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

next/genesis/projections/by-object.sx

@@ -0,0 +1,22 @@
+;; next/genesis/projections/by-object.sx
+;;
+;; Index of activities that reference each :object CID. Maps
+;; object-CID to the list of activity CIDs that target it
+;; (Update / Delete / Announce / etc.). Used for "show me
+;; everything that happened to X" queries.
+
+(DefineProjection
+  :name "by-object"
+  :doc "Object CID -> list of activity CIDs that target it."
+  :initial-state {}
+  :fold (fn
+    (state act)
+    (let
+      ((obj-cid (-> act :object)) (cid (-> act :cid)))
+      (if
+        (string? obj-cid)
+        (assoc
+          state
+          obj-cid
+          (append (or (get state obj-cid) (list)) (list cid)))
+        state))))