Add README written by hand after script's post-upload write_readme() crash

README.md

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+# soc91-labels
+
+Mirror of the R2 prefix `soc91-labels/` from `soc127-dedup` (Cloudflare R2) into a private
+HF Dataset. Generated by `scripts/handoff/mirror_r2_sidecar_prefix.py` on
+2026-05-23.
+
+Each row in the source R2 parquets is preserved, with one additional column appended:
+`source_shard_path` — the R2 object key the row came from. This lets you reconstruct
+the per-shard view if needed.
+
+## Counts
+
+| | Source (R2) | Mirror (this dataset) |
+|---|---|---|
+| Files | 58,465 | 2,719 (concat into ~60 MB chunks) |
+| Size | ~150 GB (approx, mixed schemas) | 169.94 GB |
+
+## Loading
+
+```python
+from datasets import load_dataset
+ds = load_dataset("HCAI-Lab/soc91-labels")
+# or for a single chunk:
+import pyarrow.parquet as pq
+table = pq.read_table("data_00000.parquet")
+```
+
+## Schema
+
+Schema matches the per-shard WebOrganizer sidecar parquet schema as defined in
+`src/dolma/sidecar_manifest_fields.py:43-124` (data-attribution repo), plus the appended
+`source_shard_path` column. The underlying classifier produced both an "old" schema
+(label ids only) and a "new" schema (label ids plus per-label probability vectors);
+the concatenated table promotes nullable columns so rows from both schemas coexist.
+
+Per-row fields (subset; see source for the full list):
+
+- `doc_id` — Dolma document UUID
+- `weborganizer_topic_id`, `weborganizer_topic` — top-1 topic class (24 categories)
+- `weborganizer_format_id`, `weborganizer_format` — top-1 format class (24 categories)
+- `weborganizer_topic_confidence`, `weborganizer_format_confidence` — top-1 probabilities
+- `weborganizer_topic_probabilities`, `weborganizer_format_probabilities` — full probability vectors (new-schema rows only; null on old-schema rows)
+- `source_shard_path` — the R2 object key the row originated from
+
+## Lineage
+
+- SOC-91 (initial label generation)
+- SOC-142 (inverted-quality-label fix at commit `3342baf`; affects the quality sidecars in
+  `HCAI-Lab/soc139-quality-sidecars`, not the topic/format labels here)
+
+## Notes
+
+- The chunked-write/stream-upload pipeline succeeded and committed all 2,719 chunks.
+- The original `write_readme()` step crashed (after upload) because the staging directory
+  files were already deleted by the stream-upload pattern. This README was written by
+  hand after the fact based on the script's final log output (`wrote 2719 chunks total`).