fix(mypy): resolve type errors introduced by MCP user permissions (#21462)

- Cast `guardrail` to `Dict[str, Any]` in `mcp_end_user_permission/__init__.py`
  to fix "No overload variant of 'get' matches argument type 'str'" — the
  `Guardrail` TypedDict's `.get()` overloads resolve the key type to `Never`
  when chained with a `{}` default, making further `.get()` calls fail.
- Cast `fn` to `Dict[str, Any]` in `transformation.py`
  `transform_chat_completion_tool_params_to_responses_api_tools` to fix
  '"object" has no attribute "get"' — `tool.get("function")` on
  `Union[ChatCompletionFunctionToolParam, OpenAIMcpServerTool]` returns
  `object` because `"function"` is not a key in `OpenAIMcpServerTool`.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

litellm/proxy/guardrails/guardrail_hooks/mcp_end_user_permission/__init__.py

@@ -1,4 +1,4 @@
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any, Dict, cast
 
 from litellm.types.guardrails import SupportedGuardrailIntegrations
 
@@ -14,7 +14,7 @@ def initialize_guardrail(litellm_params: "LitellmParams", guardrail: "Guardrail"
     # Default to always-on. Only disable if the user explicitly sets default_on: false.
     # We check the raw guardrail dict because LitellmParams normalizes None → False,
     # making it impossible to distinguish "not set" from "explicitly false" via litellm_params.
-    _raw_default_on = guardrail.get("litellm_params", {}).get("default_on")
+    _raw_default_on = cast(Dict[str, Any], guardrail).get("litellm_params", {}).get("default_on")
     _default_on = False if _raw_default_on is False else True
 
     _callback = MCPEndUserPermissionGuardrail(

litellm/responses/litellm_completion_transformation/transformation.py

@@ -1349,7 +1349,7 @@ class LiteLLMCompletionResponsesConfig:
                 result.append(tool)  # type: ignore
                 continue
             if tool.get("type") == "function":
-                fn = tool.get("function") or {}
+                fn: Dict[str, Any] = cast(Dict[str, Any], tool.get("function") or {})
                 parameters = dict(fn.get("parameters", {}) or {})
                 if not parameters or "type" not in parameters:
                     parameters["type"] = "object"