Function default_socket_path 

pub fn default_socket_path() -> PathBuf

Resolves the default socket path for the oxibrain daemon. Canonical per the Foundation discovery contract (mirror of oxibrain-client’s default_socket_path, which ships in 0.3.x; we pin 0.2 so the resolution lives here): $OXIBRAIN_SOCKET if set, else $HOME/.oxi/brain/oxibrain.sock. Never creates directories.