diff --git a/packages/vitec/Classes/Command/SsrFlagCommand.php b/packages/vitec/Classes/Command/SsrFlagCommand.php
new file mode 100644
index 0000000..b421497
--- /dev/null
+++ b/packages/vitec/Classes/Command/SsrFlagCommand.php
@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Evomedien\Vitec\Command;
+
+use Evomedien\Vitec\Service\SsrFlagService;
+use Symfony\Component\Console\Attribute\AsCommand;
+use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Input\InputOption;
+use Symfony\Component\Console\Output\OutputInterface;
+
+/**
+ * Shows (and on --sync repairs) the SSR routing state: the Site Set
+ * switch "vitec.ssr.enabled" versus the flag file that .htaccess
+ * evaluates. The SyncSsrFlag middleware does the same sync on every
+ * request, so this command is mainly for diagnostics and scripting.
+ *
+ *   vendor/bin/typo3 vitec:ssr-flag          # status only
+ *   vendor/bin/typo3 vitec:ssr-flag --sync   # align flag with setting
+ */
+#[AsCommand(name: 'vitec:ssr-flag', description: 'Show/sync the SSR routing flag against the vitec.ssr.enabled site setting')]
+final class SsrFlagCommand extends Command
+{
+    public function __construct(private readonly SsrFlagService $ssrFlagService)
+    {
+        parent::__construct();
+    }
+
+    protected function configure(): void
+    {
+        $this->addOption('sync', null, InputOption::VALUE_NONE, 'Create/remove the flag file so it matches the setting');
+    }
+
+    protected function execute(InputInterface $input, OutputInterface $output): int
+    {
+        $setting = $this->ssrFlagService->isEnabledInSettings();
+        $flag = $this->ssrFlagService->isFlagSet();
+
+        $output->writeln('Setting vitec.ssr.enabled: ' . ($setting ? 'ON' : 'off'));
+        $output->writeln('Flag ' . $this->ssrFlagService->getFlagPath() . ': ' . ($flag ? 'EXISTS (SSR routing active)' : 'absent (SPA as before)'));
+
+        if ($setting === $flag) {
+            $output->writeln('<info>In sync.</info>');
+            return Command::SUCCESS;
+        }
+
+        if (!$input->getOption('sync')) {
+            $output->writeln('<comment>OUT OF SYNC - run with --sync (or just hit any page: the middleware repairs it).</comment>');
+            return Command::FAILURE;
+        }
+
+        $new = $this->ssrFlagService->sync();
+        $output->writeln('<info>Synced: flag is now ' . ($new ? 'SET - SSR routing active.' : 'removed - SPA as before.') . '</info>');
+        return Command::SUCCESS;
+    }
+}
diff --git a/packages/vitec/Classes/Middleware/SyncSsrFlag.php b/packages/vitec/Classes/Middleware/SyncSsrFlag.php
new file mode 100644
index 0000000..876d5ff
--- /dev/null
+++ b/packages/vitec/Classes/Middleware/SyncSsrFlag.php
@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Evomedien\Vitec\Middleware;
+
+use Evomedien\Vitec\Service\SsrFlagService;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+
+/**
+ * Self-healing sync of the SSR routing flag (see SsrFlagService).
+ *
+ * Registered for BOTH stacks: backend, so flipping the Site Set switch
+ * takes effect with the very next backend request (the module reload
+ * right after saving), and frontend, so /_json traffic repairs the flag
+ * even if nobody is logged into the backend. When flag and setting
+ * agree - the normal case - this costs a single file_exists() per
+ * request.
+ */
+final class SyncSsrFlag implements MiddlewareInterface
+{
+    public function __construct(private readonly SsrFlagService $ssrFlagService)
+    {
+    }
+
+    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
+    {
+        $this->ssrFlagService->syncQuietly();
+        return $handler->handle($request);
+    }
+}
diff --git a/packages/vitec/Classes/Service/SsrFlagService.php b/packages/vitec/Classes/Service/SsrFlagService.php
new file mode 100644
index 0000000..adbdfc3
--- /dev/null
+++ b/packages/vitec/Classes/Service/SsrFlagService.php
@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Evomedien\Vitec\Service;
+
+use TYPO3\CMS\Core\Core\Environment;
+use TYPO3\CMS\Core\Exception\SiteNotFoundException;
+use TYPO3\CMS\Core\Site\SiteFinder;
+
+/**
+ * Keeps the SSR routing flag file in sync with the site setting
+ * "vitec.ssr.enabled" (Site Set switch, editable in the backend under
+ * Site Management > Settings).
