Public readonly reflection for queue consumers

dev/tests/integration/testsuite/Magento/Framework/MessageQueue/MessageEncoderTest.php

@@ -106,6 +106,18 @@ public function testDecode()
         $this->assertEquals('AL', $addresses[0]->getRegion()->getRegionCode());
     }
 
+    public function testEncodeDecodeReadonlyMessage()
+    {
+        $message = new ReadonlyMessage(10, 'Test Message');
+
+        $encodedMessage = $this->encoder->encode('readonly.message.created', $message);
+        $decodedMessage = $this->encoder->decode('readonly.message.created', $encodedMessage);
+
+        $this->assertInstanceOf(ReadonlyMessage::class, $decodedMessage);
+        $this->assertSame(10, $decodedMessage->entityId);
+        $this->assertSame('Test Message', $decodedMessage->name);
+    }
+
     /**
      */
     public function testDecodeInvalidMessageFormat()

dev/tests/integration/testsuite/Magento/Framework/MessageQueue/ReadonlyMessage.php

@@ -0,0 +1,24 @@
+<?php
+/**
+ * Copyright 2025 Adobe
+ * All Rights Reserved.
+ */
+declare(strict_types=1);
+
+namespace Magento\Framework\MessageQueue;
+
+/**
+ * Simple DTO used by message queue integration tests.
+ */
+class ReadonlyMessage
+{
+    /**
+     * @param int $entityId
+     * @param string $name
+     */
+    public function __construct(
+        public readonly int $entityId,
+        public readonly string $name
+    ) {
+    }
+}

dev/tests/integration/testsuite/Magento/Framework/MessageQueue/_files/encoder_communication.php

@@ -31,5 +31,10 @@
             'request' => \Magento\Catalog\Api\Data\ProductInterface::class,
             'response' => null,
         ],
+        'readonly.message.created' => [
+            'request_type' => 'object_interface',
+            'request' => \Magento\Framework\MessageQueue\ReadonlyMessage::class,
+            'response' => null,
+        ],
     ],
 ];

lib/internal/Magento/Framework/MessageQueue/README.md

@@ -1 +1,10 @@
-This component is designed to provide Message Queue Framework
+This component is designed to provide Message Queue Framework.
+
+## DTO serialization
+
+Message payloads using `object_interface` topics are serialized through the Web API data processors.
+
+- Getter methods define the payload fields; if a getter and a public property map to the same field, the getter wins.
+- Public properties without getters are supported, including promoted/readonly properties, and are converted to
+  snake_case field names.
+- Constructor hydration accepts both camelCase and snake_case keys to support promoted/readonly DTOs on decode.