This is now done per:
https://github.com/discourse/discourse/commit/0a357299b7e1f14de6dc070cae64d2163779de9b
star trek t will do an in:title search.
star trek f will do a in:first post search.
The commit also cleaned up a bit of a mess we had with our advanced search clauses where we were regexes were not bound properly … so in:first_banana for example used to work just like in:first which is very strange.