Migration

From kit 0.12.0, @rdlabo/workers-hono-kit/business-time is a deprecated re-export of this
package. Install @rdlabo/workers-timezone directly and change the import path. Existing function
names remain available; new code can use toLocalDateTime, localDateTimeToInstant, and the other
timezone-neutral names in API.

Behavior changes

The default remains Asia/Tokyo, but compatibility is not identical output for every input:

• Conversion uses IANA historical offsets rather than fixed +09:00. Historical Tokyo dates can
  therefore produce different results.
• Invalid date-only values normalize to null; invalid date-time construction throws RangeError
  rather than rolling over into another month.
• DST overlaps choose the earlier occurrence; skipped wall clocks and fully skipped dates throw.

Treat these as breaking behavior changes when migrating from the old fixed-offset implementation.
Test historical dates and validation boundaries before deployment. The compatibility import shares
the same underlying module; it is not a separate timezone configuration slot.