diff --git a/.github/workflows/compat_test.yaml b/.github/workflows/compat_test.yaml
deleted file mode 100644
index d44f4f85736..00000000000
--- a/.github/workflows/compat_test.yaml
+++ /dev/null
@@ -1,29 +0,0 @@
-# see https://github.com/rectorphp/rector/issues/9416
-name: PHPUnit and PHPStan Compat Test
-
-on:
-    push:
-        branches:
-            - main
-    pull_request: null
-
-jobs:
-    compat_test:
-        runs-on: ubuntu-latest
-
-        steps:
-            -
-                uses: shivammathur/setup-php@v2
-                with:
-                    php-version: 8.3
-                    coverage: none
-
-            - run: composer create-project "rector/rector-compat-tests:dev-main" .
-
-            - run: vendor/bin/phpunit tests/PHPStan
-
-            - run: vendor/bin/phpunit tests/Rector
-
-            - run:  vendor/bin/phpunit tests
-
-            - run:  vendor/bin/phpunit
diff --git a/.github/workflows/phpunit_and_phpstan_autoload_compat_test.yaml b/.github/workflows/phpunit_and_phpstan_autoload_compat_test.yaml
new file mode 100644
index 00000000000..85f737b3bfc
--- /dev/null
+++ b/.github/workflows/phpunit_and_phpstan_autoload_compat_test.yaml
@@ -0,0 +1,60 @@
+# see https://github.com/rectorphp/rector/issues/9416
+# compat tests project lives in /compat-tests
+name: PHPUnit and PHPStan Autoload Compat Test
+
+on:
+    push:
+        branches:
+            - main
+    pull_request: null
+    schedule:
+        - cron: '0 6 * * *'
+
+jobs:
+    compat_test:
+        strategy:
+            fail-fast: false
+            matrix:
+                actions:
+                    -
+                        name: 'Rector dev + PHPUnit 10'
+                        run: composer require "phpunit/phpunit:10.*" -W
+                        php: 8.2
+                    -
+                        name: 'Rector dev + PHPUnit 11'
+                        run: composer require "phpunit/phpunit:11.*" -W
+                        php: 8.2
+                    -
+                        name: 'Rector dev + PHPUnit 12'
+                        run: composer require "phpunit/phpunit:12.*" -W
+                        php: 8.3
+
+        name: ${{ matrix.actions.name }}
+
+        runs-on: ubuntu-latest
+
+        defaults:
+            run:
+                working-directory: compat-tests
+
+        steps:
+            -   uses: actions/checkout@v4
+
+            -
+                uses: shivammathur/setup-php@v2
+                with:
+                    php-version: ${{ matrix.actions.php }}
+                    coverage: none
+
+            -
+                uses: "ramsey/composer-install@v4"
+                with:
+                    working-directory: compat-tests
+
+            -   run: ${{ matrix.actions.run }}
+
+            -   run: vendor/bin/phpunit tests/Rector
+
+            -   run: vendor/bin/phpunit tests/PHPStan
+
+            -   run: vendor/bin/phpunit
diff --git a/compat-tests/.editorconfig b/compat-tests/.editorconfig
new file mode 100644
index 00000000000..bec95c4494f
--- /dev/null
+++ b/compat-tests/.editorconfig
@@ -0,0 +1,9 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4
diff --git a/compat-tests/.gitignore b/compat-tests/.gitignore
new file mode 100644
index 00000000000..b70e169059d
--- /dev/null
+++ b/compat-tests/.gitignore
@@ -0,0 +1,4 @@
+composer.lock
+/vendor
+
+.phpunit.result.cache
diff --git a/compat-tests/README.md b/compat-tests/README.md
new file mode 100644
index 00000000000..cde90af5c73
--- /dev/null
+++ b/compat-tests/README.md
@@ -0,0 +1,22 @@
+# Rector Compatibility Tests
+
+A small test harness that verifies [Rector](https://github.com/rectorphp/rector) keeps working alongside other tools in the PHP static-analysis ecosystem.
+
+It runs a minimal real-world setup — a custom Rector rule, a custom PHPStan rule, and a PHPUnit test suite — against multiple combinations of dependencies in CI, to catch breakage early.
