fix: wait for first result before closing stdin if SDK MCP present

[dltn]

Port SDK MCP fix from TypeScript to Python.

Now, when SDK MCP servers or hooks are present, stream_input() waits for the first result message before closing stdin, allowing bidirectional control protocol communication to complete.

Fixes repro in #266.

The query() design requires input streams to be held open by the user for SDK MCP bidirectional communication to work. This has confused a lot of folks, so we're moving towards a more explicit lifecycle design. In the meantime, this is the way we've addressed it with V1 APIs in https://github.com/anthropics/claude-agent-sdk-typescript.

🤖 Generated with Claude Code

[murtaza64]

Is this fix actually in 0.1.11? I'm seeing the same error when trying to use an SDK MCP server

edit:

Traceback (most recent call last):
  File "/Users/murtaza/infra-baymax/.venv/lib/python3.13/site-packages/claude_agent_sdk/_internal/query.py", line 320, in _handle_control_request
    await self.transport.write(json.dumps(success_response) + "\n")
  File "/Users/murtaza/infra-baymax/.venv/lib/python3.13/site-packages/claude_agent_sdk/_internal/transport/subprocess_cli.py", line 511, in write
    raise CLIConnectionError("ProcessTransport is not ready for writing")
claude_agent_sdk._errors.CLIConnectionError: ProcessTransport is not ready for writing

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/murtaza/infra-baymax/.venv/lib/python3.13/site-packages/claude_agent_sdk/_internal/query.py", line 332, in _handle_control_request
    await self.transport.write(json.dumps(error_response) + "\n")
  File "/Users/murtaza/infra-baymax/.venv/lib/python3.13/site-packages/claude_agent_sdk/_internal/transport/subprocess_cli.py", line 511, in write
    raise CLIConnectionError("ProcessTransport is not ready for writing")
claude_agent_sdk._errors.CLIConnectionError: ProcessTransport is not ready for writing

disabling the SDK MCP server gets rid of this error