Contract-First Engineering in Distributed Core Banking

In enterprise core banking modernizations, microservice decomposition often creates an unexpected governance failure: Semantic Drift. When dozens of distributed product teams build microservices independently, subtle discrepancies emerge between architectural specifications and real-world implementations. A field defined as ISO4217 currency string in a central domain model might be implemented as a raw string in one service, a numeric currency code in another, or omitted entirely in an asynchronous event payload. Relying on a "Code-First" development approach—where engineers write Java control