events: whole-series booking + 9 tests

ev/book-series! / ev/cancel-series! apply a booking/cancel to every occurrence
of one event in a window (RSVP the whole weekly class), returning per-
occurrence (occ-key status) results; capacity still enforced per occurrence
(some :booked, some :full), idempotent re-book (:already). ev/series-count,
ev/series-booked. 341/341 green.

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

lib/events/api.sx

@@ -275,3 +275,55 @@
       ((ev/would-time-conflict? b store actor occ)
         {:status :time-conflict :actor actor :occ-key (ev-occ-key occ)})
       (else (ev/book-occ! b store actor occ)))))
+
+;; ---- whole-series operations ----
+;; Apply a booking action to every occurrence of one event in [ws, we) — e.g.
+;; "RSVP to the whole weekly class". Returns a list of (occ-key status) results,
+;; one per occurrence (empty if the event id is unknown).
+(define
+  ev/book-series!
+  (fn
+    (b store actor event-id ws we)
+    (let
+      ((ev (ev/event-by-id store event-id)))
+      (if
+        (nil? ev)
+        (list)
+        (map
+          (fn (occ) (list (ev-occ-key occ) (get (ev/book-occ! b store actor occ) :status)))
+          (ev-expand ev ws we))))))
+
+;; Cancel `actor` from every occurrence of one event in [ws, we).
+(define
+  ev/cancel-series!
+  (fn
+    (b store actor event-id ws we)
+    (let
+      ((ev (ev/event-by-id store event-id)))
+      (if
+        (nil? ev)
+        (list)
+        (map
+          (fn (occ) (list (ev-occ-key occ) (get (ev/cancel! b (ev-occ-key occ) actor) :status)))
+          (ev-expand ev ws we))))))
+
+;; How many statuses in a series-result list equal `status`.
+(define
+  ev/series-count
+  (fn
+    (results status)
+    (len (filter (fn (r) (= (first (rest r)) status)) results))))
+
+;; The occurrences of one event in [ws, we) that `actor` is booked into.
+(define
+  ev/series-booked
+  (fn
+    (b store actor event-id ws we)
+    (let
+      ((ev (ev/event-by-id store event-id)))
+      (if
+        (nil? ev)
+        (list)
+        (filter
+          (fn (occ) (ev-actor-booked? b (ev-occ-key occ) actor))
+          (ev-expand ev ws we))))))