S5 — build_gaul_lookup.py: pyarrow-native build

[Polichinel]

Epic: #85 · S5 · [UNILATERAL — lowest priority]

Background

scripts/build_gaul_lookup.py builds the GAUL lookup parquet from views-datafactory's source parquets using pandas + pyarrow. It runs offline, outside the delivery path, so it touches nothing interconnected and has zero samples relevance. Pandas-free for completeness only.

Work

• Make the builder pandas-free (pure pyarrow): the join/filter/dtype/sort steps currently done with pandas (build_gaul_lookup.py ~:71-166) reimplemented on arrow tables; keep the embedded provenance metadata that _read_version reads.

Acceptance criteria

• The builder produces a lookup parquet identical to the current one from the same datafactory inputs (table contents + embedded provenance metadata).
• No pandas import in the script.

Parity / validation

Build the lookup both ways from the same inputs; assert identical arrow table and identical provenance metadata. (Downstream tests/test_enrichment.py lookup-integrity assertions must still pass against the rebuilt file.)

Dependencies

Independent; lowest urgency. Keep in sync with S4 and gaul_schema.py (the 9-column contract + rename map).

Files

scripts/build_gaul_lookup.py.