Memory leak of Agent

[8lank]

Describe the bug

Agent is leaking after a run completion.

Debug information

• Agents SDK version: (e.g. v0.3.3)
• Python version (e.g. Python 3.13)

Repro steps

async def probe():
    agent = Agent(
        name="Leaker",
        instructions="You are an agent who answers questions",
    )
    wr = weakref.ref(agent)

    result = await Runner.run(agent, "What is the capital of France?")
    print(
        result.context_wrapper.usage.input_tokens,
        result.context_wrapper.usage.output_tokens,
    )

    agent = None
    result = None
    gc.collect()

    return wr


async def prove_leak():
    wr = await probe()
    print("You are indeed a leaker:", wr() is not None)


async def main() -> None:
    await prove_leak()


if __name__ == "__main__":
    asyncio.run(main())

This is likely due to MessageOutputItem keeping a strong ref to Agent.

Expected behavior

No leak should happen.