{
  "A": {"contract_id": "A", "version": "2026-09", "columns": {"code": "string", "qty": "integer"}, "unknown_columns": "reject"},
  "B": {"contract_id": "B", "version": "2026-09", "columns": {"item_id": "string", "name": "string"}, "unknown_columns": "reject"},
  "C": {"contract_id": "C", "version": "2026-09", "columns": {"id": "string", "date": "YYYY-MM-DD"}, "unknown_columns": "reject"}
}