OptionalsystemSeeded as the first message in conversation history so the LLM has guidance before any user audio arrives. Defaults to ComposableVoiceAgent.DEFAULT_SYSTEM_PROMPT.
TTS voice in "<provider>/<voiceId>" form.
OptionalttsTest seam — TTS options forwarded to synthesize.
ai-sdk LanguageModel (e.g.
openai("gpt-5.4-mini")).