It's not a problem. If you give a work to an AI and say "rewrite this", you created a derivative work. If you don't give a work to an AI and say "write a program that does (whatever the original code does)" then you didn't. During discovery the original author will get to see the rewriter's Claude logs and see which one it is. If the rewriter deleted their Claude logs during the lawsuit they go to jail. If the rewriter deleted their Claude logs before the lawsuit the court interprets which is more likely based on the evidence.