Revert "Optimize fixpoint batch handling with single BFS expansion"

This reverts commit 42d0efe.

Author: cristianoc

analysis/reactive/src/Reactive.ml

@@ -1081,42 +1081,25 @@ let fixpoint ~(init : ('k, unit) t) ~(edges : ('k, 'k list) t) () : ('k, unit) t
     my_stats.updates_received <- my_stats.updates_received + 1;
     match delta with
     | Batch entries ->
-      (* OPTIMIZED: Process all entries with single BFS instead of per-entry BFS *)
-      (* Phase 1: Separate adds and removes, collect new roots *)
-      let new_roots = ref [] in
-      let removes = ref [] in
+      (* Process all init entries as a batch *)
+      let all_added = ref [] in
+      let all_removed = ref [] in
       entries
       |> List.iter (fun (k, v_opt) ->
-             match v_opt with
-             | Some () ->
-               if not (Hashtbl.mem state.base k) then begin
-                 Hashtbl.replace state.base k ();
-                 new_roots := k :: !new_roots
-               end
-             | None -> removes := k :: !removes);
-
-      (* Phase 2: Single BFS expansion from all new roots *)
-      let added_from_expansion =
-        if !new_roots <> [] then Fixpoint.expand state ~frontier:!new_roots
-        else []
-      in
-
-      (* Phase 3: Handle removes (may trigger contraction) *)
-      let all_added = ref added_from_expansion in
-      let all_removed = ref [] in
-      !removes
-      |> List.iter (fun k ->
-             let added, removed =
-               Fixpoint.apply_init_delta state (Remove k)
+             let d =
+               match v_opt with
+               | Some () -> Set (k, ())
+               | None -> Remove k
              in
+             let added, removed = Fixpoint.apply_init_delta state d in
              all_added := added @ !all_added;
              all_removed := removed @ !all_removed);
-
       (* Deduplicate and emit as batch *)
       let added_set = Hashtbl.create (List.length !all_added) in
       List.iter (fun k -> Hashtbl.replace added_set k ()) !all_added;
       let removed_set = Hashtbl.create (List.length !all_removed) in
       List.iter (fun k -> Hashtbl.replace removed_set k ()) !all_removed;
+      (* Net changes: added if in added_set but not removed_set, etc. *)
       let net_added =
         Hashtbl.fold
           (fun k () acc -> if Hashtbl.mem removed_set k then acc else k :: acc)