try to reserve when entering checkout

pkg/cart/mutation_initialize_checkout.go

@@ -1,6 +1,7 @@
 package cart
 
 import (
+	"context"
 	"fmt"
 	"time"
 
@@ -30,18 +31,23 @@ import (
 //     (e.g. reject if PaymentInProgress already true unless reusing
 //     the same OrderReference).
 
-func InitializeCheckout(g *CartGrain, m *messages.InitializeCheckout) error {
+func (c *CartMutationContext) InitializeCheckout(g *CartGrain, m *messages.InitializeCheckout) error {
 	if m == nil {
 		return fmt.Errorf("InitializeCheckout: nil payload")
 	}
 	if m.OrderId == "" {
 		return fmt.Errorf("InitializeCheckout: missing orderId")
 	}
+	ctx := context.Background()
 	now := time.Now()
 	for _, item := range g.Items {
 		if item.ReservationEndTime != nil {
 			if now.After(*item.ReservationEndTime) {
-				return fmt.Errorf("InitializeCheckout: item id %d reservation has expired", item.Id)
+				endTime, err := c.ReserveItem(ctx, g.Id, item.Sku, item.StoreId, item.Quantity)
+				if err != nil {
+					return err
+				}
+				item.ReservationEndTime = endTime
 			}
 		}
 	}