Add items to cart → Update quantity → Apply discount code → Checkout (convert to order)

const item = await client.cart.addItem({
  cartId: 'cart_id',
  product: 'product_id',
  variant: 'variant_id',
  option: 'option_id',
  quantity: 2,
})

const cart = await client.cart.getCart('cart_id')
// cart.itemsTotal     → items subtotal (auto-calculated)
// cart.shippingFee    → shipping fee
// cart.discountAmount → discount amount
// cart.totalAmount    → final amount (auto-calculated)
// cart.items.docs     → cart item list

// Update quantity
await client.cart.updateItem({
  cartItemId: 'item_id',
  quantity: 3,
})

// Remove item
await client.cart.removeItem({
  cartItemId: 'item_id',
})

// Clear all items
await client.cart.clearCart({ cartId: 'cart_id' })

// 1. Validate discount code (optional)
const result = await serverClient.api.validateDiscount({
  code: 'WELCOME10',
  orderAmount: cart.itemsTotal,
  customerId: 'customer_id',  // for per-customer usage validation
})
// result.valid, result.discountAmount, result.freeShipping

// 2. Apply discount code to cart
const updatedCart = await client.cart.applyDiscount({
  cartId: 'cart_id',
  discountCode: 'WELCOME10',
})
// updatedCart.discountAmount → discount amount
// updatedCart.totalAmount    → final amount after discount

// 3. Remove discount code
await client.cart.removeDiscount({ cartId: 'cart_id' })

const shipping = await serverClient.api.calculateShipping({
  orderAmount: cart.itemsTotal,
  postalCode: '63000',  // Jeju surcharge auto-applied
})
// shipping.shippingFee, shipping.freeShipping

import { generateOrderNumber } from '@01.software/sdk'

const order = await serverClient.api.checkout({
  cartId: 'cart_id',
  orderNumber: generateOrderNumber(),
  customerSnapshot: {
    email: 'customer@example.com',
    name: 'John Doe',
    phone: '010-1234-5678',
  },
  paymentId: 'payment_id',  // omit for free orders
  discountCode: 'WELCOME10', // code already applied to cart
})