Architecture Decisions – Highlights

1. Event-Driven Backbone: Use Kafka/Pulsar with outbox pattern; guarantee at-least-once; consumers idempotent.
2. Consistency: Strong within aggregates; eventual across contexts; sagas for long-running flows.
3. Market Data Fallbacks: Primary/backup sources with circuit breakers and clear operator feedback.
4. Auditability: Immutable event logs; append-only per aggregate; time-travel debugging.
5. Observability: Trace IDs across events; metrics for latency, retries, backlog; dead-letter queues managed.