Add Kitty keyboard protocol support - #5600

I've tried using this under Ghostty and pressing Shift+Space writes ";2u".

edit:
I failed to set extended-keys-format to kitty.

@gabehowe try this:

Add these lines to test.conf:

set -s extended-keys on
set -s extended-keys-format kitty

then start tmux. Run these commands and let me know what they output:

./tmux display -p 'client=#{client_key_mode}'
./tmux command-prompt -k 'display-message -p "tmux got: %%"'

Then press shift-space.

Asuming you are in the directory where you compiled this branch, you need to run the tmux you compiled, hence ./tmux.

You should see the mode "Kitty 1" and you should see "S-space".

Note, I am currently trying to see if I can get each client to discover if it supports kitty or xterm or csi-u or just plain ascii, so you may not need to specificy set the extended-keys-format to kitty if I can figure that out.

Both kitty and Ghostty return client=Ext for the first command and nothing for the second command until I focus out and focus in, at which point it displays tmux got: FocusIn.

I've just tested this on kitty and it doesn't have this behavior, so perhaps it's somehow Ghostty specific?.

Huh, it's not what I see. Are you reattaching to an existing tmux server? Also, you can't turn on kitty after you reattach, you need to start your tmux -f test.conf or start tmux like this:

tmux -L kbtest -f /dev/null start-server \; set -s extended-keys on \; set -s extended-keys-format kitty \; new

I have added autodetection for kitty in this PR: #5615

Huh, it's not what I see. Are you reattaching to an existing tmux server? Also, you can't turn on kitty after you reattach, you need to start your tmux -f test.conf or start tmux like this:

tmux -L kbtest -f /dev/null start-server \; set -s extended-keys on \; set -s extended-keys-format kitty \; new

Looks like I was attaching to an existing server. Now I get client = Kitty 1 and tmux got: S-Space and shift-space doesn't paste ;2u.
It also looks like I failed to change my config to use extended-keys-format kitty.
With it done correctly it works perfectly under ghostty in vim/nvim.

I'm sorry to have taken up your time.