Aperture Desk Job code references unannounced Valve projects, including Half-Life: Alyx 2

pcgamer.com:

Valve is having a good year so far (and also had a pretty great 2021, thanks)—part of which was the announcement of an unexpected new game, Aperture Desk Job, set in the Portal universe. It's called a 'short' by the developer, free for everyone, and a week after release one dedicated data-hound has sniffed out a breadcrumb trail that seems to reference up to four unannounced (even if rumoured) Valve projects at the developer.

Tyler McVicker has been finding hints in Valve's code for years, and is himself responsible for some of the leaks that this latest discovery seems to confirm (thanks, VGC). The full video is below, and I'll summarise his findings after:

McVicker says he's found description strings relating to «Citadel, some kind of follow up to Half-Life: Alyx, Counter-Strike: Global Offensive’s Source 2 port and a recreation of the previously cancelled Portal paint game.»

Obviously all of this has to be taken with an entire shaker full of salt, as while McVicker provides full documentation here, we simply don't know why these references have been left in the game: it could be as simple as re-using some old work, it could be what McVicker thinks it is, or it could even just be Valve developers toying with us.

Citadel has long been rumoured, as has the Source 2 port of CS: GO (some code in a Dota 2 update last year suggested the project is well underway), but a sequel to Alyx would certainly be a surprise. The Portal paint gun game could be a revival, or it could be old code, or it could be nothing.

Citadel is supposed to be some sort of alien-blasting co-op experience: «This appears to be a Combine vs. Rebels, team-based, squad-based, Class-Based, RTS/FPS hybrid,» writes McVicker, «built for both Virtual Reality and