Week 5 engineering rules

• Read docs/TASKS.md and the affected router, schema, model, and test before editing.
• Keep each agent inside an explicit file scope; one integration agent owns shared schemas and final review.
• API success is \{ "ok": true, "data": ... \}; API failure is \{ "ok": false, "data": null, "error": \{ "code": ..., "message": ... \} \}.
• Collection data contains items, total, page, and page_size; page >= 1 and 1 <= page_size <= 100.
• Validate nonblank text at the Pydantic boundary. Return 404 for absent resources and 409 for unique-name conflicts.
• Check every bulk-operation ID before mutation so one missing ID rolls back the whole request.
• Frontend optimistic edits must snapshot old state and restore it when the request fails.
• Prefer focused endpoint checks during implementation; run the complete suite only after branches are integrated.
• Never commit secrets, local databases, generated caches, or unrelated changes.