fix(agent): close untrusted-context gate bypasses

tests/test_update_plan_tool.py

@@ -8,13 +8,16 @@ import asyncio
 import json
 
 from src.agent_tools import ToolBlock, TOOL_TAGS  # import first to avoid circular
-from src.tool_execution import execute_tool_block
+from src.tool_execution import NO_TOOL_SECURITY_CONTEXT, execute_tool_block
 from src.tool_index import ALWAYS_AVAILABLE, BUILTIN_TOOL_DESCRIPTIONS
 from src.tool_security import is_public_blocked_tool
 
 
 def _run(content):
-    return asyncio.run(execute_tool_block(ToolBlock("update_plan", content)))
+    return asyncio.run(execute_tool_block(
+        ToolBlock("update_plan", content),
+        security_context=NO_TOOL_SECURITY_CONTEXT,
+    ))
 
 
 def test_valid_plan_returns_marker_and_counts():