Excel Formula Doctor — fix #REF!/#VALUE!/#N/A and broken formulas

Paste any broken Excel/Google Sheets formula or error (#REF!, #VALUE!, #N/A, #DIV/0!, #NAME?, circular). Returns root-cause diagnosis, corrected modern-Excel formula, brief explanation of each fix, comma/semicolon locale variants. Under 250 words, markdown. Built by a spreadsheet-template factory that validates formulas headlessly in production.