Introduce layers, ports and a composition root

Ports in Application/Abstractions, adapters in Infrastructure, hand-wired
AppServices (no reflection, as PublishAot requires). Adds a test project.

.gitignore

@@ -3,3 +3,7 @@
 /.idea
 /.vs
 starter/
+
+# Build output of any project in the solution
+[Bb]in/
+[Oo]bj/

StarterNG.Tests/Fakes/FakeStrings.cs

@@ -0,0 +1,26 @@
+using StarterNG.Application.Abstractions;
+
+namespace StarterNG.Tests.Fakes;
+
+/// <summary>
+/// Translation table that echoes keys back, so assertions can name the key that
+/// a screen or check would have shown.
+/// </summary>
+public sealed class FakeStrings : ILocalizedStrings
+{
+    private readonly Dictionary<string, string> _overrides = new(StringComparer.Ordinal);
+
+    public string this[string key] => _overrides.TryGetValue(key, out var value) ? value : key;
+
+    public string Opt(string key) => _overrides.TryGetValue(key, out var value) ? value : string.Empty;
+
+    public string CurrentLanguage => "English";
+
+    public string CurrentLangCode => "en";
+
+    public FakeStrings With(string key, string value)
+    {
+        _overrides[key] = value;
+        return this;
+    }
+}

StarterNG.Tests/Fakes/FixedClock.cs

@@ -0,0 +1,16 @@
+using StarterNG.Application.Abstractions;
+
+namespace StarterNG.Tests.Fakes;
+
+/// <summary>A clock frozen at a chosen instant.</summary>
+public sealed class FixedClock : IClock
+{
+    public FixedClock(DateTime now)
+    {
+        Now = now;
+    }
+
+    public DateTime Now { get; set; }
+
+    public DateTime UtcNow => Now.ToUniversalTime();
+}

StarterNG.Tests/Fakes/InMemoryFileSystem.cs

@@ -0,0 +1,131 @@
+using System.Text;
+using StarterNG.Application.Abstractions;
+
+namespace StarterNG.Tests.Fakes;
+
+/// <summary>
+/// An <see cref="IFileSystem"/> over a dictionary, so a whole MaSzyna
+/// installation can be described inline in a test.
+/// </summary>
+/// <remarks>
+/// Paths are normalised to forward slashes and compared case-insensitively,
+/// matching how the parsers treat installation paths on both platforms.
+/// </remarks>
+public sealed class InMemoryFileSystem : IFileSystem
+{
+    private readonly Dictionary<string, byte[]> _files = new(StringComparer.OrdinalIgnoreCase);
+    private readonly HashSet<string> _directories = new(StringComparer.OrdinalIgnoreCase);
+
+    public DateTime LastWriteTimeUtc { get; set; } = new(2026, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+
+    /// <summary>Adds a text file, creating its parent directories.</summary>
+    public InMemoryFileSystem WithFile(string path, string contents)
+    {
+        string key = Normalize(path);
+        _files[key] = Encoding.UTF8.GetBytes(contents);
+        AddParents(key);
+        return this;
+    }
+
+    /// <summary>Adds an empty directory.</summary>
+    public InMemoryFileSystem WithDirectory(string path)
+    {
+        string key = Normalize(path);
+        _directories.Add(key);
+        AddParents(key);
+        return this;
+    }
+
+    public bool FileExists(string path) => _files.ContainsKey(Normalize(path));
+
+    public bool DirectoryExists(string path) => _directories.Contains(Normalize(path));
+
+    public string ReadAllText(string path) => Encoding.UTF8.GetString(Bytes(path));
+
+    public string ReadAllText(string path, Encoding encoding) => encoding.GetString(Bytes(path));
+
+    public string[] ReadAllLines(string path) =>
+        ReadAllText(path).Split('\n').Select(line => line.TrimEnd('\r')).ToArray();
+
+    public Stream OpenRead(string path) => new MemoryStream(Bytes(path), writable: false);
+
+    public void WriteAllText(string path, string contents) => WithFile(path, contents);
+
+    public void WriteAllText(string path, string contents, Encoding encoding)
+    {
+        string key = Normalize(path);
+        _files[key] = encoding.GetBytes(contents);
+        AddParents(key);
+    }
+
+    public void WriteAllLines(string path, IEnumerable<string> lines) =>
+        WithFile(path, string.Join("\n", lines));
+
+    public void WriteAllBytes(string path, byte[] bytes)
+    {
+        string key = Normalize(path);
+        _files[key] = bytes;
+        AddParents(key);
+    }
+
+    public void CreateDirectory(string path) => WithDirectory(path);
+
+    public void DeleteFile(string path) => _files.Remove(Normalize(path));
+
+    public void CopyFile(string sourcePath, string destinationPath, bool overwrite)
+    {
+        string destination = Normalize(destinationPath);
+        if (!overwrite && _files.ContainsKey(destination))
+            throw new IOException($"{destinationPath} already exists");
+        WriteAllBytes(destinationPath, Bytes(sourcePath));
+    }
+
+    public IReadOnlyList<string> GetFiles(string path, string searchPattern = "*")
+    {
+        string prefix = Normalize(path) + "/";
+        var pattern = ToRegex(searchPattern);
+        return _files.Keys
+            .Where(key => key.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
+            .Where(key => !key[prefix.Length..].Contains('/'))
+            .Where(key => pattern.IsMatch(key[prefix.Length..]))
+            .OrderBy(key => key, StringComparer.OrdinalIgnoreCase)
+            .ToList();
+    }
+
+    public IReadOnlyList<string> GetDirectories(string path)
+    {
+        string prefix = Normalize(path) + "/";
+        return _directories
+            .Where(key => key.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
+            .Where(key => !key[prefix.Length..].Contains('/'))
+            .OrderBy(key => key, StringComparer.OrdinalIgnoreCase)
+            .ToList();
+    }
+
+    public DateTime GetLastWriteTimeUtc(string path) => LastWriteTimeUtc;
+
+    private byte[] Bytes(string path) =>
+        _files.TryGetValue(Normalize(path), out var bytes)
+            ? bytes
+            : throw new FileNotFoundException(path);
+
+    private void AddParents(string key)
+    {
+        int slash = key.LastIndexOf('/');
+        while (slash > 0)
+        {
+            key = key[..slash];
+            if (!_directories.Add(key))
+                return;
+            slash = key.LastIndexOf('/');
+        }
+    }
+
+    private static string Normalize(string path) =>
+        path.Replace('\\', '/').TrimEnd('/');
+
+    private static System.Text.RegularExpressions.Regex ToRegex(string searchPattern) =>
+        new("^" + System.Text.RegularExpressions.Regex.Escape(searchPattern)
+                .Replace("\\*", ".*").Replace("\\?", ".") + "$",
+            System.Text.RegularExpressions.RegexOptions.IgnoreCase);
+}

