Function nbatch_frame 

pub fn nbatch_frame(
    client_qid: u64,
    batch: &NormalizedBatch,
    ops_fragment: &str,
) -> String

Assemble one full nbatch frame for client_qid, splicing the already-encoded ops_fragment into the scalar envelope. Byte-identical to the json! frame in RouterSink::batch: {"batch":{"cv":…,"epoch":…,"normalizedFp":"…","ops":…,"seq":…}, "queryId":…,"t":"nbatch"} (all keys alphabetical).