session_name: helloworld
windows:
  - window_name: dev
    start_directory: /home/parallels
    panes:
      - shell_command: "echo foo"
      - shell_command: "echo bar"

If you press up to get the previous command, there is leading whitespace in the command, so it's not just a rendering issue.
tmuxp 1.55.0, libtmux 0.46.0