OptionaldefaultThe provider-agnostic persona (tone / speaking style), prompt-level.
OptionalprovidersProvider-specific voice settings keyed by provider (e.g. openai, elevenlabs,
gemini, assemblyai). Each value is an OPAQUE settings object merged into the matching
driver's open Config bag — the shape is a private pact with that driver.
Voice configuration: a persona plus per-provider native voice settings.