+
+## What it checks
+
+* A custom **Rector** rule (`MakeClassFinalRector`, `UseGetArgRector`) loads and applies correctly.
+* A custom **PHPStan** rule (`CustomPHPStanRule`) loads and runs alongside Rector.
+* **PHPUnit 10, 11, and 12** all work with Rector's preloaded dependencies.
+* Manually including **`nikic/php-parser`** in user code does not conflict with the copy Rector ships.
+* `rector-laravel` + `nikic/php-parser` upgrade scenarios run cleanly (see [rectorphp/rector#9470](https://github.com/rectorphp/rector/issues/9470)).
+
+This project lives inside `rector/rector-src` (under `compat-tests/`) and pulls in `rector/rector:dev-main` as a downstream dependency, so the compat suite is maintained in one place. It mirrors the standalone [rectorphp/rector-compat-tests](https://github.com/rectorphp/rector-compat-tests).
+
+## How it runs
+
+GitHub Actions runs the matrix daily (`0 6 * * *`) and on every push/PR, from the repository root `.github/workflows`:
+
+* `compat_test.yaml` — Rector dev + PHPUnit 10 / 11 / 12
+* `rector_laravel_rector_dev.yaml` — Rector + rector-laravel + php-parser
diff --git a/compat-tests/composer.json b/compat-tests/composer.json
new file mode 100644
index 00000000000..f80e8e11cde
--- /dev/null
+++ b/compat-tests/composer.json
@@ -0,0 +1,24 @@
+{
+    "name": "rector/rector-compat-tests",
+    "license": "MIT",
+    "description": "Tests for compatibility with PHPStand and PHPUnit preload magic",
+    "require-dev": {
+        "php": "^8.2",
+        "phpunit/phpunit": "10.*|11.*|12.*",
+        "nikic/php-parser": "5.4.*|5.5.*|5.6.*|5.7.*",
+        "rector/rector": "dev-main as 2.4.4",
+        "phpstan/phpstan": "^2.2",
+        "driftingly/rector-laravel": "^2.4"
+    },
+    "autoload": {
+        "psr-4": {
+            "Rector\\RectorCompatTests\\": "src"
+        }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "Rector\\RectorCompatTests\\Tests\\": "tests",
+            "Fixture\\": "fixture"
+        }
+    }
+}
diff --git a/compat-tests/fixture/FixtureWithFuncCall.php b/compat-tests/fixture/FixtureWithFuncCall.php
new file mode 100644
index 00000000000..902dca44d94
--- /dev/null
+++ b/compat-tests/fixture/FixtureWithFuncCall.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace Fixture;
+
+final class FixtureWithFuncCall
+{
+    public function run(): int
+    {
+        return strlen('hello');
+    }
+}
diff --git a/compat-tests/phpunit.xml b/compat-tests/phpunit.xml
new file mode 100644
index 00000000000..dc8c3bf57f6
--- /dev/null
+++ b/compat-tests/phpunit.xml
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+    colors="true"
+    bootstrap="vendor/autoload.php"
+>
+    <testsuites>
+        <testsuite name="Project Tests">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
+</phpunit>
diff --git a/compat-tests/rector.php b/compat-tests/rector.php
new file mode 100644
index 00000000000..7a639f351c5
--- /dev/null
+++ b/compat-tests/rector.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+use Rector\RectorCompatTests\Rector\UseGetArgRector;
+
+return RectorConfig::configure()
+    ->withPaths([
+        __DIR__ . '/src',
+        __DIR__ . '/tests',
+        __DIR__ . '/fixture',
+    ])
+    ->withRules([UseGetArgRector::class])
+    ->withTypeCoverageLevel(0)
+    ->withDeadCodeLevel(0)
+    ->withCodeQualityLevel(0);
diff --git a/compat-tests/src/PHPStan/CustomPHPStanRule.php b/compat-tests/src/PHPStan/CustomPHPStanRule.php
new file mode 100644
index 00000000000..4e528849d47
--- /dev/null
