Spreadsheets

Handle tabular data with exact values, minimal diffs, local privacy, atomic writes, and structural validation.

Invariants

1. Keep precision-sensitive amounts as strings and compute with decimal.Decimal or DuckDB DECIMAL(38, 18), never binary floats.
2. Touch only requested rows, columns, formulas, and formatting. Existing file conventions override house defaults.
3. For newly authored text tables, prefer TSV, UTF-8 without BOM, LF, one trailing newline, lowercase snake_case headers, ISO dates, . decimals, and - nulls.
4. Read unknown text tables with BOM-tolerant UTF-8; never write a BOM.
5. Write in place atomically through a sibling temporary file, validate it, then replace the target.
6. Escape external cells beginning with =, +, or @; a bare - null is exempt. Formula-prefix cells in trusted authored data are observations, not proof of injection.
7. Keep transaction, bank, exchange, and tax data local. Redact samples unless raw rows were explicitly requested.

Factual Profiling