All the developments are done in a virtual remote file system. From editing to compiling, everything is done remotely. Of course this does not fully stop people from doing manual c&p, but it still makes it hard enough to discourage it.

I have no knowledge of actual enforcement mechanisms, but it is way, way, way easier to do all development on the distributed file system that feels like a local disk than it is to copy things over locally.

If you need to do development locally, you are either doing something very wrong or extremely specialized.

So there is effectively no motivation to copy the sources over. And because everything is on this distributed file system and built from it in a very bespoke environment, I would imagine (with no inside knowledge at all), that it is easy for auditors to detect when someone starts copying things out.