AC-10472: Placing an order in GraphQL succeeds with an invalid shipping method

Author: wip44850

app/code/Magento/Quote/Model/ValidationRules/ShippingMethodValidationRule.php

@@ -49,7 +49,7 @@ public function validate(Quote $quote): array
             $shippingAddress->setStoreId($quote->getStoreId());
             $shippingMethod = $shippingAddress->getShippingMethod();
             $shippingRate = $shippingAddress->getShippingRateByCode($shippingMethod);
-            $validationResult = $shippingMethod && $shippingRate && $shippingAddress->requestShippingRates();
+            $validationResult = $shippingMethod && $shippingRate;
             if (!$validationResult) {
                 $validationErrors = [__($this->generalMessage)];
             }

app/code/Magento/QuoteGraphQl/Plugin/ShippingMethodValidationRulePlugin.php

@@ -0,0 +1,66 @@
+<?php
+/**
+ * Copyright 2025 Adobe
+ * All Rights Reserved.
+ */
+declare(strict_types=1);
+
+namespace Magento\QuoteGraphQl\Plugin;
+
+use Magento\Quote\Model\ValidationRules\ShippingMethodValidationRule;
+use Magento\Quote\Model\Quote;
+use Magento\Framework\Validation\ValidationResult;
+use Magento\Framework\Validation\ValidationResultFactory;
+
+class ShippingMethodValidationRulePlugin
+{
+    /**
+     * @var ValidationResultFactory
+     */
+    private $validationResultFactory;
+
+    /**
+     * @param ValidationResultFactory $validationResultFactory
+     */
+    public function __construct(ValidationResultFactory $validationResultFactory)
+    {
+        $this->validationResultFactory = $validationResultFactory;
+    }
+
+    /**
+     * After plugin for validate method to ensure shipping method validity.
+     *
+     * @param ShippingMethodValidationRule $subject
+     * @param ValidationResult[] $result
+     * @param Quote $quote
+     * @return ValidationResult[]
+     */
+    public function afterValidate(
+        ShippingMethodValidationRule $subject,
+        array $result,
+        Quote $quote
+    ): array {
+        $shippingAddress = $quote->getShippingAddress();
+        if (!$shippingAddress || $quote->isVirtual()) {
+            return $result;
+        }
+
+        $shippingMethod = $shippingAddress->getShippingMethod();
+        $shippingRate = $shippingMethod ? $shippingAddress->getShippingRateByCode($shippingMethod) : null;
+        $validationResult = $shippingMethod && $shippingRate && $shippingAddress->requestShippingRates();
+
+        if ($validationResult) {
+            return $result;
+        }
+
+        // If previously valid, rebuild with a generic error to mark invalid
+        $existing = $result[0] ?? null;
+        if ($existing instanceof ValidationResult && $existing->isValid()) {
+            $result[0] = $this->validationResultFactory->create([
+                'errors' => [__('The shipping method is missing. Select the shipping method and try again')]
+            ]);
+        }
+
+        return $result;
+    }
+}

app/code/Magento/QuoteGraphQl/etc/graphql/di.xml

@@ -114,4 +114,10 @@
             </argument>
         </arguments>
     </type>
+    <type name="Magento\Quote\Model\ValidationRules\ShippingMethodValidationRule">
+        <plugin name="shipping_method_validation_plugin"
+                type="Magento\QuoteGraphQl\Plugin\ShippingMethodValidationRulePlugin"
+                sortOrder="10"
+                disabled="false"/>
+    </type>
 </config>