# Spec Delta

## MODIFIED Requirements

### Requirement: Server-side cart
Authenticated shoppers SHALL have a Redis-backed cart keyed by user id, containing sku_id + qty entries. Reading the cart SHALL return, for every line, the SKU's current price, currency and stock together with the product's name, image and owning shop, so the storefront can group lines by shop and cap quantity without reading the fixed-data catalog. Lines whose SKU has become inactive or unpurchasable SHALL be omitted from the view.

#### Scenario: add and update
- **WHEN** a shopper POSTs sku + qty, then PUTs a new qty
- **THEN** GET /api/cart reflects the latest qty with current price/name snapshot

#### Scenario: unpurchasable SKU rejected
- **WHEN** adding a SKU that is inactive or whose product is not published
- **THEN** the API returns 400

#### Scenario: cart view carries shop and stock
- **WHEN** a shopper reads a cart holding SKUs from more than one shop
- **THEN** each line reports its shop and the SKU's current stock, so the storefront can group the lines per shop and cap quantity from the response alone