events: per-occurrence overrides / reschedule (RECURRENCE-ID) + 6 tests

ev-with-override re-times/re-sizes a single instance of a series (keyed by
original start). ev-expand applies overrides after EXDATE/RDATE: agenda
re-sorts, instance moved out of window is dropped (slot vacated), no-op for a
non-occurring start. assoc for immutable event update. 254/254 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` → **248/248** (Phases 1-4 + ext: fed free/busy, waitlist, EXDATE/RDATE)
+`bash lib/events/conformance.sh` → **254/254** (Phases 1-4 + ext: fed free/busy, waitlist, EXDATE/RDATE, overrides)
 
 ## Ground rules
 
@@ -86,6 +86,13 @@ lib/events/api.sx ── (events/schedule) (events/book) (events/agenda) ──
 
 ## Progress log
 
+- 2026-06-07 — Per-occurrence overrides / reschedule (RFC 5545 RECURRENCE-ID).
+  `ev-with-override event orig-start new-start new-duration` adds an :overrides
+  entry keyed by the occurrence's original start. `ev-expand` applies overrides
+  after EXDATE/RDATE: a targeted instance is re-timed/re-sized and the agenda
+  re-sorted; an instance moved out of the window is dropped (slot vacated);
+  override of a non-occurring start is a no-op. Used `assoc` for immutable
+  event update. +6 tests, 254/254 green.
 - 2026-06-07 — RRULE exceptions EXDATE/RDATE (extension). `ev-event-full`
   carries :exdate/:rdate (epoch-minute starts). Raw expansion renamed
   `ev-expand-base`; `ev-expand` now applies exceptions: RDATE adds explicit