Datasets:
Replace Parquet tiles with shuffled Arrow shards
Replace the 200 Parquet tile shards with 200 uncompressed Arrow IPC shards containing the same 4 million original JPEGs plus cached tissue fractions. Tiles follow the metadata-derived shuffle with seed 161803. Add a short dataset card; preserve all unrelated repository content, including probes.
The original release is preserved as v0-parquet at 96a5b33456fd948a0f1c90ee6901d748bde39111. This PR is intentionally unmerged; main must remain unchanged until review.
Validation: original sample-list metadata with selection seed 42 exactly matches all 4 million source tile paths. Full local verification confirmed every JPEG/path hash, independently recomputed tissue fraction, 200 one-batch shards, and the expected shuffled-order digest. Upload verification checks every Arrow file size and SHA-256 against the local files. Only shard-*.arrow and README.md are uploaded; no staging data, scripts, logs, or _SUCCESS.json.