events: federated free/busy across trusted peers + 10 tests

Peers publish busy intervals per actor (iCal free/busy model — privacy-
preserving, not event details). ev/peer-with-busy, ev/peer-busy;
ev/federated-busy unions local availability-db busy + trusted peers' published
busy (sorted); ev/federated-free? answers cross-instance availability,
half-open, trust-gated (untrusted peers ignored). 219/219 green.

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

lib/events/federation.sx

@@ -9,10 +9,20 @@
 ;; This is the trust-gated stub: peers publish plain schedules and we fold the
 ;; trusted ones into a single sorted agenda. Real transport (fed-sx / signed
 ;; fetch) slots in behind `ev/peer-agenda` without changing the merge.
+;;
+;; Federated FREE/BUSY follows the iCal model: a peer publishes BUSY intervals
+;; for an actor (not event details — privacy-preserving), and we union local +
+;; trusted-peer busy to answer "is this actor free?" across instances.
+
+(define ev/peer (fn (id store) {:id id :busy (list) :store store}))
+
+;; A peer that also publishes free/busy: `busy` is a list of
+;; (actor ((start end) ...)) pairs.
+(define ev/peer-with-busy (fn (id store busy) {:id id :busy busy :store store}))
 
-(define ev/peer (fn (id store) {:id id :store store}))
 (define ev/peer-id (fn (p) (get p :id)))
 (define ev/peer-store (fn (p) (get p :store)))
+(define ev/peer-busy-table (fn (p) (get p :busy)))
 
 (define
   ev-fed-member?
@@ -96,3 +106,60 @@
   (fn
     (agenda origin)
     (filter (fn (o) (= (get o :origin) origin)) agenda)))
+
+;; ---- federated free/busy ----
+
+;; A peer's published busy intervals for `actor` ((start end) ...), or empty.
+(define
+  ev/peer-busy
+  (fn
+    (peer actor)
+    (let
+      ((row (ev-fed-assoc actor (ev/peer-busy-table peer))))
+      (if (nil? row) (list) (first (rest row))))))
+
+(define
+  ev-fed-assoc
+  (fn
+    (k pairs)
+    (cond
+      ((empty? pairs) nil)
+      ((= (first (first pairs)) k) (first pairs))
+      (else (ev-fed-assoc k (rest pairs))))))
+
+;; All busy intervals for `actor` across the LOCAL availability db plus every
+;; TRUSTED peer's published free/busy, merged and sorted by start.
+;; `local-db` is an availability db (see availability.sx ev-build-avail).
+(define
+  ev/federated-busy
+  (fn
+    (local-db peers trust actor)
+    (let
+      ((acc (list)))
+      (begin
+        (for-each (fn (iv) (append! acc iv)) (ev-busy local-db actor))
+        (for-each
+          (fn
+            (peer)
+            (when
+              (ev/trusts? trust (ev/peer-id peer))
+              (for-each
+                (fn (iv) (append! acc iv))
+                (ev/peer-busy peer actor))))
+          peers)
+        (ev-sort-lists acc)))))
+
+;; Half-open overlap of interval (s e) with window [qs, qe).
+(define
+  ev-fed-overlaps?
+  (fn (iv qs qe) (and (< (first iv) qe) (< qs (first (rest iv))))))
+
+;; Is `actor` free across [qs, qe) considering local + trusted-peer busy?
+(define
+  ev/federated-free?
+  (fn
+    (local-db peers trust actor qs qe)
+    (not
+      (some
+        (fn (iv) (ev-fed-overlaps? iv qs qe))
+        (ev/federated-busy local-db peers trust actor)))))

lib/events/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "events",
-  "total_passed": 209,
+  "total_passed": 219,
   "total_failed": 0,
-  "total": 209,
+  "total": 219,
   "suites": [
     {"name":"calendar","passed":37,"failed":0,"total":37},
     {"name":"availability","passed":22,"failed":0,"total":22},
@@ -11,7 +11,7 @@
     {"name":"ticket","passed":31,"failed":0,"total":31},
     {"name":"notify","passed":7,"failed":0,"total":7},
     {"name":"reminders","passed":14,"failed":0,"total":14},
-    {"name":"federation","passed":13,"failed":0,"total":13}
+    {"name":"federation","passed":23,"failed":0,"total":23}
   ],
-  "generated": "2026-06-07T04:58:42+00:00"
+  "generated": "2026-06-07T05:31:56+00:00"
 }

lib/events/scoreboard.md

@@ -1,6 +1,6 @@
 # events scoreboard
 
-**209 / 209 passing** (0 failure(s)).
+**219 / 219 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -11,4 +11,4 @@
 | ticket | 31 | 31 | ok |
 | notify | 7 | 7 | ok |
 | reminders | 14 | 14 | ok |
-| federation | 13 | 13 | ok |
+| federation | 23 | 23 | ok |

lib/events/tests/federation.sx

@@ -143,6 +143,81 @@
                 (map (fn (o) (get o :origin)) pa)
                 (list (quote tokyo) (quote tokyo) (quote tokyo))))))))))
 
