Add Avalonia server-host launcher (MVP scaffold)

Cross-platform C# GUI to replace the Qt/C++ Host GUI, on the same dotnet
toolchain as the server. MVP: load/save commonwealth-server.json, Start/Stop
the CommonwealthOnline.Server process (published exe, then dll, then source
run), and stream its output to a live log. Themed to the Commonwealth Online
brand (near-black + amber). Builds clean on net8.0.

Next: player list + kick/ban via the admin port, then retire the Qt host.

.gitignore

@@ -58,3 +58,6 @@ server/bans.json
 server/.admin-token
 .DS_Store
 Thumbs.db
+
+host/bin/
+host/obj/

host/App.axaml

@@ -0,0 +1,25 @@
+<Application xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="CommonwealthOnline.Host.App"
+             RequestedThemeVariant="Dark">
+
+  <Application.Styles>
+    <FluentTheme />
+  </Application.Styles>
+
+  <Application.Resources>
+    <ResourceDictionary>
+      <Color x:Key="CoBackground">#0E120B</Color>
+      <Color x:Key="CoSurface">#171C10</Color>
+      <Color x:Key="CoAccent">#E6D28C</Color>
+      <Color x:Key="CoText">#D8D2BE</Color>
+      <Color x:Key="CoDanger">#C24B4B</Color>
+      <SolidColorBrush x:Key="CoBackgroundBrush" Color="{StaticResource CoBackground}" />
+      <SolidColorBrush x:Key="CoSurfaceBrush" Color="{StaticResource CoSurface}" />
+      <SolidColorBrush x:Key="CoAccentBrush" Color="{StaticResource CoAccent}" />
+      <SolidColorBrush x:Key="CoTextBrush" Color="{StaticResource CoText}" />
+      <SolidColorBrush x:Key="CoDangerBrush" Color="{StaticResource CoDanger}" />
+    </ResourceDictionary>
+  </Application.Resources>
+
+</Application>

host/App.axaml.cs

@@ -0,0 +1,25 @@
+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Markup.Xaml;
+using CommonwealthOnline.Host.ViewModels;
+using CommonwealthOnline.Host.Views;
+
+namespace CommonwealthOnline.Host;
+
+public partial class App : Application
+{
+    public override void Initialize() => AvaloniaXamlLoader.Load(this);
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+        {
+            desktop.MainWindow = new MainWindow
+            {
+                DataContext = new MainWindowViewModel(),
+            };
+        }
+
+        base.OnFrameworkInitializationCompleted();
+    }
+}

host/CommonwealthOnline.Host.csproj

@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <LangVersion>latest</LangVersion>
+    <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
+    <AvaloniaUseCompiledBindingsByDefault>false</AvaloniaUseCompiledBindingsByDefault>
+    <AssemblyName>CommonwealthOnline.Host</AssemblyName>
+    <RootNamespace>CommonwealthOnline.Host</RootNamespace>
+    <ApplicationIcon></ApplicationIcon>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <AvaloniaResource Include="Assets/**" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Avalonia" Version="11.1.0" />
+    <PackageReference Include="Avalonia.Desktop" Version="11.1.0" />
+    <PackageReference Include="Avalonia.Themes.Fluent" Version="11.1.0" />
+    <PackageReference Include="CommunityToolkit.Mvvm" Version="8.2.2" />
+  </ItemGroup>
+
+</Project>

host/Program.cs

@@ -0,0 +1,16 @@
+using System;
+using Avalonia;
+
+namespace CommonwealthOnline.Host;
+
+internal static class Program
+{
+    [STAThread]
+    public static void Main(string[] args) =>
+        BuildAvaloniaApp().StartWithClassicDesktopLifetime(args);
+
+    public static AppBuilder BuildAvaloniaApp() =>
+        AppBuilder.Configure<App>()
+            .UsePlatformDetect()
+            .LogToTrace();
+}

