Linux/X11 HiDPI: full-screen recording overlay is ~2x too large at 200% scale #2323

Version / environment

• Cap 0.6.0 (.deb, amd64)
• Linux Mint 22.3, MATE 1.26.2, X11 session
• Display: eDP-1 2560x1600 (344x215 mm), Intel Arrow Lake graphics (Vulkan, per the Cap log)
• Xft.dpi = 192; MATE window-scaling-factor = 0 (auto)

What happens
When I choose "record full screen", the blue selection/overlay is about 2x larger than the screen. Cap's main window renders at a normal, readable size.

Workarounds tried

• Lowering the global desktop scaling makes the overlay correct, but shrinks all UI text on the system, so it isn't practical.
• Launching with GDK_SCALE=1 (from a terminal): the overlay is correct, but Cap's main window becomes very small and can't be resized.
• GDK_SCALE=1 GDK_DPI_SCALE=2: overlay still correct, but the window stays small with huge text; buttons unreachable.
• WINIT_X11_SCALE_FACTOR=1: no visible change (overlay still 2x).
• Ctrl+ / Ctrl+scroll in the main window: no effect.
• Settings > Experimental (GPUI preview) does not exist in my build.

Notes

• The terminal log shows no error or scale-related message at startup. Only unrelated JACK/ALSA and mjpeg warnings.
• I have not verified whether the overlay window is sized in physical vs. logical pixels, or whether the window toolkit is GTK/WebKit or something else.

Expected
Overlay covers exactly the selected display at 200% desktop scaling, without needing GDK_SCALE=1.