tmux allows specifying a shell command when creating sessions, windows, and panes:

tmux new-session 'htop'
tmux new-window 'vim file.txt'
tmux split-window -h 'cargo watch'
The command runs in the new pane, and when it exits, the pane closes.

It would be great to have the same in psmux:

psmux new-session -s work "python server.py"
psmux new-window "vim file.txt"
psmux split-window -h "cargo watch"
This is useful for scripting session layouts, automated workflows, and quickly launching tools in dedicated panes without having to send-keys after creation.

FYI, claude code was able to implement this in a few minutes, but I won't presume you want that code