I was running into a very strange glitch with terminal Emacs, showing up as all sorts of weird screen tearing and graphical corruption while moving around within and between files.

tl;dr It turns out that I had inadvertently included a Unicode variation selector, which is a zero-width character (so I couldn't see it in the code) but which was throwing Emacs for an absolute loop. Removing that character fixed the problem. Follow along below the fold to learn how I figured it out.

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