — no cross-outage bleed.
• Trigger paths: a push notification the instant the controller starts (see Playground Architecture), plus a once-daily cron fallback (a Vercel Hobby-plan limit, not a deliberate design choice — the plan called for hourly). Both funnel through the same function, which always does its own real health check and never trusts the caller — a "still up" check on either path never sends email, only a genuine down→up transition does.
• A real gotcha, found and fixed: the Redis client's Redis.fromEnv() helper looks specifically for UPSTASH_REDIS_REST_URL/ UPSTASH_REDIS_REST_TOKEN env vars — but only the older KV_REST_API_URL/KV_REST_API_TOKEN naming was actually configured on Vercel, so every subscribe attempt was silently throwing. Fixed by constructing the client explicitly from the vars that actually exist, rather than keeping two copies of the same secret in sync.

Playground Feedback Confirmation Emails (Resend)

The same Resend integration also sends a thank-you email to anyone who leaves an email address with feedback, plus a notification to the project owner — both using the same branded HTML template (a shared dark-terminal themed shell used by every email this project sends).

Uptime Kuma Alert Emails (Gmail App Password)

Completely separate system: Uptime Kuma sends its own down/up alert emails via a dedicated Gmail account authenticated with an App Password (not the account's real password), with custom Liquid-templated HTML and inline CSS for a more polished look than Kuma's plaintext default. This has no relationship to Resend or the playground's queue — it's Kuma's own, independent alerting path for lab-infrastructure monitoring, not visitor-facing notifications.

External Dependencies Summary

• Resend — playground outage/recovery + feedback emails, jaysynclab.com-verified sender.
• Vercel KV / Upstash Redis — the outage-recovery queue's storage.
• Gmail (App Password) — Uptime Kuma's alert emails, unrelated to Resend.