step,rule,n_before,n_after,n_removed,rationale
1,data lines read (excluding header),1200,1200,0,all physical data lines in data/sales.csv
2,line parses (RFC-4180 CSV) into exactly 5 fields,1200,1164,36,corrupted/garbled export lines cannot be read; not reconstructed
3,"every field valid: sale_id S+5 digits, municipality alphabetic, ISO date, price integer (optionally comma thousands-separated), area numeric, both > 0",1164,1164,0,fields must be readable unambiguously; not reconstructed
4,sale_id unique (all copies of duplicated ids dropped),1164,1164,0,duplicated ids would make records ambiguous