Xbox One version of window_has_focus()?

I'm creating a game on the Xbox One using UWP. I'm trying to get the correct behavior when the player presses the Home button - when the overlay comes up, gameplay should pause.

But I can't detect when the overlay comes up. I can't detect if the player presses the Home button because that's not supported by gamepad_button_check() (since it's an OS-level thing). I thought uwp_is_constrained() would help, since the description specifically states that constrained mode can be activated when the game doesn't have the focus, but that's not the behavior I'm seeing - bringing up the overlay doesn't seem to trigger constrained mode. And of course, window_has_focus() doesn't work on the Xbox One.

Does anyone know how to detect if the Xbox overlay is up within GameMaker?