Hi, I'm back again :P
Since it's probably about time for it, and I forgot to send that email a while back, I might as well ask now: are there plans to make Wine use libdecor at some point in the future, so that there are "native" window decorations for desktops that don't provide xdg-decoration? A lot of the work here for compositor-initiated window closing is a requirement for that.
There may be performance implications for this, IIRC, since you'd have to work with another library's event loop on top of another GUI toolkit not made for games, and GTK doesn't support wl_subsurfaces normally *iirc*. SDL does it, at least, so there's that. But something to maybe consider. I'm satisfied with the default window decorations right now, myself.
--
https://gitlab.winehq.org/wine/wine/-/merge_requests/3909#note_46062