0.0.38: light gray 7px border on left/right/bottom on i3/X11 without compositor

Human explanation: When I upgraded to t3-code 0.0.38 I got a weird light gray border left/right/bottom of the window. I use ubuntu 24.04 and i3 window manager. The bug was caused by the electron version bump and it looks like this:

Version

T3-Code 0.0.38 AppImage (T3-Code-0.0.38-x86_64.AppImage), Electron 43.4.1 (bumped in #8626)

Previous version (0.0.37) had no border.

Environment

• OS: Ubuntu 24.04.4 LTS (Noble)
• WM: i3 4.23 on X11 (XDG_SESSION_TYPE=x11, $DISPLAY=:0, no WAYLAND_DISPLAY)
• No compositor: no picom/compton, xprop -root _NET_WM_CM_S0 -> not found
• Launch: ~/opt/T3-Code-*-x86_64.AppImage --force-device-scale-factor=1.75

Describe the bug

After upgrading to 0.0.38, a light gray border appears on left/right/bottom sides of the main window (top is clean). Looks like 6-7px solid #EBEBEB with 1px darker #C8C8C8 outer edge.

Screenshot pixel sampling (3840x2160 fullscreen):

• left edge at mid-height: x=0: (200,200,200), x=1-6: (235,235,235), x=7+: app bg (32,46,60) = ~7px
• right edge: ~5-7px (235,235,235)
• bottom edge just above i3bar: y=2118: (209,209,209), y=2113-2117: (235,235,235), y=2112: app bg = ~6px
• top: no border, app bg from y=0

X11 properties:

xwininfo: Border width: 0, 3840x2119+0+0
xprop _GTK_FRAME_EXTENTS(CARDINAL) = 7, 7, 0, 7
_NET_WM_WINDOW_TYPE = NORMAL, WM_CLASS = "t3code"
_MOTIF_WM_HINTS = 0x2, 0x0, 0x0, 0x0, 0x0

So this is not an i3 border (width 0), it is in-client CSD shadow area rendered opaque because there is no compositor to make it transparent.

Expected

No visible border on non-compositing X11 WMs like i3, as in 0.0.37. Either:

• detect lack of compositing / client-shadow support and render with no insets (like Chrome falls back to SSD), or
• create frameless window with hasShadow: false, or expose an option for it.

Upstream

This matches https://github.com/electron/electron/issues/52024
"Linux: frameless windows have a border on non-compositing X11 WMs, e.g. i3"

A frameless window should not have any border on i3, which is an X11 window manager which does not have a compositor out of the box and cannot support shadows. The window has a border around the sides and bottoms where the shadow would appear.

That issue notes Electron 41+ added CSD to frameless windows, and LinuxFrameLayout::Create / X11Window::CanSetDecorationInsets path falls back to a resize border when the WM doesn't advertise _GTK_FRAME_EXTENTS (i3 case).

Workaround

Running picom -b makes the 7px area transparent shadow again. Downgrading to 0.0.37 also removes it. Filing here because T3-Code owns the BrowserWindow options and Electron bump.

Start by reproducing the border with the 0.0.38 AppImage on Ubuntu 24.04/i3 without a compositor, then inspect the app's Electron BrowserWindow options and the Electron version bump. Compare against 0.0.37 and verify that the window has no visible left, right, or bottom border on non-compositing X11 while retaining the expected appearance with a compositor.