host/Services/ServerConfig.cs

@@ -0,0 +1,49 @@
+using System;
+using System.IO;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace CommonwealthOnline.Host.Services;
+
+// Mirrors CommonwealthOnline.Server Configuration. Keep the JSON shape aligned
+// with the server's own serializer so a config saved here loads there.
+public sealed class ServerConfig
+{
+    public string Host { get; set; } = "0.0.0.0";
+    public int Port { get; set; } = 7777;
+    public string ServerName { get; set; } = "Commonwealth Online Server";
+    public string ServerDescription { get; set; } = string.Empty;
+    public int MaxPlayers { get; set; } = 16;
+    public string LogVerbosity { get; set; } = "info";
+    public int AdminPort { get; set; } = 7779;
+    public bool EnableGnsTransport { get; set; }
+    public string? GnsBridgePath { get; set; }
+
+    private static readonly JsonSerializerOptions Options = new()
+    {
+        WriteIndented = true,
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+    };
+
+    public static ServerConfig Load(string path)
+    {
+        try
+        {
+            if (File.Exists(path))
+            {
+                return JsonSerializer.Deserialize<ServerConfig>(File.ReadAllText(path), Options)
+                       ?? new ServerConfig();
+            }
+        }
+        catch (Exception)
+        {
+            // Fall back to defaults on unreadable/invalid config.
+        }
+
+        return new ServerConfig();
+    }
+
+    public void Save(string path) =>
+        File.WriteAllText(path, JsonSerializer.Serialize(this, Options));
+}

host/Services/ServerController.cs

@@ -0,0 +1,106 @@
+using System;
+using System.Diagnostics;
+using System.IO;
+
+namespace CommonwealthOnline.Host.Services;
+
+// Launches the CommonwealthOnline.Server process, preferring a published
+// apphost, then a framework-dependent DLL, then a source-tree dotnet run.
+public sealed class ServerController
+{
+    private Process? _process;
+
+    public bool IsRunning => _process is { HasExited: false };
+
+    public event Action<string>? LogReceived;
+    public event Action<bool>? RunningChanged;
+
+    public void Start(string serverDir, string configPath)
+    {
+        if (IsRunning)
+        {
+            return;
+        }
+
+        var startInfo = ResolveLaunch(serverDir, configPath);
+        var process = new Process { StartInfo = startInfo, EnableRaisingEvents = true };
+        process.OutputDataReceived += (_, e) => Emit(e.Data);
+        process.ErrorDataReceived += (_, e) => Emit(e.Data);
+        process.Exited += (_, _) => RunningChanged?.Invoke(false);
+
+        _process = process;
+        process.Start();
+        process.BeginOutputReadLine();
+        process.BeginErrorReadLine();
+        RunningChanged?.Invoke(true);
+    }
+
+    public void Stop()
+    {
+        if (_process is { HasExited: false } process)
+        {
+            try
+            {
+                process.Kill(entireProcessTree: true);
+            }
+            catch (Exception)
+            {
+                // Process already gone or not killable; RunningChanged fires on Exited.
+            }
+        }
+    }
+
+    private void Emit(string? line)
+    {
+        if (!string.IsNullOrEmpty(line))
+        {
+            LogReceived?.Invoke(line);
+        }
+    }
+
+    private static ProcessStartInfo ResolveLaunch(string serverDir, string configPath)
+    {
+        var exeName = OperatingSystem.IsWindows()
+            ? "CommonwealthOnline.Server.exe"
+            : "CommonwealthOnline.Server";
+        var apphost = Path.Combine(serverDir, exeName);
+        var dll = Path.Combine(serverDir, "CommonwealthOnline.Server.dll");
+        var project = Path.Combine(serverDir, "CommonwealthOnline.Server.csproj");
+
+        var info = new ProcessStartInfo
+        {
+            WorkingDirectory = serverDir,
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            UseShellExecute = false,
+            CreateNoWindow = true,
+        };
+
+        if (File.Exists(apphost))
+        {
+            info.FileName = apphost;
+            info.ArgumentList.Add("serve");
+        }
+        else if (File.Exists(dll))
+        {
+            info.FileName = "dotnet";
+            info.ArgumentList.Add(dll);
+            info.ArgumentList.Add("serve");
+        }
+        else
+        {
+            info.FileName = "dotnet";
+            info.ArgumentList.Add("run");
+            info.ArgumentList.Add("--project");
+            info.ArgumentList.Add(project);
+            info.ArgumentList.Add("-c");
+            info.ArgumentList.Add("Release");
+            info.ArgumentList.Add("--");
+            info.ArgumentList.Add("serve");
+        }
+
+        info.ArgumentList.Add("--config");
+        info.ArgumentList.Add(configPath);
+        return info;
+    }
+}

