Function checkpoint_was_deferred 

pub fn checkpoint_was_deferred(error: &Error) -> bool

Whether a failed checkpoint only means the session was busy.

The marker is carried by the error, not by its text. It may be the root error or attached with context, and callers wrap checkpoint errors in further context. anyhow’s own downcast walks every context layer; chain() does not expose a context value, so it must not be used here.