Fix add products to cart parent SKU configurable

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

@@ -92,20 +92,24 @@ public function execute(string $maskedCartId, array $cartItems): AddProductsToCa
     public function addItemsToCart(Quote $cart, array $cartItems): array
     {
         $failedCartItems = [];
-        // add new cart items for preload
-        $skus = \array_map(
-            function ($item) {
-                return $item->getSku();
-            },
-            $cartItems
-        );
-        $this->productReader->loadProducts($skus, $cart->getStoreId());
+
+        // Collect all SKUs to pre-load: child SKUs + parent SKUs when present (GH-40598)
+        $skus = [];
+        foreach ($cartItems as $cartItem) {
+            $skus[] = $cartItem->getSku();
+            if ($cartItem->getParentSku() !== null) {
+                $skus[] = $cartItem->getParentSku();
+            }
+        }
+        $this->productReader->loadProducts(array_unique($skus), $cart->getStoreId());
+
         foreach ($cartItems as $cartItemPosition => $cartItem) {
-            $product = $this->productReader->getProductBySku($cartItem->getSku());
+            // Use the child product for stock quantity display, regardless of which product is added
+            $childProduct = $this->productReader->getProductBySku($cartItem->getSku());
             $stockItemQuantity = 0.0;
-            if ($product) {
+            if ($childProduct) {
                 $stockItem = $this->stockRegistry->getStockItem(
-                    $product->getId(),
+                    $childProduct->getId(),
                     $cart->getStore()->getWebsiteId()
                 );
                 $stockItemQuantity = $stockItem->getQty() - $stockItem->getMinQty();
@@ -146,13 +150,14 @@ private function addItemToCart(
             );
         }
 
-        $productBySku = $this->productReader->getProductBySku($sku);
+        $resolvedSku = $cartItem->getParentSku() ?? $sku;
+        $productBySku = $this->productReader->getProductBySku($resolvedSku);
         $product = isset($productBySku) ? clone $productBySku : null;
 
         if (!$product || !$product->isSaleable() || !$product->isAvailable()) {
             return [
                 $this->error->create(
-                    __('Could not find a product with SKU "%sku"', ['sku' => $sku])->render(),
+                    __('Could not find a product with SKU "%sku"', ['sku' => $resolvedSku])->render(),
                     $cartItemPosition,
                     $stockItemQuantity
                 )

app/code/Magento/QuoteConfigurableOptions/Model/Cart/BuyRequest/SuperAttributeDataProvider.php

@@ -7,7 +7,12 @@
 
 namespace Magento\QuoteConfigurableOptions\Model\Cart\BuyRequest;
 
+use Magento\Catalog\Api\Data\ProductInterface;
+use Magento\Catalog\Api\ProductRepositoryInterface;
+use Magento\ConfigurableProductGraphQl\Model\Options\Collection as OptionCollection;
+use Magento\Framework\EntityManager\MetadataPool;
 use Magento\Framework\Exception\LocalizedException;
+use Magento\Framework\Exception\NoSuchEntityException;
 use Magento\Quote\Model\Cart\BuyRequest\BuyRequestDataProviderInterface;
 use Magento\Quote\Model\Cart\Data\CartItem;
 
@@ -18,6 +23,13 @@ class SuperAttributeDataProvider implements BuyRequestDataProviderInterface
 {
     private const OPTION_TYPE = 'configurable';
 
+    public function __construct(
+        private readonly ProductRepositoryInterface $productRepository,
+        private readonly OptionCollection $optionCollection,
+        private readonly MetadataPool $metadataPool,
+    ) {
+    }
+
     /**
      * @inheritdoc
      *
@@ -26,7 +38,7 @@ class SuperAttributeDataProvider implements BuyRequestDataProviderInterface
     public function execute(CartItem $cartItem): array
     {
         $configurableProductData = [];
-        foreach ($cartItem->getSelectedOptions() as $optionData) {
+        foreach ($cartItem->getSelectedOptions() ?? [] as $optionData) {
             // phpcs:ignore Magento2.Functions.DiscouragedFunction
             $optionData = \explode('/', base64_decode($optionData->getId()));
 
@@ -41,9 +53,55 @@ public function execute(CartItem $cartItem): array
             }
         }
 
+        if (empty($configurableProductData) && $cartItem->getParentSku() !== null) {
+            $configurableProductData = $this->resolveFromParentSku(
+                $cartItem->getParentSku(),
+                $cartItem->getSku()
+            );
+        }
+
         return ['super_attribute' => $configurableProductData];
     }
 
