diff --git a/components/ILIAS/Init/classes/ErrorHandling/README.md b/components/ILIAS/Init/classes/ErrorHandling/README.md
index cef25f90620d..887ea6642fbe 100644
--- a/components/ILIAS/Init/classes/ErrorHandling/README.md
+++ b/components/ILIAS/Init/classes/ErrorHandling/README.md
@@ -4,16 +4,16 @@ This package provides responders for rendering HTTP error pages in ILIAS.
 
 ## When to use which responder
 
-- **ErrorPageResponder** (`Http\ErrorPageResponder`): Use when the DI container and all ILIAS services (UI, language, HTTP, etc.) are available. Renders a full ILIAS page with a UI-Framework MessageBox and optional back button. Use for expected errors (e.g. routing failures, access denied) that should be shown as a proper HTML page.
+- **ErrorPageResponder** (`Http\ErrorPageResponder`): Full ILIAS page: UI MessageBox when the fourth argument is `UIServices`, or `tpl.error.html` block `plain_html_fallback` when it is `ilGlobalTemplateInterface` (no `ui.factory` / `ui.renderer`). Constructor: `global_screen`, `language`, `http`, `shell`. On any `Throwable` from bootstrap or `respond()`, use `PlainTextFallbackResponder` (see `ilias.php` / `error.php`).
 
-- **PlainTextFallbackResponder** (`Http\PlainTextFallbackResponder`): Use when the DI container or other infrastructure is *not* available — for instance in the catch block of `error.php` when the bootstrap itself has failed. Sends a minimal plain-text response with `Content-Type: text/plain; charset=UTF-8` and logs the exception via `error_log`. This responder always works because it uses only PHP built-ins. The HTTP status code defaults to 500; pass a different code (e.g. 502) when the failure context is known.
+- **PlainTextFallbackResponder** (`Http\PlainTextFallbackResponder`): Use when the DI container or other infrastructure is *not* available — for instance in the catch block of `error.php` when the bootstrap itself has failed. Sends a minimal plain-text response with `Content-Type: text/plain; charset=UTF-8` and logs the exception via `error_log`. The HTTP status code defaults to 500; pass a different code when the failure context is known.
 
 ## Consumer responsibility
 
-**The consumer MUST implement a try-catch block.** Both responders must be invoked explicitly:
+**The consumer MUST implement a try-catch block.** Call `respond()` explicitly:
 
-1. Wrap the main logic (bootstrap, routing, etc.) in a `try` block.
-2. In the `catch` block, call either `ErrorPageResponder::respond()` (if DIC is available) or `PlainTextFallbackResponder::respond()` (if DIC is not available).
+1. Wrap bootstrap (and `ErrorPageResponder::respond()` when applicable) in one `try` block.
+2. In `catch (Throwable)`, call `PlainTextFallbackResponder` (optionally pass a user-facing message if you set it before the failure).
 
 Example:
 
