feed: trending objects/actors by recent activity window, deterministic tiebreak + 11 tests

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

lib/feed/conformance.sh

@@ -13,7 +13,7 @@ if [ ! -x "$SX_SERVER" ]; then
   exit 1
 fi
 
-SUITES=(basic fanout rank integration content notify home dedupe)
+SUITES=(basic fanout rank integration content notify home dedupe trending)
 
 OUT_JSON="lib/feed/scoreboard.json"
 OUT_MD="lib/feed/scoreboard.md"
@@ -40,6 +40,7 @@ run_suite() {
 (load "lib/feed/content.sx")
 (load "lib/feed/notify.sx")
 (load "lib/feed/home.sx")
+(load "lib/feed/trending.sx")
 (epoch 2)
 (eval "(define feed-test-pass 0)")
 (eval "(define feed-test-fail 0)")

lib/feed/scoreboard.json

@@ -7,9 +7,10 @@
     "content": {"pass": 15, "fail": 0},
     "notify": {"pass": 8, "fail": 0},
     "home": {"pass": 6, "fail": 0},
-    "dedupe": {"pass": 9, "fail": 0}
+    "dedupe": {"pass": 9, "fail": 0},
+    "trending": {"pass": 11, "fail": 0}
   },
-  "total_pass": 143,
+  "total_pass": 154,
   "total_fail": 0,
-  "total": 143
+  "total": 154
 }

lib/feed/scoreboard.md

@@ -12,4 +12,5 @@ _Generated by `lib/feed/conformance.sh`_
 | notify | 8 | 0 | 8 |
 | home | 6 | 0 | 6 |
 | dedupe | 9 | 0 | 9 |
-| **Total** | **143** | **0** | **143** |
+| trending | 11 | 0 | 11 |
+| **Total** | **154** | **0** | **154** |

lib/feed/tests/trending.sx

@@ -0,0 +1,82 @@
+; Follow-up — trending objects/actors by recent activity. (feed-test name got expected)
+
+; window (50,100]: X@60,X@70 (a), Y@80 (b), Z@90 (c); W@40 is too old
+(define
+  S
+  (feed/stream
+    (list
+      (feed/activity "a" "post" "X" 60 (list))
+      (feed/activity "a" "post" "X" 70 (list))
+      (feed/activity "b" "post" "Y" 80 (list))
+      (feed/activity "c" "post" "Z" 90 (list))
+      (feed/activity "d" "post" "W" 40 (list)))))
+
+; ---------- trending objects ----------
+
+(feed-test
+  "trending count (3 in window)"
+  (len (feed/trending S 100 50 10))
+  3)
+(feed-test
+  "trending top object"
+  (get
+    (nth (feed/trending S 100 50 10) 0)
+    :object)
+  "X")
+(feed-test
+  "trending top count"
+  (get
+    (nth (feed/trending S 100 50 10) 0)
+    :count)
+  2)
+(feed-test
+  "trending order (count desc, key asc tiebreak)"
+  (map
+    (fn (e) (get e :object))
+    (feed/trending S 100 50 10))
+  (list "X" "Y" "Z"))
+(feed-test
+  "trending top-2"
+  (map
+    (fn (e) (get e :object))
+    (feed/trending S 100 50 2))
+  (list "X" "Y"))
+(feed-test
+  "old object W excluded"
+  (feed/-elem?
+    "W"
+    (map
+      (fn (e) (get e :object))
+      (feed/trending S 100 50 10)))
+  false)
+(feed-test
+  "narrow window keeps only newest"
+  (map
+    (fn (e) (get e :object))
+    (feed/trending S 100 15 10))
+  (list "Z"))
+(feed-test
+  "empty window -> nothing"
+  (feed/trending S 100 5 10)
+  (list))
+
+; ---------- trending actors ----------
+
+(feed-test
+  "trending actor top"
+  (get
+    (nth (feed/trending-actors S 100 50 10) 0)
+    :actor)
+  "a")
+(feed-test
+  "trending actor count"
+  (get
+    (nth (feed/trending-actors S 100 50 10) 0)
+    :count)
+  2)
+(feed-test
+  "trending actors order"
+  (map
+    (fn (e) (get e :actor))
+    (feed/trending-actors S 100 50 10))
+  (list "a" "b" "c"))

lib/feed/trending.sx

@@ -0,0 +1,42 @@
+; feed/trending — what's hot right now: objects (or actors) ranked by activity
+; count within a recency window. Deterministic: count descending, ties broken by
+; key ascending (entries are pre-sorted by key, then stable grade-down by count).
+;
+; Requires: lib/feed/stream.sx, lib/feed/aggregate.sx (object/actor-counts),
+; lib/feed/rank.sx (feed/-desc-by).
+
+; activities within (now-window, now]
+(define
+  feed/-recent
+  (fn
+    (stream now window)
+    (feed/filter
+      stream
+      (fn (a) (and (<= (get a :at) now) (> (get a :at) (- now window)))))))
+
+; counts dict -> top-N entries {label key, :count n}, count desc, key asc
+(define
+  feed/-top-counts
+  (fn
+    (counts label n)
+    (let
+      ((entries (map (fn (k) (assoc {:count (get counts k)} label k)) (sort (keys counts)))))
+      (take (feed/-desc-by entries (fn (e) (get e :count))) n))))
+
+; top-N trending objects in the window
+(define
+  feed/trending
+  (fn
+    (stream now window n)
+    (feed/-top-counts
+      (feed/object-counts (feed/-recent stream now window))
+      :object n)))
+
+; top-N most active actors in the window
+(define
+  feed/trending-actors
+  (fn
+    (stream now window n)
+    (feed/-top-counts
+      (feed/actor-counts (feed/-recent stream now window))
+      :actor n)))

plans/feed-on-sx.md

@@ -14,7 +14,7 @@ APL, ACL visibility filtering via `lib/acl/`, federation via fed-sx.
 
 ## Status (rolling)
 
-`bash lib/feed/conformance.sh` → **143/143** (Phases 1–4 + TF-IDF + notifications + home + smart-dedupe)
+`bash lib/feed/conformance.sh` → **154/154** (Phases 1–4 + TF-IDF + notifications + home + smart-dedupe + trending)
 
 ## Ground rules
 
@@ -151,6 +151,9 @@ are function parameters. Real acl-sx / fed-sx wire in at the call site unchanged
   `feed/smart-key`: reactions (like/follow/boost/...) collapse cross-actor on
   (verb,object); posts stay distinct per actor. `feed/collapse-verbs` is
   rebindable policy; 9 tests. (143/143 total.)
+- [x] Trending — `feed/trending` / `feed/trending-actors`: objects/actors ranked
+  by activity count in a recency window, count-desc with key-asc tiebreak
+  (`trending.sx`); 11 tests. (154/154 total.)
 
 (none)