TalkModeManager is instantiated lazily in NodeRuntime and drives ElevenLabs
streaming TTS for all assistant responses when the voice screen is active.
MicCaptureManager continues to own STT and chat.send; TalkModeManager is
TTS-only (ttsOnAllResponses = true, setEnabled never called).
- talkMode.ttsOnAllResponses = true when mic is enabled or voice screen active
- Barge-in: tapping the mic button calls stopTts() before re-enabling mic
- Lifecycle: PostOnboardingTabs LaunchedEffect + VoiceTabScreen onDispose both
call setVoiceScreenActive(false) so TTS stops cleanly on tab switch or
app backgrounding
- applyMainSessionKey wires the session key into TalkModeManager so it
subscribes to the correct chat session for TTS
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