events: provisional holds (hold/confirm/release) for paid tickets + 24 tests

Booking stream gains :hold/:confirm/:release; fold tracks per-actor seat state
(:held/:confirmed). A held seat counts toward capacity so a pending payment
can't be oversold. ev/hold! (capacity-safe), ev/confirm!, ev/release!,
ev/seat-state. Holds race test mirrors the booking race. 144/144 green.

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

lib/events/tests/booking.sx

@@ -1,4 +1,4 @@
-;; lib/events/tests/booking.sx — capacity-safe transactional booking + cancel.
+;; lib/events/tests/booking.sx — capacity-safe booking, cancel, and holds.
 
 (define ev-bk-pass 0)
 (define ev-bk-fail 0)
@@ -48,7 +48,11 @@
           (ev-bk-check!
             "seats-left is zero when full"
             (ev/seats-left b "o1" 3)
-            0)))
+            0)
+          (ev-bk-check!
+            "free booking is confirmed state"
+            (ev/seat-state b "o1" (quote a))
+            :confirmed)))
       (let
         ((b (persist/open)))
         (do
@@ -228,7 +232,132 @@
           (ev-bk-check!
             "re-booked actor back on roster"
             (ev/roster b "ce")
-            (list (quote a))))))))
+            (list (quote a)))))
+      (let
+        ((b (persist/open)))
+        (do
+          (ev/book! b "h" 2 (quote a))
+          (ev-bk-check!
+            "hold reports held"
+            (get (ev/hold! b "h" 2 (quote p)) :status)
+            :held)
+          (ev-bk-check!
+            "held seat is :held state"
+            (ev/seat-state b "h" (quote p))
+            :held)
+          (ev-bk-check!
+            "held actor is on the roster"
+            (ev/roster b "h")
+            (list (quote a) (quote p)))
+          (ev-bk-check!
+            "held seat blocks the last booking"
+            (get (ev/book! b "h" 2 (quote x)) :status)
+            :full)
+          (ev-bk-check!
+            "no seats left with one held"
+            (ev/seats-left b "h" 2)
+            0)))
+      (let
+        ((b (persist/open)))
+        (do
+          (ev/hold! b "hc" 3 (quote p))
+          (ev-bk-check!
+            "confirm reports confirmed"
+            (get (ev/confirm! b "hc" (quote p)) :status)
+            :confirmed)
+          (ev-bk-check!
+            "confirmed seat is :confirmed state"
+            (ev/seat-state b "hc" (quote p))
+            :confirmed)
+          (ev-bk-check!
+            "re-confirm is already-confirmed"
+            (get (ev/confirm! b "hc" (quote p)) :status)
+            :already-confirmed)
+          (ev-bk-check!
+            "confirming a non-holder is not-held"
+            (get (ev/confirm! b "hc" (quote z)) :status)
+            :not-held)
+          (ev-bk-check!
+            "confirmed seat still occupies"
+            (ev/seats-left b "hc" 3)
+            2)))
+      (let
+        ((b (persist/open)))
+        (do
+          (ev/book! b "hr" 2 (quote a))
+          (ev/hold! b "hr" 2 (quote p))
+          (ev-bk-check!
+            "full while hold pending"
+            (ev/seats-left b "hr" 2)
+            0)
+          (ev-bk-check!
+            "release reports released"
+            (get (ev/release! b "hr" (quote p)) :status)
+            :released)
+          (ev-bk-check!
+            "release frees the held seat"
+            (ev/seats-left b "hr" 2)
+            1)
+          (ev-bk-check!
+            "released actor off the roster"
+            (ev/roster b "hr")
+            (list (quote a)))
+          (ev-bk-check!
+            "freed seat bookable after release"
+            (get (ev/book! b "hr" 2 (quote x)) :status)
+            :booked)
+          (ev/hold! b "hr2" 1 (quote q))
+          (ev/confirm! b "hr2" (quote q))
+          (ev-bk-check!
+            "release on a confirmed seat is not-held"
+            (get (ev/release! b "hr2" (quote q)) :status)
+            :not-held)
+          (ev-bk-check!
+            "cancel frees a confirmed-from-hold seat"
+            (get (ev/cancel! b "hr2" (quote q)) :status)
+            :cancelled)))
+      (let
+        ((b (persist/open)))
+        (do
+          (ev/book! b "hlast" 2 (quote x))
+          (let
+            ((snap (ev-bk-snap b "hlast")) (exp (ev-bk-seq b "hlast")))
+            (let
+              ((ra (ev/hold-with-observed b "hlast" 2 (quote p) snap exp))
+                (rb
+                  (ev/hold-with-observed
+                    b
+                    "hlast"
+                    2
+                    (quote q)
+                    snap
+                    exp)))
+              (do
+                (ev-bk-check! "hold race winner held" (get ra :status) :held)
+                (ev-bk-check!
+                  "hold race loser conflicts"
+                  (get rb :status)
+                  :conflict)
+                (ev-bk-check!
+                  "no oversell via concurrent holds"
+                  (ev-booking-count b "hlast")
+                  2)
+                (ev-bk-check!
+                  "hold loser retry gets full"
+                  (get (ev/hold! b "hlast" 2 (quote q)) :status)
+                  :full))))))
+      (let
+        ((b (persist/open)))
+        (do
+          (ev/hold! b "hi" 4 (quote p))
+          (ev-bk-check!
+            "re-holding the same actor is idempotent"
+            (get (ev/hold! b "hi" 4 (quote p)) :status)
+            :already)
+          (ev-bk-check!
+            "hold idempotency keeps one seat"
+            (ev-booking-count b "hi")
+            1))))))
 
 (define
   ev-booking-tests-run!