Amazing—it works! I’m trying to wrap my head around what you’ve done here, but it does do exactly what I wanted. Yes, the animation slider is controlled by keyframes.
I think I figured it out. I’m not using paragraph text, but I’ve been using soft returns (old habit). I just need to make sure anyone inputting text is using hard returns.
Unfortunately, I didn’t. I think my workaround was to trace my image in Illustrator, then import and extrude the resulting spline and assign my texture to it. That way I didn’t have to worry about the alpha channel. Unfortunately this is really cumbersome. I wish there were an easier fix.