StarterNG.Tests/FileDiagnosticsLogTests.cs

@@ -0,0 +1,45 @@
+using StarterNG.Infrastructure.Adapters;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class FileDiagnosticsLogTests
+{
+    private static FileDiagnosticsLog Build(out InMemoryFileSystem files)
+    {
+        files = new InMemoryFileSystem();
+        return new FileDiagnosticsLog(files, new FixedClock(new DateTime(2026, 3, 7, 14, 5, 0)),
+                                      new GamePaths("game"));
+    }
+
+    [Fact]
+    public void Log_timestamps_each_line_from_the_clock()
+    {
+        var log = Build(out _);
+
+        log.Log("scenery loaded");
+
+        Assert.Equal("2026-03-07 14:05:00  scenery loaded", log.Text);
+    }
+
+    [Fact]
+    public void Exceptions_are_logged_with_their_context_and_type()
+    {
+        var log = Build(out _);
+
+        log.Log("scenery/foo.scn", new InvalidOperationException("bad node"));
+
+        Assert.Contains("scenery/foo.scn: InvalidOperationException: bad node", log.Text);
+    }
+
+    [Fact]
+    public void Clear_drops_everything_logged_so_far()
+    {
+        var log = Build(out _);
+        log.Log("first");
+
+        log.Clear();
+
+        Assert.Equal(string.Empty, log.Text);
+    }
+}

StarterNG.Tests/GamePathsTests.cs

@@ -0,0 +1,26 @@
+using StarterNG.Infrastructure.Adapters;
+
+namespace StarterNG.Tests;
+
+public class GamePathsTests
+{
+    [Fact]
+    public void Wellknown_folders_hang_off_the_installation_root()
+    {
+        var paths = new GamePaths(Path.Combine("opt", "maszyna"));
+
+        Assert.Equal(Path.Combine("opt", "maszyna", "scenery"), paths.Scenery);
+        Assert.Equal(Path.Combine("opt", "maszyna", "dynamic"), paths.Dynamic);
+        Assert.Equal(Path.Combine("opt", "maszyna", "textures", "mini"), paths.MiniTextures);
+        Assert.Equal(Path.Combine("opt", "maszyna", "starter", "bledy.txt"), paths.DiagnosticsLog);
+    }
+
+    [Fact]
+    public void FromRoot_joins_segments_below_the_root()
+    {
+        var paths = new GamePaths("game");
+
+        Assert.Equal(Path.Combine("game", "data", "load_weights.txt"),
+                     paths.FromRoot("data", "load_weights.txt"));
+    }
+}

StarterNG.Tests/InstallationCheckTests.cs

@@ -0,0 +1,39 @@
+using StarterNG.Infrastructure;
+using StarterNG.Infrastructure.Adapters;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class InstallationCheckTests
+{
+    [Fact]
+    public void An_empty_folder_reports_every_missing_game_directory()
+    {
+        var strings = new FakeStrings().With("FaultNoDir", "missing {0}");
+        var check = new InstallationCheck(new GamePaths("game"), new InMemoryFileSystem(), strings);
+
+        var faults = check.Run();
+
+        Assert.Contains("missing /dynamic", faults);
+        Assert.Contains("missing /scenery", faults);
+        Assert.Contains("FaultNoWeights", faults);
+    }
+
+    [Fact]
+    public void A_complete_installation_reports_no_missing_directories()
+    {
+        var files = new InMemoryFileSystem()
+            .WithDirectory(Path.Combine("game", "dynamic"))
+            .WithDirectory(Path.Combine("game", "sounds"))
+            .WithDirectory(Path.Combine("game", "models"))
+            .WithDirectory(Path.Combine("game", "scenery"))
+            .WithDirectory(Path.Combine("game", "textures"))
+            .WithFile(Path.Combine("game", "data", "load_weights.txt"), "");
+        var strings = new FakeStrings().With("FaultNoDir", "missing {0}");
+
+        var faults = new InstallationCheck(new GamePaths("game"), files, strings).Run();
+
+        Assert.DoesNotContain(faults, fault => fault.StartsWith("missing "));
+        Assert.DoesNotContain("FaultNoWeights", faults);
+    }
+}

