What Content-Type to return on the attachment endpoint

[quentez]

In it's current form, the attachment endpoint only takes an entity and a digest as parameters. This means it just references a file and not a specific post having that file as attachment. The problem this creates is that different posts can reference the same attachment with different content-type, in such situation: what Content-Type should the attachment endpoint return?

From what I've been told, the current rule would be to return the Content-Type of the most recent post. But this is problematic: what if two apps use the same file with different content-type. The app that created the post first would now receive the wrong headers when retrieving files from the attachment endpoint.