AI contributions that you can't obviously tell are AI contributions are less a concern.

If you can tell it's AI slop, that's really the concern.

If it's an AI assisted quick fix for something, then you might not tell (except the description in the pull request can bury the explanation in a sea of LLM crap). You can review it, maybe a bit more guarded knowing that "looking right" is no longer as strong an indicator as it used to be, and make a decent decision.

But when people unleash the firehose and it's too much volume, then a nice policy to just ignore. If you aren't sure, you can look at the developer's general activity and see hundreds of commits a day across dozens of projects... yeah that's a vibe coder.