StarterNG.Tests/StarterNG.Tests.csproj

@@ -0,0 +1,25 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.2" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="xunit" Version="2.9.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\StarterNG\StarterNG.csproj" />
+  </ItemGroup>
+
+</Project>

StarterNG.sln

@@ -5,6 +5,8 @@ VisualStudioVersion = 18.1.11312.151 d18.0
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "StarterNG", "StarterNG\StarterNG.csproj", "{D1E8A3A3-3269-415A-94AD-D6F370D7E4FD}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "StarterNG.Tests", "StarterNG.Tests\StarterNG.Tests.csproj", "{00B068D7-2F49-4CAA-BC21-506503EBDFC8}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -21,6 +23,14 @@ Global
 		{D1E8A3A3-3269-415A-94AD-D6F370D7E4FD}.Release|Any CPU.Build.0 = Release|Any CPU
 		{D1E8A3A3-3269-415A-94AD-D6F370D7E4FD}.Release|x64.ActiveCfg = Release|x64
 		{D1E8A3A3-3269-415A-94AD-D6F370D7E4FD}.Release|x64.Build.0 = Release|x64
+		{00B068D7-2F49-4CAA-BC21-506503EBDFC8}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{00B068D7-2F49-4CAA-BC21-506503EBDFC8}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{00B068D7-2F49-4CAA-BC21-506503EBDFC8}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{00B068D7-2F49-4CAA-BC21-506503EBDFC8}.Debug|x64.Build.0 = Debug|Any CPU
+		{00B068D7-2F49-4CAA-BC21-506503EBDFC8}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{00B068D7-2F49-4CAA-BC21-506503EBDFC8}.Release|Any CPU.Build.0 = Release|Any CPU
+		{00B068D7-2F49-4CAA-BC21-506503EBDFC8}.Release|x64.ActiveCfg = Release|Any CPU
+		{00B068D7-2F49-4CAA-BC21-506503EBDFC8}.Release|x64.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

StarterNG/App.axaml.cs

@@ -8,16 +8,22 @@ using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
 using Avalonia.Threading;
+using StarterNG.Application;
 using StarterNG.Classes;
 using StarterNG.Infrastructure;
 using StarterNG.Services;
 
 namespace StarterNG;
 
-public partial class App : Application
+public partial class App : Avalonia.Application
 {
 
-    public static LocalizationService Loc { get; } = new();
+    /// <summary>
+    /// The translation table, as a static source for the XAML bindings. Code
+    /// should take <see cref="Application.Abstractions.ILocalizedStrings"/>
+    /// through its constructor rather than reading this.
+    /// </summary>
+    public static LocalizationService Loc => AppServices.Current.Localization;
 
     public override void Initialize()
     {

StarterNG/Application/Abstractions/IClock.cs

@@ -0,0 +1,15 @@
+namespace StarterNG.Application.Abstractions;
+
+using System;
+
+/// <summary>
+/// Port over the system clock. Scenery weather defaults, timetable rendering and
+/// log timestamps all depend on "now"; routing them through a clock keeps those
+/// rules deterministic under test.
+/// </summary>
+public interface IClock
+{
+    DateTime Now { get; }
+
+    DateTime UtcNow { get; }
+}

StarterNG/Application/Abstractions/IDiagnosticsLog.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Collections.Generic;
+
+namespace StarterNG.Application.Abstractions;
+
+/// <summary>
+/// Port over the starter's error log. Domain and application code depends on
+/// this interface only; the file-backed implementation and the message box that
+/// surfaces faults to the user live in Infrastructure and Presentation.
+/// </summary>
+public interface IDiagnosticsLog
+{
+    void Log(string message);
+
+    void Log(string context, Exception exception);
+
+    void Log(IEnumerable<string> messages);
+
+    /// <summary>Everything logged so far, newline separated.</summary>
+    string Text { get; }
+
+    void Clear();
+
+    void Flush();
+}

StarterNG/Application/Abstractions/IFileSystem.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+
+namespace StarterNG.Application.Abstractions;
+
+/// <summary>
+/// Port over the file system. Everything that reads or writes the MaSzyna
+/// installation goes through this interface instead of <see cref="File"/> and
+/// <see cref="Directory"/>, so parsers and use cases can be exercised against an
+/// in-memory installation in tests.
+/// </summary>
+/// <remarks>
+/// Kept deliberately narrow: only the operations the application actually
+/// performs are exposed. Paths are passed through verbatim to the adapter, which
+/// resolves them relative to the process working directory just like the
+/// framework methods it replaces.
+/// </remarks>
+public interface IFileSystem
+{
+    bool FileExists(string path);
+
+    bool DirectoryExists(string path);
+
+    string ReadAllText(string path);
+
+    string ReadAllText(string path, Encoding encoding);
+
+    string[] ReadAllLines(string path);
+
+    Stream OpenRead(string path);
+
+    void WriteAllText(string path, string contents);
+
+    void WriteAllText(string path, string contents, Encoding encoding);
+
+    void WriteAllLines(string path, IEnumerable<string> lines);
+
+    void WriteAllBytes(string path, byte[] bytes);
+
+    void CreateDirectory(string path);
+
+    void DeleteFile(string path);
+
+    void CopyFile(string sourcePath, string destinationPath, bool overwrite);
+
+    /// <summary>Top-level files, empty when the directory does not exist.</summary>
+    IReadOnlyList<string> GetFiles(string path, string searchPattern = "*");
+
+    /// <summary>Top-level directories, empty when the directory does not exist.</summary>
+    IReadOnlyList<string> GetDirectories(string path);
+
+    DateTime GetLastWriteTimeUtc(string path);
+}

