Progress notifications cause server to hang on stdio transport #1141

import asyncio
from mcp.server.lowlevel import Server
from mcp.server.stdio import stdio_server
from mcp.types import *

server = Server("progress-bug-demo")

@server.list_tools()
async def handle_list_tools() -> list[Tool]:
    return [Tool(
        name="test_tool",
        description="Demonstrates the bug",
        inputSchema={"type": "object", "properties": {}}
    )]

@server.call_tool()
async def handle_call_tool(name: str, arguments: dict) -> list[TextContent]:
    ctx = server.request_context
    progress_token = ctx.meta.progressToken if ctx.meta else None
    
    if progress_token:
        # This causes the server to hang
        await ctx.session.send_progress_notification(
            progress_token=progress_token,
            progress=0.5,
            total=1.0,
            message="Working..."
        )
    
    # This response is never sent due to the hang
    return [TextContent(type="text", text="Task completed!")]

async def main():
    async with stdio_server() as (read_stream, write_stream):
        await server.run(
            read_stream,
            write_stream,
            server.create_initialization_options()
        )

if __name__ == "__main__":
    asyncio.run(main())