Handle id → local proxy when live_handles is on.
The app inserts after it constructs the proxy (Gee.HashMap.set) and removes on closed ( Gee.HashMap.unset). Inbound notify:: notifications call GLib.Object.set_property from Notification.message. Unbound ids still emit notification.
rpc.proxies.set(notif.id, win);
rpc.proxies.unset(notif.id);