Unique session identifier for subsequent messages
OptionalresponseBrand agent's initial response
Optionalmessage?: stringConversational message from brand agent
Optionalui_elements?: SIUIElement[]Visual components to render
Optionalnegotiated_Optionalsession_Session inactivity timeout in seconds. After this duration without a message, the brand agent may terminate the session. Hosts SHOULD warn users before timeout when possible.
OptionalerrorsErrors during session initiation
Optionalext
Brand agent's response to session initiation