+++ b/compat-tests/src/PHPStan/CustomPHPStanRule.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\RectorCompatTests\PHPStan;
+
+use PhpParser\Node;
+use PhpParser\Node\Stmt\Class_;
+use PHPStan\Analyser\Scope;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleError;
+use PHPStan\Rules\RuleErrorBuilder;
+
+/**
+ * @implements Rule<Class_>
+ */
+final class CustomPHPStanRule implements Rule
+{
+    public const ERROR_MESSAGE = 'Class "%s" is not final.';
+
+    public function getNodeType(): string
+    {
+        return Class_::class;
+    }
+
+    /**
+     * @param Class_ $node
+     * @return RuleError[]
+     */
+    public function processNode(Node $node, Scope $scope): array
+    {
+        if ($node->isFinal()) {
+            return [];
+        }
+
+        $ruleErrorMessage = RuleErrorBuilder::message(
+            sprintf(self::ERROR_MESSAGE, $node->name->toString())
+        )->build();
+
+        return [$ruleErrorMessage];
+    }
+}
diff --git a/compat-tests/src/Rector/MakeClassFinalRector.php b/compat-tests/src/Rector/MakeClassFinalRector.php
new file mode 100644
index 00000000000..a675baeb453
--- /dev/null
+++ b/compat-tests/src/Rector/MakeClassFinalRector.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\RectorCompatTests\Rector;
+
+use PhpParser\Modifiers;
+use PhpParser\Node;
+use PhpParser\Node\Stmt\Class_;
+use Rector\Rector\AbstractRector;
+
+final class MakeClassFinalRector extends AbstractRector
+{
+    /**
+     * @return array<class-string<Class_>>
+     */
+    public function getNodeTypes(): array
+    {
+        return [Class_::class];
+    }
+
+    /**
+     * @param Class_ $node
+     */
+    public function refactor(Node $node)
+    {
+        if ($node->isFinal()) {
+            return null;
+        }
+
+        $node->flags |= Modifiers::FINAL;
+
+        return $node;
+    }
+}
diff --git a/compat-tests/src/Rector/UseGetArgRector.php b/compat-tests/src/Rector/UseGetArgRector.php
new file mode 100644
index 00000000000..305bd2f7e47
--- /dev/null
+++ b/compat-tests/src/Rector/UseGetArgRector.php
@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\RectorCompatTests\Rector;
+
+use PhpParser\Modifiers;
+use PhpParser\Node;
+use PhpParser\Node\Arg;
+use PhpParser\Node\Expr\FuncCall;
+use PhpParser\Node\Scalar\String_;
+use PhpParser\Node\Stmt\Class_;
+use PhpParser\Node\Stmt\Function_;
+use Rector\Rector\AbstractRector;
+
+final class UseGetArgRector extends AbstractRector
+{
+    /**
+     * @return array<class-string<Class_>>
+     */
+    public function getNodeTypes(): array
+    {
+        return [FuncCall::class];
+    }
+
+    /**
+     * @param FuncCall $node
+     */
+    public function refactor(Node $node)
+    {
+        // here we should load Rector's php-parser 5.6, that already has getArg() method
+        $firstArg = $node->getArg('', 0);
+        if (! $firstArg instanceof Arg) {
+            return null;;
+        }
+
+        $firstArg->value = new String_('changed_value');
+
+        return $node;
+    }
+}
diff --git a/compat-tests/tests/ConflictingPhpParserLibraryTest.php b/compat-tests/tests/ConflictingPhpParserLibraryTest.php
new file mode 100644
index 00000000000..d2eca54f610
--- /dev/null
+++ b/compat-tests/tests/ConflictingPhpParserLibraryTest.php
@@ -0,0 +1,20 @@
+<?php declare(strict_types=1);
+
+namespace BBurnichon\RectorIssue9437\Tests;
+
+use PHPUnit\Framework\TestCase;
+use PHPUnit\Runner\Version;
+
+final class ConflictingPhpParserLibraryTest extends TestCase
+{
+    public function testItShouldNotConflictWhenIncludingPhpParserManually(): void
+    {
