make installworld broke / how to recover

[tech-lists]

On Thu, Feb 22, 2018 at 03:10:17AM -0800, Jack L. wrote:
>maybe try a clean buildworld, update /usr/src to the latest version, rm -rf
>/usr/obj, then make buildworld && make installworld && make kernel and see
>if that fixes the issue?

Is there a documented way of say booting to memstick, starting fixit,
mounting the zfs from the broken system then building/installing a 
new world? Is there enough "environment" and utilities to do this on the
fixit disk?

[never had this happen before, anticipate steep learning curve]

-- 
J.