Function save_final_state 

pub(crate) fn save_final_state(state: &AppState, block_id: &str)

Clear session:active_pid (so the next boot doesn’t read this as an interrupted session) and mark the local instance row stopped. The session id itself is left everywhere it is — block meta, instance row, shared registry — so reopening the agent resumes it (spec §4.2 step 6).