UTC timestamps rendered with date-fns format() or toLocaleTimeString() use the
runtime's local timezone, causing the server (UTC) and client (PDT) to produce
different output. suppressHydrationWarning was hiding the mismatch but the
visual time-flip was still visible on load.
- Add useHasMounted hook (useSyncExternalStore-based, no extra render cycle)
- Gate UTC timestamp formatting behind isMounted in EventSchedule and
UpcomingCalendarPanel; SSR always renders the stable YYYY-MM-DD eventDate string
- Fix formatEventDate in date-utils.ts (and EventSchedule private copy) to parse
YYYY-MM-DD as local midnight instead of UTC midnight, fixing the off-by-one day
bug for UTC-negative users across all callers
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
8a9cffd076