Support detect context parameter with generic alias and forward reference

[SigureMo]

Motivation and Context

In my use case, I use PEP 563 (from __future__ import annotations) and a Context with generic parameters (i.e. Context[ServerSession, AppContext]) to annotate the Context in the tool function. But it doesn't detect Context parameters correctly. Here is a minimal reproduction:

# example.py
from __future__ import annotations

from collections.abc import AsyncIterator
from contextlib import asynccontextmanager
from dataclasses import dataclass

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

mcp = FastMCP("My App")


@dataclass
class AppContext:
    magic: "int"


@asynccontextmanager
async def app_lifespan(server: FastMCP) -> AsyncIterator[AppContext]:
    yield AppContext(magic=42)


mcp = FastMCP("My App", lifespan=app_lifespan)


@mcp.tool()
def get_magic(ctx: Context[ServerSession, AppContext]) -> str:
    magic = ctx.request_context.lifespan_context.magic
    return str(magic)

uv run --extra "cli" mcp dev example.py

So I tried to tweak the Context parameter detection logic a bit and it seems to work.

How Has This Been Tested?

uv run pytest tests/server/fastmcp/test_server.py

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context