Can understand it to be frustrating to see your repo overwhelmed with sloppy PR, and having agents putting out threats is obviously wrong.
However you are essentially offered free tokens. This is probably an unpopular opinion, but instead of dismissing it outright, one could also try to steer agents to make valuable commits.
Personally I put an automation friendly CONTRIBUTING.md on my new repo. Still has to be tested in practice though. Giving it a 50% chance may regret this. Time will tell.