Default ted untitled buffers to Plain Text instead of C#

[Copilot]

ted started new/untitled buffers with C# highlighting even when no file type was known. This changes the default to plain text while preserving extension-based highlighting when a path is available.

• Default highlighting

  • Remove the constructor-time C# highlighting assignment from TedApp.
  • Initialize the language status item as Plain Text for untitled buffers.

• Auto-detection remains unchanged

  • Keep SetDocument as the source of truth for file-extension-based highlighting.
  • Opening or binding a document with an extension still selects the matching syntax definition.

• Integration coverage

  • Add coverage for the untitled-buffer default (Plain Text / no highlighting).
  • Update highlighting detection coverage to assert the normal path-based behavior through AppFixture<TedApp>.

Editor = new Editor
{
    GutterOptions = GutterOptions.LineNumbers | GutterOptions.Folding,
    ConvertTabsToSpaces = true,
    ReadOnly = readOnly,
    ViewportSettings = ViewportSettingsFlags.HasScrollBars
};

LanguageShortcut = new Shortcut (Key.Empty, "Plain Text", null)
{
    MouseHighlightStates = MouseState.None
};

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• www.jetbrains.com
  • Triggering command: /usr/share/dotnet/dotnet /usr/share/dotnet/dotnet exec --runtimeconfig /home/REDACTED/.nuget/packages/jetbrains.resharper.globaltools/2026.1.1/tools/net8.0/any/cleanupcode.unix.runtimeconfig.json /home/REDACTED/.nuget/packages/jetbrains.resharper.globaltools/2026.1.1/tools/net8.0/any/cleanupcode.exe Terminal.Gui.Editor.slnx --profile=TG.Editor Full Cleanup (dns block)
  • Triggering command: /usr/share/dotnet/dotnet /usr/share/dotnet/dotnet exec --runtimeconfig /home/REDACTED/.nuget/packages/jetbrains.resharper.globaltools/2026.1.1/tools/net8.0/any/cleanupcode.unix.runtimeconfig.json /home/REDACTED/.nuget/packages/jetbrains.resharper.globaltools/2026.1.1/tools/net8.0/any/cleanupcode.exe Terminal.Gui.Editor.slnx --profile=TG.Editor Full Cleanup --no-build --exclude=third_party/**/* (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)