Motivation
Regarding the interface layer: I think we need to make a cleaner distinction between pure interface and underlying function, basically creating a new layer (although I think that core is basically that layer already, partially).

For example, the add_readme function should probably be named the add_readme_file function and the add_readme function should be what is currently in the interface layer.

The motivation is that it's hard to test at the moment because it's stuck at the typer level.

Summary of desired enhancement
Refactor the interfaces layer to make the widen the distinction between interface and implementation.