Constant WS_EVENT_MUX_OBJ_BATCHED_UPDATES 

pub const WS_EVENT_MUX_OBJ_BATCHED_UPDATES: &str = "waveobj:batchedupdates";

One WS frame carrying an ARRAY of MuxObjUpdates from a single atomic backend transition. Mirrored in frontend/app/store/mps-events.ts (WpsEvent.MuxObjBatchedUpdates) — the frontend applies the whole array in one Solid batch() flush. See broadcast_mux_obj_updates below.