fix: labels for custom fields in join requests

lib/mv_web/live/join_live.ex

@@ -216,19 +216,48 @@ defmodule MvWeb.JoinLive do
 
   defp build_join_fields_with_labels(allowlist) do
     member_field_strings = Mv.Constants.member_fields() |> Enum.map(&Atom.to_string/1)
+    custom_field_name_by_id = custom_field_name_map(allowlist, member_field_strings)
 
     Enum.map(allowlist, fn %{id: id, required: required} ->
       label =
         if id in member_field_strings do
           MemberFields.label(String.to_existing_atom(id))
         else
-          gettext("Field")
+          Map.get(custom_field_name_by_id, id, gettext("Field"))
         end
 
       %{id: id, label: label, required: required}
     end)
   end
 
+  defp custom_field_name_map(allowlist, member_field_strings) do
+    custom_field_ids =
+      allowlist
+      |> Enum.map(& &1.id)
+      |> Enum.reject(&(&1 in member_field_strings))
+
+    case custom_field_ids do
+      [] ->
+        %{}
+
+      ids ->
+        Mv.Membership.CustomField
+        |> Ash.Query.select([:id, :name])
+        |> Ash.read(domain: Mv.Membership, authorize?: false)
+        |> case do
+          {:ok, fields} ->
+            allowed_ids = MapSet.new(ids)
+
+            fields
+            |> Enum.filter(&MapSet.member?(allowed_ids, &1.id))
+            |> Map.new(&{&1.id, &1.name})
+
+          {:error, _} ->
+            %{}
+        end
+    end
+  end
+
   defp initial_form_params(join_fields) do
     join_fields
     |> Enum.map(fn f -> {f.id, ""} end)