In app-shells/sandboxshell-0.3, line 38 of /etc/sandboxshell.conf adds 2 directories to the variable SANDBOX_WRITE. Using the default PORTAGE_TMPDIR, the first directory is effectively PORTAGE_BUILDDIR, but the second becomes "/var/tmp/portage//homedir". I just started using sandboxshell to help learn portage, so I'm not sure what's needed here, but this doesn't look right.
that is correct, /var/tmp/portage/homedir should be added