I'm so frustrated that I can't even remember what it was called. I got the third ability (after the tethering and double-jumping), which was acquired just after defeating the boss that you have to drag electric globes to.

I went into the next room to the left after using the hacking-circle ability for the first time, and then the game crashed (exactly as if I hit Alt+F4) when I tried using the circle on one of those floating yellow, docile lines of code. So I lost all of that progress.

While I'm at it, what in-game bug report form is there? I could find nothing.

By the way, it was confusing that the descriptive text for double-jumping had the "assign to Z, X, or C" prompt even when it's not actually to be assigned.

I can't seem to replicate this at all (and the code for that ability doesn't actually affect the floating strings so I'm not sure how that would correlate to a crash in the first place). What OS are you running the game on?
(I tried to insert a gif of myself using that ability on the floating code string, but the gif was too large to insert)
I'm not too sure what to do about this bug if I can't replicate it.

Secondly, if you hit ~ a "Feedback" button appears where you can submit formal bug reports.

Thirdly, the ability for double jump explicitly says the base double jump is automatically equipped.  The upgrade, the Rocket Jump is equipped via ZXC