Native Excel period-binding verification — 2026-09-12

Result: 14 scenarios / 48 cell checks pass in desktop Excel 16.0, build 20326, using a new hidden COM instance with macros, events and link updates disabled. Existing user workbooks were not opened or modified.

The disposable workbooks came from the real toWorkbook implementation and the existing RFC 0041 conformance source, with explicit synthetic custom calculations. Expected numeric values came from evaluateCalc at each declaration's existing rounding boundary. Tests compare exact values; no new tolerance was introduced.

Coverage: all five period series, native sorting, numeric edits, real zero, blank period and scalar inputs, nonnumeric text, duplicate and changed keys, case-sensitive identity validation, explicit zero/null overrides, absolute monthly lookup, negative half-away rounding, a $100M fractional spread, and native save/reopen. #N/A and #VALUE! were checked as distinct deliberate error states. All seven additional worksheet views were exported through Excel and inspected.

Reproduce from Windows with desktop Excel, after npm run build:

node scripts/gen-excel-period-verification.mjs $env:TEMP/uwmd-period-verification
./scripts/verify-excel-periods.ps1 -Directory $env:TEMP/uwmd-period-verification

Use an empty disposable directory. The generator creates synthetic .xlsx files and a manifest. The verifier changes only those copies, writes verification.json, saves a recalculated copy and exports new sheets to PDF for visual review. It closes its own Excel instance in a finally block. It does not install software, alter dependencies, attach to an active workbook, or change user account settings.

The implementation uses the existing ExcelJS dependency because the subject of verification is this repository's converter. No alternate authoring library was used to replace or mask its generated workbook behavior.

Limitations: the tested engine/version is recorded above. Function compatibility does not constitute a test of every Excel release or third-party spreadsheet engine. Workbook identity guards support value edits and row permutations of the exported key set; structural edits and deliberate helper tampering are outside this first contract. Native tests are optional maintainer checks; CI covers deterministic source, schema, serialization and command behavior.