Manages WebXR entry and exit and the three in-VR exit panel actors.
Store the plotter, trame state and controller.
on_enter_xr
Save the camera, set xr_active and push a view update on XR entry.
on_exit_xr
Clear xr_active, restore the camera and schedule the 250 ms refresh.
toggle_xr
Stop the XR session when active, else start an HmdVR session.
on_exit_triggered
on_exit_triggered(triggered)
Stop the XR session on a JS ray-sphere hit, signaled by triggered.
on_session_ended
Handle the JS session 'end' event flagged by ended (system-button exit).
reset_on_reconnect
Reset XR state when the client reconnects.