AgentExecutionStep.might_yield raises NotImplementedError for A2AAgent

[groganz]

Summary

AgentExecutionStep.might_yield handles Agent, Swarm, ManagerWorkers, and OciAgent but raises NotImplementedError for A2AAgent, preventing any flow that contains an A2A step from being served via A2AServer.

Reproduction

1. Create a flow with an A2AAgent inside an AgentExecutionStep (i.e. an AgentNode in agent.json that references a child agent served over A2A).
2. Call AgentSpecLoader.load_json(spec_str) to convert the spec, then A2AServer.serve_agent(agent).
3. On startup, might_yield is evaluated and raises:

NotImplementedError: A2AAgent not supported in agent execution step

Expected behaviour

A2AAgent is a first-class agent type per the AgentSpec. might_yield should return True when caller_input_mode == CallerInputMode.ALWAYS (the same logic that applies to other agent types that can yield), allowing orchestrator flows to call child A2A agents without patching the runtime.

Workaround

We monkey-patch AgentExecutionStep.might_yield at container startup:

_orig_might_yield = AgentExecutionStep.might_yield.fget

def _patched_might_yield(self):
    if isinstance(self.agent, A2AAgent):
        return self.caller_input_mode == CallerInputMode.ALWAYS
    return _orig_might_yield(self)

AgentExecutionStep.might_yield = property(_patched_might_yield)

Environment

• wayflowcore[a2a]==26.1.1
• Python 3.11