Append UI element in message as user

Is that possible to attach UI element as a user response? For example, I want to make a chat UI where user can upload files. I want to append some UI element together with the message to indicate files have been added.

I find this works as expected if the role is "assistant", but as "user" it just render it as plan text. Is that a bug or expected behaviour?

shinychat::chat_append(
        "chat", 
        role = "user",
        response = list(
          list(
            div(
              span(bsicons::bs_icon("filetype-pdf", size = "1.5em"),
                   shiny::strong("client_contract.pdf"),
                   bsicons::bs_icon("cloud", size = "1.5em"),
                   shiny::strong("examples")
              )
            )
          )
        )

Start with the shinychat::chat_append call shown in the issue and compare how the response is rendered for role "user" versus "assistant". Verify whether UI elements are intentionally treated as plain text for user messages; done means the expected behavior is documented or UI elements render consistently for the requested role.