Tobin Baker on Nostr: really dumb question: presumably measuring a neutrino's mass (however that is done) ...

really dumb question: presumably measuring a neutrino's mass (however that is done) collapses it into a mass eigenstate (with measured mass as the eigenvalue), but what collapses a neutrino into a flavor eigenstate? i.e., how is flavor "measured" (and what does the eigenvalue mean operationally)?