This looks awesome!
To the tune of how boundaries can be awesome, we had a JavaScript project which was 1 codebase split across background and foreground pages (chrome extension). Implementing a boundary type system ensured that we never put background-only concepts in the foreground (where they would break). I caught several errors that I added in once this boundary checker was implemented.
Having a similar type of concept for organizing Elixir code would be really useful. I’m convinced that “people policies” are not enough, only tools can guarantee it. The compiler seems like the right place for it.
