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/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)))