I would be satisfied if the language supported this use case by offering a “void my warranty” annotation that let a given source file access the privates of a given import.

Companies with monorepos could easily just ban the annotation. OSS projects could easily close any user complaint if the repro requires the annotation.

This seems like a great compromise to me. It would let you unambiguously mark which parts of the api are private, in a machine checkable way, which is undoubtedly better than putting it into comments. But it would offer an escape hatch for people who don’t mind voiding their warranty.