Apple bough a port of UniSoft SYSVr2 to the Apple platoform and dubbed it A/UX. Version 2 onward were technically significant as ToolBox and Finder had been ported to Unix and allowed MacOS apps to run on top of Unix. They didn't offer process virtualization so they could all crash eachother out.
"/mac/sys — This directory contains the system folders for startup and login. The System file provided with Release 2.0 of A/UX is almost identical in functionality to the System file provided with Release 6.0.5 of the Macintosh system software."
Additionally I always thought the Gestalt Manager was a System 7 thing and was surprised to learn it was introduced along with system 6.0.4 and A/UX so applications could tell if they were running on it: https://developer.apple.com/library/archive/documentation/ma...
Still, since you didn't need to run MacOS apps much, it wasn't really a problem. MacOS couldn't crash the Unix or X subsystems, or anything (else) on them, and nothing else could crash MacOS.
