- associate target windows with the selected prefix through the guest PID,
X11 _NET_WM_PID, NSpid and the loader socket; fail closed when ownership is
unknown;
- let --once run without either opt-in gate, matching the documented
diagnostic;
- route SIGHUP through the restore handler;
- cache non-empty WM_CLASS results per window and prune stale entries;
- cover unreadable /proc, host PID mapping and prefix ownership in tests.