LuneOS tries to keep webOS alive

The Nexus 4 hardware buttons are power and volume up/ down. The Home button is software [ If an app is truly full screen you can summon the software buttons with a down swipe at the top edge ]. This is also true for Back. But that doesn't make any difference to the functionality of either in Android unless the OS has somewhat but not entirely crashed, such that touch screen isn't working but hardware buttons are.

The _issue_ is that "back" in Android, as with a modern web browser, has unpredictable consequences. Not literally impossible to predict of course, but requiring such a complicated model of what's happening that ordinary users end up modelling it as "Sometimes it will do what you expected and sometimes not". This confusion was true for the hardware "back" button on my oldest Android phone, and it's true for the software "back" button on my Nexus devices.

One problem is that Android (intentionally, and _almost_ seamlessly) hides some context from the user by not making you explicitly start / stop programs. This means that sometimes what you think of as analogous to "I'll switch back to that other program" is actually implemented as "let's run the other program again and tell it to restore as much context from its last session as possible". The "back" button is one of the leaks where you can see this hidden context, as an app must go to great lengths to remember why you were where you were, or else "back" won't always take you exactly where you expected.