> I had been hoping someone would introduce the non-virtualenv package management solution that every single other language has where there's a dependency list and version requirements (including of the language itself) in a manifest file (go.mod, package.json, etc) and everything happens in the context of that directory alone without shell shenanigans.

Isn't that exactly a pyproject.toml via the the uv add/sync/run interface? What is that missing that you need?