# API and Backend Work

## Purpose

Guide server-side, service, API, data, and integration changes with attention to contracts, compatibility, failure handling, and operational impact.

## When to use

- Modifying endpoints, handlers, services, jobs, or data flows
- Adding or changing schemas, persistence, or integration behavior
- Working on backend business logic or infrastructure-facing code
- Investigating performance, reliability, or contract issues on the server side

## Inputs to gather

- API contracts, schema, storage models, and service boundaries
- Existing validation, auth, error handling, and observability patterns
- Compatibility constraints for clients, data, and deployments
- Current tests and representative request or event flows

## How to work

- Trace the full request or job lifecycle before changing a boundary.
- Preserve compatibility intentionally or document the break clearly.
- Handle validation, authorization, error responses, and retries in line with existing system behavior.
- Consider migration, rollout, and operational visibility when data or contracts change.
- Add or update tests at the right layer for the change.

## Output expectations

- Working backend change with contract implications made explicit
- Notes on schema, config, data, or rollout impact
- Verification results covering the critical paths

## Quality checklist

- Inputs and outputs are validated appropriately.
- Failure handling is explicit and consistent.
- Compatibility and migration impact are understood.
- Logging, metrics, or observability concerns are addressed when relevant.

## Handoff notes

- Call out any required coordination with frontend, data migration, configuration, or deployment steps.
- Note backwards-incompatible changes clearly and early.