Domain Modeling

Structural default: full ports & adapters, applied by default

Hexagonal architecture (ports and adapters) on any non-trivial feature — not gated behind "does a second implementation exist yet." Business logic never imports framework/transport/persistence code directly.

• Domain/application layer: business rules, use cases. No framework imports, no direct DB/HTTP calls.
• Ports: interfaces the application layer depends on (UserRepositoryPort, BillingGatewayPort) — model capabilities, not technologies.
• Adapters: concrete implementations at the edge (Postgres repository, HTTP client, queue consumer). Adapters depend inward on ports; nothing depends outward on adapters.
• Composition root: one place where concrete adapters get wired to use cases — avoid scattering instantiation/service-locator lookups throughout the codebase.