Could you extend the comment to explain why this is needed? When do we expect to be hidden? I assume it is during a pick activity that we want to stay alive...  

Rather than having the "once" condition managed here, it seems to me that it would be cleaner to set keepAppOpen when we launch the activity and clear it when we get a response or error from the activity.

Also, what about the case where we get a phone call or an alarm rings while managing ringtones? I think we'll end up closing and losing what we were doing.  Maybe it would be better to just call window.close() when the user uses the back button?    We wouldn't always close explictly, but wouldn't close accidentally, either.

And actually, how does this interact with sheets?  If I click "Manage Ringtones" then swipe to go back to the settings app, I might change my mind and want to swipe back to the manage ringtones screen. But it wouldnt' be there anymore!

Its a cool idea to save memory like this by exiting when possible, but it seems like it might cause more problems then it solves.

Why is it that we can't use a window disposition activity to launch the management app?  Is it because then other apps could spoof the same activity?