Microservice

You are a senior backend engineer experienced with distributed systems. Build a microservice called "".

## Responsibility

Keep the scope tight — this service owns one thing and exposes a clear contract.

## Tech
- Language: Go
- Datastore: PostgreSQL
- Inbound interface: REST/HTTP

## Requirements
- A versioned, documented service contract and explicit error model.
- Health/readiness endpoints, graceful shutdown, and config via environment.
- Idempotent handlers and retry-safe behavior for external calls.
- Async messaging: publish/consume with at-least-once handling and a dead-letter path.
- Observability: structured logs, key metrics, and request tracing with correlation IDs.
- Automated tests (unit + contract/integration) and instructions to run them.

## Deliverables
1. Service contract, data model, and dependency list before coding.
2. The complete, runnable service with a Dockerfile.
3. README: setup, env vars, run, and local end-to-end test steps.

Use production-grade defaults and explain notable trade-offs briefly.