You were right and I was wrong, sorry about that. The popup does exist, and you had already earned it.
The last step of chapter 4 asks for the first array at a Grid Foundry. All of that walks back to trash. You had cleaned every tip, so there was nothing left to build it out of. The ending costs about 80 kg and you had spent the rest getting to it.
So you finished the game and the game failed to notice. That is on me.
Next build: if there is no trash left anywhere, the ending turns up on its own. Your save will pick it up the moment you load it.
Thanks for saying something. No test of mine would have caught this, because it never occurred to me to strip the whole world first.