Filter error array by unique values

app/code/Magento/QuoteGraphQl/Model/Cart/AddProductsToCart.php

@@ -8,7 +8,7 @@
 namespace Magento\QuoteGraphQl\Model\Cart;
 
 use Magento\Framework\GraphQl\Exception\GraphQlInputException;
-use Magento\Framework\Message\AbstractMessage;
+use Magento\Framework\Message\MessageInterface;
 use Magento\Quote\Api\CartRepositoryInterface;
 use Magento\Quote\Model\Quote;
 
@@ -55,29 +55,15 @@ public function execute(Quote $cart, array $cartItems): void
         }
 
         if ($cart->getData('has_error')) {
-            throw new GraphQlInputException(
-                __('Shopping cart error: %message', ['message' => $this->getCartErrors($cart)])
-            );
+            $e = new GraphQlInputException(__('Shopping cart errors'));
+            $errors = $cart->getErrors();
+            foreach ($errors as $error) {
+                /** @var MessageInterface $error */
+                $e->addError(new GraphQlInputException(__($error->getText())));
+            }
+            throw $e;
         }
 
         $this->cartRepository->save($cart);
     }
-
-    /**
-     * Collecting cart errors
-     *
-     * @param Quote $cart
-     * @return string
-     */
-    private function getCartErrors(Quote $cart): string
-    {
-        $errorMessages = [];
-
-        /** @var AbstractMessage $error */
-        foreach ($cart->getErrors() as $error) {
-            $errorMessages[] = $error->getText();
-        }
-
-        return implode(PHP_EOL, $errorMessages);
-    }
 }

app/code/Magento/QuoteGraphQl/Model/Cart/AddSimpleProductToCart.php

@@ -72,7 +72,12 @@ public function execute(Quote $cart, array $cartItemData): void
         }
 
         if (is_string($result)) {
-            throw new GraphQlInputException(__($result));
+            $e = new GraphQlInputException(__('Cannot add product to cart'));
+            $errors = array_unique(explode("\n", $result));
+            foreach ($errors as $error) {
+                $e->addError(new GraphQlInputException(__($error)));
+            }
+            throw $e;
         }
     }