Cloudflare CAPTCHA on at least one ampersand

I use Cloudflare's CAPTCHA (they call it a "Managed Challenge") on simonwillison.net/search/ to prevent crawlers from following every single possible combination of my faceted search UI. This was getting pretty annoying, since I had to wait for the challenge every time I searched my own site. I don't particularly care about regular ?q=term searches. Where things get messy is if a crawler starts…