Backend Patterns

Layer ownership

• application: use-case orchestration and business flow
• infrastructure: providers, repositories, external integrations
• interface: transport adapters (oRPC, HTTP/OpenAPI, webhooks)

Core rules

1. Keep provider SDK calls in infrastructure adapters only.
2. Keep transport logic out of use cases.
3. Keep business invariants in application/domain code.
4. Keep contract/output mapping explicit at adapter boundaries.

Use-case style

• one primary use-case service per business action
• commands mutate state, queries read state
• prefer simple CQS over full CQRS unless proven necessary

Reliability baseline

• transactional core state changes
• side effects via async/event handlers when possible
• fail-fast env validation on startup
• health/readiness endpoints required for operations

Related deep reference

For detailed examples and naming conventions, see docs/architecture/23-backend-patterns.md.