AKServices Incident Note — 16 Oct 2025
=====================================

Title: Wallet settlement acknowledgment duplication
Severity: Minor (communication noise only)
Start: 16 Oct 2025, 21:14 IST
End: 16 Oct 2025, 21:49 IST
Duration: 35 minutes

Summary
-------
A deployment of the notification worker introduced a race condition that retried IMPS settlement acknowledgments even after a success callback. Retailers received duplicate "settlement credited" emails/SMS for two batches.

Customer Impact
---------------
- 134 retailers received duplicate acknowledgments.
- No duplicate payouts or ledger changes occurred.
- Helpdesk volume increased briefly while retailers confirmed if a second credit was coming.

Root Cause
----------
The worker's idempotency key used `batch_id + timestamp` instead of the persisted payout reference. During retry, a new timestamp generated a new key, so the check always inserted another record and fired another notification.

Fix & Mitigations
-----------------
1. Patched worker to use the immutable payout reference and added a checksum guard.
2. Cleared duplicate rows from notification log to avoid future replays.
3. Emailed affected retailers explaining it was informational only.

Follow-up Actions
-----------------
- Added automated unit tests for payout worker idempotency.
- Monitoring rule now compares outgoing count vs. settlement ledger entries every hour.
- Documented scenario in SCREEN_LOCK_FIX_SUMMARY.md appendix for compliance review.