App Groups are per-device, so the watch cannot read the file the phone writes
and has to be handed the data. Three delivery paths: application context for
the latest state, a complication push only when the next appointment actually
changed (the budget is small), and a reply to the watch asking directly.
Sign-out pushes an empty signed-out snapshot. Clearing our own container is not
enough — the watch holds its own copy and would keep rendering the previous
user's calendar.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
