If you pin python version using .python-version, then the virtual environment can't be activated. See reproduction below: -> % mkdir uv-venv-bug && cd uv-venv-bug [~/uv-venv-bug] -> % uv python pin ...

This was enabled recently in Serenity so I though we could do the same? I checked with python 3.9.7 and it builds just fine. Haven't done any tests beyond that though.