Quick/bulk-pay were already atomic (X1); the audit found the row write +
applyBalanceDelta split across two un-transactional statements on manual
POST /payments, autopay-confirm, DELETE (unpay), restore, and PUT (edit,
where the bill-balance write and the payment UPDATE weren't atomic). A
failure between the two could leave a payment without its balance
adjustment (or a balance reversed without the row deleted). Each is now a
single db.transaction(). Behavior-preserving.
tests/paymentsRoute.test.js pins the create→delete→restore→edit balance
round-trip + double-restore no-op. Full suite 186 green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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