Adding the ability to send extra context on setMessage and append.

[gavriguy]

Hi,

useChat has currently the option to add a body property to send extra context to the server.

I'm suggesting to allow the ability to send extra context when the user sends a chat prompt. for example:

• The appearance status (light or dark)
• The current step in a form wizard that is stored in the app state or in a query parm
• A screenshot capture image of the current screen.
• the current in an embedded video the user is at.

I know we can use append to send (system, assistant) messages but it will be nice to be able to send it with the message send by the user in chat in one transaction .