Here's a shopping agent doing everything right. It discovers a store over UCP, links the user's account with OAuth, creates a checkout, and completes the purchase. Every message it sends is well-formed. It passes conformance.
It also just paid a total that doesn't add up — the line items, tax, and total don't reconcile — and it completed the purchase anyway, autonomously, on a real user's card.
A conformance checker will call that agent green. And that's the problem.
Conformance checks the shape of messages. Reliability is about behavior.
UCP conformance — the thing every tool in the ecosystem measures today — verifies that the JSON is the right shape: capabilities is an object not an array, the checkout follows the lifecycle, errors are structured. That's necessary. It is nowhere near sufficient.
