Fix assignment and empty-cart problems

Buyer steps

The cart is empty

Add an item before assigning destinations. The expected OrderRoutes state is a single prompt to add items, with no previous assignments and no save button.

An item is unassigned

Return to the cart, choose one of the merchant's two destination presets for every item, and save again. Checkout can require complete assignment before the buyer continues.

Assignment, pricing, validation, or save failed

Stay on the cart, correct the destination choice or requested detail, and retry. The documented recovery keeps the buyer on the cart instead of treating an incomplete assignment as a completed checkout step.

The last cart item was removed

Shopify should show its native empty-cart state, and OrderRoutes should show only the add-items prompt. Old assignments and the save button should no longer appear.

Merchant support steps

1. Confirm that both merchant-configured destination presets are present.
2. Ask the buyer which step failed, without requesting an address, checkout token, account value, or order identifier.
3. Have the buyer assign every current cart item and retry from the cart.
4. If the final-item state stays stale, preserve a sanitized description and route it for technical review. Do not claim success or ask the buyer to work around the assignment controls.

If the last-item state does not clear as described, stop and contact support. Do not rely on stale assignments or bypass the assignment controls.