fed-sx-m1: Step 4b-proj — 7 bootstrap projections + manifest update + 9 new parse tests (31 total)

next/genesis/projections/by-actor.sx

@@ -0,0 +1,15 @@
+;; next/genesis/projections/by-actor.sx
+;;
+;; Index of activity CIDs grouped by :actor. Maps actor-id to a
+;; list of CIDs in append order. Powers the per-actor outbox
+;; listing (Step 8) without re-scanning the full log.
+
+(DefineProjection
+  :name "by-actor"
+  :doc "Actor-id -> list of activity CIDs (append order)."
+  :initial-state {}
+  :fold (fn
+    (state act)
+    (let
+      ((a (-> act :actor)) (cid (-> act :cid)))
+      (assoc state a (append (or (get state a) (list)) (list cid))))))