Problem: setup_python_env() skips uv sync when .venv/ exists. If a
previous sync was interrupted (e.g. network timeout), the directory
exists but is broken, and every subsequent session silently uses a
corrupt environment.
Solution: remove the isdirectory guard and always run uv sync. It is
idempotent and near-instant when dependencies are already installed,
so the only cost is one subprocess call per session.
Barrett Ruth
976838d981