+ *
+ * The flag file is what public/.htaccess checks per request (RewriteCond
+ * ... -f): if it exists, page requests are proxied to the SSR node on the
+ * Solr VPS; if not, the SPA fallback serves _frontend/index.html as
+ * before. TYPO3 itself never routes differently - the flag only steers
+ * Apache, which is why a plain file is used: zero runtime cost in the
+ * hot path and trivially inspectable on the server.
+ *
+ * Saving site settings in the TYPO3 v14 backend fires NO event (core
+ * SiteWriter::writeSettings dispatches nothing, checked 2026-11-09), so
+ * the sync runs self-healingly from the SyncSsrFlag middleware on every
+ * frontend and backend request - a mismatch costs one file operation
+ * once, agreement costs a file_exists(). The vitec:ssr-flag CLI command
+ * offers the same sync plus a status view.
+ */
+final class SsrFlagService
+{
+    public function __construct(private readonly SiteFinder $siteFinder)
+    {
+    }
+
+    public function getFlagPath(): string
+    {
+        return Environment::getVarPath() . '/vitec-ssr-on.flag';
+    }
+
+    /**
+     * True as soon as ANY site enables the setting (there is only the
+     * "vitec" site; iterating keeps us independent of the identifier).
+     */
+    public function isEnabledInSettings(): bool
+    {
+        try {
+            foreach ($this->siteFinder->getAllSites() as $site) {
+                if ((bool)$site->getSettings()->get('vitec.ssr.enabled', false)) {
+                    return true;
+                }
+            }
+        } catch (SiteNotFoundException) {
+            // No sites configured - treat as disabled.
+        }
+        return false;
+    }
+
+    public function isFlagSet(): bool
+    {
+        return is_file($this->getFlagPath());
+    }
+
+    /**
+     * Creates or removes the flag file so it matches the setting.
+     *
+     * @return bool|null The new state if something changed, null if the
+     *                   flag already matched the setting.
+     */
+    public function sync(): ?bool
+    {
+        $desired = $this->isEnabledInSettings();
+        if ($desired === $this->isFlagSet()) {
+            return null;
+        }
+        if ($desired) {
+            file_put_contents(
+                $this->getFlagPath(),
+                "SSR routing is ON (site setting vitec.ssr.enabled).\n"
+                . "Managed by SsrFlagService - do not create/delete manually,\n"
+                . "flip the switch in Site Management > Settings instead.\n"
+                . 'Last sync: ' . date('c') . "\n"
+            );
+        } else {
+            @unlink($this->getFlagPath());
+        }
+        return $desired;
+    }
+
+    /**
+     * Sync variant for the request hot path: never lets an IO hiccup
+     * (read-only FS, concurrent unlink ...) break request handling.
+     */
+    public function syncQuietly(): void
+    {
+        try {
+            $this->sync();
+        } catch (\Throwable) {
+            // Intentionally silent - next request retries.
+        }
+    }
+}
diff --git a/packages/vitec/Configuration/RequestMiddlewares.php b/packages/vitec/Configuration/RequestMiddlewares.php
index 416997a..49d6d08 100755
--- a/packages/vitec/Configuration/RequestMiddlewares.php
+++ b/packages/vitec/Configuration/RequestMiddlewares.php
@@ -46,5 +46,23 @@ return [
                 'typo3/cms-frontend/site',
             ],
         ],
+        // Self-healing sync of the SSR routing flag file against the
+        // Site Set switch vitec.ssr.enabled (no core event fires on
+        // settings save, hence per-request sync; cheap file_exists when
+        // nothing changed). Also registered for the backend below.
