step,rule,n_before,n_after,n_removed,rationale
1_structure,line has exactly 5 CSV fields and sale_id matches S+5 digits,1200,1164,36,corrupted/garbled export lines cannot be read unambiguously; not reconstructed
2_fields,"municipality in control list, ISO date, positive integer price (plain or quoted thousands-separated), positive numeric area",1164,1164,0,fields must be readable unambiguously
3_dedup,drop repeated sale_id (keep first),1164,1164,0,sale_id must be unique