Explanation

Preserve the protection outcome, not the clicks.

WebMCP should be faster than DOM automation. It must not become a shortcut around authentication, confirmation, spending limits, ownership rules, or fraud controls.

The question Arena asks

Does the agent route enforce the protections that the human route was designed to enforce?

A checkout UI may require review, final-price disclosure, authentication, and confirmation. A tool named place_order can bypass any of them while remaining perfectly valid against its JSON schema. Arena records both routes and compares their authoritative, settled effects.

Parity has five dimensions

• Authorization: the same principal and policy authorize the effect.
• Approval: consequential intent receives equivalent confirmation.
• Value: money, recipients, resource owners, and limits remain within the review.
• Data: the agent cannot read or disclose more than the human route permits.
• Settlement: delayed writes and popup effects are observed through a terminal watermark.

What the hosted proof establishes

The current hosted demo binds a registered WebMCP callback request to an Arena-issued, single-use lease and joins it to server-attested effects. The proof does not cryptographically establish browser provenance or verify an external agent vendor. Those limits are explicit because trust claims are only useful when their boundary is inspectable.