> Why does the emulator have to do this? Can’t it be a plug-in for bash/zsh/whatnot?

I've no interest in using it because I'm a cheap bastard and am not going to pay $20/month for a key, but if I were going to use it I'd want it in the terminal emulator. If it were a shell plugin I'd have to install it in my shell on my Mac, the shells on my two Raspberry Pis, the shell on my Amazon Lightsail instance, and the shells on the half-dozen or so servers at work that I regularly ssh to from home. Oh, and also the shells in the Linux VMs I run my work test environment in.