- WebSocketManager in backend/websocket/manager.py with per-experiment and global subscriptions
- Redis pub/sub bridge (sync + async) broadcasting events to relevant WebSocket clients
- Deque-based replay buffers with since_ts/limit filtering for reconnection support
- Runtime subscribe/unsubscribe and stats API
- Enhanced /ws endpoint in main.py with subscribe/unsubscribe/replay actions
- 35 tests in test_ws_manager.py, all passing
