Field alias is published in the tool schema but forwarded as an invalid Python keyword

Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK.
• I confirm that I searched the issue tracker before opening this issue.

Description

For a function parameter annotated with Field(alias="externalX"), the generated tool schema correctly requires externalX. At runtime, however, that wire name is forwarded directly to the original function, so the call fails with:

ToolError: Error executing tool f: f() got an unexpected keyword argument 'externalX'

I expected the schema-valid input to be mapped back to the Python parameter x before invocation.

Example Code

import asyncio
from typing import Annotated

try:
    from mcp.server.mcpserver.tools.base import Tool
except ImportError:  # MCP Python SDK 1.x
    from mcp.server.fastmcp.tools.base import Tool

from pydantic import Field


AliasInt = Annotated[int, Field(alias="externalX", ge=1)]


def f(x: AliasInt) -> int:
    return x


async def main() -> None:
    tool = Tool.from_function(f)
    print(tool.parameters)
    print(await tool.run({"externalX": 1}, None))


asyncio.run(main())

The printed schema requires externalX, then the call fails with the error above.

Python & MCP Python SDK

Stable reproduction:
- Python 3.13.13
- mcp 1.28.1
- pydantic 2.13.4

Current main reproduction:
- modelcontextprotocol/python-sdk commit 2713b53b127afc094dc97d6067df9f69b647661c
- mcp 2.0.0b2
- mcp-types 2.0.0b2
- Python 3.13.13

Start by reading the Tool.from_function and Tool.run entry points and run the provided reproduction with an aliased parameter. Trace how the schema name externalX is passed to the function, then add coverage showing that schema-valid input invokes f with x and returns successfully.