You may want to take wider angle photos of the engine bay area you want members to view.
Here are some more photos. It's a vacuum line of some sort, I had another look around with an inspection camera after getting the car started up, I'm at a loss for where to plug it in. I'd be most grateful to anyone with a relevant manual page to share. As I mentioned in the original post, it seems to fit into a clip that's also attached to the hard plastic hose with the flex joint sticking out of the firewall just beside/above in the photos, but routing it that way, towards the firewall doesn't point it towards anything that makes sense to connect. The hose is quite short, unless it somehow got broken during the repair, but I don't see the other end of it sticking out anywhere.