The good news is that the game is actually open-sourced
The bad news is that it's not the newest version because I accidentally erased it installing arch
source link:
Hi Sentry!
The game's source code doesn't have any license, which means the game is actually "source available" and might discourage people from making use of it. Consider putting a license such as GNU GPLv3 or Expat license (also known as MIT) in a LICENSE file which will make the game free and open source.