StarterNG/Application/Abstractions/IGamePaths.cs

@@ -0,0 +1,34 @@
+namespace StarterNG.Application.Abstractions;
+
+/// <summary>
+/// The layout of a MaSzyna installation. Replaces the
+/// <c>Directory.GetCurrentDirectory()</c> calls and hard-coded "scenery/",
+/// "dynamic", "textures/mini/" literals that were previously spread across
+/// parsers, views and the loader.
+/// </summary>
+public interface IGamePaths
+{
+    /// <summary>Installation root: the folder holding eu07.exe.</summary>
+    string Root { get; }
+
+    /// <summary>Scenery definitions (*.scn).</summary>
+    string Scenery { get; }
+
+    /// <summary>Rolling stock: dynamic/&lt;maker&gt;/&lt;vehicle&gt;/textures.txt.</summary>
+    string Dynamic { get; }
+
+    /// <summary>Vehicle thumbnails used by the depot and the consist strip.</summary>
+    string MiniTextures { get; }
+
+    /// <summary>Simulator data files (load_weights.txt and friends).</summary>
+    string Data { get; }
+
+    /// <summary>Starter-owned configuration: presets, profiles, key bindings.</summary>
+    string StarterConfig { get; }
+
+    /// <summary>The starter's own error log (starter/bledy.txt).</summary>
+    string DiagnosticsLog { get; }
+
+    /// <summary>Resolves a path relative to <see cref="Root"/>.</summary>
+    string FromRoot(params string[] segments);
+}

StarterNG/Application/Abstractions/ILocalizedStrings.cs

@@ -0,0 +1,22 @@
+namespace StarterNG.Application.Abstractions;
+
+/// <summary>
+/// Port over the translation table. Anything that needs a user-facing string
+/// takes this, rather than reaching for the concrete localization service or a
+/// static on <c>App</c>.
+/// </summary>
+public interface ILocalizedStrings
+{
+    /// <summary>
+    /// Translation for a key. Missing keys return the key itself (and are logged
+    /// once), so an untranslated screen stays usable.
+    /// </summary>
+    string this[string key] { get; }
+
+    /// <summary>Lookup for a key that may legitimately be absent; "" when missing.</summary>
+    string Opt(string key);
+
+    string CurrentLanguage { get; }
+
+    string CurrentLangCode { get; }
+}

StarterNG/Application/Abstractions/IProcessLauncher.cs

@@ -0,0 +1,42 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace StarterNG.Application.Abstractions;
+
+/// <summary>
+/// A process the starter has launched or adopted. Exposes only what the starter
+/// needs — whether the simulator is still up, and a way to await its exit — so
+/// the presentation layer never handles <see cref="System.Diagnostics.Process"/>
+/// directly.
+/// </summary>
+public interface IProcessHandle
+{
+    bool HasExited { get; }
+
+    Task WaitForExitAsync(CancellationToken cancellationToken = default);
+}
+
+/// <summary>
+/// Port over process creation: starting the simulator, opening a file, folder or
+/// URL in the desktop shell, and adopting an already running simulator.
+/// </summary>
+public interface IProcessLauncher
+{
+    /// <summary>
+    /// Starts an executable with the given arguments. Returns null when the
+    /// process could not be created; <paramref name="error"/> then carries the
+    /// reason for display.
+    /// </summary>
+    IProcessHandle? Start(string executablePath, IReadOnlyList<string> arguments, string? workingDirectory,
+                          out string? error);
+
+    /// <summary>
+    /// Hands a path or URL to the desktop shell (explorer, xdg-open, ...).
+    /// Returns false and logs when the shell refused it.
+    /// </summary>
+    bool OpenInShell(string pathOrUrl);
+
+    /// <summary>The first running process with that name, or null.</summary>
+    IProcessHandle? FindRunning(string processName);
+}

