            from openpyxl import load_workbook
            from openpyxl.utils.datetime import to_excel,from_excel,CALENDAR_WINDOWS_1900
            base=folder.parent if (folder.parent/'windows.xlsx').exists() else folder;rows=[]
            for name in ['windows.xlsx','mac.xlsx']:
                wb=load_workbook(base/name);value=wb.active['A1'].value;serial=to_excel(value,wb.epoch);rows.append({'file':name,'epoch':wb.epoch.date().isoformat(),'serial':serial,'date':value.date().isoformat()})
            check('不同epoch回读同一个日期',rows[0]['date']==rows[1]['date']=='2026-10-01');check('原始serial相差1462天',rows[0]['serial']-rows[1]['serial']==1462);wrong=from_excel(rows[1]['serial'],CALENDAR_WINDOWS_1900).date().isoformat();check('错用epoch能被反例发现',wrong!='2026-10-01');cout('date-system-audit.csv',rows);result={'books':rows,'wrong_windows_decode':wrong,'direct_serial_merge_safe':False}
