Ensure a seekable plain .sigs.ndjson (+ its .idx) exists for source, decompressing a .br/.zst/.gz
once into a hash-keyed cache the first time and reusing it on every later startup. The index may be
supplied by the caller (e.g. embedded in a manifest) so no separate .idx file needs to ship.
Ensure a seekable plain
.sigs.ndjson(+ its.idx) exists forsource, decompressing a.br/.zst/.gzonce into a hash-keyed cache the first time and reusing it on every later startup. The index may be supplied by the caller (e.g. embedded in a manifest) so no separate.idxfile needs to ship.