events: RRULE EXDATE/RDATE exceptions + 8 tests

ev-event-full carries :exdate/:rdate. ev-expand-base = raw expansion;
ev-expand applies exceptions: RDATE adds in-window occurrences, EXDATE removes
matching starts, de-duped, EXDATE wins over RDATE and the rrule (RFC 5545).
RDATE-only events supported; plain ev-event unaffected. 248/248 green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/events/calendar.sx

@@ -140,6 +140,20 @@
 ;;   monthly :bymonthday -> (list 15 -1)       day of month (negative from end)
 (define ev-event (fn (id dtstart duration rrule capacity) {:duration duration :id id :dtstart dtstart :capacity capacity :rrule rrule}))
 
+;; Event with EXDATE/RDATE exceptions. exdate/rdate are lists of epoch-minute
+;; starts to exclude from / add to the expansion (RFC 5545 VEVENT properties).
+(define
+  ev-event-full
+  (fn
+    (id dtstart duration rrule capacity exdate rdate)
+    {:duration duration
+      :id id
+      :dtstart dtstart
+      :capacity capacity
+      :rrule rrule
+      :exdate exdate
+      :rdate rdate}))
+
 (define ev-occ (fn (id start dur) {:id id :start start :end (+ start dur)}))
 
 ;; ---- DAILY expansion ----
@@ -360,9 +374,10 @@
                   n2)))))))))
 
 ;; ---- top-level expansion ----
+;; Raw expansion (RRULE / single event), before EXDATE/RDATE are applied.
 ;; Returns a list of occurrence dicts {:id :start :end} within the window.
 (define
-  ev-expand
+  ev-expand-base
   (fn
     (event win-start win-end)
     (let
@@ -431,9 +446,75 @@
                     win-end
                     acc
                     0)))
-              (else (error (str "ev-expand: unsupported freq: " freq))))
+              (else (error (str "ev-expand-base: unsupported freq: " freq))))
             acc))))))
 
+;; ---- EXDATE / RDATE (RFC 5545 exceptions) ----
+;; Applied AFTER raw expansion: RDATE adds explicit occurrences within the
+;; window, EXDATE removes occurrences whose start matches (EXDATE wins over
+;; RDATE). Both are VEVENT-level: (get event :exdate) / (get event :rdate) are
+;; lists of epoch-minute starts; nil for plain events.
+
+(define
+  ev-num-member?
+  (fn
+    (n xs)
+    (cond
+      ((empty? xs) false)
+      ((= n (first xs)) true)
+      (else (ev-num-member? n (rest xs))))))
+
+;; Drop duplicate-start occurrences from a start-sorted list (keep one).
+(define
+  ev-dedupe-by-start
+  (fn
+    (occs)
+    (cond
+      ((empty? occs) occs)
+      ((empty? (rest occs)) occs)
+      ((= (get (first occs) :start) (get (first (rest occs)) :start))
+        (ev-dedupe-by-start (rest occs)))
+      (else (cons (first occs) (ev-dedupe-by-start (rest occs)))))))
+
+(define
+  ev-apply-exceptions
+  (fn
+    (event base win-start win-end)
+    (let
+      ((id (get event :id))
+        (duration (get event :duration))
+        (exdate (ev-or (get event :exdate) (list)))
+        (rdate (ev-or (get event :rdate) (list))))
+      (let
+        ((rdate-occs
+           (reduce
+             (fn
+               (acc d)
+               (if
+                 (and (>= d win-start) (<= d win-end))
+                 (cons (ev-occ id d duration) acc)
+                 acc))
+             (list)
+             rdate)))
+        (let
+          ((no-ex
+             (filter
+               (fn (o) (not (ev-num-member? (get o :start) exdate)))
+               (append base rdate-occs))))
+          (ev-dedupe-by-start (ev-sort-occs no-ex)))))))
+
+;; Expand an event into occurrence dicts within the window, applying any
+;; EXDATE/RDATE exceptions. This is the public entry point.
+(define
+  ev-expand
+  (fn
+    (event win-start win-end)
+    (ev-apply-exceptions
+      event
+      (ev-expand-base event win-start win-end)
+      win-start
+      win-end)))
+
 ;; ---- multi-event expansion (sorted by start) ----
 
 ;; Insertion of one occurrence into a start-ascending list.