I went to fire up one of my many, many docker containers (I love using docker for development environments) and was welcomed with:
Error response from daemon: json: cannot unmarshal object into Go struct field Process.capabilities of type string
And I commenced panicking.
Then I calmed down and opened the issue with the maintainer of the docker overlay, who pointed me in the right direction. Docker 17.06 is apparently incompatible with <code>docker-runc-1.0.0_rc2_p20170310</code>. Lately, docker-runc has been updated and now it seem the new runc,
app-emulation/docker-runc-1.0.0_rc3_p20170607, is incompatible with docker 17.05 but works with 17.06. So be mindful of the docker-runc version you are running when working with bleeding-edge docker on gentoo.