Romanian CUI check digit algorithm (key 753217532) validates CUIs before ANAF lookup. New sanitize_cui() fixes OCR typos (O→0, I→1) and verifies checksum, logging warnings for invalid CUIs. Applied at both ANAF batch verification and per-order import steps. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>