+;; ---- federated free/busy ----
+(define
+  ev-fd-fb-run-all!
+  (fn
+    ()
+    (let
+      ((local-db
+         (ev-avail-db
+           (list (ev-occ (quote yoga) (ev-dt 2026 6 1 9 0) 60))
+           (list (list (quote nia) (str (quote yoga) "@" (ev-dt 2026 6 1 9 0))))))
+        (berlin
+          (ev/peer-with-busy
+            (quote berlin)
+            (ev/empty)
+            (list
+              (list (quote nia)
+                (list (list (ev-dt 2026 6 1 14 0) (ev-dt 2026 6 1 15 0)))))))
+        (paris
+          (ev/peer-with-busy
+            (quote paris)
+            (ev/empty)
+            (list
+              (list (quote nia)
+                (list (list (ev-dt 2026 6 1 11 0) (ev-dt 2026 6 1 12 0))))))))
+      (let
+        ((peers (list berlin paris)))
+        (do
+          ;; peer-busy reads a peer's published intervals
+          (ev-fd-check!
+            "peer-busy returns published intervals for an actor"
+            (ev/peer-busy berlin (quote nia))
+            (list (list (ev-dt 2026 6 1 14 0) (ev-dt 2026 6 1 15 0))))
+          (ev-fd-check!
+            "peer-busy empty for an actor with nothing published"
+            (ev/peer-busy berlin (quote zed))
+            (list))
+          ;; federated-busy unions local + trusted-peer busy, sorted
+          (ev-fd-check!
+            "federated-busy unions local + trusted peer, sorted"
+            (ev/federated-busy local-db (list berlin) (list (quote berlin)) (quote nia))
+            (list
+              (list (ev-dt 2026 6 1 9 0) (ev-dt 2026 6 1 10 0))
+              (list (ev-dt 2026 6 1 14 0) (ev-dt 2026 6 1 15 0))))
+          (ev-fd-check!
+            "untrusted peer busy is excluded from federated-busy"
+            (ev/federated-busy local-db peers (list (quote berlin)) (quote nia))
+            (list
+              (list (ev-dt 2026 6 1 9 0) (ev-dt 2026 6 1 10 0))
+              (list (ev-dt 2026 6 1 14 0) (ev-dt 2026 6 1 15 0))))
+          ;; federated-free? considers both local and trusted-peer commitments
+          (ev-fd-check!
+            "free locally and on peers in an open window"
+            (ev/federated-free? local-db peers (list (quote berlin)) (quote nia) (ev-dt 2026 6 1 16 0) (ev-dt 2026 6 1 17 0))
+            true)
+          (ev-fd-check!
+            "not free during a LOCAL booking"
+            (ev/federated-free? local-db peers (list (quote berlin)) (quote nia) (ev-dt 2026 6 1 9 30) (ev-dt 2026 6 1 9 45))
+            false)
+          (ev-fd-check!
+            "not free during a TRUSTED PEER busy interval"
+            (ev/federated-free? local-db peers (list (quote berlin)) (quote nia) (ev-dt 2026 6 1 14 30) (ev-dt 2026 6 1 14 45))
+            false)
+          (ev-fd-check!
+            "free during an UNTRUSTED peer's busy interval (paris not trusted)"
+            (ev/federated-free? local-db peers (list (quote berlin)) (quote nia) (ev-dt 2026 6 1 11 15) (ev-dt 2026 6 1 11 45))
+            true)
+          (ev-fd-check!
+            "not free once paris is trusted too"
+            (ev/federated-free? local-db peers (list (quote berlin) (quote paris)) (quote nia) (ev-dt 2026 6 1 11 15) (ev-dt 2026 6 1 11 45))
+            false)
+          (ev-fd-check!
+            "federated-free? half-open at a busy edge"
+            (ev/federated-free? local-db peers (list (quote berlin)) (quote nia) (ev-dt 2026 6 1 15 0) (ev-dt 2026 6 1 16 0))
+            true))))))
+
 (define
   ev-federation-tests-run!
   (fn
@@ -152,4 +227,5 @@
       (set! ev-fd-fail 0)
       (set! ev-fd-failures (list))
       (ev-fd-run-all!)
+      (ev-fd-fb-run-all!)
       {:failures ev-fd-failures :total (+ ev-fd-pass ev-fd-fail) :passed ev-fd-pass :failed ev-fd-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` → **209/209** (Phases 1-4 complete: calendar, booking, notify, federation)
+`bash lib/events/conformance.sh` → **219/219** (Phases 1-4 + ext: federated free/busy)
 
 ## Ground rules
 
@@ -81,11 +81,18 @@ lib/events/api.sx ── (events/schedule) (events/book) (events/agenda) ──
 ## Phase 4 — Federation
 - [x] cross-instance events (peer calendar) — trust-gated stub
 - [x] tests: federated agenda merge
-- [ ] federated availability/free-busy across trusted peers
+- [x] federated availability/free-busy across trusted peers
 - [ ] real transport behind `ev/peer-agenda` (fed-sx / signed fetch)
 
 ## Progress log
 
+- 2026-06-07 — Federated free/busy (extension). Peers publish BUSY intervals
+  per actor (iCal free/busy model — privacy-preserving, not event details).
+  `ev/peer-with-busy`, `ev/peer-busy`; `ev/federated-busy` unions local
+  availability-db busy + trusted peers' published busy (sorted);
+  `ev/federated-free?` answers "is X free in [qs,qe)?" across instances,
+  half-open, trust-gated (untrusted peers' busy ignored; revocation immediate).
+  +10 tests, 219/219 green.
 - 2026-06-07 — **Phase 4: federation (trust-gated stub).** `federation.sx`:
   a peer publishes a schedule (events store); `ev/federated-agenda` merges the
   local agenda (origin :local) with every TRUSTED peer's agenda, sorted by