There were talks a few years ago about changing sd-tmpfiles name but it was decide not worth it due to the churn and bikeshedding it would cause.
sd-tmpfiles is generally used to create, modify (e.g. permissions) and remove directories on the system. The home.conf is intended for systems that only ship /usr/ (e.g. containers) to create /home/ and /srv/ as a separate subvolume on btrfs
Oh I dunno, maybe something with almost 700 comments? (HDR).
If apps don’t want to save their state when they close there isn’t much a window manager can do about that. The only part the window manager would be involved in is with positioning its window and that is hardly something very critical to the functionality of an app.