feat(cart): enhance item update functionality to support variant changes and improve cart editing policies

app/Domains/Purchase/Services/Checkout/StartCheckoutService.php

@@ -24,6 +24,7 @@ class StartCheckoutService
         private readonly CatalogSelectionResolver $selections,
         private readonly PurchaseItemSnapshotFactory $snapshots,
         private readonly InsufficientStockMessageBuilder $stockMessages,
+        private readonly PurchaseResponseLoader $responses,
     ) {}
 
     /** @param array<string, mixed> $purchaseData */
@@ -382,6 +383,6 @@ class StartCheckoutService
 
     private function loadPurchase(Purchase $purchase): Purchase
     {
-        return $purchase->load(['items.imageAttachment']);
+        return $this->responses->load($purchase);
     }
 }