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

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

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)