Scrollback rendering issue on SSHMUX + default unix domain

[junkblocker]

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

Linux Wayland

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

DE: KDE Plasma 6.2.4 /
WM: KWin (Wayland)

WezTerm version

wezterm 20250102_112944_d8f4cb35

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

Yes, and I updated the version box above to show the version of the nightly that I tried

Describe the bug

Run a unix domain locally. Then spawn a tab in the same window to a SSHMUX domain. Run something that produces a few screenfuls of output in the SSHMUX domain tab. Try to scroll back up.

The scroll rendering a lot of blank regions. These regions get filled in after multiple tens of seconds later.

From my debugging, this only happens when I set default_domain to the unix domain (see config).

To Reproduce

1. Use the config and launch wezterm to get a local mux tab. Let's call it TAB-1
2. wezterm cli spawn --domain-name SSHMUX:somesshserveryouhave . Let's call it TAB-2
3. Switch to TAB-2 if not focused.
4. Run `find /usr`` or something. You only need 3-4 screens worth of output.
5. Use mouse or other mechanism to try to scroll back up to the beginning of the command.
6. Do this with and without default_domain = 'unix' specified in the config.
7. Observer that when default_domain is set, the scrolled previous screen does not render for a while.
8. Observe that when default_domain is NOT set, the scrolling is fine.

Configuration

local wezterm = require "wezterm"
local config = wezterm.config_builder()

config.unix_domains = {
    {
        name = "unix",
    },
}

-- PROBLEMATIC
config.default_domain = "unix"

return config

Expected Behavior

Scrolling should not hiccup while rendering in SSHMUX domains.

Logs

Did not see anything relevant.

Anything else?

No response

[junkblocker]

Seems default_domain is not always affecting this behavior. I just observed this with default_domain unset too.

[junkblocker]

cli spawn'ed ssh domain is practically useless due to this. I don't want to have to go back to using tmux for ssh'ed hosts with complicated keys swapping and not have the integrated mux experience :(

[junkblocker]

It seems that the issue occurs with wezterm cli spawn --domain-name "SSHMUX:host" form but not with wezterm connect --new-tab SSHMUX:host form. The latter does not create a new tab in the current window is why I've been using the first form.