fix(mcp): document /mcp-rest/tools/call request body in OpenAPI schema

The endpoint uses a raw Request object to read its JSON body, so FastAPI
could not infer the body schema. The generated OpenAPI spec showed no
parameters, causing LLMs that consume the spec to generate tool calls
with empty bodies (HTTP 500).

Fix: add openapi_extra to the @router.post decorator with an explicit
requestBody schema (server_id, name, arguments) and a concrete example.
No behavioral changes — the body is still read via request.json().

Fixes #32121

litellm/proxy/_experimental/mcp_server/rest_endpoints.py

@@ -735,7 +735,44 @@ if MCP_AVAILABLE:
                 "message": f"An unexpected error occurred: {str(e)}",
             }
 
-    @router.post("/tools/call", dependencies=[Depends(user_api_key_auth)])
+    @router.post(
+        "/tools/call",
+        dependencies=[Depends(user_api_key_auth)],
+        openapi_extra={
+            "requestBody": {
+                "required": True,
+                "content": {
+                    "application/json": {
+                        "schema": {
+                            "type": "object",
+                            "required": ["name"],
+                            "properties": {
+                                "server_id": {
+                                    "type": "string",
+                                    "description": "ID of the MCP server that owns the tool. Required unless calling a virtual tool (mcp_tool_search or mcp_tool_call).",
+                                },
+                                "name": {
+                                    "type": "string",
+                                    "description": "Name of the MCP tool to invoke.",
+                                },
+                                "arguments": {
+                                    "type": "object",
+                                    "description": "Key-value arguments forwarded to the tool.",
+                                    "additionalProperties": True,
+                                    "default": {},
+                                },
+                            },
+                        },
+                        "example": {
+                            "server_id": "17a4490465f74d3696caf12b30220166",
+                            "name": "places_api-getPlaces",
+                            "arguments": {"query": "coffee shops in London"},
+                        },
+                    }
+                },
+            }
+        },
+    )
     async def call_tool_rest_api(
         request: Request,
         user_api_key_dict: UserAPIKeyAuth = Depends(user_api_key_auth),