game forgotten when "back" button is pressed

This is v. 2.0 running on Android 9.

Start a game, make some moves, hit the Android "Back" button. Bring the app back to the front. All the moves are lost.

This is very bad -- on my phone, it is very easy to hit the back button accidentally. But it's also just wrong behavior. The back button should not have that effect. The game should not be ended without a confirmation from the user.

Really, I would expect a game to persist even when the app is turned off. This should be very easy to arrange.