events: iCalendar (RFC 5545) export + 21 tests

ical.sx serializes events to VEVENT/VCALENDAR text for import by standard
clients: UTC basic-format stamps, DURATION (PT#H#M), full RRULE
(FREQ/INTERVAL/COUNT/UNTIL/BYDAY incl. monthly ordinals 2TU/-1FR/BYMONTHDAY)
plus EXDATE/RDATE. Line-oriented (ev/event->ical-lines / ev/events->ical-lines)
with ev/ical-render joining CRLF for the wire format. 332/332 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` → **311/311** (Phases 1-4 + 10 ext: …timezones+DST, e2e delivery pipeline, cross-event conflict-checked booking)
+`bash lib/events/conformance.sh` → **332/332** (Phases 1-4 + 11 ext: …e2e delivery, conflict-checked booking, iCalendar export)
 
 ## Ground rules
 
@@ -88,6 +88,13 @@ lib/events/api.sx ── (events/schedule) (events/book) (events/agenda) ──
 
 ## Progress log
 
+- 2026-06-07 — iCalendar (RFC 5545) export (extension). `ical.sx` serializes
+  events to VEVENT / VCALENDAR text for import by standard clients. UTC
+  basic-format stamps (YYYYMMDDTHHMM00Z), DURATION (PT#H#M), and the full RRULE
+  model (FREQ/INTERVAL/COUNT/UNTIL/BYDAY incl. monthly ordinals "2TU"/"-1FR"/
+  BYMONTHDAY) plus EXDATE/RDATE. Line-oriented: `ev/event->ical-lines` /
+  `ev/events->ical-lines` return content lines; `ev/ical-render` joins with
+  CRLF (wire format). +21 tests, 332/332 green.
 - 2026-06-07 — Cross-event conflict-checked booking (extension). Capacity is
   per-event, but `ev/book-checked!` also prevents an attendee double-booking
   THEMSELVES across different events: it consults the actor's persist-derived