Help with a TMUX binding

[al3xandru]

TMUX uses Ctrl-b as a prefix for its keybindings. I am using Goku to define some complex modifications. The one I am looking for suggestions is for the TMUX Ctrl-b x which kills a panel but asks for y confirmation.

I have tried

:simlayers {
    :b-tmux-mode {:key :b}  ;; this enables keeping the `b` key down and pressing another key
}

{:des "Tmux"
  :rules [
      [:x [:!Tb :x :y]]
   ]}

The attempt was hoping to send Ctrl-b x then followed by the y needed for the confirmation. This doesn't seem to work as the y is somehow sent to the remaining panel in tmux.

Please share any suggestions/ideas/feedback