diff --git a/src/langbot/pkg/provider/modelmgr/modelmgr.py b/src/langbot/pkg/provider/modelmgr/modelmgr.py
index 7031dfa6e..cac971906 100644
--- a/src/langbot/pkg/provider/modelmgr/modelmgr.py
+++ b/src/langbot/pkg/provider/modelmgr/modelmgr.py
@@ -161,9 +161,14 @@ class ModelManager:
             self.ap.logger.info('LangBot Space Models service is disabled, skipping sync.')
             return
 
-        # Space model synchronization is a legacy OSS-singleton facility. A
-        # cloud instance must receive tenant model projections from its control
-        # plane and must never infer one Workspace for this global operation.
+        # Space model synchronization is a legacy OSS-singleton facility. Cloud
+        # receives tenant model projections from its control plane and must not
+        # resolve an OSS-local Workspace outside a tenant-scoped unit of work.
+        cloud_runtime = getattr(getattr(self.ap.persistence_mgr, 'mode', None), 'value', None) == 'cloud_runtime'
+        if cloud_runtime:
+            self.ap.logger.info('Skipping legacy LangBot Space model sync in Cloud Runtime.')
+            return
+
         try:
             binding = await self.ap.workspace_service.get_local_execution_binding()
         except WorkspaceError as exc:
diff --git a/tests/unit_tests/provider/test_model_manager.py b/tests/unit_tests/provider/test_model_manager.py
index a9aafff86..5c2005ccd 100644
--- a/tests/unit_tests/provider/test_model_manager.py
+++ b/tests/unit_tests/provider/test_model_manager.py
@@ -8,6 +8,7 @@ and error handling without calling real LLM APIs.
 from __future__ import annotations
 
 import pytest
+from types import SimpleNamespace
 from unittest.mock import AsyncMock, Mock
 
 from langbot.pkg.provider.modelmgr.modelmgr import ModelManager
@@ -70,6 +71,20 @@ async def test_model_manager_skips_space_sync_when_disabled(mock_app_for_modelmg
     app.space_service.get_models.assert_not_called()
 
 
+@pytest.mark.asyncio
+async def test_model_manager_skips_legacy_space_sync_in_cloud_runtime(mock_app_for_modelmgr):
+    """Cloud startup must not resolve an OSS-local Workspace for legacy model sync."""
+    app = mock_app_for_modelmgr
+    app.instance_config.data = {'space': {'disable_models_service': False}}
+    app.persistence_mgr.mode = SimpleNamespace(value='cloud_runtime')
+
+    model_mgr = ModelManager(app)
+    model_mgr.load_models_from_db = AsyncMock()
+    await model_mgr.initialize()
+
+    app.workspace_service.get_local_execution_binding.assert_not_awaited()
+
+
 # ============================================================================
 # Model Loading Tests
 # ============================================================================