ev/reschedule-notifications: when an event carries per-occurrence overrides,
reads the roster at each overridden occurrence's original occ-key and emits a
reschedule message per booked attendee (old-start/new-start/new-duration).
Idempotency key = original-key/reschedule/new-start. 272/272 green.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>