workaround
tmuxを起動するhomeディレクトリの .bashrc
に以下の設定を追加する
~/.bashrc
[[ $SSH_AUTH_SOCK != $HOME/.ssh/sock && -S $SSH_AUTH_SOCK ]] \
&& ln -snf "$SSH_AUTH_SOCK" "$HOME/.ssh/sock" \
&& export SSH_AUTH_SOCK="$HOME/.ssh/sock"
参考:
https://werat.github.io/2017/02/04/tmux-ssh-agent-forwarding.html
https://serverok.in/ssh-agent-forwarding-with-tmux
https://gist.github.com/martijnvermaat/8070533
https://qiita.com/sonots/items/2d7950a68da0a02ba7e4