Event Sourcing over CRUD for Financial Transaction Audit Trails

Decision: Use Event Sourcing over CRUD for financial transaction audit trails. Context: The team currently uses standard CRUD in PostgreSQL, but updates overwrite previous states, losing business context needed for compliance. Alternative considered — database triggers with a history_logs table — was rejected because triggers only capture row-level changes (e.g., status changed from 1 to 2) without the reason for the change or user intent. Decision: Store immutable domain events (TransactionCreated, TransactionApproved, StatusUpdated) in Kafka as the event log, and build a materialized view in Postgres for fast frontend reads. Reference architecture: Martin Fowler's Event Sourcing Pattern article. Implementation files: src/services/transactionService.ts (event producers) and src/events/eventStore.ts (consumer/store logic).