gtk-titlebar-hide-when-maximized=true not respected when gtk-titlebar-style=tabs

[hazzery]

Issue Description

I quite like the new gtk-titlebar-style = tabs that was released with 1.2, it prevents the title bar from using up additional vertical space when using multiple tabs. However, I also really like not having any window decoration what so ever when in full-screen. Apparently, I cannot have my cake and eat it too, as Ghostty will show the titlebar when full-screened if gtk-titlebar-style = tabs. I only have a problem with this there is only a single tab, the titlebar/tab-bar should definitely show up when there are multiple tabs.

Not sure if this is relevent, but $ glxinfo | grep "OpenGL version" gives:
OpenGL version string: 4.6 (Compatibility Profile) Mesa 25.2.4

Expected Behavior

The titlebar does not show when the window is maximised and there is only a single tab; the exact same behavior you get with gtk-titlebar-style = native

Actual Behavior

The title bar is shown when the window is maximized/full-screened and only a single tab is present.

Reproduction Steps

1. Open Ghostty.
2. Maximize the Ghostty window
3. Observe the presence of the titlebar

Ghostty Logs

No response

Ghostty Version

Ghostty 1.2.3-1.fc42

Version
  - version: 1.2.3-1.fc42
  - channel: tip
Build Config
  - Zig version   : 0.14.1
  - build mode    : builtin.OptimizeMode.ReleaseFast
  - app runtime   : apprt.Runtime.gtk
  - font engine   : font.main.Backend.fontconfig_freetype
  - renderer      : renderer.generic.Renderer(renderer.OpenGL)
  - libxev        : io_uring
  - kernel version: 6.16.8-400.asahi.fc42.aarch64+16k
  - desktop env   : gnome
  - GTK version   :
    build         : 4.18.6
    runtime       : 4.18.6
  - libadwaita    : enabled
    build         : 1.7.7
    runtime       : 1.7.8
  - libX11        : enabled
  - libwayland    : enabled

OS Version Information

Fedora Linux Asahi Remix 42 (Forty Two [Adams])

(Linux only) Display Server

Wayland

(Linux only) Desktop Environment/Window Manager

GNOME 48

Minimal Ghostty Configuration

gtk-titlebar-style = tabs

Additional Relevant Configuration

No response

I acknowledge that:

• I have reviewed the FAQ and confirm that my issue is NOT among them.
• I have searched the Ghostty repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
• I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (```) on separate lines.