I found out what the actual issue was with saves — it wasn’t that
xScripts needed to be recompiled (although it helped load previous
saves from the Windows build on Steam), it was that Ruby 2.1 doesn’t
seem to work with the saves, @mathewv might have determined this when
selecting 2.2 as the minimum. I have Ruby 2.3 on my system, installed
through Homebrew, so that is what I selected for my particular build.
The .app happens to be a tweaked version of the one provided when
grabbing a copy of the game from Steam, as I am unfamiliar with the
process of collecting frameworks into an app bundle, at least with
cmake/qmake. All you need to do is replace the .app in
~/Library/Application Support/Steam/SteamApps/OneShot/ to play on Mac!