Use proper generic for Context

[Kludex]

Now you can use the Context with a proper lifespan state.

I suggest running a type checker in this project. I can see a lot of typing issues using Pyright on strict mode.

from contextlib import asynccontextmanager
from dataclasses import dataclass
from typing import AsyncIterator

from mcp.server.fastmcp.server import Context, FastMCP


@dataclass
class State:
    count: int


@asynccontextmanager
async def lifespan(mcp: FastMCP) -> AsyncIterator[State]:
    yield State(count=0)


mcp = FastMCP()


@mcp.tool()
def my_tool(x: int, ctx: Context[State]) -> int:
    count = ctx.request_context.lifespan_context.count
    return count


mcp.run()