Obviously it only works when the app is launched via Briefcase, but like --shutdown-on-exit, it could still be useful for all kinds of scripted situations.

Yes, that was the intention of these options.

If you need a permanent connection to the Android device, you would have to use ADB manually. For this it would also be practical to have access to the ADB downloaded by briefcase. E.g. via a new command briefcase tool adb. Then you would use briefcase tool adb forward tcp:5555 tcp:6666 to have a permanent connection. And to close this connection you can use briefcase tool adb forward tcp:5555 --remove. This would give you complete freedom to do every configuration with ADB without searching for the path where ADB is downloaded or manually downloading ADB. But this would be a different feature.

There are some similar ideas in #747.