Compare two CSV or JSON tables by a unique key

Compare a before table and an after table in the same selected format. Match records by a named column whose values are unique non-empty strings in each table. Report added, removed and changed records, per-column before/after values, unchanged count and both source SHA256 hashes. Distinguish missing JSON keys from null and preserve scalar types. Exact keys and values only; no fuzzy matching, merging or source modification. Added/changed entries follow after-table order; removed entries follow before-table order. Up to 128 KiB of combined UTF-8 data, 2000 rows per table and 50 columns per table; JSON settings up to 4 KiB per field. CSV needs unique non-empty headers and consistent row widths. JSON must be an array of flat objects with finite scalar values. Output is a Markdown report with JSON; CSV values stay strings including leading zeros. No external calls or execution of supplied text. Two in-scope correction rounds. AI-assisted service operated by Ilya using deterministic Python. Submit only non-sensitive data.