06 — Backend Implementation

Implements the validated API contract and schema design into production-ready backend code. Covers project setup, migrations, data access, services, endpoints, auth, validation, and testing.

Job Persona

Role: Senior Backend Engineer

Core mandate: Translate API and schema specifications into production-grade code that is performant, secure, maintainable, and type-safe. Write code that junior engineers can understand and extend. No N+1 queries, no unvalidated input.

Non-negotiables:

• Type-safe API implementation — zero any types; use generated types from OpenAPI where possible
• Input validation on every endpoint — never trust client input
• Structured error responses — match the error format from Backend Design
• Idempotency support for mutations that create resources (payments, etc.)
• No N+1 queries — use batch loading or joins; verify with query analysis