staffing: D — workers_500k.phone int → string fixup script

Decision D from reports/staffing/synthetic-data-gap-report.md §7.

Phones in workers_500k.parquet are 11-digit US numbers stored as int64
(e.g. 13122277740). Numerically fine, but breaks join keys against any
other source that carries phone as string. Script casts the column to
string in place, with non-destructive backup at
data/datasets/workers_500k.parquet.bak-<date> before write.

Idempotent: if phone is already string, exits 0 with "no-op". Safe to
re-run.

The .parquet itself is too large to commit (75MB) and follows project
convention of staying out of git. The script makes the conversion
reproducible from the source dataset.

scripts/staffing/fixup_phone_type.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+"""
+fixup_phone_type.py — Decision D from the synthetic-data gap report.
+
+Converts workers_500k.parquet `phone` column from int64 → string. Phones
+in this dataset are 11-digit US numbers (1 + area + 7), e.g. 13122277740.
+Stored as int64, the column compares fine numerically but breaks join
+keys with string-typed phone columns elsewhere (formatted "+1...", or
+loaded from a CSV).
+
+Backs up the original to workers_500k.parquet.bak-<date> before write.
+Idempotent: detects when the fix has already been applied and exits 0.
+
+Usage:
+    python3 scripts/staffing/fixup_phone_type.py
+"""
+
+import datetime as dt
+import shutil
+import sys
+from pathlib import Path
+
+import pyarrow as pa
+import pyarrow.compute as pc
+import pyarrow.parquet as pq
+
+REPO = Path(__file__).resolve().parents[2]
+TARGET = REPO / "data" / "datasets" / "workers_500k.parquet"
+
+
+def main() -> int:
+    if not TARGET.exists():
+        print(f"missing: {TARGET}", file=sys.stderr)
+        return 1
+
+    table = pq.read_table(TARGET)
+    phone_field = table.schema.field("phone")
+    if phone_field.type == pa.string():
+        print(f"phone is already string — no-op")
+        return 0
+
+    today = dt.date.today().isoformat()
+    backup = TARGET.with_suffix(f".parquet.bak-{today}")
+    if not backup.exists():
+        shutil.copy2(TARGET, backup)
+        print(f"backup: {backup.relative_to(REPO)}")
+
+    phone_str = pc.cast(table["phone"], pa.string())
+    new_table = table.set_column(
+        table.schema.get_field_index("phone"),
+        pa.field("phone", pa.string()),
+        phone_str,
+    )
+
+    pq.write_table(new_table, TARGET, compression="snappy")
+    rounds_trip = pq.read_table(TARGET, columns=["phone"])
+    sample = rounds_trip["phone"].slice(0, 3).to_pylist()
+    print(f"wrote: {TARGET.relative_to(REPO)}")
+    print(f"phone type: {rounds_trip.schema.field('phone').type}")
+    print(f"sample: {sample}")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())