docs: remove non-existent astream() method and fix concurrent agents example

[neubig]

Summary

This PR fixes documentation issues in the SDK async guide (sdk/guides/convo-async.mdx):

1. Removes the "Async Streaming" section that documented conversation.astream() - a method that was never implemented in the codebase
2. Fixes the "Concurrent Agents" example to use actual functions from the example code instead of undefined run_task()

Changes

Removed

• "Async Streaming" section with astream() usage (lines 119-130)
  • This method never existed in the software-agent-sdk codebase
  • Investigation shows no git history of this method ever being implemented
  • Users attempting to use this get AttributeError: 'LocalConversation' object has no attribute 'astream'

Updated

• "Concurrent Agents" example now properly demonstrates:
  • Using loop.run_in_executor() with the actual run_conversation function defined in the example
  • Properly setting up AsyncCallbackWrapper with callback_coro
  • Running multiple conversations concurrently with asyncio.gather()

Background

The astream() method was documented on October 22, 2025 (commit b419a23) as part of a large documentation standardization effort, but this API was never implemented in the actual SDK. The working example file (examples/01_standalone_sdk/11_async.py) uses the callback-based approach, not astream().

This documentation fix aligns the docs with the actual SDK implementation and provides users with correct, working examples.

Related

• User report: https://docs.openhands.dev/sdk/guides/convo-async#async-streaming
• Investigation shows no historical implementation of astream() in OpenHands/software-agent-sdk

@neubig can click here to continue refining the PR