Setting config options inside wezterm.on() does not apply settings

[BrayanLope5]

What Operating System(s) are you seeing this problem on?

Linux Wayland

Which Wayland compositor or X11 Window manager(s) are you using?

Hyprland

WezTerm version

wezterm 20240203-110809-5046fc22

Did you try the latest nightly build to see if the issue is better (or worse!) than your current version?

No, and I'll explain why below

Describe the bug

I am trying to change the default_prog from inside an event. Not sure this is the correct terms to use, I know a little bit of python and fish but am an not a developer.
I have tried other events instead of gui-startup, I have tried changing the setting from the global scope, just like any other setting, but mux.all_windows() always seems to report zero windows on the first loading of the config file. I've used wezterm.log_info() to check. This makes it useless since the default program will have been launched already by the time we get the correct number of windows reported.
The default_prog variable does get the correct value but it doesn't seem to be applied to the config. I am under the impression that gui-startup should run before the default program. Am I not understanding how Lua's scope rules work?

To Reproduce

No response

Configuration

wezterm.on('gui-startup', function(cmd)
  local window_names = #mux.all_windows()

  if window_names == 0 then
    -- Attach zellij session when there are no wezterm gui windows open.
    config.default_prog = { '/usr/bin/zellij', 'attach', '--create', 'options', '--default-shell', '/usr/bin/fish' }
  else
    -- If there is at least one wezter gui dindow already open, open zellij welcome
    config.default_prog = { '/usr/bin/zellij', '--layout', 'welcome' }
  end
end)

Expected Behavior

For the default program of my choosing to be launched. Instead the default shell, bash, is launched.

Logs

Debug Overlay
wezterm version: 20240203-110809-5046fc22 x86_64-unknown-linux-gnu
Window Environment: Wayland
Lua Version: Lua 5.4
OpenGL: Mesa Intel(R) HD Graphics 520 (SKL GT2) 4.6 (Compatibility Profile) Mesa 24.2.6-arch1.1
Enter lua statements or expressions and hit Enter.
Press ESC or CTRL-D to exit

Anything else?

No response

[BrayanLope5]

Doing some more debugging it seems to be a scope problem. The callback function does not seem to change the global config, a reference of the config value seems to be necessary? But I am not sure how or where to change what is passed to the callback function.