The DCA from Security Breach. Was trying to fix himself in RUIN.
I believe that the DCA was also trying to repair himself. There is a new thing found in Ruin, gives a clue for their repair attempt. Specifically, Sun. Before, in the base game, at the back of the attendants head, there was no attachment available at that time. To refresh memories, I have an Image here. To show the full head.
This is the biggest full shot, I could ever take from a Screenshot. This is a pretty big view. And just how it's shown, there is no extra piece.
This is the side shot from the Ruin attendants port. There is a piece. So, how did it get there? Did an employee attempt to put one in, but failed? Or did Sun?
Well, it is speculated from base game that Sun had been trying to fix himself, since the very start. To fix the problem.
But since, he's got all sorts of programming, it was not easy for him to do. It was not accessible for him to do it, but it was clear that he tried to find ways to change something.
To customize himself, even. While Moon was trying to get rid of Sun, by pulling out the plugs on the port, he couldn't do it completely, because it was a risk.
All of this time while Sun was fighting for freedom, he was also trying to find a solution. He tried all he could, to find new parts, to find a solution, while fighting to keep Moon at bay, to stop him from destroying himself.
That, when he met Cassie, he found the perfect tool for the perfect solution, because he eventually found a part, and install it in and wait for someone to come around and fix him. Because, he couldn't do it himself.
But, it's likely that he found something to use, and install for the idea to use a gadget to fix the problem. And that gadget was the Faz Wrench. The Faz wrench was the only missing piece of the Puzzle. That's the solution, to fix the problem.
To reboot the programming of the evil one, to bring it back to its default state. The state to bring back the Moon from when he was reprogrammed, to watch over the kids.