diff --git a/src/Symfony/Bundle/FrameworkBundle/FrameworkBundle.php b/src/Symfony/Bundle/FrameworkBundle/FrameworkBundle.php
index 2197610896eb5..1aebc9b9a4b0b 100644
--- a/src/Symfony/Bundle/FrameworkBundle/FrameworkBundle.php
+++ b/src/Symfony/Bundle/FrameworkBundle/FrameworkBundle.php
@@ -60,6 +60,7 @@
 use Symfony\Component\Mime\DependencyInjection\AddMimeTypeGuesserPass;
 use Symfony\Component\PropertyInfo\DependencyInjection\PropertyInfoPass;
 use Symfony\Component\Routing\DependencyInjection\RoutingResolverPass;
+use Symfony\Component\Runtime\SymfonyRuntime;
 use Symfony\Component\Serializer\DependencyInjection\SerializerPass;
 use Symfony\Component\Translation\DependencyInjection\TranslationDumperPass;
 use Symfony\Component\Translation\DependencyInjection\TranslationExtractorPass;
@@ -91,7 +92,16 @@ class FrameworkBundle extends Bundle
 {
     public function boot()
     {
-        ErrorHandler::register(null, false)->throwAt($this->container->getParameter('debug.error_handler.throw_at'), true);
+        if (class_exists(SymfonyRuntime::class)) {
+            $handler = set_error_handler('var_dump');
+            restore_error_handler();
+        } else {
+            $handler = [ErrorHandler::register(null, false)];
+        }
+
+        if (\is_array($handler) && $handler[0] instanceof ErrorHandler) {
+            $handler[0]->throwAt($this->container->getParameter('debug.error_handler.throw_at'), true);
+        }
 
         if ($this->container->getParameter('kernel.http_method_override')) {
             Request::enableHttpMethodParameterOverride();
diff --git a/src/Symfony/Bundle/FrameworkBundle/composer.json b/src/Symfony/Bundle/FrameworkBundle/composer.json
index 3bae1c3862618..f5b156df49f9b 100644
--- a/src/Symfony/Bundle/FrameworkBundle/composer.json
+++ b/src/Symfony/Bundle/FrameworkBundle/composer.json
@@ -86,6 +86,7 @@
         "symfony/mime": "<4.4",
         "symfony/property-info": "<4.4",
         "symfony/property-access": "<5.3",
+        "symfony/runtime": "<5.4.45|>=6.0,<6.4.13|>=7.0,<7.1.6",
         "symfony/serializer": "<5.2",
         "symfony/service-contracts": ">=3.0",
         "symfony/security-csrf": "<5.3",
diff --git a/src/Symfony/Component/Console/Application.php b/src/Symfony/Component/Console/Application.php
index bb5341882181a..fbb3b0eb009a7 100644
--- a/src/Symfony/Component/Console/Application.php
+++ b/src/Symfony/Component/Console/Application.php
@@ -165,9 +165,9 @@ public function run(?InputInterface $input = null, ?OutputInterface $output = nu
             }
         }
 
-        $this->configureIO($input, $output);
-
         try {
+            $this->configureIO($input, $output);
+
             $exitCode = $this->doRun($input, $output);
         } catch (\Exception $e) {
             if (!$this->catchExceptions) {
diff --git a/src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php b/src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php
index 74fa6179480ed..791fda7d83a9d 100644
--- a/src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php
+++ b/src/Symfony/Component/HttpKernel/EventListener/DebugHandlersListener.php
@@ -57,7 +57,7 @@ public function __construct(?callable $exceptionHandler = null, ?LoggerInterface
             $deprecationLogger = $fileLinkFormat;
         }
 
-        $handler = set_exception_handler('is_int');
+        $handler = set_exception_handler('var_dump');
         $this->earlyHandler = \is_array($handler) ? $handler[0] : null;
         restore_exception_handler();
 
@@ -84,7 +84,7 @@ public function configure(?object $event = null)
         $this->firstCall = $this->hasTerminatedWithException = false;
         $hasRun = null;
 