StarterNG/Application/AppServices.cs

@@ -0,0 +1,75 @@
+using System;
+using StarterNG.Application.Abstractions;
+using StarterNG.Infrastructure.Adapters;
+using StarterNG.Services;
+
+namespace StarterNG.Application;
+
+/// <summary>
+/// The composition root: the single place where concrete adapters are chosen and
+/// wired to the ports the rest of the application depends on.
+/// </summary>
+/// <remarks>
+/// Hand-written on purpose. The starter publishes with <c>PublishAot</c> and
+/// <c>PublishTrimmed</c>, which rules out reflection-based containers; the object
+/// graph is small enough that explicit construction is also the clearest
+/// documentation of what depends on what.
+///
+/// <see cref="Current"/> is a service locator and is used in exactly one kind of
+/// place — the entry point and the view constructors Avalonia creates for us,
+/// which cannot take arguments. Everything below that boundary receives its
+/// dependencies through its constructor; new code must not reach for
+/// <see cref="Current"/>.
+/// </remarks>
+public sealed class AppServices
+{
+    private static AppServices? _current;
+
+    private AppServices(IGamePaths paths, IFileSystem files, IClock clock)
+    {
+        Paths = paths;
+        Files = files;
+        Clock = clock;
+
+        var log = new FileDiagnosticsLog(files, clock, paths);
+        Log = log;
+        Processes = new SystemProcessLauncher(log);
+        Localization = new LocalizationService(log);
+    }
+
+    /// <summary>
+    /// The graph built by the entry point. Throws when read before
+    /// <see cref="Initialize"/>, which would mean a static initializer somewhere
+    /// ran ahead of the composition root.
+    /// </summary>
+    public static AppServices Current =>
+        _current ?? throw new InvalidOperationException(
+            "AppServices.Current read before Initialize(); the composition root must be built first.");
+
+    /// <summary>Builds the production graph. Called once, from the entry point.</summary>
+    public static AppServices Initialize(IGamePaths? paths = null, IFileSystem? files = null, IClock? clock = null)
+    {
+        _current = new AppServices(
+            paths ?? GamePaths.ForCurrentDirectory(),
+            files ?? new PhysicalFileSystem(),
+            clock ?? new SystemClock());
+        return _current;
+    }
+
+    public IGamePaths Paths { get; }
+
+    public IFileSystem Files { get; }
+
+    public IClock Clock { get; }
+
+    public IDiagnosticsLog Log { get; }
+
+    public IProcessLauncher Processes { get; }
+
+    /// <summary>
+    /// Exposed as the concrete service rather than <see cref="ILocalizedStrings"/>
+    /// because the XAML binds to it as a change-notifying source; code should take
+    /// the port.
+    /// </summary>
+    public LocalizationService Localization { get; }
+}

StarterNG/Infrastructure/Adapters/FileDiagnosticsLog.cs

@@ -0,0 +1,150 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using StarterNG.Application.Abstractions;
+
+namespace StarterNG.Infrastructure.Adapters;
+
+/// <summary>
+/// <see cref="IDiagnosticsLog"/> that mirrors every line into starter/bledy.txt.
+/// Writing is best-effort: a read-only or full installation directory degrades to
+/// an in-memory log rather than taking the starter down, and a single retry is
+/// made at <see cref="Flush"/> time.
+/// </summary>
+/// <remarks>
+/// Instance state replaces the previous static <c>Diagnostics</c> accumulator, so
+/// tests can assert on what a use case logged without touching disk (pair it with
+/// an in-memory <see cref="IFileSystem"/>).
+/// </remarks>
+public sealed class FileDiagnosticsLog : IDiagnosticsLog
+{
+    private readonly IFileSystem _files;
+    private readonly IClock _clock;
+    private readonly string _logPath;
+
+    private readonly object _gate = new();
+    private readonly List<string> _lines = new();
+
+    private StreamWriter? _writer;
+    private bool _writerFailed;
+
+    public FileDiagnosticsLog(IFileSystem files, IClock clock, IGamePaths paths)
+    {
+        _files = files;
+        _clock = clock;
+        _logPath = paths.DiagnosticsLog;
+    }
+
+    public string LogPath => _logPath;
+
+    public string Text
+    {
+        get { lock (_gate) return string.Join(Environment.NewLine, _lines); }
+    }
+
+    public void Log(string message)
+    {
+        string line = $"{_clock.Now.ToString("yyyy-MM-dd HH:mm:ss", CultureInfo.InvariantCulture)}  {message}";
+        lock (_gate)
+        {
+            _lines.Add(line);
+            Append(line);
+        }
+    }
+
+    public void Log(string context, Exception exception) =>
+        Log($"{context}: {exception.GetType().Name}: {exception.Message}");
+
+    public void Log(IEnumerable<string> messages)
+    {
+        foreach (string message in messages)
+            Log(message);
+    }
+
+    public void Clear()
+    {
+        lock (_gate)
+        {
+            _lines.Clear();
+            CloseWriter();
+            try
+            {
+                if (_files.FileExists(_logPath))
+                    _files.DeleteFile(_logPath);
+            }
+            catch
+            {
+                // A log we cannot delete is not worth failing a user action over.
+            }
+        }
+    }
+
+    public void Flush()
+    {
+        lock (_gate)
+        {
+            if (_lines.Count == 0)
+                return;
+
+            try
+            {
+                _writer?.Flush();
+            }
+            catch (Exception ex)
+            {
+                _writerFailed = true;
+                _lines.Add($"log flush failed: {ex.GetType().Name}: {ex.Message}");
+            }
+
+            if (!_writerFailed && _writer is not null)
+                return;
+
+            // The streaming writer never came up (or died mid-session): fall back
+            // to one bulk write so the session is not lost entirely.
+            try
+            {
+                _files.CreateDirectory(Path.GetDirectoryName(_logPath)!);
+                _files.WriteAllLines(_logPath, _lines);
+            }
+            catch
+            {
+                // Nothing left to try; the in-memory log still backs the UI.
+            }
+        }
+    }
+
+    private void Append(string line)
+    {
+        if (_writerFailed)
+            return;
+
+        try
+        {
+            if (_writer is null)
+            {
+                _files.CreateDirectory(Path.GetDirectoryName(_logPath)!);
+                _writer = new StreamWriter(_logPath, append: false) { AutoFlush = true };
+            }
+            _writer.WriteLine(line);
+        }
+        catch
+        {
+            _writerFailed = true;
+            CloseWriter();
+        }
+    }
+
+    private void CloseWriter()
+    {
+        try
+        {
+            _writer?.Dispose();
+        }
+        catch
+        {
+            // Disposing a broken writer is allowed to fail.
+        }
+        _writer = null;
+    }
+}

