How do I get Claude to write a useful MFTF test, not a brittle one?

Anchor on data and test fixtures, not on UI selectors. Prompt template: "Write an MFTF test that creates a SimpleProductFixture, adds it to the cart as a guest, places the order, and asserts the order is in Sales/Order grid by SKU. Use Magento_Catalog's built-in data entity and the storefront action groups; do not write new page.xml selectors." Then: vendor/bin/mftf run StoryName. The trick is forcing it to reuse Magento's published action groups (StorefrontAddSimpleProductToCartActionGroup, etc.) — tests built on those survive Magento upgrades; tests built on raw CSS selectors break on the next patch release.