I was recently talking to a coworker about this same topic. I told them that one of my fears about LLMs is that the flood of vide-coded sloptributions would eventually make FOSS less free. Maintainers wouldn't be able to keep up with the volume, and would resort to locking down contributions to well established community members and contributors.
Basically, gone will be the days of skilled randos contributing freely to projects, or beginners jumping in to help with easy, small issues/fixes. Now you'll need to be well known, be vetted formally by other contributors, etc.
The agents.md compute sabotage idea is interesting, essentially Anubis but for your repository.