Default text input callback doesn't await interrupt(), losing assistant message from chat context

[mmsbrggr]

Bug Description

When a user sends a text message while the agent is speaking, the interrupted assistant message is missing from
chat_ctx for the next LLM call.

The default text input callback in voice/room_io/types.py: calls sess.interrupt() without awaiting the
returned future, then immediately calls generate_reply(). Since generate_reply copies chat_ctx before the
interrupt cleanup has a chance to commit the truncated assistant message, the LLM never sees what the assistant was
saying when it got interrupted.

def _default_text_input_cb(sess, ev):
    sess.interrupt()           # returns Future[None], not awaited
    sess.generate_reply(...)   # copies chat_ctx before cleanup commits

Voice interruptions don't have this problem because STT turn detection introduces enough delay for the cleanup to
finish.

Expected Behavior

After a text interruption, the next LLM call should include the truncated assistant message in chat context, same as voice interruptions.

Reproduction Steps

1. Start a voice agent session with text input enabled
2. Let the agent start speaking a response
3. Send a text message mid-response via the data channel
4. Observe that the next LLM call's chat context is missing the interrupted assistant message

Operating System

Linux (also reproducible on macOS)

Models Used

Any LLM/TTS/STT combination, not model-specific.

Package Versions

livekit-agents 1.4.1

Session/Room/Call IDs

No response

Proposed Solution

Make the default callback async and await the interrupt future:

  async def _default_text_input_cb(sess, ev):
      await sess.interrupt()
      sess.generate_reply(user_input=ev.text)

Additional Context

No response

Screenshots and Recordings

No response

[jp-paper]

I am piggybacking on this issue to share some observations as I have been looking into this callback myself recently.

• The text_input_cb does not update the user state, which would streamline implementations relying on it
• It would be useful to have sess.generate_reply(user_input=...) accept str | ChatMessage, when text_input_cb is overridden to receive stringified JSON (ex: to receive text + attachments), it would be convenient to pass a ChatMessage with ImageContent directly and have it added to the session history (especially as this is what is happening in the implementation)