Lets the migration run while another process still has the original files
open for reading: --copy uses shutil.copy2 instead of move, and skips the
now-empty-directory cleanup since the legacy train/ etc. dirs stay populated
by design.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Introduces raw/<kind>/<gen>/<detector>/shard-NNN.root and
processed/<kind>/<gen>/<schema>/<detector>/shard-NNN.parquet as the dataset
convention, plus scripts to operate on it: migrate_geant_steps.py for the
one-time move into this layout, bump_dataset_version.py to cut new
gen/schema versions with a logged reason, steps_to_parquet_parallel.py to
convert ROOT shards to parquet in parallel and place them correctly, and
create_root_files.py to generate new ROOT shards via a minicalosim
executable. The loader gains .manifest file support so pools/ (train/dev/
holdout shard lists) can be passed straight to `giant train`.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
lars