RealtimeModel.update_options() does not send session.update to OpenAI (race condition with _opts mutation)

[strukturedkaos]

Summary

RealtimeModel.update_options() mutates the model-level _opts before forwarding to active sessions, causing RealtimeSession.update_options() to see no diff and skip sending session.update to OpenAI.

Environment

• livekit-agents: 1.5.x
• livekit-plugins-openai: 1.5.x
• Model: gpt-realtime-1.5

Steps to Reproduce

1. Start an OpenAI Realtime session via LiveKit
2. Call agentSession._llm.update_options(speed=1.5) (or any other option like voice, turn_detection, etc.)
3. Observe that no session.update event is sent to OpenAI
4. The change has no audible/observable effect

Root Cause

In realtime_model.py:

RealtimeModel.update_options() (around line 649):

# Mutates _opts FIRST
if is_given(speed):
    self._opts.speed = speed

# THEN forwards to sessions
for sess in self._sessions:
    sess.update_options(speed=speed, ...)

RealtimeSession.update_options() (around line 1207):

if is_given(speed):
    if self._realtime_model._opts.speed != speed:  # Always False! Already mutated above
        audio_output.speed = speed
        has_audio_config = True
    self._realtime_model._opts.speed = speed

The session compares against the model's _opts, which was already mutated by the model-level call. The diff always sees "no change" and skips sending the update.

Affected Options

All options using this pattern:

• speed
• voice
• turn_detection
• input_audio_transcription
• input_audio_noise_reduction
• tool_choice
• tracing
• max_response_output_tokens

Workaround

Call RealtimeSession.update_options() directly on active sessions:

for sess in llm._sessions:
    sess.update_options(speed=1.5)

This works because the session-level call hasn't had its comparison poisoned by prior mutation.

Suggested Fix

In RealtimeModel.update_options(), forward to sessions before mutating _opts:

def update_options(self, *, speed=NOT_GIVEN, ...):
    # Forward to sessions FIRST (while _opts still has old values)
    for sess in self._sessions:
        sess.update_options(speed=speed, ...)
    
    # THEN mutate model opts
    if is_given(speed):
        self._opts.speed = speed
    ...

Additional Context

• The workaround requires accessing llm._sessions, which is a private attribute
• There's no public API to enumerate active sessions from AgentSession
• Initial session setup works correctly (only live updates are broken)

Related Issues

• LiveKit OpenAI Realtime sends noise_reduction as a string in session.update (server expects an object) #3466 (similar update_options / session.update issues with noise_reduction)
• OpenAI Realtime Crash on 1.2.9 (not in 1.2.8), and voice changing to masculine voice id #3445 (voice changing unexpectedly, related to session update handling)