fix(mcp): coerce skill_search top_k instead of raising 500 on malformed input

The MCP-REST skill_search dispatch validated raw tool arguments through a
pydantic model directly, so a non-numeric top_k raised a ValidationError
that the endpoint's catch-all turned into an HTTP 500. Mirrors the
agent_search branch's tolerant coerce_top_k handling instead.

litellm/proxy/_experimental/mcp_server/rest_endpoints.py

@@ -8,7 +8,6 @@ from typing import TYPE_CHECKING, Any, Final, Literal
 import anyio
 import httpx
 from fastapi import APIRouter, Depends, HTTPException, Query, Request, status
-from pydantic import BaseModel, ConfigDict
 
 from litellm._logging import verbose_logger
 from litellm.constants import MCP_CLIENT_TIMEOUT, MCP_TOOL_LISTING_TIMEOUT
@@ -163,12 +162,6 @@ if MCP_AVAILABLE:
             request_path=request.scope.get("_original_path") or request.url.path,
         )
 
-    class _SkillSearchToolArguments(BaseModel):
-        model_config = ConfigDict(extra="ignore")
-
-        query: str = ""
-        top_k: int = DEFAULT_SKILL_SEARCH_TOP_K
-
     async def _handle_virtual_mcp_tool(
         request: Request,
         data: dict[str, Any],
@@ -211,10 +204,11 @@ if MCP_AVAILABLE:
                 user_api_key_dict=user_api_key_dict,
             )
         if tool_name == SKILL_SEARCH_TOOL_NAME:
-            skill_search_args: Final = _SkillSearchToolArguments.model_validate(tool_arguments)
             return await handle_skill_search(
-                query=skill_search_args.query,
-                top_k=skill_search_args.top_k,
+                query=str(tool_arguments.get("query", "")),
+                top_k=coerce_top_k(
+                    tool_arguments.get("top_k", DEFAULT_SKILL_SEARCH_TOP_K), default=DEFAULT_SKILL_SEARCH_TOP_K
+                ),
                 user_api_key_dict=user_api_key_dict,
             )
         rest_client_ip: Final = IPAddressUtils.get_mcp_client_ip(request)

tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_tool_search.py

@@ -744,6 +744,31 @@ class TestCallToolRestApiVirtualTools:
         assert mock_search.await_args.kwargs["top_k"] == 1
         assert mock_search.await_args.kwargs["agents"] == (translator,)
 
+    @pytest.mark.asyncio
+    async def test_skill_search_call_tolerates_malformed_top_k(self) -> None:
+        """Regression: a caller-supplied non-numeric top_k must be coerced to the default,
+        the same as agent_search, instead of raising a pydantic ValidationError that the
+        endpoint's catch-all turns into an HTTP 500."""
+        from mcp.types import CallToolResult, TextContent
+
+        from litellm.llms.litellm_proxy.skills.skill_search import DEFAULT_SKILL_SEARCH_TOP_K
+
+        user_api_key_dict = UserAPIKeyAuth(api_key="k", object_permission=_make_perm(mcp_tool_search_enabled=True))
+        request = self._make_request(
+            {"name": SKILL_SEARCH_TOOL_NAME, "arguments": {"query": "translate a document", "top_k": "not-a-number"}}
+        )
+        fake_result = CallToolResult(content=[TextContent(type="text", text="[]")], isError=False)
+        with patch(  # test-quality-ok: the embedding router only resolves via proxy_server globals, no injection seam
+            "litellm.proxy._experimental.mcp_server.tool_search.handle_skill_search",
+            new_callable=AsyncMock,
+            return_value=fake_result,
+        ) as mock_search:
+            result = await self._get_call_fn()(request=request, user_api_key_dict=user_api_key_dict)
+
+        assert result.isError is False
+        assert mock_search.await_args.kwargs["top_k"] == DEFAULT_SKILL_SEARCH_TOP_K
+        assert mock_search.await_args.kwargs["query"] == "translate a document"
+
     @pytest.mark.asyncio
     async def test_agent_search_call_reports_missing_embedding_model_as_tool_error(self) -> None:
         from litellm.proxy.agent_endpoints.agent_search import AgentSearchNotConfigured
@@ -817,7 +842,9 @@ class TestCallToolRestApiVirtualTools:
         assert "mcp_tool_search.embedding_model" in result.content[0].text
 
     @pytest.mark.asyncio
-    async def test_mcp_tool_search_reports_invalid_settings_as_tool_error(self, monkeypatch: pytest.MonkeyPatch) -> None:
+    async def test_mcp_tool_search_reports_invalid_settings_as_tool_error(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
         monkeypatch.setattr(litellm, "mcp_tool_search", {"top_k": 0})
         user_api_key_dict = UserAPIKeyAuth(api_key="k", object_permission=_make_perm(mcp_tool_search_enabled=True))
         result = await self._get_call_fn()(request=self._semantic_request(), user_api_key_dict=user_api_key_dict)