- Frontend sends user_timezone (IANA, from Intl.DateTimeFormat) with
every message POST; threaded through route → generation_task → build_context
- System prompt now tells the LLM the user's timezone so it creates
events with the correct UTC offset (e.g. 15:00+01:00 not 15:00Z)
- Calendar tool guidance updated to require UTC offset in all event
datetimes
- EventSlideOver: dateFromIso/timeFromIso now use JS Date to convert
stored UTC times to local time for display; toIso includes local
timezone offset when saving so the correct UTC time is stored
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>