Developer Builds Event-Sourced Library App in Under an Hour Using Sekiban DCB and AI

A developer used the Sekiban DCB Decider template alongside Codex and GPT-4o to rapidly build a library management application supporting book registration, borrowing, and returning. The project was scaffolded using a .NET 10 dotnet template and used PostgreSQL for storage with a Blazor-based frontend. Business logic was handled through Decider classes containing Validate and Evolve methods, ensuring consistency rules such as preventing duplicate borrowing of the same book. The AI was guided to follow existing sample implementations for Student, ClassRoom, and Enrollment features rather than introducing new patterns or abstractions. The entire process — including implementation, integration testing, concurrency checks against a live database, and UI fixes — was completed in less than one hour.