[BUG] Kitty's content area clipped with `prefer_no_csd=false`

[jinliu]

Submission checklist

• I have searched existing issues and confirmed this is not a duplicate.
• I am using the latest release or a recent build of main.
• I confirmed this happens in Umbriel itself, not in a desktop shell, a portal backend, or a single application.
• I checked whether my configuration causes it, for example by reproducing with the packaged examples/config.toml.

Bug description

The top corners of Kitty's content area is clipped when CSD is showing.

The corner radius changes with Umbriel's corner_radius setting, so I guess it's Umbriel, not Kitty, who does the clipping.

Config file:
config.tar.gz

Steps to reproduce

1. Set prefer_no_osd=false
2. Launch kitty.

Expected behavior

Top corners of the content area not clipped.

Actual behavior

Top corners of the content area clipped.

Umbriel version

umbriel 0.1.0 (2363484)

Last working version

No response

Session type

Native session (TTY or display manager)

Installation method

Source build (just install)

Affected area

Rendering (blur, shadows, borders, corners, animation)

Distribution

Arch-based

Environment information

GPU and driver: AMD Ryzen 5 5600H
wlroots: 0.20. SceneFx: submodule
Outputs: 3200x2000 @ 90.000 Hz
kernel: 7.1.11-zen1-1-zen

Logs and error output

Additional context

No response