pub fn runtime_dir() -> Result<PathBuf>Expand description
Per-platform runtime dir for the control socket: $XDG_RUNTIME_DIR/mcpmesh
when that var is set, non-empty, and absolute (Linux); otherwise $TMPDIR/mcpmesh, or
std::env::temp_dir()/mcpmesh when TMPDIR is unset (macOS — its per-user $TMPDIR is
itself private). Returns the path only; the daemon creates it 0700 + verifies
ownership before binding (a bind-time concern — see cli ipc::bind_control_socket).