Function nbatch_ops_fragment 

pub fn nbatch_ops_fragment(batch: &NormalizedBatch) -> String

Encode batch.ops as its […] JSON array — the fragment nbatch_frame splices into each subscriber’s envelope. RouterSink::batch encodes it ONCE per batch, outside the router lock, then assembles a frame per subscriber (only the envelope’s queryId/seq/epoch differ across a fan-out).