AFAIK you can't copyright AI generated content. I don't know where that gets blurry when it's mixed in with your own content (ie, how much do you need to modify it to own it), but I think that by that definition these companies couldn't claim your code at all. Also, with the lawsuit that happened to Anthropic where they had to pay billions for ingesting copyrighted content, it might actually end up working the other way around.