@@ -21,13 +21,13 @@ Example:
 try {
     entry_point('ILIAS Legacy Initialisation Adapter');
     global $DIC;
-    new ErrorPageResponder(
-        $DIC->globalScreen(),
+    (new ErrorPageResponder(
+        $DIC->offsetExists('global_screen') ? $DIC->globalScreen() : null,
         $DIC->language(),
-        $DIC->ui(),
-        $DIC->http()
-    )->respond($message, 500, $back_target);
-} catch (Throwable $e) {
-    new PlainTextFallbackResponder()->respond($e);
+        $DIC->http(),
+        $DIC->ui()
+    ))->respond($message, 500, $back_target);
+} catch (Throwable $t) {
+    (new PlainTextFallbackResponder())->respond($t);
 }
 ```
diff --git a/components/ILIAS/Init/resources/error.php b/components/ILIAS/Init/resources/error.php
index 55764207b53f..ccbd9acad2ce 100644
--- a/components/ILIAS/Init/resources/error.php
+++ b/components/ILIAS/Init/resources/error.php
@@ -26,6 +26,7 @@
 use ILIAS\Init\ErrorHandling\Http\ErrorPageResponder;
 use ILIAS\Init\ErrorHandling\Http\PlainTextFallbackResponder;
 
+$message = null;
 try {
     require_once '../vendor/composer/vendor/autoload.php';
 
@@ -49,15 +50,19 @@
     );
 
     new ErrorPageResponder(
-        $DIC->globalScreen(),
+        $DIC->offsetExists('global_screen') ? $DIC->globalScreen() : null,
         $DIC->language(),
-        $DIC->ui(),
-        $DIC->http()
+        $DIC->http(),
+        $DIC->ui()
     )->respond(
         $message,
         StatusCode::HTTP_INTERNAL_SERVER_ERROR,
         $back_target
     );
 } catch (Throwable $e) {
-    new PlainTextFallbackResponder()->respond($e);
+    new PlainTextFallbackResponder()->respond(
+        $e,
+        StatusCode::HTTP_INTERNAL_SERVER_ERROR,
+        $message
+    );
 }
diff --git a/components/ILIAS/Init/resources/ilias.php b/components/ILIAS/Init/resources/ilias.php
index bf42ab16c6cd..f57945a4c7ab 100644
--- a/components/ILIAS/Init/resources/ilias.php
+++ b/components/ILIAS/Init/resources/ilias.php
@@ -18,9 +18,10 @@
 
 declare(strict_types=1);
 
-use ILIAS\HTTP\StatusCode;
 use ILIAS\Data\Factory as DataFactory;
+use ILIAS\HTTP\StatusCode;
 use ILIAS\Init\ErrorHandling\Http\ErrorPageResponder;
+use ILIAS\Init\ErrorHandling\Http\PlainTextFallbackResponder;
 
 if (!file_exists('../ilias.ini.php')) {
     die('The ILIAS setup is not completed. Please run the setup routine.');
@@ -28,39 +29,82 @@
 
 require_once '../vendor/composer/vendor/autoload.php';
 require_once __DIR__ . '/../artifacts/bootstrap_default.php';
-entry_point('ILIAS Legacy Initialisation Adapter');
-
-/** @var \ILIAS\DI\Container $DIC */
-global $DIC;
 
 try {
+    entry_point('ILIAS Legacy Initialisation Adapter');
+    global $DIC;
     $DIC->ctrl()->callBaseClass();
 } catch (ilCtrlException $e) {
+    global $DIC;
+
     if (defined('DEVMODE') && DEVMODE) {
         throw $e;
     }
 
-    $DIC->logger()->root()->error($e->getMessage());
-    $DIC->logger()->root()->error($e->getTraceAsString());
+    if ($DIC->offsetExists('ilLoggerFactory')) {
+        $DIC->logger()->root()->error($e->getMessage());
+        $DIC->logger()->root()->error($e->getTraceAsString());
+    }
 
-    $DIC->language()->loadLanguageModule('error');
-    $df = new DataFactory();
-    $back_target = $df->link(
-        $DIC->language()->txt('error_back_to_repository'),
-        $df->uri(ILIAS_HTTP_PATH . '/ilias.php?baseClass=ilRepositoryGUI')
-    );
+    $repository_href = defined('ILIAS_HTTP_PATH')
+        ? ILIAS_HTTP_PATH . '/ilias.php?baseClass=ilRepositoryGUI'
+        : '/ilias.php?baseClass=ilRepositoryGUI';
 
-    new ErrorPageResponder(
-        $DIC->globalScreen(),
-        $DIC->language(),
-        $DIC->ui(),
-        $DIC->http()
-    )->respond(
-        $DIC->language()->txt('http_404_not_found'),
-        StatusCode::HTTP_NOT_FOUND,
-        $back_target
-    );
+    $public_message = null;
+    if ($DIC->offsetExists('lng')) {
+        $DIC->language()->loadLanguageModule('error');
+        $public_message = $DIC->language()->txt('http_404_not_found');
+    }
+
+    $can_html_error_page = $DIC->offsetExists('lng')
+        && $DIC->offsetExists('http')
+        && $DIC->offsetExists('tpl')
+        && $DIC->offsetExists('ui.factory')
+        && $DIC->offsetExists('ui.renderer');
+
+    $can_plain_html_error_page = $DIC->offsetExists('lng')
+        && $DIC->offsetExists('http')
+        && $DIC->offsetExists('tpl')
+        && (
+            !$DIC->offsetExists('ui.factory')
+            || !$DIC->offsetExists('ui.renderer')
+        );
+
+    try {
+        if ($can_html_error_page || $can_plain_html_error_page) {
+            $df = $DIC->offsetExists(\ILIAS\Data\Factory::class)
+                ? $DIC[\ILIAS\Data\Factory::class]
+                : new DataFactory();
+            $back_target = $df->link(
