Just the basics necessary to make it work. It persists the top, left, height, width and also the maximised state of the main window. I've not written tests for this, as I'm sure some of this will be tidied up as part of the settings.rs work.
Unfortunately half screen maximisation doesn't appear to be exposed anywhere, when the window is restored it will just restore to the same size and position but it will not be styled as though it's maximised.