backend: server-side engineering without framework cosplay

Build backend behavior that stays correct when requests duplicate, users race, dependencies fail, schemas evolve, and operators need to understand an incident. The deliverable is not merely code that returns the happy-path response. It is a verified contract, with its data, security, recovery, and operational behavior made explicit.

Purpose and boundaries

Use this skill when a task changes or evaluates any of these surfaces:

• HTTP, RPC, GraphQL, CLI, webhook, queue, cron, or agent-tool boundary;
• persistent data, migrations, indexes, transactions, or consistency rules;
• authentication, session, authorization, tenancy, or sensitive-data handling;
• asynchronous work, event delivery, retries, external calls, caches, or files;
• service observability, health behavior, reliability, or failure recovery.