Resolve local calendar intent
A local appointment combines a civil date/time and a named time zone, then resolves to an instant with an explicit daylight-saving policy. Some local times do not exist during a spring transition; others occur twice during an autumn transition. Require a defined choice rather than guessing. Calendar month arithmetic is anchored to the original date and follows explicit month-end rules; repeated addition of a month can otherwise drift.
Keep the entered zone and civil intent when users need to see or edit local appointments. Use the time builtins in types and builtins. Recurring schedule policy is authored business behavior, covered in scheduling.