diff --git a/src/langbot/pkg/box/connector.py b/src/langbot/pkg/box/connector.py
index df3a0d7fa..e10e8b9ac 100644
--- a/src/langbot/pkg/box/connector.py
+++ b/src/langbot/pkg/box/connector.py
@@ -368,6 +368,10 @@ class BoxRuntimeConnector(ManagedRuntimeConnector):
         if not self._control_token and allow_generate:
             self._control_token = secrets.token_urlsafe(48)
         if not self._control_token:
+            if getattr(getattr(self.ap, 'deployment', None), 'mode', 'oss') == 'cloud':
+                raise BoxRuntimeUnavailableError(
+                    f'{BOX_CONTROL_TOKEN_ENV} must be configured with a strong shared secret for a Cloud Box runtime'
+                )
             return ''
         try:
             self._control_token = validate_control_token(self._control_token)
diff --git a/src/langbot/pkg/plugin/connector.py b/src/langbot/pkg/plugin/connector.py
index f2dbff418..0279ab285 100644
--- a/src/langbot/pkg/plugin/connector.py
+++ b/src/langbot/pkg/plugin/connector.py
@@ -264,6 +264,11 @@ class PluginRuntimeConnector(ManagedRuntimeConnector):
         if not self._control_token and allow_generate:
             self._control_token = secrets.token_urlsafe(48)
         if not self._control_token:
+            if self.runtime_profile == 'shared':
+                raise PluginRuntimeNotConnectedError(
+                    f'{PLUGIN_RUNTIME_CONTROL_TOKEN_ENV} must be configured with a strong shared secret '
+                    'for a Cloud Plugin Runtime'
+                )
             return {}
         try:
             self._control_token = validate_runtime_secret(
diff --git a/tests/unit_tests/box/test_box_connector.py b/tests/unit_tests/box/test_box_connector.py
index 4d769f244..0949801c6 100644
--- a/tests/unit_tests/box/test_box_connector.py
+++ b/tests/unit_tests/box/test_box_connector.py
@@ -24,7 +24,7 @@ from langbot.pkg.box.connector import BoxRuntimeConnector
 _CONTROL_TOKEN = 'box-control-token-that-is-longer-than-32-bytes'
 
 
-def make_app(logger: Mock, runtime_endpoint: str = ''):
+def make_app(logger: Mock, runtime_endpoint: str = '', *, cloud: bool = False):
     return SimpleNamespace(
         logger=logger,
         workspace_service=SimpleNamespace(instance_uuid='instance-a'),
@@ -42,6 +42,7 @@ def make_app(logger: Mock, runtime_endpoint: str = ''):
                 }
             }
         ),
+        deployment=SimpleNamespace(mode='cloud' if cloud else 'oss'),
     )
 
 
@@ -315,6 +316,14 @@ def test_external_box_runtime_control_headers_are_tokenless_when_secret_is_unset
     assert connector.get_control_headers() == {BOX_INSTANCE_HEADER: 'instance-a'}
 
 
+def test_cloud_box_runtime_rejects_missing_control_secret(monkeypatch: pytest.MonkeyPatch):
+    monkeypatch.delenv(BOX_CONTROL_TOKEN_ENV, raising=False)
+    connector = BoxRuntimeConnector(make_app(Mock(), runtime_endpoint='http://box-runtime:5410', cloud=True))
+
+    with pytest.raises(BoxRuntimeUnavailableError, match=BOX_CONTROL_TOKEN_ENV):
+        connector.get_control_headers()
+
+
 def test_external_box_runtime_rejects_invalid_configured_control_token(monkeypatch: pytest.MonkeyPatch):
     monkeypatch.setenv(BOX_CONTROL_TOKEN_ENV, 'too-short')
     connector = BoxRuntimeConnector(make_app(Mock(), runtime_endpoint='http://box-runtime:5410'))
diff --git a/tests/unit_tests/plugin/test_connector_ping.py b/tests/unit_tests/plugin/test_connector_ping.py
index 3b3aee016..d44b1ca2b 100644
--- a/tests/unit_tests/plugin/test_connector_ping.py
+++ b/tests/unit_tests/plugin/test_connector_ping.py
@@ -15,7 +15,7 @@ from langbot_plugin.runtime.security import (
 )
 
 
-def make_connector() -> PluginRuntimeConnector:
+def make_connector(*, cloud: bool = False) -> PluginRuntimeConnector:
     app = SimpleNamespace(
         logger=Mock(),
         instance_config=SimpleNamespace(
@@ -34,6 +34,7 @@ def make_connector() -> PluginRuntimeConnector:
                 'space': {'url': ''},
             }
         ),
+        deployment=SimpleNamespace(mode='cloud' if cloud else 'oss'),
     )
     return PluginRuntimeConnector(app, AsyncMock())
 
@@ -332,6 +333,14 @@ def test_external_runtime_control_headers_are_empty_when_secret_is_unset(monkeyp
     assert connector._control_headers(allow_generate=False) == {}
 
 
+def test_cloud_runtime_rejects_missing_control_secret(monkeypatch):
+    monkeypatch.delenv(PLUGIN_RUNTIME_CONTROL_TOKEN_ENV, raising=False)
+    connector = make_connector(cloud=True)
+
+    with pytest.raises(PluginRuntimeNotConnectedError, match=PLUGIN_RUNTIME_CONTROL_TOKEN_ENV):
+        connector._control_headers(allow_generate=False)
+
+
 def test_local_runtime_control_headers_generate_ephemeral_secret(monkeypatch):
     monkeypatch.delenv(PLUGIN_RUNTIME_CONTROL_TOKEN_ENV, raising=False)
     connector = make_connector()