What problem does it solve? When building a use-case block in a DDD-style architecture, developers often re-implement aggregate invariants inside the service layer or reach directly into another bounded context's internals, breaking boundary integrity. This Skill guides the worker to realize a thin Application Service that delegates rules to the owning aggregate root and reads other contexts only through consumer-owned ports. ## Core Features & Use Cases - Boundary-honoring orchestration: Routes mutations through the aggregate root that owns the invariant and reads foreign contexts only via the port's interface in primitives. - Bounce detection: Flags any raw-field evaluation (e.g. attivo == true) as a domain decision that belongs in a root/port predicate, not the service. - AC-testing with fake ports: Translates the user's natural-language tests_nl into acceptance tests verified against a fake port, keeping the block green on its own while preserving the aggregate's invariant tests. - Use Case: While building an order-confirmation use-case, the worker calls the Order aggregate root to apply state changes, reads pricing through a PricingPort interface, and verifies behavior with a fake port before the worker-composer welds real implementations in D2. ## Quick Start Ask the worker to realize the application-service block from the building-block manifest, honoring the aggregate boundary and testing with a fake port.
