OptionalfirstMessage?: stringFirst-message override ('' = suppress the canned greeting so the call opens in-character / context-aware). Pass as overrides.agent.firstMessage.
Pass as overrides.agent.prompt.prompt when starting the EL session.
Optionallanguage?: stringServer-resolved agent language (ISO 639-1, e.g. 'zh'). Pass as overrides.agent.language so the call opens in the user's language.
EL conversation token (open WebRTC with @elevenlabs/client).
Optionalvoice?: stringServer-resolved EL voice id (the user's cloned/localized voice). Pass as overrides.tts.voiceId so the call isn't a stock default voice.
Ephemeral client secret (ek_…); open WebRTC directly to OpenAI.
Voice-plane credentials, discriminated by provider (see startCall).