The : prompt would benefit from a few basic editing behaviors to make interactive command entry smoother:

• visible cursor while the prompt is active
• left/right arrow movement within the command line
• up/down navigation through prompt history
• no passthrough of those keys to the underlying shell while the prompt is active

Right now, Up / Down can leak through and trigger shell history, which makes the prompt feel unfocused and awkward to use.

Adding these would make command mode feel much more complete and align it more closely with tmux.