Function spawn 

pub fn spawn(
    fs_watch_pool: Arc<FsWatchPool>,
    mstore: Arc<Store>,
    id_store: Arc<Store>,
    broker: Arc<Broker>,
)

Start both layers. Call once at server startup with a fully-built AppState’s fs_watch_pool/mstore/id_store. Returns immediately — both loops run as spawned background tasks for the lifetime of the process (no shutdown handle; srv itself owns the process lifetime).