# 003 Observability Via Interfaces

Context
- Logging, metrics, and tracing are required, but inner layers must stay independent from OpenTelemetry.
- The project needs request logging and metrics middleware.

Decision
- Define observability interfaces in `usecase/interface.py`.
- Implement those interfaces with OpenTelemetry adapters in `adapter/otel/`.
- Use request logging middleware and metrics middleware in the FastAPI adapter.
- Do not add a custom trace middleware by default.
- Use standard ASGI/FastAPI OpenTelemetry instrumentation for request spans.

Consequences
- Usecases stay portable and framework-agnostic.
- Trace behavior remains consistent with OpenTelemetry defaults.
- Extra span enrichment can be added later without changing inner-layer contracts.