Introduce the siblingannex module in obicompactvec to store per-slot minorant flags and sibling counts in a memory-mapped annex file. Add a scatter-gather pipeline in obikindex to compute these values across index layers and write them to .psib files. Implement central_canonical_neighbors in obikseq for generating strand-aware k-mer variants around the middle base. Expose rolling statistics in obiskbuilder and update dependency graphs accordingly.