Stop Hand-Coding Lunar Calendars: Why Rokuyo Conversion Silently Fails

As AI agents increasingly power date-dependent services in Japanese markets—from wedding planners to moving-day advisors—calendar accuracy has become mission-critical. Yet LLM-generated lunar conversion code silently produces wrong answers on specific dates without any errors, making these bugs virtually undetectable by standard testing. The solution is elegantly simple: use a dedicated calendar API instead of hand-coded logic, eliminating this entire class of errors with minimal code.