+        if (Version::id() >= 12) {
+            $this->markTestSkipped('This test requires PHPUnit < 12');
+        }
+
+        include_once dirname(__DIR__, 1) . '/vendor/nikic/php-parser/lib/PhpParser/Parser.php';
+
+        $this->assertTrue(true);
+    }
+}
\ No newline at end of file
diff --git a/compat-tests/tests/PHPStan/CustomPHPStanRule/CustomPHPStanRuleTest.php b/compat-tests/tests/PHPStan/CustomPHPStanRule/CustomPHPStanRuleTest.php
new file mode 100644
index 00000000000..9c10ac2d360
--- /dev/null
+++ b/compat-tests/tests/PHPStan/CustomPHPStanRule/CustomPHPStanRuleTest.php
@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\RectorCompatTests\Tests\PHPStan\CustomPHPStanRule;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+use Rector\RectorCompatTests\PHPStan\CustomPHPStanRule;
+
+final class CustomPHPStanRuleTest extends RuleTestCase
+{
+    public function testRule(): void
+    {
+        $this->analyse([__DIR__ . '/Fixture/NonFinalClass.php'], [
+            [sprintf(CustomPHPStanRule::ERROR_MESSAGE, "NonFinalClass"), 7]
+        ]);
+    }
+
+    protected function getRule(): Rule
+    {
+        return new CustomPHPStanRule();
+    }
+}
diff --git a/compat-tests/tests/PHPStan/CustomPHPStanRule/Fixture/NonFinalClass.php b/compat-tests/tests/PHPStan/CustomPHPStanRule/Fixture/NonFinalClass.php
new file mode 100644
index 00000000000..fbfc5fa60d4
--- /dev/null
+++ b/compat-tests/tests/PHPStan/CustomPHPStanRule/Fixture/NonFinalClass.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\RectorCompatTests\Tests\PHPStan\CustomPHPStanRule\Fixture;
+
+class NonFinalClass
+{
+
+}
diff --git a/compat-tests/tests/Rector/MakeClassFinalRector/Fixture/some_non_final_class.php.inc b/compat-tests/tests/Rector/MakeClassFinalRector/Fixture/some_non_final_class.php.inc
new file mode 100644
index 00000000000..b13de3a3abd
--- /dev/null
+++ b/compat-tests/tests/Rector/MakeClassFinalRector/Fixture/some_non_final_class.php.inc
@@ -0,0 +1,19 @@
+<?php
+
+namespace Rector\RectorCompatTests\Tests\Rector\MakeClassFinalRector\Fixture;
+
+class SomeNonFinalClass
+{
+}
+
+?>
+-----
+<?php
+
+namespace Rector\RectorCompatTests\Tests\Rector\MakeClassFinalRector\Fixture;
+
+final class SomeNonFinalClass
+{
+}
+
+?>
diff --git a/compat-tests/tests/Rector/MakeClassFinalRector/MakeClassFinalRectorTest.php b/compat-tests/tests/Rector/MakeClassFinalRector/MakeClassFinalRectorTest.php
new file mode 100644
index 00000000000..a2d8b1a48fa
--- /dev/null
+++ b/compat-tests/tests/Rector/MakeClassFinalRector/MakeClassFinalRectorTest.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Rector\RectorCompatTests\Tests\Rector\MakeClassFinalRector;
+
+use Rector\Testing\PHPUnit\AbstractRectorTestCase;
+
+final class MakeClassFinalRectorTest extends AbstractRectorTestCase
+{
+    public function test(): void
+    {
+        $this->doTestFile(__DIR__ . '/Fixture/some_non_final_class.php.inc');
+    }
+
+    public function provideConfigFilePath(): string
+    {
+        return __DIR__ . '/config/configured_rule.php';
+    }
+}
diff --git a/compat-tests/tests/Rector/MakeClassFinalRector/config/configured_rule.php b/compat-tests/tests/Rector/MakeClassFinalRector/config/configured_rule.php
new file mode 100644
index 00000000000..acb5c3999dc
--- /dev/null
+++ b/compat-tests/tests/Rector/MakeClassFinalRector/config/configured_rule.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+use Rector\RectorCompatTests\Rector\MakeClassFinalRector;
+
+return RectorConfig::configure()
+    ->withRules([MakeClassFinalRector::class]);