Function clip_sequence_payload 

pub fn clip_sequence_payload(cigar: &str, seq: &str) -> String

Encodes only recoverable soft-clipped bases for segment-evidence sidecars.

Storing full read sequences would inflate the BSJ sidecar substantially. The final segments stage only needs clipped subsequences, so the compact L:<seq>,R:<seq> payload keeps I/O bounded while retaining the local evidence validated by Scan1/Scan2.