Once the build of the stage1 completes, you can't chroot into it, due to a missing libtinfo. In theory, Portage deps should have made sure this library exists in /tmp/stage1root:

This may be related to FL-9835 – it's likely that if ncurses is built with tinfo set on the fchroot environment, then we need ncurses[tinfo] on the stage1, because bash WILL link against it. Just an educated guess, no proof that this is the actual problem yet.