+    /**
+     * Resolves super_attribute from parent_sku + child sku (GH-40598 fallback).
+     */
+    private function resolveFromParentSku(string $parentSku, string $childSku): array
+    {
+        try {
+            $parentProduct = $this->productRepository->get($parentSku);
+            $childProduct  = $this->productRepository->get($childSku);
+        } catch (NoSuchEntityException) {
+            throw new LocalizedException(__('Could not find a product with SKU "%1" or "%2".', $parentSku, $childSku));
+        }
+
+        $configurableLinks = $parentProduct->getExtensionAttributes()?->getConfigurableProductLinks() ?? [];
+        if (!in_array($childProduct->getId(), $configurableLinks, strict: true)) {
+            throw new LocalizedException(
+                __('The product "%1" is not a variant of "%2".', $childSku, $parentSku)
+            );
+        }
+
+        $linkField = $this->metadataPool->getMetadata(ProductInterface::class)->getLinkField();
+        $parentLinkId = (int) $parentProduct->getData($linkField);
+
+        $this->optionCollection->addProductId($parentLinkId);
+        $options = $this->optionCollection->getAttributesByProductId($parentLinkId);
+
+        $superAttributesData = [];
+        foreach ($options as $option) {
+            $code = $option['attribute_code'];
+            foreach ($option['values'] as $optionValue) {
+                if ($optionValue['value_index'] === $childProduct->getData($code)) {
+                    $superAttributesData[$option['attribute_id']] = $optionValue['value_index'];
+                    break;
+                }
+            }
+        }
+
+        return $superAttributesData;
+    }
+
     /**
      * Checks whether this provider is applicable for the current option
      *

app/code/Magento/QuoteConfigurableOptions/Test/Unit/Model/Cart/BuyRequest/SuperAttributeDataProviderTest.php

