diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index 7e81cef..6e2581c 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -5,4 +5,8 @@ parameters:
         - src/
         - tests/
 
+    fileExtensions:
+        - php
+        - phpt
+
     reportUnmatchedIgnoredErrors: false
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index fb514a6..acf5e2b 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -11,7 +11,8 @@
     <testsuites>
         <testsuite name="Framework X test suite">
             <directory>./tests/</directory>
-            <exclude>./tests/integration/</exclude>
+            <directory suffix=".phpt">./tests/</directory>
+            <exclude>./tests/integration/vendor/</exclude>
         </testsuite>
     </testsuites>
     <coverage>
diff --git a/phpunit.xml.legacy b/phpunit.xml.legacy
index a35d140..8113110 100644
--- a/phpunit.xml.legacy
+++ b/phpunit.xml.legacy
@@ -9,7 +9,8 @@
     <testsuites>
         <testsuite name="Framework X test suite">
             <directory>./tests/</directory>
-            <exclude>./tests/install-as-dep/</exclude>
+            <directory suffix=".phpt">./tests/</directory>
+            <exclude>./tests/integration/vendor/</exclude>
         </testsuite>
     </testsuites>
     <filter>
diff --git a/src/App.php b/src/App.php
index 808e3d9..519e157 100644
--- a/src/App.php
+++ b/src/App.php
@@ -5,8 +5,6 @@
 use FrameworkX\Io\MiddlewareHandler;
 use FrameworkX\Io\RedirectHandler;
 use FrameworkX\Io\RouteHandler;
-use FrameworkX\Runner\HttpServerRunner;
-use FrameworkX\Runner\SapiRunner;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
 use React\Http\Message\Response;
@@ -22,7 +20,7 @@ class App
     /** @var RouteHandler */
     private $router;
 
-    /** @var HttpServerRunner|SapiRunner|callable(callable(ServerRequestInterface):(ResponseInterface|PromiseInterface<ResponseInterface>)):void */
+    /** @var callable(callable(ServerRequestInterface):(ResponseInterface|PromiseInterface<ResponseInterface>)):void */
     private $runner;
 
     /**
@@ -257,8 +255,8 @@ public function redirect(string $route, string $target, int $code = Response::ST
      * the `X_EXPERIMENTAL_RUNNER` environment variable to the desired runner
      * class name ({@see Container::getRunner()}).
      *
-     * @see HttpServerRunner::__invoke()
-     * @see SapiRunner::__invoke()
+     * @see \FrameworkX\Runner\HttpServerRunner::__invoke()
+     * @see \FrameworkX\Runner\SapiRunner::__invoke()
      * @see Container::getRunner()
      */
     public function run(): void
diff --git a/src/Runner/NullRunner.php b/src/Runner/NullRunner.php
new file mode 100644
index 0000000..8fc5e17
--- /dev/null
+++ b/src/Runner/NullRunner.php
@@ -0,0 +1,41 @@
+<?php
+
+namespace FrameworkX\Runner;
+
+/**
+ * Application runner stub that does nothing when invoked.
+ *
+ * This experimental application runner can be used in environments where the
+ * application lifecycle is managed externally. It can be useful for integration
+ * testing or when embedding the application in other systems.
+ *
+ * Note that this runner is not intended for production use and is not loaded by
+ * default. You need to explicitly configure your application to use this runner
+ * through the `X_EXPERIMENTAL_RUNNER` environment variable:
+ *
+ * ```php
+ * $container = new Container([
+ *     // 'X_EXPERIMENTAL_RUNNER' => fn(?string $X_EXPERIMENTAL_RUNNER = null): ?string => $X_EXPERIMENTAL_RUNNER,
+ *     // 'X_EXPERIMENTAL_RUNNER' => fn(bool|string $ACME = false): ?string => $ACME ? NullRunner::class : null,
+ *     'X_EXPERIMENTAL_RUNNER' => NullRunner::class
+ * ]);
+ *
+ * $app = new App($container);
+ * ```
+ *
+ * Likewise, you may pass this runner through an environment variable from your
+ * integration tests, see also included PHPT test files for examples.
+ *
+ * @see \FrameworkX\Container::getRunner()
+ */
+class NullRunner
+{
+    /**
+     * @param callable(\Psr\Http\Message\ServerRequestInterface):(\Psr\Http\Message\ResponseInterface|\React\Promise\PromiseInterface<\Psr\Http\Message\ResponseInterface>) $handler
+     * @return void
+     */
+    public function __invoke(callable $handler): void
+    {
+        // NO-OP
+    }
+}
diff --git a/tests/AppTest.php b/tests/AppTest.php
index 2b8eb52..fee95df 100644
--- a/tests/AppTest.php
+++ b/tests/AppTest.php
@@ -9,6 +9,7 @@
 use FrameworkX\Io\MiddlewareHandler;
 use FrameworkX\Io\RouteHandler;
 use FrameworkX\Runner\HttpServerRunner;
+use FrameworkX\Runner\NullRunner;
 use FrameworkX\Tests\Fixtures\InvalidAbstract;
 use FrameworkX\Tests\Fixtures\InvalidConstructorInt;
 use FrameworkX\Tests\Fixtures\InvalidConstructorIntersection;
@@ -949,6 +950,18 @@ public function testRunWillInvokeCustomRunnerFromContainerEnvironmentVariable():
         $app->run();
     }
 
