<%# Files are posted as a message's own attachment, which gets its preview when it's posted; the composer adds none to the rich text. One that's there anyway is shown by its name, with no preview: Action Text's partial links to a URL that makes one on view, and nothing else in the app would make it. %>

<% if caption = blob.try(:caption) %> <%= caption %> <% else %> <%= blob.filename %> <%= number_to_human_size blob.byte_size %> <% end %>