In some situations, it would make debugging sandbox violations easier if the sandbox were to terminate immediately. This could be controlled by env var SANDBOX_TERMINATE. I guess libsandbox needs to signal the process group?
kill()ing the process group should do it. I'll be looking into this in the weeks to come, as I have to debug some ebuilds failing to emerge in g/fbsd. I'll update this bug report if I come with any useful patch.
Theoretically added this to svn. Uses SANDBOX_ABORT=1.