> The dream is using something like Nix to not only reproducibly build a container image but also all of the infrastructure manifests which reference it. I _think_ this is achievable in Nix if you're willing to deal with all of the pain of actually using Nix;

We did that at an old job. Basically, Nix built images + K8s manifests + a script to push the images. Our CI job boiled down to `nix-build && ./result/push-images && kubectl apply -f ./result/manifests -R`. This is similar to how NixOS' nixos-rebuild boils down to `nix-build && ./result/activate`.