Function session_end 

pub fn session_end(session: Option<&str>) -> usize

When a session ends, the memories injected during it fire together: they served one sitting, so their links gain weight and the next sitting like it walks a heavier path (Hebb, through the pack’s fire). The seen file goes with the session. Returns how many fired; nothing to fire, or no pack, is zero and not an error, since a hook must not stop a runner from ending.