Mark fake activities, revert some error return types for safety

lib/pleroma/ecto_type/activity_pub/object_validators/object_id.ex

@@ -19,7 +19,7 @@ def cast(object) when is_binary(object) do
 
   def cast(%{"id" => object}), do: cast(object)
 
-  def cast(o), do: {:error, o}
+  def cast(_), do: :error
 
   def dump(data), do: {:ok, data}
 

lib/pleroma/object/fetcher.ex

@@ -215,7 +215,8 @@ defp prepare_activity_params(data) do
       "type" => "Create",
       # Should we seriously keep this attributedTo thing?
       "actor" => data["actor"] || data["attributedTo"],
-      "object" => data
+      "object" => data,
+      "_akkoma_fake" => true,
     }
     |> Maps.put_if_present("to", data["to"])
     |> Maps.put_if_present("cc", data["cc"])

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -637,10 +637,10 @@ defp handle_incoming_normalised(
     end
   end
 
-  defp handle_incoming_normalised(%{"object" => o}, options),
+  defp handle_incoming_normalised(%{"object" => o, "_akkoma_fake" => true}, options),
     do: handle_incoming_normalised(o, options)
 
-  defp handle_incoming_normalised(o, _), do: {:error, {:unknown_object_class, o}}
+  defp handle_incoming_normalised(o, _), do: :error
 
   @spec get_obj_helper(String.t(), Keyword.t()) :: {:ok, Object.t()} | nil
   def get_obj_helper(id, options \\ []) do