# Proposal

## Why

Cart, orders, shipments and invoices are the last mocked domains, and they cannot move one at a time: the fixed-data adapter keeps `cart -> orders -> shipments` in one shared state, so a live cart with a mock checkout dies on `EMPTY_CART` and mock invoices 404 on live order ids.

## What Changes

- Flip `cart`, `orders`, `shipments` and `invoices` to live **together**, so one purchase runs end to end.
- **BREAKING** (data): cart and order state moves from `localStorage` to Redis/Postgres; existing mock carts and orders do not carry over.
- Extend the cart line with its shop and stock so the cart keeps grouping per shop and the stepper caps at real stock; `CartItemView` already joins both (`apps/api/src/cart.rs:68-74`).
- Ask an anonymous shopper to sign in rather than fail: a live `addCartItem` answers 401 on a public page, which redirects to `/login?redirect=…`.
- Stop the shared contract lying: `Shipment.items` is required in TS but never returned, and `Invoice.invoice_no` is nullable live but non-null in TS.
- Keep `MOCK_ADDRESSES` behind checkout: live checkout takes the address in the request body.

## Capabilities

### New Capabilities

(none)

### Modified Capabilities

- `cart`: the cart view carries each line's shop and current stock.
- `frontend-mall`: the shopping and transaction flows run against the live API, and an anonymous add-to-cart prompts sign-in.

## Impact

`apps/api/src/cart.rs`; `packages/shared/src/{api,types}.ts`; the mall's `plugins/api.ts`, `nuxt.config.ts`, cart/checkout/order/invoice pages and `middleware/auth.ts`. The contract change means all three frontends rebuild.

## Non-goals

No addresses, favourites, coupons or storefront content. No stock check on add-to-cart; checkout stays the authority. Store names on order surfaces keep their generic fallback until Wave 4.