rtime interface calls the shim create:
which eventuall calls newBundle: https://github.com/containerd/containerd/blob/b61988670c7c951a0bf4f11f6ea9d926f3e79d35/runtime/v2/bundle.go#L49
via https://github.com/containerd/containerd/blob/b61988670c7c951a0bf4f11f6ea9d926f3e79d35/runtime/v2/bundle.go#L49 and the taskmanager (which implements runtimeplatfom [rtime] https://github.com/containerd/containerd/blob/f7b8b118127771f2b0c55f605d3b378437270dfc/runtime/v2/manager.go#L420
https://github.com/containerd/containerd/blob/97064b0772af58f770a48276d0a0bb3746a92378/task.go#L141