I often see people wedging injector blades into things eg. Ender's, Ronson, etc. but haven't given it enough thought to guess if there's a reasonable way to do that here.

Thanks and you too. I had two negative tests but saw some anecdotes that these kits have a very high (like >50%) false negative rate (but few false positives) so I'd probably have to do a bunch to really say anything conclusive. Especially since they apparently do even less well with current variants.

pre-1850s usually straight razors with extra short tails, called monkey tails,

Pretty sure those are "stub tails", monkey tails are long like that Tedalus and, most famously, the De Pew "Perfect Razor". Some French razors were even made with no tail at all.