xcape VS ahk-caps-ctrl-esc

Don't know about i3, but you can achieve this in Linux/X11 using for example xcape: https://github.com/alols/xcape

I guess that xcape is what you're looking for.

You can use xcape (I assume xorg only; https://github.com/alols/xcape) to set any key including super/meta to trigger a custom keyboard shortcut on release.

Caps Lock is both Control and Escape depending on whether you hold or tap it. I use xcape.

All you need is dual mode modifiers - remap your spacebar to act as Ctrl when pressed and generate space symbol when released. You can make it with xcape on linux and with dual-key-remap on windows. It is also something for macos, but I never used it.

I have the same setup on linux. Using xcape and xmodmap together.

This version, by fenwar, is likely better, but I've never gotten round to trying it myself. (Because mine works fine for me).

I found an AutoHotKey script that does that for me. The only thing I'm considering changing is adding some sort of time-out. I'll sometimes hit caps-lock, pause for a second, realize that I didn't want to hit a shortcut key, and end up sending an escape to whatever I have going on. But other than that, it works quite well.