test(e2e): add custom-cart-method recipe e2e tests

[itsjustriley]

WHY are these changes introduced?

Adds e2e test coverage for the custom-cart-method recipe, which enables customers to change product variants directly within the cart using inline dropdown selectors. This continues the systematic testing of recipes to ensure all user-facing changes are validated.

This PR is stacked on #3545 (subscriptions tests).

WHAT is this pull request doing?

Adds e2e/specs/recipes/custom-cart-method.spec.ts with 4 comprehensive tests covering:

• Product option selectors display in cart line items
• Variant changes update product link URLs to reflect new selection
• Cart maintains single line item (no duplication) when variant changes
• Updates happen without page reload (cart dialog stays visible)

Tests use locator('select') for dropdown elements, verify URL changes to confirm variant updates, check cart dialog visibility to ensure no reload, reuse CartUtil for cart operations, and follow established patterns from existing recipe tests.

The custom-cart-method recipe implements the updateLineByOptions cart method, allowing customers to change product variants (size, color, etc.) without removing and re-adding items.

HOW to test your changes?

# Run custom-cart-method recipe tests only
npx playwright test --project=recipes custom-cart-method

# Run all recipe tests
npx playwright test --project=recipes

All tests pass (34 total: 6 bundles + 6 combined-listings + 5 subscriptions + 4 custom-cart-method + 7 infinite-scroll + 6 markets).

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[shopify]

Oxygen deployed a preview of your recipe-test-custom-cart-method branch. Details:

Storefront	Status	Preview link	Deployment details	Last update (UTC)
Skeleton (skeleton.hydrogen.shop)	✅ Successful (Logs)	Preview deployment	Inspect deployment	March 9, 2026 2:00 PM

Learn more about Hydrogen's GitHub integration.

[binks-code-reviewer]

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📋 History

✅ 1 findings → ✅ No issues

[binks-code-reviewer]

selectDifferentOption can accidentally select placeholder/empty option

The helper builds enabledOptionValues from all non-disabled options and selects the first value different from initialValue. If the <select> contains an enabled placeholder option like <option value="">Select…</option>, nextValue may become an empty string. Selecting "" may be a no-op, fail validation, or cause UI reversion, leading to intermittent failures depending on product configuration.