v3.0.0-beta.4

Minor Changes

• #388 f053fb9 Thanks @BramKaashoek! - Add support for External and ExternalAmount tax modes on carts.

  New behavior

  • External tax mode — LineItem, CustomLineItem, and shipping methods can now carry an externalTaxRate:
    • createCart honors LineItemDraft.externalTaxRate, CustomLineItemDraft.externalTaxRate, and CartDraft.externalTaxRateForShippingMethod.
    • addLineItem, addCustomLineItem, and setShippingMethod/setCustomShippingMethod accept externalTaxRate.
    • New update actions: setLineItemTaxRate, setCustomLineItemTaxRate, setShippingMethodTaxRate.
  • ExternalAmount tax mode — explicit gross amounts can be supplied per item and at the cart level:
    • New update actions: setLineItemTaxAmount, setCustomLineItemTaxAmount, setShippingMethodTaxAmount, setCartTotalTax.
    • In this mode the cart's taxedPrice is whatever setCartTotalTax last set; it is no longer aggregated from line items. taxedShippingPrice continues to mirror shippingInfo.taxedPrice.
  • All tax calculations now respect cart.taxRoundingMode (HalfEven / HalfUp / HalfDown) instead of always using Math.round.

  Cart total recomputation after update actions

  CartUpdateHandler.apply now recomputes cart.taxedPrice and cart.taxedShippingPrice after every update batch (except in ExternalAmount mode, where the cart total is authoritative via setCartTotalTax).

  This fixes a pre-existing latent bug: previously these fields were only computed once during create() and were never refreshed after update actions, so e.g. running setShippingMethod after cart creation would leave the cart-level aggregate stale. It didn't show up before because LineItem.taxedPrice was never populated in any mode, so the aggregate had no contributors that could drift. With the new tax-mode work, line items and custom line items now actually carry taxedPrice, which made the gap observable and required fixing.