Can I set a pattern to watch for any file scoped message?

No. Not specifying a file name when you use file scoping is virtually the same as specifying that you want to match to file-scoped messages about every file in the universe.

A session attribute may be set on a file-scoped pattern to emulate file-in-session scoping; however, a tt_session_join call will not update the session attribute of a pattern that is scoped as TT_FILE.