Revert "AC-15054: Product Add to Cart issue in Rest API"

This reverts commit a22d447.

Author: sumesh-GL

app/code/Magento/Quote/Plugin/UpdateCartId.php

@@ -63,8 +63,6 @@ public function beforeSave(
     /**
      * Validate product's website assignment for guest cart item
      *
-     * @param CartItemInterface $cartItem
-     * @return void
      * @throws LocalizedException
      */
     private function validateProductWebsiteAssignment(CartItemInterface $cartItem): void

app/code/Magento/Quote/Test/Unit/Plugin/Webapi/ValidateProductWebsiteAssignmentTest.php

@@ -301,6 +301,65 @@ public function testBeforeSaveProductWebsiteIdsNotArray()
         $this->plugin->beforeSave($this->cartItemRepositoryMock, $this->cartItemMock);
     }
 
+    /**
+     * Test validation when product is not found
+     */
+    public function testBeforeSaveProductNotFound()
+    {
+        $sku = 'test-product';
+        $quoteId = 1;
+        $storeId = 1;
+        $productId = 123;
+
+        $this->cartItemMock->expects($this->once())
+            ->method('getSku')
+            ->willReturn($sku);
+
+        $this->cartItemMock->expects($this->once())
+            ->method('getQuoteId')
+            ->willReturn($quoteId);
+
+        $this->cartRepositoryMock->expects($this->once())
+            ->method('getActive')
+            ->with($quoteId)
+            ->willReturn($this->quoteMock);
+
+        $this->quoteMock->expects($this->once())
+            ->method('getAllItems')
+            ->willReturn([$this->quoteItemMock]);
+
+        $this->quoteItemMock->expects($this->once())
+            ->method('getSku')
+            ->willReturn($sku);
+
+        $this->quoteItemMock->expects($this->once())
+            ->method('getStoreId')
+            ->willReturn($storeId);
+
+        $this->quoteItemMock->expects($this->once())
+            ->method('getProductId')
+            ->willReturn($productId);
+
+        $this->storeManagerMock->expects($this->once())
+            ->method('getStore')
+            ->with($storeId)
+            ->willReturn($this->storeMock);
+
+        $this->storeMock->expects($this->once())
+            ->method('getWebsiteId')
+            ->willReturn(1);
+
+        $this->productRepositoryMock->expects($this->once())
+            ->method('getById')
+            ->with($productId, false, $storeId)
+            ->willThrowException(new NoSuchEntityException(__('Product not found')));
+
+        $this->expectException(LocalizedException::class);
+        $this->expectExceptionMessage('Product that you are trying to add is not available.');
+
+        $this->plugin->beforeSave($this->cartItemRepositoryMock, $this->cartItemMock);
+    }
+
     /**
      * Test validation skips when no SKU provided
      */
@@ -531,4 +590,42 @@ public function testBeforeSaveWebsiteIdZero()
         // If we reach this point, validation passed
         $this->assertTrue(true);
     }
+
+    /**
+     * Test validation when no matching quote item found for SKU
+     */
+    public function testBeforeSaveNoMatchingQuoteItem()
+    {
+        $sku = 'test-product';
+        $quoteId = 1;
+        $differentSku = 'different-product';
+
+        $this->cartItemMock->expects($this->once())
+            ->method('getSku')
+            ->willReturn($sku);
+
+        $this->cartItemMock->expects($this->once())
+            ->method('getQuoteId')
+            ->willReturn($quoteId);
+
+        $this->cartRepositoryMock->expects($this->once())
+            ->method('getActive')
+            ->with($quoteId)
+            ->willReturn($this->quoteMock);
+
+        $this->quoteMock->expects($this->once())
+            ->method('getAllItems')
+            ->willReturn([$this->quoteItemMock]);
+
+        $this->quoteItemMock->expects($this->once())
+            ->method('getSku')
+            ->willReturn($differentSku); // Different SKU
+
+        // No further method calls expected since no matching item found
+        // Method returns void, so we just verify no exception is thrown
+        $this->plugin->beforeSave($this->cartItemRepositoryMock, $this->cartItemMock);
+
+        // If we reach this point, validation passed
+        $this->assertTrue(true);
+    }
 }

dev/tests/api-functional/testsuite/Magento/Quote/Api/ValidateProductWebsiteAssignmentTest.php

@@ -5,7 +5,7 @@
  */
 declare(strict_types=1);
 
-namespace Magento\Quote\Api;
+namespace Magento\Quote\Test\Api;
 
 use Magento\Catalog\Test\Fixture\Product;
 use Magento\Customer\Test\Fixture\Customer;