- loadFromJSON and the localStorage startup load now run employees through
normalizeEmployees(): fills missing constraints, drops unusable rows,
de-duplicates ids, and discards invalid vacation ranges — preventing
later crashes (e.g. c.neverDays on undefined) and same-day double-books.
- Excel import is wrapped in try/catch with a typeof XLSX guard and user
feedback; the Excel export button gets the same guard.
- createEmployee reuses the shared defaultConstraints() factory.
Adds normalizeEmployees tests (defaults, dropping, dedup, vacations) and a
loadFromJSON normalization test.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
ferdi2goandClaude Opus 4.8
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