Can I vibe code OrderBump?

Build a custom Shopify app to replace OrderBump for pre-purchase checkout upsells using modern Shopify app architecture.

1. SYSTEM ARCHITECTURE
- Build a standard Shopify Remix app using standard App Bridge authentication.
- Implement a Checkout UI Extension targeting `purchase.checkout.cart-line-list.render-after`.
- Store configuration rules in a Postgres database using Prisma ORM.

2. DATA MODEL
Create an `UpsellRule` model with:
- `id`: String (UUID)
- `shop`: String (Shopify domain)
- `triggerVariantIds`: String array
- `offerVariantId`: String
- `title`: String
- `description`: String
- `discountType`: Enum (PERCENTAGE, FIXED_AMOUNT)
- `discountValue`: Float
- `priority`: Int
- `active`: Boolean

3. EXTENSION LOGIC
- On extension load, fetch the cart lines via the `useCartLines` hook.
- Send cart variant IDs to an app backend endpoint `/api/evaluate-upsell`.
- The backend evaluates `UpsellRule` records where `shop` matches, checking if any cart line matches `triggerVariantIds` and the `offerVariantId` is not already in the cart.
- Return the highest-priority matching offer rule object to the extension.
- Render a styled Checkout UI component containing: offer title, image, price with applied discount calculation, and an 'Add' button.
- When clicked, call the `applyCartLinesChange` hook to add the `offerVariantId` to the checkout line items with an explicit custom attribute marking it as an upsell.

4. FAILURE MODES & EDGE CASES
- Handle variant inventory checks: if the offer variant is out of stock, evaluate the next priority rule.
- Ensure non-blocking failure: if the backend endpoint times out or fails (500 response), render nothing silently without interrupting checkout load times.
- Check if the offer product is already in the cart; if so, do not display the offer.

5. OUT OF SCOPE
- Do not build multi-variant A/B split testing.
- Do not build legacy checkout.liquid integration.

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