fix: gate deferred MCP tool execution (#2513)

* fix: gate deferred MCP tool execution

* style: format deferred tool middleware

* fix: address deferred tool review feedback

backend/packages/harness/deerflow/agents/middlewares/deferred_tool_filter_middleware.py

@@ -16,6 +16,9 @@ from typing import override
 from langchain.agents import AgentState
 from langchain.agents.middleware import AgentMiddleware
 from langchain.agents.middleware.types import ModelCallResult, ModelRequest, ModelResponse
+from langchain_core.messages import ToolMessage
+from langgraph.prebuilt.tool_node import ToolCallRequest
+from langgraph.types import Command
 
 logger = logging.getLogger(__name__)
 
@@ -35,7 +38,7 @@ class DeferredToolFilterMiddleware(AgentMiddleware[AgentState]):
         if not registry:
             return request
 
-        deferred_names = {e.name for e in registry.entries}
+        deferred_names = registry.deferred_names
         active_tools = [t for t in request.tools if getattr(t, "name", None) not in deferred_names]
 
         if len(active_tools) < len(request.tools):
@@ -43,6 +46,28 @@ class DeferredToolFilterMiddleware(AgentMiddleware[AgentState]):
 
         return request.override(tools=active_tools)
 
+    def _blocked_tool_message(self, request: ToolCallRequest) -> ToolMessage | None:
+        from deerflow.tools.builtins.tool_search import get_deferred_registry
+
+        registry = get_deferred_registry()
+        if not registry:
+            return None
+
+        tool_name = str(request.tool_call.get("name") or "")
+        if not tool_name:
+            return None
+
+        if not registry.contains(tool_name):
+            return None
+
+        tool_call_id = str(request.tool_call.get("id") or "missing_tool_call_id")
+        return ToolMessage(
+            content=(f"Error: Tool '{tool_name}' is deferred and has not been promoted yet. Call tool_search first to expose and promote this tool's schema, then retry."),
+            tool_call_id=tool_call_id,
+            name=tool_name,
+            status="error",
+        )
+
     @override
     def wrap_model_call(
         self,
@@ -51,6 +76,17 @@ class DeferredToolFilterMiddleware(AgentMiddleware[AgentState]):
     ) -> ModelCallResult:
         return handler(self._filter_tools(request))
 
+    @override
+    def wrap_tool_call(
+        self,
+        request: ToolCallRequest,
+        handler: Callable[[ToolCallRequest], ToolMessage | Command],
+    ) -> ToolMessage | Command:
+        blocked = self._blocked_tool_message(request)
+        if blocked is not None:
+            return blocked
+        return handler(request)
+
     @override
     async def awrap_model_call(
         self,
@@ -58,3 +94,14 @@ class DeferredToolFilterMiddleware(AgentMiddleware[AgentState]):
         handler: Callable[[ModelRequest], Awaitable[ModelResponse]],
     ) -> ModelCallResult:
         return await handler(self._filter_tools(request))
+
+    @override
+    async def awrap_tool_call(
+        self,
+        request: ToolCallRequest,
+        handler: Callable[[ToolCallRequest], Awaitable[ToolMessage | Command]],
+    ) -> ToolMessage | Command:
+        blocked = self._blocked_tool_message(request)
+        if blocked is not None:
+            return blocked
+        return await handler(request)

backend/packages/harness/deerflow/tools/builtins/tool_search.py

@@ -112,6 +112,15 @@ class DeferredToolRegistry:
     def entries(self) -> list[DeferredToolEntry]:
         return list(self._entries)
 
+    @property
+    def deferred_names(self) -> set[str]:
+        """Names of tools that are still hidden from model binding."""
+        return {entry.name for entry in self._entries}
+
+    def contains(self, name: str) -> bool:
+        """Return whether *name* is still deferred."""
+        return any(entry.name == name for entry in self._entries)
+
     def __len__(self) -> int:
         return len(self._entries)