diff --git a/services/nginx/app/routes/superuserReplicationRoute.php b/services/nginx/app/routes/superuserReplicationRoute.php
index b9dddddc..3a76574e 100644
--- a/services/nginx/app/routes/superuserReplicationRoute.php
+++ b/services/nginx/app/routes/superuserReplicationRoute.php
@@ -16,7 +16,7 @@ class superuserReplicationRoute
         $this->get('/superuser/replication', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_view');
+            $this->requireClassicSuperuserPermission('superuser_replication_view');
             $refresh = $this->toBool($this->getParameter('refresh'), false);
             $response->success((new replication_manager())->summary($refresh));
         }, [
@@ -26,7 +26,7 @@ class superuserReplicationRoute
         $this->post('/superuser/replication/databases', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_manage');
+            $this->requireClassicSuperuserPermission('superuser_replication_manage');
             $host = (new replication_manager())->addHost('database', $this->getParametersAsArray(), $this->actorUserId());
             $response->success($host, 201);
         }, [
@@ -36,7 +36,7 @@ class superuserReplicationRoute
         $this->post('/superuser/replication/redis', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_manage');
+            $this->requireClassicSuperuserPermission('superuser_replication_manage');
             $host = (new replication_manager())->addHost('redis', $this->getParametersAsArray(), $this->actorUserId());
             $response->success($host, 201);
         }, [
@@ -46,7 +46,7 @@ class superuserReplicationRoute
         $this->post('/superuser/replication/minio', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_manage');
+            $this->requireClassicSuperuserPermission('superuser_replication_manage');
             $host = (new replication_manager())->addHost('minio', $this->getParametersAsArray(), $this->actorUserId());
             $response->success($host, 201);
         }, [
@@ -56,7 +56,7 @@ class superuserReplicationRoute
         $this->post('/superuser/replication/compose-template', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_manage');
+            $this->requireClassicSuperuserPermission('superuser_replication_manage');
             $response->success(replication_manager::composeTemplate($this->getParametersAsArray()));
         }, [
             'superuser_replication_manage' => 'Generate Docker Compose templates for replication-ready database, Redis, and MinIO hosts',
@@ -65,7 +65,7 @@ class superuserReplicationRoute
         $this->post('/superuser/replication/test-credentials', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_manage');
+            $this->requireClassicSuperuserPermission('superuser_replication_manage');
             $parameters = $this->getParametersAsArray();
             $response->success((new replication_manager())->testCredentials(
                 (string)($parameters['kind'] ?? ''),
@@ -78,7 +78,7 @@ class superuserReplicationRoute
         $this->post('/superuser/replication/{kind}/{id}/test', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_manage');
+            $this->requireClassicSuperuserPermission('superuser_replication_manage');
             $response->success((new replication_manager())->testHost(
                 (string)$this->fromRoute('kind'),
                 $this->routeId(),
@@ -91,7 +91,7 @@ class superuserReplicationRoute
         $this->post('/superuser/replication/{kind}/{id}/provision', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_manage');
+            $this->requireClassicSuperuserPermission('superuser_replication_manage');
             try {
                 $result = (new replication_manager())->provisionHost(
                     (string)$this->fromRoute('kind'),
@@ -113,7 +113,7 @@ class superuserReplicationRoute
         $this->post('/superuser/replication/{kind}/{id}/promote', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_promote');
+            $this->requireClassicSuperuserPermission('superuser_replication_promote');
             try {
                 $response->success((new replication_manager())->promoteHost(
                     (string)$this->fromRoute('kind'),
@@ -130,7 +130,7 @@ class superuserReplicationRoute
         $this->patch('/superuser/replication/{kind}/{id}', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_manage');
+            $this->requireClassicSuperuserPermission('superuser_replication_manage');
             try {
                 $response->success((new replication_manager())->renameHost(
                     (string)$this->fromRoute('kind'),
@@ -148,7 +148,7 @@ class superuserReplicationRoute
         $this->delete('/superuser/replication/{kind}/{id}', function () {
             global $response;
 
-            $this->requirePermission('superuser_replication_remove');
+            $this->requireClassicSuperuserPermission('superuser_replication_remove');
             try {
                 $response->success((new replication_manager())->removeHost(
                     (string)$this->fromRoute('kind'),
@@ -163,6 +163,23 @@ class superuserReplicationRoute
         ]);
     }
 
+    /**
+     * Replication controls alter infrastructure state and must only be used by
+     * a classic superuser session. Subuser bearer tokens can carry a delegated
+     * customer context via X-Customer-Number, so do not allow them to fall back
+     * to plain string user permission checks for these routes.
+     */
+    private function requireClassicSuperuserPermission(string $permission): bool
+    {
+        global $response;
+
+        if ((new authentication())->get_subuser() !== false) {
+            $response->error('Subuser sessions cannot manage replication.', 403);
+        }
+
+        return $this->requirePermission($permission);
+    }
+
     private function routeId(): int
     {
         $id = (int)$this->fromRoute('id');
diff --git a/services/nginx/app/tests/Unit/Replication/SuperuserReplicationRouteWiringTest.php b/services/nginx/app/tests/Unit/Replication/SuperuserReplicationRouteWiringTest.php
index 9f5d225d..59e6b78e 100644
--- a/services/nginx/app/tests/Unit/Replication/SuperuserReplicationRouteWiringTest.php
+++ b/services/nginx/app/tests/Unit/Replication/SuperuserReplicationRouteWiringTest.php
@@ -14,10 +14,10 @@ it('registers superuser replication endpoints and permissions', function (): voi
     expect($content)->toContain('/superuser/replication/{kind}/{id}/provision');
     expect($content)->toContain('/superuser/replication/{kind}/{id}/promote');
     expect($content)->toContain("\$this->patch('/superuser/replication/{kind}/{id}'");
-    expect($content)->toContain("requirePermission('superuser_replication_view')");
-    expect($content)->toContain("requirePermission('superuser_replication_manage')");
-    expect($content)->toContain("requirePermission('superuser_replication_promote')");
-    expect($content)->toContain("requirePermission('superuser_replication_remove')");
+    expect($content)->toContain("requireClassicSuperuserPermission('superuser_replication_view')");
+    expect($content)->toContain("requireClassicSuperuserPermission('superuser_replication_manage')");
+    expect($content)->toContain("requireClassicSuperuserPermission('superuser_replication_promote')");
+    expect($content)->toContain("requireClassicSuperuserPermission('superuser_replication_remove')");
 });
 
 it('documents replication management in openapi', function (): void {
@@ -36,3 +36,16 @@ it('documents replication management in openapi', function (): void {
     expect($content)->toContain('SuperuserReplicationHostRenameRequest');
     expect($content)->toContain('SuperuserReplicationComposeTemplateRequest');
 });
+
+it('rejects subuser sessions before checking replication permissions', function (): void {
+    $content = file_get_contents(app_path('routes/superuserReplicationRoute.php'));
+
+    expect($content)->not->toBeFalse();
+    expect($content)->toContain('private function requireClassicSuperuserPermission(string $permission): bool');
+    expect($content)->toContain('get_subuser() !== false');
+    expect($content)->toContain("Subuser sessions cannot manage replication.");
+    expect($content)->toContain("\$response->error('Subuser sessions cannot manage replication.', 403);");
+    expect($content)->toContain('return $this->requirePermission($permission);');
+    expect(preg_match_all("/requireClassicSuperuserPermission\\('superuser_replication_/", $content))->toBe(10);
+    expect($content)->not->toContain("requirePermission('superuser_replication_");
+});