diff --git a/src/langbot/pkg/box/service.py b/src/langbot/pkg/box/service.py
index 7c5dbaadb..55d4f39ab 100644
--- a/src/langbot/pkg/box/service.py
+++ b/src/langbot/pkg/box/service.py
@@ -1843,10 +1843,17 @@ class BoxService:
         can read settings such as a service base URL. A per-call ``env`` supplied
         by the agent or caller overrides the matching defaults. Non-dict configs
         and non-string keys or values are ignored.
+
+        The setting is instance-wide, so it is disabled in multi-workspace
+        deployments to keep operator values from reaching every tenant's sandbox.
         """
         raw_env = self._local_config().get('env')
         if not isinstance(raw_env, dict):
             return {}
+        if self._cloud_managed:
+            if raw_env:
+                self.ap.logger.warning('box.local.env is ignored in multi-workspace deployments.')
+            return {}
 
         env: dict[str, str] = {}
         for key, value in raw_env.items():
diff --git a/src/langbot/templates/config.yaml b/src/langbot/templates/config.yaml
index 098cdcb9f..cd43709db 100644
--- a/src/langbot/templates/config.yaml
+++ b/src/langbot/templates/config.yaml
@@ -391,6 +391,8 @@ box:
         workspace_quota_mb: null  # Optional disk quota override (>= 0). null = profile default.
         # Extra environment variables injected into every Box exec payload.
         # The agent-supplied per-call env overrides matching keys. Values must be strings.
+        # Every sandbox command, including untrusted agent commands, can read them;
+        # do not put secrets here. Loaded at startup; ignored in multi-workspace deployments.
         env: {}
     # Default nsjail cgroup memory limit for each MCP stdio server process, in MB.
     # Node.js MCP servers (npx/bunx) need more memory than Python ones because V8
diff --git a/tests/unit_tests/box/test_box_service.py b/tests/unit_tests/box/test_box_service.py
index 68f680ec4..dd849316f 100644
--- a/tests/unit_tests/box/test_box_service.py
+++ b/tests/unit_tests/box/test_box_service.py
@@ -466,6 +466,26 @@ def test_box_build_spec_ignores_invalid_local_env_entries():
     assert spec.env == {}
 
 
+def test_box_build_spec_ignores_local_env_in_multi_workspace_deployment():
+    logger = Mock()
+    app = make_app(logger)
+    app.deployment = SimpleNamespace(multi_workspace_enabled=True)
+    app.instance_config.data['box'].update(
+        {
+            'backend': 'nsjail',
+            'admission': {'required': True, 'workspace_quota_mb': 32},
+        }
+    )
+    app.instance_config.data['box']['local']['env'] = {'JENKINS_BASE_URL': 'https://jenkins.example.com'}
+    service = BoxService(app, client=Mock())
+
+    spec = service.build_spec({'cmd': 'echo hi', 'session_id': 'cloud-env', 'env': {'PER_CALL': '1'}})
+
+    assert service.default_env == {}
+    assert spec.env == {'PER_CALL': '1'}
+    logger.warning.assert_any_call('box.local.env is ignored in multi-workspace deployments.')
+
+
 @pytest.mark.asyncio
 async def test_box_service_get_sessions_delegates_to_client():
     client = Mock()