I was talking more generally about the "You can't patent or copyright code that was generated with an LLM". Who can prove that I didn't write the code myself?

I was talking more generally about the "You can't patent or copyright code that was generated with an LLM". Who can prove that I didn't write the code myself? And if I did, how am I to prove it? That goes in both directions. It's not like there is a watermark in the code telling the whole wide world that this was AI generated or human made. So I write code (with or without an AI assistant) and claim copyright... they generate the same code. I sue them. How does any of us prove that we wrote the code by hand?