Event Sourcing over CRUD for Audit Trails

DECIDED: The team chose Event Sourcing over standard CRUD with database triggers for financial transaction audit trails. Instead of storing mutable state in PostgreSQL, we will store a sequence of immutable domain events (TransactionCreated, TransactionApproved, StatusUpdated). Kafka will serve as the immutable event log, with materialized views in Postgres for fast frontend reads.

ALTERNATIVE CONSIDERED: Database triggers with a history_logs table were considered, but rejected because triggers only see row-level changes (e.g., status changed from 1 to 2) and lose business context — they don't capture why the change happened or the user intent behind it.

FILES: src/services/transactionService.ts (event producers), src/events/eventStore.ts (consumer/store logic).

REFERENCE: Martin Fowler's Event Sourcing Pattern article — industry-standard reference architecture for this approach.