Version-2 B-tree (its writer's own node size and single-leaf layout), Extensible Array and Fixed Array datasets written by FileBuilder, with and without deflate, resized up and down along both dimensions and written at random against a model; h5py, h5dump and h5rs check read the result, and h5py resizes and rewrites every dataset afterwards. Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>