StarterNG/Infrastructure/Adapters/GamePaths.cs

@@ -0,0 +1,41 @@
+using System.IO;
+using StarterNG.Application.Abstractions;
+
+namespace StarterNG.Infrastructure.Adapters;
+
+/// <summary>
+/// The stock MaSzyna layout, rooted at the process working directory (the
+/// starter ships inside the installation folder, next to eu07.exe).
+/// </summary>
+public sealed class GamePaths : IGamePaths
+{
+    public GamePaths(string root)
+    {
+        Root = root;
+    }
+
+    /// <summary>The installation the starter was launched from.</summary>
+    public static GamePaths ForCurrentDirectory() => new(Directory.GetCurrentDirectory());
+
+    public string Root { get; }
+
+    public string Scenery => Path.Combine(Root, "scenery");
+
+    public string Dynamic => Path.Combine(Root, "dynamic");
+
+    public string MiniTextures => Path.Combine(Root, "textures", "mini");
+
+    public string Data => Path.Combine(Root, "data");
+
+    public string StarterConfig => Path.Combine(Root, "starter");
+
+    public string DiagnosticsLog => Path.Combine(StarterConfig, "bledy.txt");
+
+    public string FromRoot(params string[] segments)
+    {
+        string result = Root;
+        foreach (string segment in segments)
+            result = Path.Combine(result, segment);
+        return result;
+    }
+}

StarterNG/Infrastructure/Adapters/PhysicalFileSystem.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using StarterNG.Application.Abstractions;
+
+namespace StarterNG.Infrastructure.Adapters;
+
+/// <summary>
+/// <see cref="IFileSystem"/> backed by the real disk. The only place in the
+/// application allowed to touch <see cref="File"/> and <see cref="Directory"/>.
+/// </summary>
+public sealed class PhysicalFileSystem : IFileSystem
+{
+    public bool FileExists(string path) => File.Exists(path);
+
+    public bool DirectoryExists(string path) => Directory.Exists(path);
+
+    public string ReadAllText(string path) => File.ReadAllText(path);
+
+    public string ReadAllText(string path, Encoding encoding) => File.ReadAllText(path, encoding);
+
+    public string[] ReadAllLines(string path) => File.ReadAllLines(path);
+
+    public Stream OpenRead(string path) => File.OpenRead(path);
+
+    public void WriteAllText(string path, string contents) => File.WriteAllText(path, contents);
+
+    public void WriteAllText(string path, string contents, Encoding encoding) =>
+        File.WriteAllText(path, contents, encoding);
+
+    public void WriteAllLines(string path, IEnumerable<string> lines) => File.WriteAllLines(path, lines);
+
+    public void WriteAllBytes(string path, byte[] bytes) => File.WriteAllBytes(path, bytes);
+
+    public void CreateDirectory(string path) => Directory.CreateDirectory(path);
+
+    public void DeleteFile(string path) => File.Delete(path);
+
+    public void CopyFile(string sourcePath, string destinationPath, bool overwrite) =>
+        File.Copy(sourcePath, destinationPath, overwrite);
+
+    public IReadOnlyList<string> GetFiles(string path, string searchPattern = "*") =>
+        Directory.Exists(path) ? Directory.GetFiles(path, searchPattern) : Array.Empty<string>();
+
+    public IReadOnlyList<string> GetDirectories(string path) =>
+        Directory.Exists(path) ? Directory.GetDirectories(path) : Array.Empty<string>();
+
+    public DateTime GetLastWriteTimeUtc(string path) => File.GetLastWriteTimeUtc(path);
+}

StarterNG/Infrastructure/Adapters/SystemClock.cs

@@ -0,0 +1,12 @@
+using System;
+using StarterNG.Application.Abstractions;
+
+namespace StarterNG.Infrastructure.Adapters;
+
+/// <summary><see cref="IClock"/> backed by the machine clock.</summary>
+public sealed class SystemClock : IClock
+{
+    public DateTime Now => DateTime.Now;
+
+    public DateTime UtcNow => DateTime.UtcNow;
+}

