references/feature-implementation.md

# Focused feature implementation

Turn the request into a short acceptance contract: input, output, errors, authorization, compatibility and user-visible states.

Inspect sibling code before scaffolding. Identify contract ownership and callers. Where applicable use additive schema changes and backward-compatible defaults. Add validation at the correct boundary, not only in the UI.

Prefer one vertical slice: request → behavior → persistence/integration → observability → tests. Implement meaningful error handling; do not replace tested structures with a speculative new framework.

Coverage by change type:
- HTTP API: success, validation, auth/ownership, errors, serialized contract.
- UI: loading, empty, error, keyboard, responsive layout and state reset.
- Background jobs: idempotency, retry, replay, checkpoint, concurrency.
- AI calls: schema validation, latency budget, timeouts and prompt-injection boundaries.

If framework or package APIs have changed, consult its current official docs before coding.