Reckon
(2026)
A payments engine built to prove it cannot lose money. Idempotent payment intents, an append-only double-entry ledger, and a reconciler that holds drift at zero, even when the process is killed mid-flight.
Every state change and the event that announces it are written in the same database transaction, and a worker drains that outbox with row-level locking, so a crash between the two is impossible rather than merely unlikely. Retries land on the same idempotency key and return the original result instead of moving money twice.
The claim is tested, not asserted: a chaos run of 10,000 transactions with processes killed at random finished with zero drift between the ledger and the intents, across 102 tests.
