We have the same annoying problem

Did you try to change your bell setting in Terminal/Bell panel ?

I just tried to change it from alert sound to none and then disconnecting and reconnecting the Internet connection. The result is the same: the kitty window which is hidden in the tray still steal focus when it is reconnecting.

Can you test this build ?
Is the focus still stolen ?

Yes the focus is still stolen with that build.

If you want to test it yourself you could also use Process Hacker, close the kitty connection to port 22 in the Network tab in Process Hacker, and see the Process Hacker window losing focus after a while, while kitty is reconnecting.

I did not reproduce. Can you send me a memory dump of the session that steal the focus ?
I need to be exactly in the same situation.

I hooked the kitty process to winapioverride and found that these two functions are called when it steal focus

https://github.com/cyd01/KiTTY/blob/master/0.74_My_PuTTY/windows/window.c#L3336

BringWindowToTop( hwnd ) ;
SetForegroundWindow( hwnd ) ;

Maybe a check can be added there to skip calling those functions if the window is currently hidden in the tray.

For what it's worth, I'm seeing the exact problem with 0.74.2.7, it's not just @char101.

I came here to see if there was a solution :).

I can't think of a single situation where it's appropriate to steal focus.
If I'm looking at the window, great. If not then I'm looking at something else and the window should stay where I left it.
It's better to let the user select when they want to focus the window, there is no reason to call SetForegroundWindow. Windows are automatically set to the foreground when you start an application.

I may have used the wrong term here. Flashing seems to meant that the taskbar icon is flashing, while what I meant was the kitty window appear and disappear for a very short time (although I guess it isn't what is happening here). The actual problem is that the currently foreground window (e.g. the editor I'm typing in) will suddenly lose focus.

I thought to something else.
Can you download this last build ?

That's exactly what @char101 has proposed.

Can you download this last build ?

Unfortunately the focus is still lost with this build.

Winapioverride still shows that BringWindowToTop and SetForegroundWindow is still called when kitty is reconnecting while it is hidden in the tray.

Are you sure ?
I've double checked, and it is not called anymore.

I have just tested it again (kitty-debug.exe, Last-Modified: Tue, 03 Nov 2020 22:10:29 GMT) and now it does not steal focus anymore. Thanks.

Keep this debug build.
I don't known when I will upload a new release on Fosshub.

I already downloaded the new release from the release page on github though, so no need to wait for fosshub.