+    public function testRunReturnsImmediatelyWithNullRunnerFromContainerEnvironmentVariable(): void
+    {
+        $container = new Container([
+            'X_EXPERIMENTAL_RUNNER' => NullRunner::class
+        ]);
+
+        $app = new App($container);
+
+        $this->expectOutputString('');
+        $app->run();
+    }
+
     public function testGetMethodAddsGetRouteOnRouter(): void
     {
         $router = $this->createMock(RouteHandler::class);
diff --git a/tests/Runner/NullRunnerTest.php b/tests/Runner/NullRunnerTest.php
new file mode 100644
index 0000000..eda32dd
--- /dev/null
+++ b/tests/Runner/NullRunnerTest.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace FrameworkX\Tests\Runner;
+
+use FrameworkX\Runner\NullRunner;
+use PHPUnit\Framework\TestCase;
+
+class NullRunnerTest extends TestCase
+{
+    public function testInvokeReturnsImmediately(): void
+    {
+        $runner = new NullRunner();
+
+        $this->expectOutputString('');
+        $runner(function () {
+            throw new \BadFunctionCallException('Should not be called');
+        });
+    }
+}
diff --git a/tests/integration/public/index.php b/tests/integration/public/index.php
index 8bca0ce..1fceb3a 100644
--- a/tests/integration/public/index.php
+++ b/tests/integration/public/index.php
@@ -26,7 +26,14 @@ function asleep(float $s): PromiseInterface
     });
 }
 
-$app = new FrameworkX\App();
+$container = new FrameworkX\Container([
+    FrameworkX\AccessLogHandler::class => function (?string $X_EXPERIMENTAL_RUNNER = null) {
+        // log to /dev/null when running in experimental runner mode to avoid cluttering output
+        return new FrameworkX\AccessLogHandler($X_EXPERIMENTAL_RUNNER !== null ? (DIRECTORY_SEPARATOR !== '\\' ? '/dev/null' : __DIR__ . '\\nul') : null);
+    }
+]);
+
+$app = new FrameworkX\App($container);
 
 $app->get('/', function () {
     return React\Http\Message\Response::plaintext(
diff --git a/tests/integration/tests/AppInvokeIndexReturnsResponse.phpt b/tests/integration/tests/AppInvokeIndexReturnsResponse.phpt
new file mode 100644
index 0000000..4db264f
--- /dev/null
+++ b/tests/integration/tests/AppInvokeIndexReturnsResponse.phpt
@@ -0,0 +1,25 @@
+--TEST--
+Loading index file with NullRunner allows invoking the app
+--INI--
+# suppress legacy PHPUnit 7 warning for Xdebug 3
+xdebug.default_enable=
+--ENV--
+X_EXPERIMENTAL_RUNNER=FrameworkX\Runner\NullRunner
+--FILE--
+<?php
+
+require __DIR__ . '/../../../vendor/autoload.php';
+require __DIR__ . '/../public/index.php';
+
+/** @var FrameworkX\App $app */
+assert($app instanceof FrameworkX\App);
+
+$request = new React\Http\Message\ServerRequest('GET', '/');
+$response = $app($request);
+assert($response instanceof Psr\Http\Message\ResponseInterface);
+
+echo $response->getBody();
+
+?>
+--EXPECT--
+Hello world!
diff --git a/tests/integration/tests/AppStopsWithoutOutputWithNullRunner.phpt b/tests/integration/tests/AppStopsWithoutOutputWithNullRunner.phpt
new file mode 100644
index 0000000..80bf4b7
--- /dev/null
+++ b/tests/integration/tests/AppStopsWithoutOutputWithNullRunner.phpt
@@ -0,0 +1,11 @@
+--TEST--
+Loading index file with NullRunner stops immediately without output
+--INI--
+# suppress legacy PHPUnit 7 warning for Xdebug 3
+xdebug.default_enable=
+--ENV--
+X_EXPERIMENTAL_RUNNER=FrameworkX\Runner\NullRunner
+--FILE_EXTERNAL--
+../public/index.php
+--EXPECTREGEX--
+^$