refactor: apply review changes to joinrequest

lib/membership/join_request.ex

@@ -80,6 +80,7 @@ defmodule Mv.Membership.JoinRequest do
     validate present(:email), on: [:create]
   end
 
+  # Attributes are backend-internal for now; set public? true when exposing via AshJsonApi/AshGraphql
   attributes do
     uuid_primary_key :id
 
@@ -130,4 +131,17 @@ defmodule Mv.Membership.JoinRequest do
     create_timestamp :inserted_at
     update_timestamp :updated_at
   end
+
+  # Public helpers (used by SetConfirmationToken change and domain confirm_join_request)
+
+  @doc """
+  Returns the SHA256 hash of the confirmation token (lowercase hex).
+
+  Used when creating a join request (submit) and when confirming by token.
+  Only one implementation ensures algorithm changes stay in sync.
+  """
+  @spec hash_confirmation_token(String.t()) :: String.t()
+  def hash_confirmation_token(token) when is_binary(token) do
+    :crypto.hash(:sha256, token) |> Base.encode16(case: :lower)
+  end
 end