How do you form a group nobody can admit they're in?

Arun invoiced a design agency ₹1,20,000 in January. It's August. He is in a 4,000-member designers' Discord. He could post the agency's name right now and warn everyone. He won't, and you already know why: the freelancer who publicly names a client stops getting briefs. He'd pay for it alone, and everyone else would benefit. Here's the part that makes it a systems problem rather than a sad story. Three other people in that same Discord are owed money by that same agency. None of them knows. Each one is running the same arithmetic Arun is, arriving at the same answer, and saying nothing. Four people who together have real leverage. Individually, none of them can afford the first move. I built an agent for this over a hackathon weekend. The interesting part wasn't the AI. It was that every obvious solution destroys the thing you're trying to protect. The obvious version, and why it dies "Just make a private channel for victims of bad clients." To join, you say who b