transmogrfier: be more selective about Delete retry

If something else renders the Delete invalid,
there’s no point in retrying anyway

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -560,8 +560,11 @@ defp handle_incoming_normalised(
            Pipeline.common_pipeline(data, local: false) do
       {:ok, activity}
     else
-      {:error, {:validate, _}} = e ->
+      {:error, {:validate, {:error, %Ecto.Changeset{errors: errors}}}} = e ->
+        if errors[:object] == {"can't find object", []} do
           # Check if we have a create activity for this
+          # (e.g. from a db prune without --prune-activities)
+          # We'd still like to process side effects so insert a tombstone and retry
           with {:ok, object_id} <- ObjectValidators.ObjectID.cast(data["object"]),
                %Activity{data: %{"actor" => actor}} <-
                  Activity.create_by_object_ap_id(object_id) |> Repo.one(),
@@ -572,6 +575,9 @@ defp handle_incoming_normalised(
           else
             _ -> e
           end
+        else
+          e
+        end
 
       {:error, _} = e ->
         e