Pledge and unveil allow you to do privileged setup within the process, e.g. obtaining a bunch of file descriptors, or doing other things that need caps, then ho

Pledge and unveil allow you to do privileged setup within the process, e.g. obtaining a bunch of file descriptors, or doing other things that need caps, then holding onto them and then dropping those privs. That's not possible with an external container/sandbox launcher, you need to interleave it with the control flow. Seccomp&co are too low-level. Jail launchers are too coarse.