@@ -0,0 +1,195 @@
+<?php
+/**
+ * Copyright 2026 Adobe
+ * All Rights Reserved.
+ */
+declare(strict_types=1);
+
+namespace Magento\QuoteConfigurableOptions\Test\Unit\Model\Cart\BuyRequest;
+
+use Magento\Catalog\Api\Data\ProductExtensionInterface;
+use Magento\Catalog\Api\Data\ProductInterface;
+use Magento\Catalog\Api\ProductRepositoryInterface;
+use Magento\Catalog\Model\Product;
+use Magento\ConfigurableProductGraphQl\Model\Options\Collection as OptionCollection;
+use Magento\Framework\EntityManager\EntityMetadataInterface;
+use Magento\Framework\EntityManager\MetadataPool;
+use Magento\Framework\Exception\LocalizedException;
+use Magento\Framework\Exception\NoSuchEntityException;
+use Magento\Framework\TestFramework\Unit\Helper\MockCreationTrait;
+use Magento\Quote\Model\Cart\Data\CartItem;
+use Magento\Quote\Model\Cart\Data\SelectedOption;
+use Magento\QuoteConfigurableOptions\Model\Cart\BuyRequest\SuperAttributeDataProvider;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @covers \Magento\QuoteConfigurableOptions\Model\Cart\BuyRequest\SuperAttributeDataProvider
+ * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
+ */
+class SuperAttributeDataProviderTest extends TestCase
+{
+    use MockCreationTrait;
+
+    private SuperAttributeDataProvider $provider;
+    private ProductRepositoryInterface&MockObject $productRepository;
+    private OptionCollection&MockObject $optionCollection;
+    private MetadataPool&MockObject $metadataPool;
+
+    protected function setUp(): void
+    {
+        $this->productRepository = $this->createMock(ProductRepositoryInterface::class);
+        $this->optionCollection  = $this->createMock(OptionCollection::class);
+        $this->metadataPool      = $this->createMock(MetadataPool::class);
+
+        $this->provider = new SuperAttributeDataProvider(
+            $this->productRepository,
+            $this->optionCollection,
+            $this->metadataPool,
+        );
+    }
+
+    public function testExecuteResolvesFromSelectedOptions(): void
+    {
+        $uid = base64_encode('configurable/93/57');
+        $selectedOption = $this->createMock(SelectedOption::class);
+        $selectedOption->method('getId')->willReturn($uid);
+
+        $result = $this->provider->execute(new CartItem('simple-child', 1.0, null, [$selectedOption]));
+
+        $this->assertSame(['super_attribute' => ['93' => '57']], $result);
+    }
+
+    public function testExecuteIgnoresNonConfigurableSelectedOptions(): void
+    {
+        $uid = base64_encode('custom-option/10/20');
+        $selectedOption = $this->createMock(SelectedOption::class);
+        $selectedOption->method('getId')->willReturn($uid);
+
+        $result = $this->provider->execute(new CartItem('simple-child', 1.0, null, [$selectedOption]));
+
+        $this->assertSame(['super_attribute' => []], $result);
+    }
+
+    public function testExecuteFallsBackToParentSkuWhenNoSelectedOptions(): void
+    {
+        [$parentMock, $childMock] = $this->buildProductMocks(
+            parentId: 10,
+            childId: 42,
+            configurableLinks: [42],
+            linkFieldValue: 10,
+            options: [['attribute_code' => 'color', 'attribute_id' => 93, 'values' => [['value_index' => 5]]]],
+            childAttributeValue: 5
+        );
+
+        $this->productRepository->method('get')->willReturnMap([
+            ['ParentItem',         false, null, false, $parentMock],
+            ['ParentItem-Variant', false, null, false, $childMock],
+        ]);
+
+        $result = $this->provider->execute(new CartItem('ParentItem-Variant', 1.0, 'ParentItem'));
+
+        $this->assertSame(['super_attribute' => [93 => 5]], $result);
+    }
+
+    public function testSelectedOptionsTakePriorityOverParentSku(): void
+    {
+        $uid = base64_encode('configurable/93/57');
+        $selectedOption = $this->createMock(SelectedOption::class);
+        $selectedOption->method('getId')->willReturn($uid);
+
+        $this->productRepository->expects($this->never())->method('get');
+
+        $result = $this->provider->execute(new CartItem('ParentItem-Variant', 1.0, 'ParentItem', [$selectedOption]));
+
+        $this->assertSame(['super_attribute' => ['93' => '57']], $result);
+    }
+
+    public function testExecuteReturnsEmptyWhenNoSelectedOptionsAndNoParentSku(): void
+    {
+        $this->productRepository->expects($this->never())->method('get');
+
+        $result = $this->provider->execute(new CartItem('simple-standalone', 1.0));
+
+        $this->assertSame(['super_attribute' => []], $result);
+    }
+
+    public function testExecuteThrowsWhenChildIsNotVariantOfParent(): void
+    {
+        $extensionAttributes = $this->createPartialMockWithReflection(
+            ProductExtensionInterface::class,
+            ['getConfigurableProductLinks']
+        );
+        $extensionAttributes->method('getConfigurableProductLinks')->willReturn([99]);
+
+        $parentMock = $this->createMock(Product::class);
+        $parentMock->method('getId')->willReturn(10);
+        $parentMock->method('getExtensionAttributes')->willReturn($extensionAttributes);
+        $parentMock->method('getData')->willReturn(10);
+
+        $childMock = $this->createMock(Product::class);
+        $childMock->method('getId')->willReturn(42);
+
+        $this->productRepository->method('get')->willReturnMap([
+            ['ParentItem',   false, null, false, $parentMock],
+            ['other-simple', false, null, false, $childMock],
+        ]);
+
+        $this->expectException(LocalizedException::class);
+        $this->expectExceptionMessage('not a variant');
+
+        $this->provider->execute(new CartItem('other-simple', 1.0, 'ParentItem'));
+    }
+
+    public function testExecuteThrowsWhenProductNotFound(): void
+    {
+        $this->productRepository->method('get')->willThrowException(new NoSuchEntityException());
+
+        $this->expectException(LocalizedException::class);
+
+        $this->provider->execute(new CartItem('ParentItem-Variant', 1.0, 'NonExistentParent'));
+    }
+
+    public function testExecuteThrowsOnMalformedSelectedOptionUid(): void
+    {
+        $uid = base64_encode('configurable/only-two-parts');
+        $selectedOption = $this->createMock(SelectedOption::class);
+        $selectedOption->method('getId')->willReturn($uid);
+
+        $this->expectException(LocalizedException::class);
+
+        $this->provider->execute(new CartItem('simple-child', 1.0, null, [$selectedOption]));
+    }
+
+    private function buildProductMocks(
+        int $parentId,
+        int $childId,
+        array $configurableLinks,
+        int $linkFieldValue,
+        array $options,
+        mixed $childAttributeValue,
+    ): array {
+        $extensionAttributes = $this->createPartialMockWithReflection(
+            ProductExtensionInterface::class,
+            ['getConfigurableProductLinks']
+        );
+        $extensionAttributes->method('getConfigurableProductLinks')->willReturn($configurableLinks);
+
+        $parentMock = $this->createMock(Product::class);
+        $parentMock->method('getId')->willReturn($parentId);
+        $parentMock->method('getExtensionAttributes')->willReturn($extensionAttributes);
+        $parentMock->method('getData')->willReturn($linkFieldValue);
+
+        $childMock = $this->createMock(Product::class);
+        $childMock->method('getId')->willReturn($childId);
+        $childMock->method('getData')->willReturn($childAttributeValue);
+
+        $productMetadata = $this->createMock(EntityMetadataInterface::class);
+        $productMetadata->method('getLinkField')->willReturn('entity_id');
+        $this->metadataPool->method('getMetadata')->with(ProductInterface::class)->willReturn($productMetadata);
+
+        $this->optionCollection->method('getAttributesByProductId')->with($linkFieldValue)->willReturn($options);
+
+        return [$parentMock, $childMock];
+    }
+}

app/code/Magento/QuoteConfigurableOptions/composer.json

@@ -4,6 +4,8 @@
     "require": {
         "php": "~8.3.0||~8.4.0||~8.5.0",
         "magento/framework": "*",
+        "magento/module-catalog": "*",
+        "magento/module-configurable-product-graph-ql": "*",
         "magento/module-quote": "*"
     },
     "type": "magento2-module",

app/code/Magento/QuoteConfigurableOptions/etc/module.xml

@@ -6,5 +6,10 @@
  */
 -->
 <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
-    <module name="Magento_QuoteConfigurableOptions"/>
+    <module name="Magento_QuoteConfigurableOptions">
+        <sequence>
+            <module name="Magento_ConfigurableProductGraphQl"/>
+            <module name="Magento_Catalog"/>
+        </sequence>
+    </module>
 </config>