handle dynamic json data and examples for subscription details

pkg/cart/mutation_add_item.go

@@ -28,14 +28,23 @@ func AddItem(g *CartGrain, m *messages.AddItem) error {
 		return fmt.Errorf("AddItem: invalid quantity %d", m.Quantity)
 	}
 
-	// Fast path: merge with existing item having same SKU
-	if existing, found := g.FindItemWithSku(m.Sku); found {
-		if existing.StoreId == m.StoreId {
-			existing.Quantity += int(m.Quantity)
-			existing.Stock = StockStatus(m.Stock)
-			existing.StoreId = m.StoreId
-			return nil
+	// Merge with any existing item having same SKU and matching StoreId (including both nil).
+	for _, existing := range g.Items {
+		if existing.Sku != m.Sku {
+			continue
 		}
+		sameStore := (existing.StoreId == nil && m.StoreId == nil) ||
+			(existing.StoreId != nil && m.StoreId != nil && *existing.StoreId == *m.StoreId)
+		if !sameStore {
+			continue
+		}
+		existing.Quantity += int(m.Quantity)
+		existing.Stock = StockStatus(m.Stock)
+		// If existing had nil store but new has one, adopt it.
+		if existing.StoreId == nil && m.StoreId != nil {
+			existing.StoreId = m.StoreId
+		}
+		return nil
 	}
 
 	g.mu.Lock()