Application Layer

To refactor a fat controller, extract the business workflow into a Service Object that implements the Result Monad pattern, separating infrastructure calls and validation from core logic.

Railway Oriented Programming is a design pattern for chaining operations where each step either succeeds or fails, preventing deeply nested error handling and ensuring explicit error propagation.

You can separate CLI controllers from domain logic by adopting a thin controller pattern, moving complex multi-step operations into Service Objects that manage business workflows.

No dependencies are required to implement this clean application layer architecture, as it relies on TypeScript design patterns like Service Objects and Result Monads rather than external libraries.

A CLI command violates the Single Responsibility Principle by centralizing validation, infrastructure calls, and business logic, which you can fix by encapsulating complex operations in Service Objects.

The best way to handle explicit error propagation is using Result Monads within Railway Oriented Programming, which structures operations to cleanly pass success or failure states without deep nesting.