Function spawn_reconciler 

pub fn spawn_reconciler(
    sessions: Arc<SessionRegistry>,
    finalizer: Finalizer,
    idle_s: u64,
    tick_s: u64,
    breaker: BreakerConfig,
    metrics: Arc<Registry>,
) -> JoinHandle<()>

Start the periodic reconciler tick: spool recovery, promotion retry, pending-close completion, idle-session finalization, and finalized-session eviction.