FIX/McpWorkbench_errors_properties_and_grace_shutdown (#6444)

## Why are these changes needed?
Our McpWorkbench required properties however mongodb-lens's some tools
do not has it. I will fix it from when properties is None, -> {}
Our McpWorkbench now does not have stop routine with without async with
McpWorkbench(params) as workbench: and lazy init. So, I will adding def
__del__: pass just insert that, It could show error.

## Related issue number

Closes #6425

## Checks

- [ ] I've included any doc changes needed for
<https://microsoft.github.io/autogen/>. See
<https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md> to
build and test documentation locally.
- [x] I've added tests (if relevant) corresponding to the changes
introduced in this PR.
- [x] I've made sure all auto checks have passed.

Author: SongChiYoung

python/packages/autogen-ext/src/autogen_ext/tools/mcp/_workbench.py

@@ -177,7 +177,7 @@ async def list_tools(self) -> List[ToolSchema]:
             description = tool.description or ""
             parameters = ParametersSchema(
                 type="object",
-                properties=tool.inputSchema["properties"],
+                properties=tool.inputSchema.get("properties", {}),
                 required=tool.inputSchema.get("required", []),
                 additionalProperties=tool.inputSchema.get("additionalProperties", False),
             )
@@ -279,3 +279,7 @@ def _to_config(self) -> McpWorkbenchConfig:
     @classmethod
     def _from_config(cls, config: McpWorkbenchConfig) -> Self:
         return cls(server_params=config.server_params)
+
+    def __del__(self) -> None:
+        # Ensure the actor is stopped when the workbench is deleted
+        pass

python/packages/autogen-ext/tests/tools/test_mcp_tools.py

@@ -571,3 +571,27 @@ async def test_mcp_workbench_server_filesystem() -> None:
         tool = tools[0]
         result = await new_workbench.call_tool(tool["name"], {"path": "README.md"}, CancellationToken())
         assert result is not None
+
+
+@pytest.mark.asyncio
+async def test_lazy_init_and_finalize_cleanup() -> None:
+    params = StdioServerParams(
+        command="npx",
+        args=[
+            "-y",
+            "@modelcontextprotocol/server-filesystem",
+            ".",
+        ],
+        read_timeout_seconds=60,
+    )
+    workbench = McpWorkbench(server_params=params)
+
+    # Before any call, actor should not be initialized
+    assert workbench._actor is None  # type: ignore[reportPrivateUsage]
+
+    # Trigger list_tools → lazy start
+    await workbench.list_tools()
+    assert workbench._actor is not None  # type: ignore[reportPrivateUsage]
+    assert workbench._actor._active is True  # type: ignore[reportPrivateUsage]
+
+    del workbench