Under normal usage, iOS will kill apps a lot earlier than 10 minutes. In the general case it's really not possible to do this, and I would argue that shipping with a flaky feature is probably worse than not shipping with it at all.
In any case, there's a property `UIApplication.backgroundTimeRemaining` that tells you how long you have, so you can use that to calculate the appropriate notification time.
And yes, the app in question of course does exactly that notification dance (I've used it since long before it got its current name). GP is talking about a new feature to keep sessions open in bg for a loong time. I've disabled it, not for fear of tracking but because it seems like a silly way to forget connections open and drain the battery for no reason.
App has indeed also always supported mosh... me I just attach to tmux. But I agree with whoever wrote it's better to have such a bg hack feature than not, for those who find it useful.