Support Kitty's Unicode placeholders feature and support running loooooooongcat within tmux

[haya14busa]

Tested with Ghostty terminal and tmux version=3.5a 🐱🐱🐱🐱🐱

Document: https://github.com/kovidgoyal/kitty/blob/04fbf63eabc8ec6120ca39ace3508c45384edf42/docs/graphics-protocol.rst#unicode-placeholders

[yoichi]

Unfortunately it didn't work in my environment.
I've tested with tmux 3.5a with Kitty 0.38.1 and Ghostty 1.1.3 on macOS 15.4.1

I confirm that CheckKittyGraphicsProtocol returns false and it was reaching the code path with "If we didn't get the graphics response, assume no support" comment.

Is there anything else I should look into?

[yoichi]

I have confirmed that there is no response for graphicsQuery even with the printf command.

[yoichi]

I found that I must set allow-passthrough option of tmux.
https://github.com/tmux/tmux/wiki/FAQ#what-is-the-passthrough-escape-sequence-and-how-do-i-use-it

Then it works!

[yoichi]

Currently, option settings are required, so I thought it would be a good idea to add a comment like the one below.

	// Requires the allow-passthrough option set to on or all for this to work
	// https://github.com/tmux/tmux/wiki/FAQ#what-is-the-passthrough-escape-sequence-and-how-do-i-use-it

[yoichi]

After this change, with Terminal.app on macOS, longcat stops processing at

yoichi@Mac longcat % ./longcat 
Ga=q,i=22896,s=1,v=1,t=d,f=24;AAAA

If I press some key, then the image is displayed in pixterm mode as before.