+                $DIC->language()->txt('error_back_to_repository'),
+                $df->uri($repository_href)
+            );
+            $shell = $can_html_error_page
+                ? $DIC->ui()
+                : $DIC['tpl'];
+            new ErrorPageResponder(
+                $DIC->offsetExists('global_screen') ? $DIC->globalScreen() : null,
+                $DIC->language(),
+                $DIC->http(),
+                $shell
+            )->respond(
+                $public_message ?? '',
+                StatusCode::HTTP_NOT_FOUND,
+                $back_target
+            );
+        }
+        new PlainTextFallbackResponder()->respond($e, StatusCode::HTTP_NOT_FOUND, $public_message);
+    } catch (Throwable $t) {
+        new PlainTextFallbackResponder()->respond(
+            $t,
+            StatusCode::HTTP_NOT_FOUND,
+            $public_message
+        );
+    }
 }
 
+/** @var \ILIAS\DI\Container $DIC */
+global $DIC;
+
 $DIC['ilBench']->save();
 $DIC['http']?->close();
diff --git a/components/ILIAS/Init/src/ErrorHandling/Http/ErrorPageResponder.php b/components/ILIAS/Init/src/ErrorHandling/Http/ErrorPageResponder.php
index f80efb4f37f7..e063e8d22dfd 100644
--- a/components/ILIAS/Init/src/ErrorHandling/Http/ErrorPageResponder.php
+++ b/components/ILIAS/Init/src/ErrorHandling/Http/ErrorPageResponder.php
@@ -24,6 +24,7 @@
 use ilLanguage;
 use ILIAS\Data\Link;
 use ilGlobalTemplate;
+use ilGlobalTemplateInterface;
 use ILIAS\DI\UIServices;
 use ILIAS\HTTP\Response\ResponseHeader;
 use ILIAS\HTTP\Services as HTTPServices;
@@ -33,6 +34,11 @@
  * Responder that renders a full ILIAS error page (UI-Framework MessageBox)
  * and sends it with the appropriate HTTP status code.
  *
+ * Pass {@see UIServices} as {@code $shell} for a MessageBox. If {@code ui.factory}
+ * / {@code ui.renderer} are not available, pass {@see ilGlobalTemplateInterface}
+ * (e.g. {@code $DIC['tpl']}) — {@code tpl.error.html} is then filled via
+ * {@code plain_html_fallback} (simple alert + link).
+ *
  * Use this when the DI container and all ILIAS services are available.
  * The consumer MUST wrap the main logic in a try-catch and call
  * {@see respond()} in the catch block for expected errors (e.g., routing
@@ -41,14 +47,21 @@
  *
  * The error message is rendered via MessageBox::failure(). If a back target
  * (Data\Link) is provided, it is embedded into the MessageBox via withButtons().
+ *
+ * {@see GlobalScreenServices} may be null when ilCtrl fails during
+ * {@see ilInitialisation::initILIAS()} before GlobalScreen is registered; the
+ * external context claim is skipped in that case.
  */
-class ErrorPageResponder
+readonly class ErrorPageResponder
 {
+    /**
+     * @param UIServices|ilGlobalTemplateInterface $shell {@see UIServices} or main page template without UI stack.
+     */
     public function __construct(
-        private readonly GlobalScreenServices $global_screen,
-        private readonly ilLanguage $language,
-        private readonly UIServices $ui,
-        private readonly HTTPServices $http
+        private ?GlobalScreenServices $global_screen,
+        private ilLanguage $language,
+        private HTTPServices $http,
+        private UIServices|ilGlobalTemplateInterface $shell,
     ) {
     }
 
@@ -56,28 +69,53 @@ public function respond(
         string $error_message,
         int $status_code,
         ?Link $back_target = null
-    ): void {
-        $this->global_screen->tool()->context()->claim()->external();
+    ): never {
+        $this->global_screen?->tool()->context()->claim()->external();
+
         $this->language->loadLanguageModule('error');
 
-        $message_box = $this->ui->factory()->messageBox()->failure($error_message);
+        $local_tpl = new ilGlobalTemplate('tpl.error.html', true, true);
+
+        if ($this->shell instanceof UIServices) {
+            $message_box = $this->shell->factory()->messageBox()->failure($error_message);
+
+            if ($back_target !== null) {
+                $message_box = $message_box->withButtons([
+                    $this->shell->factory()->button()->standard(
+                        $back_target->getLabel(),
+                        ilUtil::secureUrl((string) $back_target->getURL())
+                    ),
+                ]);
+            }
 
-        if ($back_target !== null) {
-            $ui_button = $this->ui->factory()->button()->standard(
-                $back_target->getLabel(),
-                ilUtil::secureUrl((string) $back_target->getURL())
+            $local_tpl->setCurrentBlock('msg_box');
+            $local_tpl->setVariable(
+                'MESSAGE_BOX',
+                $this->shell->renderer()->render($message_box)
             );
-            $message_box = $message_box->withButtons([$ui_button]);
