Almost certainly not. All you would really need to do to stop this is limit who can submit pull requests to verified devs. Things go back to the way they were during the clunkier, before times when everyone used Subversion, when there were more hoops to jump through to contribute code. Make it so you need an existing contributor to "mentor" first-time contributors (making sure they aren't an AI, are writing competent code that follows project standards, etc.) before giving access to submit dozens of pull requests.

Need some way to sort contributors by "trust", e.g. if their PRs have been accepted before, if their account has existed before GenAI was invented, etc

ive seen developers complain about shitty prs before ai, ive seen devs literally not accept prs because they dont want to waste time understanding someone else's code. so no, this is a non issue.