# ADR-0005: Keep Service Contracts Protocol-Neutral

Status: Accepted  
Date: 2026-07-05

## Context

MyGO exposes REST today and is designed to support additional protocols. Business services need contracts that transport adapters can reuse.

## Decision

- Services return domain results and `model.AppError` values.
- HTTP handlers own REST response DTOs.
- `internal/api` maps domain error kinds to REST responses.
- HTTP packages obtain application behavior through service contracts and authenticated principals.
- Architecture tests enforce the package dependency boundaries.

## Consequences

- Additional protocol adapters can reuse the existing services.
- Each protocol adapter defines its own response mapping.
- Service tests exercise business behavior without constructing HTTP requests.
- Error responses can include `error.log_id` for failures recorded by the server.