A manually-installed venv inside the cloned repo can be destroyed by the
agent running a relative-path command against its own checkout (rm -rf venv,
uv venv venv, etc.), silently wiping the running runtime mid-session. Moving
the canonical manual-install venv to ~/.hermes/venvs/hermes-dev means no
relative path from the agent's workspace resolves to its own runtime, making
the bug class impossible without any command-detection code.
Closes the root cause of #7779. The managed install.sh layout is unchanged.
c6c1fd8b6b