- New src/lib/person-validation.ts exports validatePersonFields (pure function) - 8 unit tests covering: valid PERSON, lastName missing/undefined, firstName missing/undefined for PERSON, non-PERSON types without firstName - Both edit and new-person server actions now call the shared helper instead of inline if-chains, making the logic testable and non-duplicated Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>