host/ViewModels/MainWindowViewModel.cs

@@ -0,0 +1,97 @@
+using System.Collections.ObjectModel;
+using System.IO;
+using Avalonia.Threading;
+using CommonwealthOnline.Host.Services;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+
+namespace CommonwealthOnline.Host.ViewModels;
+
+public partial class MainWindowViewModel : ObservableObject
+{
+    private const int MaxLogLines = 2000;
+
+    private readonly ServerController _controller = new();
+    private readonly string _serverDir = System.IO.Directory.GetCurrentDirectory();
+    private readonly string _configPath =
+        Path.Combine(System.IO.Directory.GetCurrentDirectory(), "commonwealth-server.json");
+
+    [ObservableProperty] private string _serverName;
+    [ObservableProperty] private string _host;
+    [ObservableProperty] private int _port;
+    [ObservableProperty] private int _maxPlayers;
+    [ObservableProperty] private int _adminPort;
+    [ObservableProperty] private string _logVerbosity;
+    [ObservableProperty] private bool _enableGnsTransport;
+    [ObservableProperty] private bool _isRunning;
+    [ObservableProperty] private string _statusText = "Stopped";
+
+    public ObservableCollection<string> Log { get; } = new();
+
+    public string[] VerbosityOptions { get; } = { "error", "warning", "info", "debug" };
+
+    public MainWindowViewModel()
+    {
+        var config = ServerConfig.Load(_configPath);
+        _serverName = config.ServerName;
+        _host = config.Host;
+        _port = config.Port;
+        _maxPlayers = config.MaxPlayers;
+        _adminPort = config.AdminPort;
+        _logVerbosity = config.LogVerbosity;
+        _enableGnsTransport = config.EnableGnsTransport;
+
+        _controller.LogReceived += line =>
+            Dispatcher.UIThread.Post(() => Append(line));
+        _controller.RunningChanged += running =>
+            Dispatcher.UIThread.Post(() =>
+            {
+                IsRunning = running;
+                StatusText = running ? "Running" : "Stopped";
+                StartCommand.NotifyCanExecuteChanged();
+                StopCommand.NotifyCanExecuteChanged();
+            });
+    }
+
+    private void Append(string line)
+    {
+        Log.Add(line);
+        while (Log.Count > MaxLogLines)
+        {
+            Log.RemoveAt(0);
+        }
+    }
+
+    private ServerConfig CurrentConfig() => new()
+    {
+        ServerName = ServerName,
+        Host = Host,
+        Port = Port,
+        MaxPlayers = MaxPlayers,
+        AdminPort = AdminPort,
+        LogVerbosity = LogVerbosity,
+        EnableGnsTransport = EnableGnsTransport,
+    };
+
+    [RelayCommand]
+    private void Save() => CurrentConfig().Save(_configPath);
+
+    [RelayCommand(CanExecute = nameof(CanStart))]
+    private void Start()
+    {
+        Save();
+        Append($"[host] starting server on {Host}:{Port}...");
+        _controller.Start(_serverDir, _configPath);
+    }
+
+    private bool CanStart() => !IsRunning;
+
+    [RelayCommand(CanExecute = nameof(CanStop))]
+    private void Stop()
+    {
+        Append("[host] stopping server...");
+        _controller.Stop();
+    }
+
+    private bool CanStop() => IsRunning;
+}

