A package path is one argument. Git status uses NUL records and returns git's status. A failed coverage command leaves reports unread, coverage keeps the longest path match, and site walks no longer recurse.
Node resolves a relative import from the real path of the module. A symlinked test was loading the original source, so every mutant survived. Modules that reach the file under test are now real copies in the overlay.
Each worker keeps a private copy of the file under test and links the rest of the project, so the original tree stays put. The default is one worker per core, and --max-workers can set a lower cap.
Robert C. Martin