from_fastapi: tuple responses containing a model fail with an unresolved schema reference

What happened?

A FastAPI endpoint returning tuple[Item, int] works over HTTP, but after conversion with FastMCP.from_fastapi(), Client.call_tool() raises PointerToNowhere: '/components/schemas/Item' does not exist while validating the successful response. I expected structured_content to contain {"result": [{"name": "example"}, 2]}.

Example Code

import asyncio

from fastapi import FastAPI
from pydantic import BaseModel

from fastmcp import Client, FastMCP


class Item(BaseModel):
    name: str


app = FastAPI()


@app.post("/items", operation_id="get_item")
def get_item() -> tuple[Item, int]:
    return Item(name="example"), 2


async def main() -> None:
    server = FastMCP.from_fastapi(app)
    async with Client(server) as client:
        result = await client.call_tool("get_item")
        print(result.structured_content)


asyncio.run(main())

Version Information

Reproduced on main at 490049f0f9742922f4af16c937db0b898dc9802b, with MCP 2.0.0, FastAPI 0.139.2, Pydantic 2.13.4, and jsonschema 4.26.0. Python 3.12 on Windows and Ubuntu.