more changes

pkg/cart/mutation_add_item.go

@@ -2,6 +2,7 @@ package cart
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"log"
 	"time"
@@ -16,13 +17,14 @@ import (
 // This replaces the legacy switch-based logic previously found in CartGrain.Apply.
 //
 // Behavior:
-//   * Validates quantity > 0
-//   * If an item with same SKU exists -> increases quantity
-//   * Else creates a new CartItem with computed tax amounts
-//   * Totals recalculated automatically via WithTotals()
+//   - Validates quantity > 0
+//   - If an item with same SKU exists -> increases quantity
+//   - Else creates a new CartItem with computed tax amounts
+//   - Totals recalculated automatically via WithTotals()
 //
 // NOTE: Any future field additions in messages.AddItem that affect pricing / tax
 // must keep this handler in sync.
+var ErrPaymentInProgress = errors.New("payment in progress")
 
 func (c *CartMutationContext) AddItem(g *CartGrain, m *messages.AddItem) error {
 	ctx := context.Background()
@@ -32,6 +34,9 @@ func (c *CartMutationContext) AddItem(g *CartGrain, m *messages.AddItem) error {
 	if m.Quantity < 1 {
 		return fmt.Errorf("AddItem: invalid quantity %d", m.Quantity)
 	}
+	if g.PaymentInProgress > 0 {
+		return ErrPaymentInProgress
+	}
 
 	// Merge with any existing item having same SKU and matching StoreId (including both nil).
 	for _, existing := range g.Items {