But of course, if the FAST program is still active. Doesn't seem to be working at the Mexican border any more, at least at the major crossings like Tijuana.

Presumably, a functional cross-border HSR system would pre-clear *everybody* at their point of boarding if not before (several TSA Pre-Check style programs are available such as Global Entry), or at least at the station before the border. Would obviously make no sense to have a fast train that parks for a while at the border itself. Given Cascadia HSR's slow pace of development and lack of funding for anything much beyond concept development, of course, all of this is academic for now.