chore(checkpoint): save club core backend and pending pos fixes

project/frontend/src/app/api/checkout/route.ts

@@ -100,6 +100,17 @@ function parseItems(raw: RawItem[] | undefined): {
   });
 }
 
+async function readErrorMessage(response: Response, fallback: string): Promise<string> {
+  const text = await response.text();
+  if (!text) return fallback;
+  try {
+    const data = JSON.parse(text) as { error?: { message?: string }; message?: string };
+    return data.error?.message ?? data.message ?? text;
+  } catch {
+    return text;
+  }
+}
+
 async function syncCart(
   cookies: string,
   items: { productId: string; variantId: string; quantity: number }[],
@@ -125,7 +136,9 @@ async function syncCart(
   }
 
   const nextByVariant = new Map(items.map((item) => [item.variantId, item]));
+  const currentByVariant = new Map(serverItems.map((item) => [item.variantId, item]));
   const operations: Promise<Response>[] = [];
+
   for (const item of serverItems) {
     if (!nextByVariant.has(item.variantId)) {
       operations.push(
@@ -136,20 +149,35 @@ async function syncCart(
       );
     }
   }
+
   for (const item of items) {
-    operations.push(
-      fetch(`${API}/cart/items`, {
-        method: 'POST',
-        headers: { 'Content-Type': 'application/json', Cookie: cookies },
-        body: JSON.stringify(item),
-      }),
-    );
+    const existing = currentByVariant.get(item.variantId);
+    if (!existing) {
+      operations.push(
+        fetch(`${API}/cart/items`, {
+          method: 'POST',
+          headers: { 'Content-Type': 'application/json', Cookie: cookies },
+          body: JSON.stringify(item),
+        }),
+      );
+      continue;
+    }
+    if (existing.quantity !== item.quantity) {
+      operations.push(
+        fetch(`${API}/cart/items/${item.variantId}`, {
+          method: 'PATCH',
+          headers: { 'Content-Type': 'application/json', Cookie: cookies },
+          body: JSON.stringify({ quantity: item.quantity }),
+        }),
+      );
+    }
   }
+
   const results = await Promise.all(operations);
   for (const response of results) {
     if (!response.ok && response.status !== 404) {
-      const message = await response.text();
-      return { ok: false, status: response.status, message: message || 'Error al sincronizar el carrito' };
+      const message = await readErrorMessage(response, 'Error al sincronizar el carrito');
+      return { ok: false, status: response.status, message };
     }
   }
   return { ok: true };