feed: verb-aware smart dedupe — reactions collapse cross-actor, posts stay per-actor + 9 tests

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

lib/feed/dedupe.sx

@@ -46,11 +46,31 @@
       ((a (get ev :activity)))
       (list (get ev :to) (get a :actor) (get a :verb) (get a :object)))))
 
+; verbs whose duplicates collapse across actors (reactions, not authorship).
+; rebindable: callers can (set! feed/collapse-verbs ...) to tune the policy.
+(define
+  feed/collapse-verbs
+  (list "like" "favourite" "follow" "boost" "repost"))
+
+; per-verb key: collapse-verbs fold on (verb object); the rest key on
+; (actor verb object).
+(define
+  feed/smart-key
+  (fn
+    (a)
+    (if
+      (feed/-elem? (get a :verb) feed/collapse-verbs)
+      (feed/collapse-key a)
+      (feed/activity-key a))))
+
 ; --- ready-made dedupers ----------------------------------------------------
 
 (define feed/dedupe-activities (fn (s) (feed/dedupe s feed/activity-key)))
 
 (define feed/dedupe-collapse (fn (s) (feed/dedupe s feed/collapse-key)))
 
+; verb-aware: reactions collapse cross-actor, posts stay distinct per actor
+(define feed/dedupe-smart (fn (s) (feed/dedupe s feed/smart-key)))
+
 ; dedupe an inbox: at most one event per receiver per (actor verb object)
 (define feed/dedupe-inbox (fn (inbox) (feed/dedupe inbox feed/event-key)))