Fix handoff closure bug and add multiple handoffs test

[tconley1428]

Summary

• Fixed a Python closure bug in _convert_agent where handoff functions were incorrectly captured by reference instead of by value
• Added test case validating correct handoff routing with multiple agents

Problem

The _convert_agent function had a closure bug where the async def on_invoke function was defined inside a loop and captured the original_invoke variable by reference. This caused all handoff calls to route to the last agent processed in the loop instead of the intended agent.

For example, when calling transfer_to_planner, it would incorrectly route to the writer agent instead of the planner agent.

Solution

• Used a default parameter (invoke_func=original_invoke) to capture the handoff function by value instead of by reference
• This ensures each handoff closure captures its own unique function reference

Test

Added test_multiple_handoffs_workflow that:

• Creates a workflow with multiple agents (Planner, Writer)
• Verifies transfer_to_planner correctly routes to the Planner agent
• Validates the handoff mechanism works as expected with multiple handoffs

🤖 Generated with Claude Code

[THardy98]

LGTM - as a sanity check, could we add an assertion after the planner response to check that the subsequent handoff to the writer is also correct

[tconley1428]

It actually doesn't bother handing off to the writer because the planner doesn't have the writer as a subagent and the planner doesn't know what to plan. Sufficient to test the issue though.