invoke asyn method in mcp tool through StreamableHttpTransport cause early return from tool call

Describe the bug
when calling a asyn method in tool callbak, always raise an error "No connection established for request ID".

this error will be catched internal, makes tool call looks like pending.

To Reproduce
Steps to reproduce the behavior:

1. register a echo tool like following:

server.registerTool(
'echo',
{
title: 'Echo Tool',
description: 'Echoes back the provided message',
inputSchema: { message: z.string() }
},
async ({ message }) => {
logger.info(Echo tool called with message: ${message});

      // await aync call will cause the response return immediately
      await new Promise(resolve => {
        setTimeout(resolve, 1)
      })

      // when returning from this, the reported error will be raised
      return {
        content: [{ type: 'text', text: `Tool echo: ${message}` }]
      };
    }
  );

Expected behavior
async call in a tool should be allowed.

Logs

Additional context
error screenshot

Start with the StreamableHttpTransport request lifecycle and the server.registerTool callback shown in the reproduction. Reproduce the issue with the delayed async echo tool and trace why the connection is unavailable after the await. Done means an async tool returns its content normally without the "No connection established for request ID" error.