inputs_for with union type not working with update action

server_ash.exs

Application.put_env(:sample, SamplePhoenix.Endpoint,
  http: [ip: {127, 0, 0, 1}, port: 5001],
  server: true,
  live_view: [signing_salt: "aaaaaaaa"],
  secret_key_base: String.duplicate("a", 64)
)

Mix.install([
  {:plug_cowboy, "~> 2.7"},
  {:jason, "~> 1.0"},
  {:phoenix, "1.7.12"},
  {:phoenix_live_view, "0.20.14"},
  {:ash, "2.21.12"},
  {:ash_phoenix, "1.3.4"}
])

defmodule SamplePhoenix.ErrorView do
  def render(template, _), do: Phoenix.Controller.status_message_from_template(template)
end

defmodule NormalContent do
  use Ash.Resource, data_layer: :embedded

  attributes do
    attribute :body, :string, allow_nil?: false
  end
end

defmodule Content do
  use Ash.Type.NewType,
    subtype_of: :union,
    constraints: [
      types: [
        normal: [
          type: NormalContent,
          tag: :type,
          tag_value: :normal
        ]
      ]
    ]
end

defmodule Post do
  use Ash.Resource, data_layer: Ash.DataLayer.Ets, api: Api

  attributes do
    uuid_primary_key :id
    attribute :title, :string, allow_nil?: false
    attribute :content, Content, allow_nil?: false
  end

  actions do
    defaults [:create, :update]
  end
end

defmodule Api do
  use Ash.Api

  resources do
    resource Post
  end
end

defmodule SamplePhoenix.SampleLive do
  use Phoenix.LiveView, layout: {__MODULE__, :live}

  def mount(_params, _session, socket) do
    mode = "update"

    form =
      case mode do
        "create" ->
          Post
          |> AshPhoenix.Form.for_create(:create, forms: [auto?: true])
          |> to_form()
          |> AshPhoenix.Form.add_form(:content, params: %{"type" => "normal"})

        "update" ->
          post =
            Post
            |> Ash.Changeset.new()
            |> Ash.Changeset.change_attributes(%{
              title: "title",
              content: %{"type" => "normal", "body" => "body"}
            })
            |> Api.create!()

          post
          |> AshPhoenix.Form.for_update(:update, forms: [auto?: true])
          |> to_form()
      end

    socket =
      socket
      |> assign(form: form)
      |> assign(result: nil)

    {:ok, socket}
  end

  # layout
  def render("live.html", assigns) do
    ~H"""
    <script src="https://cdn.jsdelivr.net/npm/[email protected]/priv/static/phoenix.min.js">
    </script>
    <script
      src="https://cdn.jsdelivr.net/npm/[email protected]/priv/static/phoenix_live_view.min.js"
    >
    </script>
    <script>
      let liveSocket = new window.LiveView.LiveSocket("/live", window.Phoenix.Socket)
      liveSocket.connect()
    </script>
    <style>
      * { font-size: 1.1em; }
    </style>
    <%= @inner_content %>
    """
  end

  # render
  def render(assigns) do
    ~H"""
    <.form id="form" for={@form} phx-change="validate" phx-submit="save">
      <div>
        <label for={@form[:title].name}>title</label>
        <input
          type="text"
          id={@form[:title].id}
          name={@form[:title].name}
          value={@form[:title].value}
        />
      </div>

      <.inputs_for :let={fc} field={@form[:content]}>
        <div>
          <label for={@form[:title].name}>body</label>
          <input type="hidden" id={fc[:type].id} name={fc[:type].name} value={:normal} />
          <input type="text" id={fc[:body].id} name={fc[:body].name} value={fc[:body].value} />
        </div>
      </.inputs_for>

      <button type="submit" disabled={[email protected]?}>Save</button>
    </.form>

    <div :if={@result}>
      <%= inspect(@result) %>
    </div>

    <%= inspect(@form) %>
    """
  end

  def handle_event("validate", %{"form" => params}, socket) do
    form = socket.assigns.form |> AshPhoenix.Form.validate(params)

    socket =
      socket
      |> assign(form: form)

    {:noreply, socket}
  end

  def handle_event("save", _params, socket) do
    socket =
      case socket.assigns.form |> AshPhoenix.Form.submit() do
        {:ok, result} ->
          socket |> assign(result: result)

        {:error, form} ->
          socket |> assign(form: form)
      end

    {:noreply, socket}
  end
end

defmodule Router do
  use Phoenix.Router
  import Phoenix.LiveView.Router

  pipeline :browser do
    plug(:accepts, ["html"])
  end

  scope "/", SamplePhoenix do
    pipe_through(:browser)

    live("/", SampleLive, :index)
  end
end

defmodule SamplePhoenix.Endpoint do
  use Phoenix.Endpoint, otp_app: :sample
  socket("/live", Phoenix.LiveView.Socket)
  plug(Router)
end

{:ok, _} = Supervisor.start_link([SamplePhoenix.Endpoint], strategy: :one_for_one)
Process.sleep(:infinity)