fix: shipping cost calculation and performance optimization

- Fix shipping cost not included in checkout total
- Add useShippingMethodSelector hook for proper abstraction
- Remove blocking initCheckout from Header for better performance
- Checkout now initializes lazily when cart opens or item added

src/app/[locale]/checkout/page.tsx

@@ -19,6 +19,7 @@ import { DEFAULT_PAYMENT_METHOD } from "@/lib/config/paymentMethods";
 import { GET_CHECKOUT_BY_ID } from "@/lib/saleor/queries/Checkout";
 import type { Checkout } from "@/types/saleor";
 import { createCheckoutService, type Address } from "@/lib/services/checkoutService";
+import { useShippingMethodSelector } from "@/lib/hooks/useShippingMethodSelector";
 
 interface ShippingAddressUpdateResponse {
   checkoutShippingAddressUpdate?: {
@@ -31,6 +32,8 @@ interface CheckoutQueryResponse {
   checkout?: Checkout;
 }
 
+
+
 interface ShippingMethod {
   id: string;
   name: string;
@@ -92,8 +95,16 @@ export default function CheckoutPage() {
   const [selectedShippingMethod, setSelectedShippingMethod] = useState<string>("");
   const [isLoadingShipping, setIsLoadingShipping] = useState(false);
 
+  // Hook to manage shipping method selection (both manual and auto)
+  const { selectShippingMethodWithApi } = useShippingMethodSelector({
+    checkoutId: checkout?.id ?? null,
+    onSelect: setSelectedShippingMethod,
+    onRefresh: refreshCheckout,
+  });
+
   const lines = getLines();
-  const total = getTotal();
+  // Use checkout.totalPrice directly for reactive updates when shipping method changes
+  const total = checkout?.totalPrice?.gross?.amount || getTotal();
 
   // Debounced shipping method fetching
   useEffect(() => {
@@ -147,10 +158,12 @@ export default function CheckoutPage() {
         console.log("Available shipping methods:", availableMethods);
         
         setShippingMethods(availableMethods);
-        
+
         // Auto-select first method if none selected
         if (availableMethods.length > 0 && !selectedShippingMethod) {
-          setSelectedShippingMethod(availableMethods[0].id);
+          const firstMethodId = availableMethods[0].id;
+          // Use the hook to both update UI and call API
+          await selectShippingMethodWithApi(firstMethodId);
         }
       } catch (err) {
         console.error("Error fetching shipping methods:", err);
@@ -210,6 +223,10 @@ export default function CheckoutPage() {
     setShippingAddress((prev) => ({ ...prev, email: value }));
   };
 
+  const handleShippingMethodSelect = async (methodId: string) => {
+    await selectShippingMethodWithApi(methodId);
+  };
+
   const handleSubmit = async (e: React.FormEvent) => {
     e.preventDefault();
 
@@ -576,7 +593,7 @@ export default function CheckoutPage() {
                                 name="shippingMethod"
                                 value={method.id}
                                 checked={selectedShippingMethod === method.id}
-                                onChange={(e) => setSelectedShippingMethod(e.target.value)}
+                                onChange={(e) => handleShippingMethodSelect(e.target.value)}
                                 className="w-4 h-4"
                               />
                               <span className="font-medium">{method.name}</span>