events: reschedule notifications + 7 tests

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>

plans/events-on-sx.md

@@ -18,7 +18,7 @@ capacity rules, transactional booking, and a flow-driven notification dispatcher
 
 ## Status (rolling)
 
-`bash lib/events/conformance.sh` → **265/265** (Phases 1-4 + ext: fed free/busy, waitlist, EXDATE/RDATE, overrides, booking-notify)
+`bash lib/events/conformance.sh` → **272/272** (Phases 1-4 + 6 ext: fed f/b, waitlist, EXDATE/RDATE, overrides, booking-notify, reschedule-notify)
 
 ## Ground rules
 
@@ -86,6 +86,13 @@ lib/events/api.sx ── (events/schedule) (events/book) (events/agenda) ──
 
 ## Progress log
 
+- 2026-06-07 — Reschedule notifications (extension). When an event carries
+  per-occurrence overrides, `ev/reschedule-notifications` reads the roster at
+  each overridden occurrence's ORIGINAL occ-key and produces a reschedule
+  message per booked attendee (old-start, new-start, new-duration). Idempotency
+  key = original-key/reschedule/new-start. `ev/reschedule-notify->msg` for the
+  notify wire shape. Combines overrides (calendar) + rosters (booking) + the
+  message-derivation pattern. +7 tests, 272/272 green.
 - 2026-06-07 — Booking lifecycle notifications (extension). `booking-notify.sx`
   walks the booking stream into ordered notifications classified by kind:
   :booked / :promoted / :held / :confirmed / :released / :cancelled /