You're technically correct (which is the best kind of correct!). But I would opine that, if your build system is not hermetic, i.e. you don't inject time and do

You're technically correct (which is the best kind of correct!). But I would opine that, if your build system is not hermetic, i.e. you don't inject time and don't prevent access to the external world, you cannot know whether your build is reproducible or not.