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>

lib/events/calendar.sx

@@ -503,17 +503,69 @@
                (append base rdate-occs))))
           (ev-dedupe-by-start (ev-sort-occs no-ex)))))))
 
+;; ---- per-occurrence overrides (RFC 5545 RECURRENCE-ID) ----
+;; A single instance of a recurring series can be detached and rescheduled. The
+;; event carries :overrides — a list of (orig-start {:start :duration}) — keyed
+;; by the occurrence's ORIGINAL start. Applied after EXDATE/RDATE. A moved
+;; instance whose new start leaves the window is dropped from this window (the
+;; original slot is vacated); an instance moved INTO the window from outside is
+;; out of scope for a windowed expansion (known stub limitation).
+
+(define
+  ev-assoc-lookup
+  (fn
+    (k pairs)
+    (cond
+      ((empty? pairs) nil)
+      ((= (first (first pairs)) k) (first (rest (first pairs))))
+      (else (ev-assoc-lookup k (rest pairs))))))
+
+(define
+  ev-apply-overrides
+  (fn
+    (id base overrides)
+    (map
+      (fn
+        (o)
+        (let
+          ((ov (ev-assoc-lookup (get o :start) overrides)))
+          (if (nil? ov) o (ev-occ id (get ov :start) (get ov :duration)))))
+      base)))
+
+;; Add an override that reschedules the occurrence originally at `orig-start`
+;; to `new-start` with `new-duration`.
+(define
+  ev-with-override
+  (fn
+    (event orig-start new-start new-duration)
+    (assoc
+      event
+      :overrides
+      (cons
+        (list orig-start {:start new-start :duration new-duration})
+        (ev-or (get event :overrides) (list))))))
+
 ;; Expand an event into occurrence dicts within the window, applying any
-;; EXDATE/RDATE exceptions. This is the public entry point.
+;; EXDATE/RDATE exceptions and per-occurrence overrides. 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)))
+    (let
+      ((excepted
+         (ev-apply-exceptions
+           event
+           (ev-expand-base event win-start win-end)
+           win-start
+           win-end))
+        (overrides (ev-or (get event :overrides) (list)))
+        (id (get event :id)))
+      (if
+        (empty? overrides)
+        excepted
+        (filter
+          (fn (o) (and (>= (get o :start) win-start) (<= (get o :start) win-end)))
+          (ev-sort-occs (ev-apply-overrides id excepted overrides)))))))
 
 ;; ---- multi-event expansion (sorted by start) ----
 

lib/events/scoreboard.json

@@ -1,10 +1,10 @@
 {
   "lang": "events",
-  "total_passed": 248,
+  "total_passed": 254,
   "total_failed": 0,
-  "total": 248,
+  "total": 254,
   "suites": [
-    {"name":"calendar","passed":45,"failed":0,"total":45},
+    {"name":"calendar","passed":51,"failed":0,"total":51},
     {"name":"availability","passed":22,"failed":0,"total":22},
     {"name":"api","passed":24,"failed":0,"total":24},
     {"name":"booking","passed":82,"failed":0,"total":82},
@@ -13,5 +13,5 @@
     {"name":"reminders","passed":14,"failed":0,"total":14},
     {"name":"federation","passed":23,"failed":0,"total":23}
   ],
-  "generated": "2026-06-07T06:25:58+00:00"
+  "generated": "2026-06-07T06:51:44+00:00"
 }

lib/events/scoreboard.md

@@ -1,10 +1,10 @@
 # events scoreboard
 
-**248 / 248 passing** (0 failure(s)).
+**254 / 254 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
-| calendar | 45 | 45 | ok |
+| calendar | 51 | 51 | ok |
 | availability | 22 | 22 | ok |
 | api | 24 | 24 | ok |
 | booking | 82 | 82 | ok |

lib/events/tests/calendar.sx

@@ -530,6 +530,54 @@
           (len (ev-expand plain (ev-date 2026 6 1) (ev-date 2026 7 1)))
           3)))))
 
+;; ---- per-occurrence overrides (reschedule one instance) ----
+(define
+  ev-cal-ov-run-all!
+  (fn
+    ()
+    (let
+      ((base (ev-event (quote standup) (ev-dt 2026 6 1 9 0) 30 {:freq :daily :count 4} 1)))
+      (do
+        ;; reschedule one instance to a new time + duration
+        (let
+          ((moved (ev-with-override base (ev-dt 2026 6 2 9 0) (ev-dt 2026 6 2 14 0) 45)))
+          (let
+            ((occs (ev-expand moved (ev-date 2026 6 1) (ev-date 2026 6 5))))
+            (do
+              (ev-cal-check!
+                "override moves only the targeted instance"
+                (map (fn (o) (ev-dt-tod (get o :start))) occs)
+                (list 540 840 540 540))
+              (ev-cal-check!
+                "override applies the new duration"
+                (map (fn (o) (- (get o :end) (get o :start))) occs)
+                (list 30 45 30 30))
+              (ev-cal-check!
+                "override keeps the series length"
+                (len occs)
+                4))))
+        ;; an instance moved out of the window vacates its slot
+        (let
+          ((movedout (ev-with-override base (ev-dt 2026 6 2 9 0) (ev-dt 2026 6 20 9 0) 30)))
+          (ev-cal-check!
+            "instance moved out of window is dropped, slot vacated"
+            (ev-cal-starts (ev-expand movedout (ev-date 2026 6 1) (ev-date 2026 6 5)))
+            (list (list 2026 6 1) (list 2026 6 3) (list 2026 6 4))))
+        ;; override for a non-existent original start is a no-op
+        (let
+          ((noop (ev-with-override base (ev-dt 2026 6 9 9 0) (ev-dt 2026 6 9 14 0) 45)))
+          (ev-cal-check!
+            "override for a non-occurring start is a no-op"
+            (len (ev-expand noop (ev-date 2026 6 1) (ev-date 2026 6 5)))
+            4))
+        ;; overrides re-sort the agenda when an instance moves earlier
+        (let
+          ((early (ev-with-override base (ev-dt 2026 6 3 9 0) (ev-dt 2026 6 1 7 0) 30)))
+          (ev-cal-check!
+            "an instance moved earlier re-sorts into place"
+            (map (fn (o) (ev-dt-tod (get o :start))) (ev-expand early (ev-date 2026 6 1) (ev-date 2026 6 5)))
+            (list 420 540 540 540)))))))
+
 (define
   ev-calendar-tests-run!
   (fn
@@ -540,4 +588,5 @@
       (set! ev-cal-failures (list))
       (ev-cal-run-all!)
       (ev-cal-ex-run-all!)
+      (ev-cal-ov-run-all!)
       {:failures ev-cal-failures :total (+ ev-cal-pass ev-cal-fail) :passed ev-cal-pass :failed ev-cal-fail})))

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