XLSX checks in GitHub Actions

The repo includes .github/actions/runstamp-check. It runs runstamp check xlsx, writes the verified output and emits a JSON report with no workbook bytes.

- uses: ./.github/actions/runstamp-check
  with:
    input-file: test/fixtures/customer.xlsx
    writes-file: test/fixtures/customer.writes.json
    output-file: artifacts/customer.checked.xlsx
    report-file: artifacts/runstamp-report.json
    baseline-file: test/fixtures/customer.baseline.json
    runstamp-version: 2.0.4
    mode: report

Roll it out in stages:

1. Use mode: report and inspect failures.
2. Create a baseline with update-baseline: true in a reviewed change.
3. Switch to mode: block once the workbook, write plan and expected evidence are accepted.
4. Add managed history only as a separate opt-in step. The local action uploads no documents or reports to Runstamp.

Pin an exact CLI version. Never update baselines automatically in an ordinary pull request.