To add to the pessimism, the 3-letter agencies --
-- already have this, don't you think? I mean, if non-spook devs can come up with an app like this in a couple of months, then surely the spook-devs who have been working on this stuff since phones got smart have already gotten there.
The squeeze right now is the testing. Your app can't know that the person you just brushed past is CoV-SARS-2 positive unless they've tested positive, and if -- as in many countries -- you're only testing 0.5% of the population, then the app is a cool toy but fails as a tool to prevent infection.