[Someone]

I don’t understand. Any MacOS Finder that had an open file handle into an application bundle runs on the Unix version of MacOS, and that allows deletion of open files (the inode stays around until the process exits), doesn’t it?

Or did/does the Finder check whether to-be-deleted files are open? Or did I forget how older Mac file systems behaved?

[ksherlock]

If "years" means decades, it would have been classic MacOS which played by a very different set of rules.

[StilesCrisis]

Finder does check this, yes. You can't delete open files in Finder.

[gwbas1c]

It was an open file handle on Unix OSX to a dylib.