The app embed and test slots

Nothing in your theme files is edited. Everything goes through Shopify theme app extensions:

1. App embed: Setup → Turn on. This enables the lightweight Proofsplit runtime on every page. Proofsplit publishes your approved tests into your store, so they load with the page: no extra request and no flicker. Only Proofsplit slots wait briefly (at most 1 second) while the runtime decides, never the whole page.
2. Test slots (app blocks): use the Add links to place a block where you want to test, for example the Reassurance line under Add to cart or the Free-shipping bar in the cart. Each block shows your default content. During a test, assigned shoppers see the approved variant instead.
3. Verify: Setup reads your live theme and shows which slots are placed where. Once shoppers visit, it shows Receiving data.

In the theme editor and on your storefront password page, Proofsplit never runs a test or counts a visit. If anything fails to load, every block keeps showing your default content, so nothing breaks.