The dispatcher drained a single global FIFO (oldest 20), so one
tenant's billing burst starved every other space's email indefinitely.
Now round-robins an oldest-first candidate window across spaces with a
per-space cap (PER_SPACE=5, BATCH=20). Status writes are guarded with
.eq('status','pending') so an overlapping run can't flip a row another
run already advanced (no false 'failed' on an already-sent row).
Independent audit verdict was NOT SAFE; all findings fixed:
- dispatcher Idempotency-Key is now per-attempt (${id}:${attempts}),
not row id alone, so a transient-failure response cached by Resend
cannot permanently suppress every retry and silently lose an email.
- enqueueDues is fully try/catch wrapped so a notifications-table or
render failure can never throw into / wedge the Stripe money path.
- dues_lapsed dedupe falls back to the subscription id when periodEnd
is null (canceled/deleted subs), so future lapses no longer collapse
to one key and get suppressed. New test; suite 499.
- documented the dispatcher's once/min concurrency assumption.
POST /api/cron/notifications drains <=20 pending rows/min, sends via the
transport with the row id as Resend Idempotency-Key (overlap-safe),
marks sent or increments attempts (retryable -> stay pending, permanent
or budget-exhausted -> failed). Constant-time CRON_SECRET bearer check;
503 when unset. ~4.5/s spacing under Resend's 5/s limit. proxy.ts
whitelists /api/cron (no session; own shared secret). CRON_SECRET added
to .env.example.
Moheeb Zara