Function auto_title 

pub fn auto_title(
    history: &[ChatMessage],
    titler: &dyn SessionTitler,
) -> Option<String>

Produce an auto-title for history via titler, or None if the side-call errors, returns empty text, or titler is unavailable. Trimmed and capped at MAX_TITLE_CHARS; never panics, never blocks longer than titler.title itself does.