[Ji-One1]

The preceding layers need one command that runs the add-only scenario against an existing storefront. This PR connects those layers and gives the operator a result and artifact location.

What this changes

• Add pnpm storefront-e2e, argument validation, limits, exit codes, signal handling, and a terminal summary.
• Require --country and --language before browser startup. They configure catalog queries and the buyer goal; they do not set the market or verify browser/effective API context.
• Wire the owned browser, early Stagehand observer, catalog scenario, selected Standard Events, buyer, and same-session cart reader. Resolve model credentials only when the buyer starts.
• Remove Stagehand flow-log variables before SDK loading. Document setup, verdicts, private artifacts, and known limits. Standard Event records keep only the focused payload fields from Define read-only Standard Event evidence #4311, with no event cart IDs; captured checkout URLs remain private, unredacted diagnostics.
• Update the documentation and scripted browser fixtures for blocked checkout without automatic buyer stop. Cover continued execution, recovery to a readable storefront page, a blocked popup that leaves the original page readable, and an unrecovered same-tab error page that makes the cart read inconclusive. These fixtures do not test model recovery. Checkout capture does not confirm an add or suppress the configured cart reader.

Developer impact

Uses Node 24 source execution and built workspace packages. Internal tooling only; no published Hydrogen changes or changeset. The existing scripted Playwright suite remains separate.

Risk

Use a storefront where a guest add is permitted. The agent changes its session cart and makes model calls. Private artifacts and terminal output retain recorded values; screenshots are not masked. The Storefront API supplies catalog data only. Cart proof requires the storefront's same-session AJAX endpoint.

How to Test

1. From the repository root, use Node 24, run pnpm install and pnpm run build:pkgs, and install Chrome or set PLAYWRIGHT_BROWSER_EXECUTABLE_PATH.
2. Set a supported model credential, such as ANTHROPIC_API_KEY.
3. Run pnpm storefront-e2e https://<your-storefront> --country US --language EN with values suited to that storefront.
4. Read the terminal reason and saved result.json, evidence, and screenshots. For a pass, confirm one unit of the pinned variant in the recorded session-cart assertion. No purchase should occur.

Stack: 14/15. Previous: #4321. Optional report: #4323.