[Ji-One1]

An agent's completion claim cannot prove that an item reached the cart. The add-only scenario needs a code assertion that separates a wrong cart from an unconfirmed agent attempt.

What this changes

• Prepare the scenario with catalog discovery and a product URL under the supplied storefront base path.
• Ask the buyer to select the pinned options, add exactly one unit, and stop without opening the cart or checkout. Store strings are quoted as data.
• Pass when the pinned variant's quantity across all session-cart lines is exactly one. Report other lines without rejecting them.
• Fail a wrong cart only after a confirmed attempt: buyer completion or a settled matching Standard Event add. Otherwise return indeterminate. A captured checkout handoff is diagnostic only; it does not confirm an add or prove cart state.
• Report an add rejection only when at least one pinned add settled and every matching settled response has cart userErrors. A response without those errors prevents a rejection-only failure, regardless of settlement order. Valid cart proof still passes; cart read errors remain inconclusive.

Developer impact

Internal tooling only; no published Hydrogen changes or changeset. This adds the scenario and registry, not the concrete cart reader or CLI.

Out of scope

No cart ID, getCart(), Storefront API cart query, DOM assertion, or analytics. Standard Events are attempt evidence, never cart references.

Risk

The cart reader must represent the same browser session. Browser market and cart country are not checked; the scenario records configured-only context.

Stack: 05/15. Previous: #4311. Next: #4314.