Function body_within 

pub fn body_within(
    conversation: &Conversation,
    system: &str,
    cap: usize,
) -> Value

The body of a request that is at most cap bytes: the conversation trimmed to what is left of cap once the rest of the body is counted in, that rest, and nothing else. body is this with REQUEST_CAP; a cap of usize::MAX sends the conversation as it is kept, which is what the trimmed request is measured against.