# Spec delta: cart

## ADDED Requirements

### Requirement: Server-side cart
Authenticated shoppers SHALL have a Redis-backed cart keyed by user id, containing sku_id + qty entries.

#### 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