A selection of a chunked dataset with a fill value is compared with the full read in every index, through a map and through positioned reads. An LZ4 chunk larger than 256 MiB is bounded by the chunk size, not refused. The wasm package test reads the 4 GiB-chunk fixture and gets a clean error in every index. Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>