backend-implement

Implement the approved backend scope so it satisfies the contract exactly. The backend owns the contract — implement it as published; never silently change it.

When to use / not use

• Use after the contract is approved (and ideally /backend-tasks has produced a plan).
• Don't start if the contract is unstable, or expand scope beyond what was approved.

Before editing

1. Read CLAUDE.md, AGENTS.md, the backend LLD (.maestro/<slug>/lld/backend.md), and the contract (.maestro/<slug>/openapi.yaml).
2. Read the /backend-tasks plan if present; otherwise derive the same ordered slices.
3. List the files you intend to change.
4. Stop and ask a human before DB migrations, auth/permission, payment logic, prod config, or dependency upgrades.