Event Sourcing over CRUD for Audit Trails

Decision: Adopt Event Sourcing over standard CRUD for financial transaction audit trails. Implicit alternatives considered and rejected: (1) Database triggers with history_logs table — rejected because triggers capture row-level changes without business context (e.g., why a status changed, user intent); (2) Plain CRUD in PostgreSQL — rejected because updates overwrite previous states, making it impossible to satisfy compliance requests for full history (e.g., who changed transaction #8821 from pending to approved). Implementation plan: Use Kafka as the immutable event log storing domain events (TransactionCreated, TransactionApproved, StatusUpdated), and build a materialized view in Postgres for fast frontend reads. Reference: Martin Fowler's 'Event Sourcing Pattern' article. Files: src/services/transactionService.ts (event producers), src/events/eventStore.ts (consumer/store logic).