Fix for communication.xml Handlers merging processs

app/etc/di.xml

@@ -229,6 +229,17 @@
         </arguments>
     </type>
     <preference for="Magento\AsynchronousOperations\Model\ConfigInterface" type="Magento\WebapiAsync\Model\Config\Proxy" />
+    <virtualType name="Magento\Framework\Communication\Config\Reader\XmlReader" type="Magento\Framework\Config\Reader\Filesystem">
+        <arguments>
+            <argument name="converter" xsi:type="object">Magento\Framework\Communication\Config\Reader\XmlReader\Converter</argument>
+            <argument name="schemaLocator" xsi:type="object">Magento\Framework\Communication\Config\Reader\XmlReader\SchemaLocator</argument>
+            <argument name="fileName" xsi:type="string">communication.xml</argument>
+            <argument name="idAttributes" xsi:type="array">
+                <item name="/config/topic" xsi:type="string">name</item>
+                <item name="/config/topic/handler" xsi:type="string">name</item>
+            </argument>
+        </arguments>
+    </virtualType>
     <type name="Magento\Framework\Communication\Config\CompositeReader">
         <arguments>
             <argument name="readers" xsi:type="array">

dev/tests/integration/testsuite/Magento/Framework/Communication/_files/valid_communication_expected.php

@@ -33,6 +33,10 @@
                 'type' => \Magento\Customer\Api\CustomerRepositoryInterface::class,
                 'method' => 'delete',
             ],
+            'customerCreatedExtra' => [
+                'type' => \Magento\Customer\Api\CustomerRepositoryInterface::class,
+                'method' => 'save',
+            ],
             'saveNameNotDisabled' => [
                 'type' => \Magento\Customer\Api\CustomerRepositoryInterface::class,
                 'method' => 'save',

dev/tests/integration/testsuite/Magento/Framework/Communication/_files/valid_communication_extra.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0"?>
+<!--
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+-->
+<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Communication/etc/communication.xsd">
+    <topic name="customerAdded" request="string[]">
+        <handler name="customerCreatedExtra" type="Magento\Customer\Api\CustomerRepositoryInterface" method="save"/>
+    </topic>
+</config>

dev/tests/integration/testsuite/Magento/Framework/Communication/_files/valid_communication_input.php

@@ -35,6 +35,10 @@
                         'type' => \Magento\Customer\Api\CustomerRepositoryInterface::class,
                         'method' => 'delete',
                     ],
+                    'customerCreatedExtra' => [
+                        'type' => \Magento\Customer\Api\CustomerRepositoryInterface::class,
+                        'method' => 'save',
+                    ],
                     'saveNameNotDisabled' => [
                         'type' => \Magento\Customer\Api\CustomerRepositoryInterface::class,
                         'method' => 'save',

dev/tests/static/testsuite/Magento/Test/Php/_files/phpstan/blacklist/common.txt

@@ -9,6 +9,7 @@ lib/internal/Magento/Framework/Interception/Test/Unit/Code/Generator/Interceptor
 lib/internal/Magento/Framework/Interception/Test/Unit/Config/ConfigTest.php
 dev/tests/integration/framework/deployTestModules.php
 dev/tests/integration/testsuite/Magento/Framework/Code/Generator/AutoloaderTest.php
+dev/tests/integration/testsuite/Magento/Framework/Communication/ConfigTest.php
 dev/tests/integration/testsuite/Magento/Framework/Filter/DirectiveProcessor/SimpleDirectiveTest.php
 dev/tests/integration/testsuite/Magento/Framework/Session/ConfigTest.php
 dev/tests/integration/testsuite/Magento/Framework/Session/SessionManagerTest.php