StarterNG/Infrastructure/Adapters/SystemProcessLauncher.cs

@@ -0,0 +1,106 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using StarterNG.Application.Abstractions;
+
+namespace StarterNG.Infrastructure.Adapters;
+
+/// <summary>
+/// <see cref="IProcessLauncher"/> backed by <see cref="Process"/>. The only place
+/// in the application that starts an operating-system process.
+/// </summary>
+public sealed class SystemProcessLauncher : IProcessLauncher
+{
+    private readonly IDiagnosticsLog _log;
+
+    public SystemProcessLauncher(IDiagnosticsLog log)
+    {
+        _log = log;
+    }
+
+    public IProcessHandle? Start(string executablePath, IReadOnlyList<string> arguments, string? workingDirectory,
+                                 out string? error)
+    {
+        var info = new ProcessStartInfo
+        {
+            FileName = executablePath,
+            WorkingDirectory = workingDirectory ?? string.Empty,
+            UseShellExecute = false
+        };
+        foreach (string argument in arguments)
+            info.ArgumentList.Add(argument);
+
+        try
+        {
+            var process = Process.Start(info);
+            if (process is null)
+            {
+                error = executablePath;
+                _log.Log($"start {executablePath}: process not created");
+                return null;
+            }
+
+            error = null;
+            return new ProcessHandle(process);
+        }
+        catch (Exception ex)
+        {
+            error = ex.Message;
+            _log.Log($"start {executablePath}", ex);
+            return null;
+        }
+    }
+
+    public bool OpenInShell(string pathOrUrl)
+    {
+        try
+        {
+            Process.Start(new ProcessStartInfo(pathOrUrl) { UseShellExecute = true });
+            return true;
+        }
+        catch (Exception ex)
+        {
+            _log.Log($"open {pathOrUrl}", ex);
+            return false;
+        }
+    }
+
+    public IProcessHandle? FindRunning(string processName)
+    {
+        try
+        {
+            var process = Process.GetProcessesByName(processName).FirstOrDefault();
+            return process is null ? null : new ProcessHandle(process);
+        }
+        catch (Exception ex)
+        {
+            _log.Log($"lookup {processName}", ex);
+            return null;
+        }
+    }
+
+    private sealed class ProcessHandle : IProcessHandle
+    {
+        private readonly Process _process;
+
+        public ProcessHandle(Process process)
+        {
+            _process = process;
+        }
+
+        public bool HasExited
+        {
+            get
+            {
+                try { return _process.HasExited; }
+                catch { return true; }
+            }
+        }
+
+        public Task WaitForExitAsync(CancellationToken cancellationToken = default) =>
+            _process.WaitForExitAsync(cancellationToken);
+    }
+}

StarterNG/Infrastructure/Diagnostics.cs

@@ -1,130 +1,41 @@
 using System;
 using System.Collections.Generic;
-using System.Globalization;
-using System.IO;
 using System.Threading.Tasks;
 using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Threading;
+using StarterNG.Application;
 using StarterNG.Views;
 
 namespace StarterNG.Infrastructure;
 
+/// <summary>
+/// Compatibility facade over <see cref="Application.Abstractions.IDiagnosticsLog"/>
+/// plus the fault dialog.
+/// </summary>
+/// <remarks>
+/// The log itself now lives in <c>Infrastructure.Adapters.FileDiagnosticsLog</c>
+/// and is reached through the composition root. This static shim keeps the
+/// existing call sites compiling while they are migrated to constructor-injected
+/// logging; new code should take <c>IDiagnosticsLog</c> instead.
+/// </remarks>
 public static class Diagnostics
 {
-    private static readonly object Gate = new();
-    private static readonly List<string> Lines = new();
+    private static Application.Abstractions.IDiagnosticsLog Log_ => AppServices.Current.Log;
 
-    private static StreamWriter? _writer;
-    private static bool _writerFailed;
+    public static string LogPath => AppServices.Current.Paths.DiagnosticsLog;
 
-    public static string LogPath =>
-        Path.Combine(Directory.GetCurrentDirectory(), "starter", "bledy.txt");
+    public static string Text => Log_.Text;
 
-    public static string Text
-    {
-        get { lock (Gate) return string.Join(Environment.NewLine, Lines); }
-    }
+    public static void Clear() => Log_.Clear();
 
-    public static void Clear()
-    {
-        lock (Gate)
-        {
-            Lines.Clear();
-            CloseWriter();
-            try
-            {
-                if (File.Exists(LogPath))
-                    File.Delete(LogPath);
-            }
-            catch
-            {
-            }
-        }
-    }
+    public static void Log(string message) => Log_.Log(message);
 
-    public static void Log(string message)
-    {
-        string line = $"{DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss", CultureInfo.InvariantCulture)}  {message}";
-        lock (Gate)
-        {
-            Lines.Add(line);
-            Append(line);
-        }
-    }
+    public static void Log(IEnumerable<string> messages) => Log_.Log(messages);
 
-    public static void Log(IEnumerable<string> messages)
-    {
-        foreach (string message in messages)
-            Log(message);
-    }
+    public static void Log(string context, Exception ex) => Log_.Log(context, ex);
 
-    public static void Log(string context, Exception ex) =>
-        Log($"{context}: {ex.GetType().Name}: {ex.Message}");
-
-    public static void Flush()
-    {
-        lock (Gate)
-        {
-            if (Lines.Count == 0)
-                return;
-
-            try
-            {
-                _writer?.Flush();
-            }
-            catch (Exception ex)
-            {
-                _writerFailed = true;
-                Lines.Add($"log flush failed: {ex.GetType().Name}: {ex.Message}");
-            }
-
-            if (!_writerFailed && _writer is not null)
-                return;
-
-            try
-            {
-                Directory.CreateDirectory(Path.GetDirectoryName(LogPath)!);
-                File.WriteAllLines(LogPath, Lines);
-            }
-            catch
-            {
-            }
-        }
-    }
-
-    private static void Append(string line)
-    {
-        if (_writerFailed)
-            return;
-
-        try
-        {
-            if (_writer is null)
-            {
-                Directory.CreateDirectory(Path.GetDirectoryName(LogPath)!);
-                _writer = new StreamWriter(LogPath, append: false) { AutoFlush = true };
-            }
-            _writer.WriteLine(line);
-        }
-        catch
-        {
-            _writerFailed = true;
-            CloseWriter();
-        }
-    }
-
-    private static void CloseWriter()
-    {
-        try
-        {
-            _writer?.Dispose();
-        }
-        catch
-        {
-        }
-        _writer = null;
-    }
+    public static void Flush() => Log_.Flush();
 
