> Correct me if I'm wrong, don't process launches use the `env` kwarg for Popen, not the raw os.environ['PATH']?

If you don't provide env, it'll use the current process's environment, and if you do provide it without copying at least some entries, chances are your process won't start (and in general, you copy the current value and add to it). I've never seen anyone try to reset PATH here, nor would I recommend it.