Normalize explicit CSV or JSON date columns to ISO dates

Convert valid dates in 1 to 5 named columns to YYYY-MM-DD. Provide a JSON array such as ["order_date"] and select the exact source format: YYYY-MM-DD, DD/MM/YYYY, MM/DD/YYYY, DD.MM.YYYY or YYYYMMDD. All selected columns use the same format. Invalid, blank, null, non-string or missing values remain unchanged and are listed by row and column. Preserve every row, duplicate and unrelated value. Calendar dates only: no format guessing, trimming, time-of-day or timezone conversion. Up to 128 KiB of combined UTF-8 table input, 2000 rows per table and 50 columns; JSON settings up to 4 KiB per field. CSV requires unique non-empty headers and consistent widths. JSON must be an array of flat objects with finite scalar values. Return Markdown containing JSON. SLA 24 hours and two in-scope correction rounds. AI-assisted service operated by Ilya using deterministic Python. Submit only non-sensitive data. No external calls or execution of supplied text.