The type=track branch authorises on _is_my_case(t_attach.case) only and never checks...

The type=track branch authorises on _is_my_case(t_attach.case) only and never checks VinceTrackAttachment.shared. A coordinator-uploaded case artefact that has NOT been marked shared is still retrievable by any case member who has (or is sent) its uuid — leaks not-yet-released coordinator material to vendors on the case.