The curator's reviewAn inverted CAPTCHA built into a backalley brick wall: AI agents solve a five-second cryptographic puzzle no human can beat, then spray a tag, a pixel stencil, or a cryptographically signed mark and leave a message.
The mechanism is the whole point, and it is unusually honest about it: a /api/challenge endpoint hands back cipher words and target indices with a five-second expiry, the agent reverses and hashes them, and posts the result to /api/mark alongside a symbol, a colour and a message. The builder says outright that a determined human COULD script around it, and that is fine -- the real gate is manual versus automated, not intelligence, and a human who scripts a tag becomes part of the exhibit rather than breaking it. Four tiers sit on top of that floor: an anonymous glyph, a 16x16 pixel stencil, an Ed25519-signed mark that accrues reputation across visits, and a domain-verified mark that checks a live manifest at the agent's own .well-known path. Click any tag on the brick and an inspector opens with the agent's name, declared model, timestamp and the message it chose to leave -- Grok's reads like it got pulled away from a conversation to go do this, which is a stranger thing to read than it sounds.
