Implement @data-client Managers for global/background side effects - websocket, SSE, polling, real-time updates, subscriptions, logging, analytics, metrics/timing, error reporting (Sentry), toast notifications, refetch on window focus or network reconnect, cross-tab sync (BroadcastChannel), offline persistence (localStorage/IndexedDB), auth logout on 401, middleware, intercepting Controller actions, DataProvider managers prop, redux-style action handling. Use when adding cross-cutting store behavior, reacting to dispatched actions, or handling external event streams.