+            $local_tpl->parseCurrentBlock();
+        } else {
+            $local_tpl->setCurrentBlock('plain_html_fallback');
+            $local_tpl->setVariable(
+                'ERROR_MESSAGE',
+                htmlspecialchars($error_message, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8')
+            );
+            if ($back_target !== null) {
+                $local_tpl->setVariable(
+                    'LINK_HREF',
+                    ilUtil::secureUrl((string) $back_target->getURL())
+                );
+                $local_tpl->setVariable(
+                    'LINK_TEXT',
+                    htmlspecialchars($back_target->getLabel(), ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8')
+                );
+            } else {
+                $local_tpl->setVariable('LINK_HREF', '');
+                $local_tpl->setVariable('LINK_TEXT', '');
+            }
+            $local_tpl->parseCurrentBlock();
         }
 
-        $local_tpl = new ilGlobalTemplate('tpl.error.html', true, true);
-        $local_tpl->setCurrentBlock('msg_box');
-        $local_tpl->setVariable(
-            'MESSAGE_BOX',
-            $this->ui->renderer()->render($message_box)
-        );
-        $local_tpl->parseCurrentBlock();
-
         $this->http->saveResponse(
             $this->http
                 ->response()
@@ -85,9 +123,17 @@ public function respond(
                 ->withHeader(ResponseHeader::CONTENT_TYPE, 'text/html')
         );
 
-        $this->ui->mainTemplate()->setContent($local_tpl->get());
-        $this->ui->mainTemplate()->printToStdout();
+        $main = $this->mainShellTemplate();
+        $main->setContent($local_tpl->get());
+        $main->printToStdout();
 
         $this->http->close();
     }
+
+    private function mainShellTemplate(): ilGlobalTemplateInterface
+    {
+        return $this->shell instanceof UIServices
+            ? $this->shell->mainTemplate()
+            : $this->shell;
+    }
 }
diff --git a/components/ILIAS/Init/src/ErrorHandling/Http/PlainTextFallbackResponder.php b/components/ILIAS/Init/src/ErrorHandling/Http/PlainTextFallbackResponder.php
index 0a05876c432f..c0f7536c8a15 100644
--- a/components/ILIAS/Init/src/ErrorHandling/Http/PlainTextFallbackResponder.php
+++ b/components/ILIAS/Init/src/ErrorHandling/Http/PlainTextFallbackResponder.php
@@ -51,11 +51,15 @@ class PlainTextFallbackResponder
      * The status code defaults to 500 (Internal Server Error). The caller may pass
      * a different code when the failure context is known.
      *
-     * @param int $status_code HTTP status code (default: 500).
+     * @param int         $status_code    HTTP status code (default: 500).
+     * @param string|null $public_message If set, shown instead of the exception message (details stay in error_log).
      * @throws Throwable in DEVMODE
      */
-    public function respond(Throwable $e, int $status_code = StatusCode::HTTP_INTERNAL_SERVER_ERROR): never
-    {
+    public function respond(
+        Throwable $e,
+        int $status_code = StatusCode::HTTP_INTERNAL_SERVER_ERROR,
+        ?string $public_message = null
+    ): never {
         if (defined('DEVMODE') && DEVMODE) {
             throw $e;
         }
@@ -65,8 +69,8 @@ public function respond(Throwable $e, int $status_code = StatusCode::HTTP_INTERN
             header('Content-Type: text/plain; charset=UTF-8');
         }
 
-        $incident_id = session_id() . '_' . (new \Random\Randomizer())->getInt(1, 9999);
-        $timestamp = (new DateTimeImmutable())
+        $incident_id = session_id() . '_' . new \Random\Randomizer()->getInt(1, 9999);
+        $timestamp = new DateTimeImmutable()
             ->setTimezone(new DateTimeZone('UTC'))
             ->format('Y-m-d\TH:i:s\Z');
 
@@ -77,7 +81,8 @@ public function respond(Throwable $e, int $status_code = StatusCode::HTTP_INTERN
         if ($e instanceof PDOException) {
             echo "Message: A database error occurred. Please contact the system administrator with the incident id.\n";
         } else {
-            echo "Message: {$e->getMessage()}\n";
+            $display = $public_message ?? $e->getMessage();
+            echo "Message: {$display}\n";
         }
 
         error_log(sprintf(
diff --git a/templates/default/tpl.error.html b/templates/default/tpl.error.html
index 219e2d866d32..3e7a0e506c06 100755
--- a/templates/default/tpl.error.html
+++ b/templates/default/tpl.error.html
@@ -1,3 +1,9 @@
 <!-- BEGIN msg_box -->
 {MESSAGE_BOX}
-<!-- END msg_box -->
\ No newline at end of file
+<!-- END msg_box -->
+<!-- BEGIN plain_html_fallback -->
+<div class="alert alert-danger" role="alert">{ERROR_MESSAGE}</div>
+<p>
+	<a class="btn btn-default" href="{LINK_HREF}">{LINK_TEXT}</a>
+</p>
+<!-- END plain_html_fallback -->