+        'vitec/sync-ssr-flag' => [
+            'target' => \Evomedien\Vitec\Middleware\SyncSsrFlag::class,
+            'after' => [
+                'typo3/cms-core/normalized-params-attribute',
+            ],
+        ],
+    ],
+    'backend' => [
+        'vitec/sync-ssr-flag' => [
+            'target' => \Evomedien\Vitec\Middleware\SyncSsrFlag::class,
+            'after' => [
+                'typo3/cms-core/normalized-params-attribute',
+            ],
+        ],
     ],
 ];
diff --git a/packages/vitec/Configuration/Sets/Vitecset/settings.definitions.yaml b/packages/vitec/Configuration/Sets/Vitecset/settings.definitions.yaml
index beabfc6..b8a302e 100644
--- a/packages/vitec/Configuration/Sets/Vitecset/settings.definitions.yaml
+++ b/packages/vitec/Configuration/Sets/Vitecset/settings.definitions.yaml
@@ -132,3 +132,10 @@ settings:
     category: seo
     type: string
     default: ''
+
+  vitec.ssr.enabled:
+    label: 'SSR delivery (serve pages from the SSR node)'
+    description: 'ON: page requests are proxied by .htaccess to the SSR server (React Router SSR on the Solr VPS) - the flag file var/vitec-ssr-on.flag is kept in sync automatically within seconds. OFF: pages are served as today (SPA shell from _frontend/). JSON under /_json, /typo3, /api etc. are never affected. Safe rollback switch.'
+    category: VITEC
+    type: bool
+    default: false
diff --git a/public/.htaccess b/public/.htaccess
index e6bc0b8..20d9563 100644
--- a/public/.htaccess
+++ b/public/.htaccess
@@ -345,6 +345,29 @@ AddDefaultCharset utf-8
 	RewriteCond %{QUERY_STRING} __typo3_install
 	RewriteCond %{REQUEST_FILENAME} !-f
 	RewriteRule ^.*$ %{ENV:CWD}index.php [QSA,L]
+	# --- VITEC SSR routing (flag-gated) -----------------------------------
+	# Active ONLY while the flag file below exists. Mirrors the SPA
+	# fallback's exclusions but PROXIES page requests to the SSR node on
+	# the Solr VPS instead of serving the React shell (mod_proxy incl.
+	# https target verified on this host 2026-11-09, see Nextcloud
+	# vitec-solr/ssr/README-SSR-Setup.md). The flag is written/removed by
+	# EXT:vitec (Site Set switch "vitec.ssr.enabled" -> SsrFlagService,
+	# synced by the SyncSsrFlag middleware / vitec:ssr-flag command).
+	# Emergency off without TYPO3: delete the flag file.
+	RewriteCond /usr/www/users/vitecevo/live/var/vitec-ssr-on.flag -f
+	RewriteRule ^$ https://vitec-ssr.evomedien.de/ [P,L]
+	RewriteCond /usr/www/users/vitecevo/live/var/vitec-ssr-on.flag -f
+	RewriteCond %{REQUEST_FILENAME} !-f
+	RewriteCond %{REQUEST_FILENAME} !-d
+	RewriteCond %{REQUEST_FILENAME} !-l
+	RewriteCond %{REQUEST_URI} !^/_json(/|$)
+	RewriteCond %{REQUEST_URI} !^/typo3(/|$)
+	RewriteCond %{REQUEST_URI} !^/download/
+	RewriteCond %{REQUEST_URI} !^/api/
+	RewriteCond %{REQUEST_URI} !^/_frontend/
+	RewriteCond %{REQUEST_URI} !^/sitemap
+	RewriteRule ^(.*)$ https://vitec-ssr.evomedien.de/$1 [P,L]
+	# ----------------------------------------------------------------------
 	# The root path needs its own rule: for "/" REQUEST_FILENAME is the
 	# docroot DIRECTORY, so the !-d guard below skips it and DirectoryIndex
 	# would hand it to TYPO3 (JSON). The homepage JSON lives at /_json/.