host/Views/MainWindow.axaml

@@ -0,0 +1,73 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="clr-namespace:CommonwealthOnline.Host.ViewModels"
+        x:Class="CommonwealthOnline.Host.Views.MainWindow"
+        x:DataType="vm:MainWindowViewModel"
+        Width="920" Height="640"
+        MinWidth="760" MinHeight="520"
+        Title="Commonwealth Online — Server Host"
+        Background="{StaticResource CoBackgroundBrush}">
+
+  <Grid RowDefinitions="Auto,*,Auto" Margin="18">
+
+    <Image Grid.Row="0" Source="/Assets/logo.png" Height="88"
+           HorizontalAlignment="Left" Margin="0,0,0,14" />
+
+    <Grid Grid.Row="1" ColumnDefinitions="330,*">
+
+      <StackPanel Grid.Column="0" Spacing="9" Margin="0,0,18,0">
+        <TextBlock Text="SERVER" Foreground="{StaticResource CoAccentBrush}"
+                   FontWeight="Bold" FontSize="13" />
+        <TextBox Watermark="Server name" Text="{Binding ServerName}" />
+        <Grid ColumnDefinitions="*,*">
+          <TextBox Grid.Column="0" Watermark="Host" Text="{Binding Host}" Margin="0,0,4,0" />
+          <TextBox Grid.Column="1" Watermark="Port" Text="{Binding Port}" Margin="4,0,0,0" />
+        </Grid>
+        <Grid ColumnDefinitions="*,*">
+          <TextBox Grid.Column="0" Watermark="Max players" Text="{Binding MaxPlayers}" Margin="0,0,4,0" />
+          <TextBox Grid.Column="1" Watermark="Admin port" Text="{Binding AdminPort}" Margin="4,0,0,0" />
+        </Grid>
+        <TextBlock Text="LOG VERBOSITY" Foreground="{StaticResource CoAccentBrush}"
+                   FontWeight="Bold" FontSize="12" Margin="0,4,0,0" />
+        <ComboBox HorizontalAlignment="Stretch"
+                  ItemsSource="{Binding VerbosityOptions}"
+                  SelectedItem="{Binding LogVerbosity}" />
+        <CheckBox Content="Enable GNS transport" IsChecked="{Binding EnableGnsTransport}"
+                  Foreground="{StaticResource CoTextBrush}" />
+        <Button Content="Save config" Command="{Binding SaveCommand}"
+                HorizontalAlignment="Stretch" />
+      </StackPanel>
+
+      <Border Grid.Column="1" Background="{StaticResource CoSurfaceBrush}"
+              CornerRadius="4" Padding="10">
+        <ScrollViewer>
+          <ItemsControl ItemsSource="{Binding Log}">
+            <ItemsControl.ItemTemplate>
+              <DataTemplate>
+                <TextBlock Text="{Binding}" Foreground="{StaticResource CoTextBrush}"
+                           FontFamily="Cascadia Mono,Consolas,monospace" FontSize="12"
+                           TextWrapping="Wrap" />
+              </DataTemplate>
+            </ItemsControl.ItemTemplate>
+          </ItemsControl>
+        </ScrollViewer>
+      </Border>
+
+    </Grid>
+
+    <Grid Grid.Row="2" ColumnDefinitions="Auto,*,Auto,Auto" Margin="0,14,0,0">
+      <TextBlock Grid.Column="0" Text="Status:" Foreground="{StaticResource CoTextBrush}"
+                 VerticalAlignment="Center" Margin="0,0,6,0" />
+      <TextBlock Grid.Column="1" Text="{Binding StatusText}"
+                 Foreground="{StaticResource CoAccentBrush}" FontWeight="Bold"
+                 VerticalAlignment="Center" />
+      <Button Grid.Column="2" Content="Start" Command="{Binding StartCommand}"
+              Margin="0,0,8,0" Padding="26,7"
+              Background="{StaticResource CoAccentBrush}" Foreground="#0E120B" FontWeight="Bold" />
+      <Button Grid.Column="3" Content="Stop" Command="{Binding StopCommand}"
+              Padding="26,7"
+              Background="{StaticResource CoDangerBrush}" Foreground="White" FontWeight="Bold" />
+    </Grid>
+
+  </Grid>
+</Window>

host/Views/MainWindow.axaml.cs

@@ -0,0 +1,11 @@
+using Avalonia.Controls;
+
+namespace CommonwealthOnline.Host.Views;
+
+public partial class MainWindow : Window
+{
+    public MainWindow()
+    {
+        InitializeComponent();
+    }
+}