It doesn't. I was also disappointed by this. I'm in Australia and we kept our numbers low by locking down hard and early and distinguishing between community transmission and infection via incoming travellers. We did often hit long periods of no community transmission and only had outbreaks due to breaches in protocol or sloppiness by some people's part.
I've been a heavy Jenkins user for the last three years and I can completely see where you (and Concourse team) are coming from. The page comparing Jenkins and Concourse hits all my right buttons (complexity in build specification, minimal pipeline, etc) but I find that having to BOSH the hell out of a new system (pun intended) just to get CI running seems like a PITA to me (it's the one thing preventing me from recommending it as a solution atm). Maybe I'm missing something, but it seems like a lot of complexity is added to the deployment/worker management system that is pretty much a requirement if you want slaves external to the master. Is there a way to not have to use BOSH (BOSH Lite still tries to shoehorn things I don't want/need) to run Concourse builds? We use a combination of VMWare/KVM VMs, LXC and Docker containers for our builds and we have our own working deployment system (Puppet manages all our state successfully for VMs and LXC containers) which I would like to integrate with Concourse. I really hope I'm missing something because what I saw when I tried out Concourse for a week, made me swoon.