You explained your modular, layered architecture with service and repository layers for scalability. How did you ensure that your FastAPI services handle error management and maintain data integrity?

We designed the application with a clear separation of concerns: the API layer, the service layer, and the repository layer. The service layer contains business logic and orchestrates calls to the repository, which handles all database interactions. Error handling is centralized in the service layer; we catch domain exceptions and translate them into HTTP responses. For data integrity, we use database transactions in the repository layer, ensuring that either all changes succeed or none do. We also employ optimistic locking and version checks to prevent lost updates. By keeping error handling in the service layer and data consistency in the repository, we maintain a clean boundary that makes the FastAPI endpoints simple, testable, and resilient to failures.