When using realtime agent with websocket, truncate events are sent even when no interruption

[nbondoux]

Describe the bug

When using realtime agent with websocket, and not using playback tracker, truncate events are sent even when there is no interruption.

1. the llm answers an error message since the audio_end_ms parameter is bigger than the length of the message to truncate
2. it seems truncate events have side effect, even when they don't truncate anything. We observed a change of behaviour from the model, with the tendency to repeat itself.
   I would suggest to send truncate events only when it is needed

Debug information

• Agents SDK version: 0.6.9
• Python version: Python 3.13

Repro steps

Expected behavior

truncate event to be generated only when truncation is needed.

[nbondoux]

I want to reopen the ticket as I think there is a small issue with the fix:
The fix seems right by adding a limit based on the delta received, but this is wrong:

if not self._ongoing_response:
    logger.debug(
        "Skipping truncate because no response is in progress. "
        f"Item id: {current_item_id}, "
        f"elapsed ms: {elapsed_ms}, "
        f"content index: {current_item_content_index}"

sending truncate event is unrelated to receiving or not the response.done event

Thanks,
Nicolas

[nbondoux]

@seratch

[seratch]

submitted #2385 for fixing it. if you have any suggestions, please feel free to let me know