Group CSV or JSON rows and calculate exact decimal totals

Summarize one table by 1 to 5 explicit grouping columns. Supply rules such as {"group_by":["category"],"value_column":"amount"}. Return row count, exact sum, minimum and maximum per group in first-appearance order. Group values distinguish scalar types, case and whitespace. Every row must contain every required field. Amounts must be decimal strings or JSON integers, with at most 24 digits and 12 decimal places; no floats, blanks, currency symbols, thousands separators or exponent notation. Totals are decimal strings. No rounding or inferred business rules. 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.