Payment system (Stripe-like ledger)

Move money without ever charging a customer twice or losing a cent when networks time out. Every mutation carries an end-to-end Idempotency-Key, records immutable double-entry ledger postings (sum of debits = sum of credits) in an ACID transaction with an outbox, and reconciles daily against external card networks.

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Duration 45:00

Requirements checklist

Authorize, capture, and refund payments via external Payment Service Providers (PSPs / card networks) and settle balances to merchants.Record every balance movement in an immutable double-entry ledger where every transaction's debits equal its credits.End-to-end idempotency: retrying a timed-out charge with the same Idempotency-Key returns the original result without double-charging.Daily automated reconciliation between internal ledger entries and external PSP settlement files.Zero double charges (`duplicateEffect`) and zero lost acknowledged transactions (`ackedWriteLost`).Strict monetary precision: integer minor units (cents) plus currency code — never IEEE-754 floats.Auditability: ledger entries are append-only; corrections are compensating reversal entries, never `UPDATE` or `DELETE`.

Clarifying questions

Are we building the merchant-facing payment gateway/ledger, or card-issuing rails?
Do we support multi-currency transactions and foreign-exchange conversion?
How are payouts to merchants scheduled (instant vs T+2 rolling settlement)?
What happens when an external PSP times out and neither confirms nor denies a charge?

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requirements

Suggested time: about 6 minutes. Defines exact failure semantics across client retries, DB crashes, and PSP timeouts.

Notes for requirements