-        $handler = set_exception_handler('is_int');
+        $handler = set_exception_handler('var_dump');
         $handler = \is_array($handler) ? $handler[0] : null;
         restore_exception_handler();
 
diff --git a/src/Symfony/Component/Runtime/GenericRuntime.php b/src/Symfony/Component/Runtime/GenericRuntime.php
index fa9364881363e..7c202c282e27e 100644
--- a/src/Symfony/Component/Runtime/GenericRuntime.php
+++ b/src/Symfony/Component/Runtime/GenericRuntime.php
@@ -71,15 +71,15 @@ public function __construct(array $options = [])
         if ($debug) {
             umask(0000);
             $_SERVER[$debugKey] = $_ENV[$debugKey] = '1';
-
-            if (false !== $errorHandler = ($options['error_handler'] ?? BasicErrorHandler::class)) {
-                $errorHandler::register($debug);
-                $options['error_handler'] = false;
-            }
         } else {
             $_SERVER[$debugKey] = $_ENV[$debugKey] = '0';
         }
 
+        if (false !== $errorHandler = ($options['error_handler'] ?? BasicErrorHandler::class)) {
+            $errorHandler::register($debug);
+            $options['error_handler'] = false;
+        }
+
         $this->options = $options;
     }
 
diff --git a/src/Symfony/Component/Runtime/Internal/BasicErrorHandler.php b/src/Symfony/Component/Runtime/Internal/BasicErrorHandler.php
index 6f41af585e616..d4e90a386c356 100644
--- a/src/Symfony/Component/Runtime/Internal/BasicErrorHandler.php
+++ b/src/Symfony/Component/Runtime/Internal/BasicErrorHandler.php
@@ -30,10 +30,10 @@ public static function register(bool $debug): void
         }
 
         if (0 <= \ini_get('zend.assertions')) {
-            ini_set('zend.assertions', 1);
-            ini_set('assert.active', $debug);
-            ini_set('assert.exception', 1);
+            ini_set('zend.assertions', (int) $debug);
         }
+        ini_set('assert.active', 1);
+        ini_set('assert.exception', 1);
 
         set_error_handler(new self());
     }
diff --git a/src/Symfony/Component/Runtime/Internal/SymfonyErrorHandler.php b/src/Symfony/Component/Runtime/Internal/SymfonyErrorHandler.php
index 40c125a91e333..0dfc7de0ca7a0 100644
--- a/src/Symfony/Component/Runtime/Internal/SymfonyErrorHandler.php
+++ b/src/Symfony/Component/Runtime/Internal/SymfonyErrorHandler.php
@@ -24,12 +24,31 @@ class SymfonyErrorHandler
 {
     public static function register(bool $debug): void
     {
-        BasicErrorHandler::register($debug);
+        if (!class_exists(ErrorHandler::class)) {
+            BasicErrorHandler::register($debug);
 
-        if (class_exists(ErrorHandler::class)) {
+            return;
+        }
+
+        error_reporting(-1);
+
+        if (!\in_array(\PHP_SAPI, ['cli', 'phpdbg', 'embed'], true)) {
+            ini_set('display_errors', $debug);
+        } elseif (!filter_var(\ini_get('log_errors'), \FILTER_VALIDATE_BOOL) || \ini_get('error_log')) {
+            // CLI - display errors only if they're not already logged to STDERR
+            ini_set('display_errors', 1);
+        }
+
+        if (0 <= \ini_get('zend.assertions')) {
+            ini_set('zend.assertions', (int) $debug);
+        }
+        ini_set('assert.active', 1);
+        ini_set('assert.exception', 1);
+
+        if ($debug) {
             DebugClassLoader::enable();
-            restore_error_handler();
-            ErrorHandler::register(new ErrorHandler(new BufferingLogger(), $debug));
         }
+
+        ErrorHandler::register(new ErrorHandler(new BufferingLogger(), $debug));
     }
 }