     private static Window? Owner =>
         (Avalonia.Application.Current?.ApplicationLifetime as IClassicDesktopStyleApplicationLifetime)
@@ -132,7 +43,7 @@ public static class Diagnostics
 
     public static Task ReportAsync(string message, string? title = null)
     {
-        Log(message.Replace(Environment.NewLine, " | "));
+        Log_.Log(message.Replace(Environment.NewLine, " | "));
 
         var owner = Owner;
         if (owner is null)
@@ -152,31 +63,13 @@ public static class Diagnostics
             Dispatcher.UIThread.Post(() => _ = ReportAsync(message, title));
     }
 
-    public static List<string> CheckInstallation()
-    {
-        var faults = new List<string>();
-        string root = Directory.GetCurrentDirectory();
-
-        foreach (string folder in new[] { "dynamic", "sounds", "models", "scenery", "textures" })
-            if (!Directory.Exists(Path.Combine(root, folder)))
-                faults.Add(string.Format(App.Loc["FaultNoDir"], "/" + folder));
-
-        if (!File.Exists(Path.Combine(root, "data", "load_weights.txt")))
-            faults.Add(App.Loc["FaultNoWeights"]);
-
-        if (Classes.GameData.Instance.Sceneries.Count == 0)
-            faults.Add(App.Loc["FaultNoScenery"]);
-
-        if (Classes.GameData.Instance.Vehicles.Textures.Count == 0)
-            faults.Add(App.Loc["FaultNoVehicles"]);
-
-        if (Classes.Physics.IndexedCount == 0)
-            faults.Add(App.Loc["FaultNoPhysics"]);
-
-        if (Classes.Settings.Instance.ResolveExecutable(out var problem) is var _ &&
-            problem == Classes.ExeProblem.NotFound)
-            faults.Add(App.Loc["FaultNoExe"]);
-
-        return faults;
-    }
+    /// <summary>
+    /// Sanity check of the installation the starter was launched from.
+    /// </summary>
+    public static List<string> CheckInstallation() =>
+        new InstallationCheck(
+                AppServices.Current.Paths,
+                AppServices.Current.Files,
+                AppServices.Current.Localization)
+            .Run();
 }

StarterNG/Infrastructure/InstallationCheck.cs

@@ -0,0 +1,56 @@
+using System.Collections.Generic;
+using System.IO;
+using StarterNG.Application.Abstractions;
+using StarterNG.Classes;
+
+namespace StarterNG.Infrastructure;
+
+/// <summary>
+/// Verifies that the folder the starter runs from actually looks like a MaSzyna
+/// installation, and reports what is missing in the user's language.
+/// </summary>
+/// <remarks>
+/// Depends only on ports, so a broken installation can be described in a test by
+/// handing it an empty in-memory file system.
+/// </remarks>
+public sealed class InstallationCheck
+{
+    private static readonly string[] RequiredFolders = { "dynamic", "sounds", "models", "scenery", "textures" };
+
+    private readonly IGamePaths _paths;
+    private readonly IFileSystem _files;
+    private readonly ILocalizedStrings _strings;
+
+    public InstallationCheck(IGamePaths paths, IFileSystem files, ILocalizedStrings strings)
+    {
+        _paths = paths;
+        _files = files;
+        _strings = strings;
+    }
+
+    public List<string> Run()
+    {
+        var faults = new List<string>();
+
+        foreach (string folder in RequiredFolders)
+            if (!_files.DirectoryExists(_paths.FromRoot(folder)))
+                faults.Add(string.Format(_strings["FaultNoDir"], "/" + folder));
+
+        if (!_files.FileExists(Path.Combine(_paths.Data, "load_weights.txt")))
+            faults.Add(_strings["FaultNoWeights"]);
+
+        if (GameData.Instance.Sceneries.Count == 0)
+            faults.Add(_strings["FaultNoScenery"]);
+
+        if (GameData.Instance.Vehicles.Textures.Count == 0)
+            faults.Add(_strings["FaultNoVehicles"]);
+
+        if (Physics.IndexedCount == 0)
+            faults.Add(_strings["FaultNoPhysics"]);
+
+        if (Settings.Instance.ResolveExecutable(out var problem) is var _ && problem == ExeProblem.NotFound)
+            faults.Add(_strings["FaultNoExe"]);
+
+        return faults;
+    }
+}

StarterNG/Program.cs

@@ -1,6 +1,7 @@
 using Avalonia;
 using System;
 using System.Threading.Tasks;
+using StarterNG.Application;
 using StarterNG.Infrastructure;
 
 namespace StarterNG;
@@ -11,6 +12,10 @@ static class Program
     [STAThread]
     public static void Main(string[] args)
     {
+        // Composition root first: everything below, including the crash handlers,
+        // resolves its collaborators from this graph.
+        AppServices.Initialize();
+
         AppDomain.CurrentDomain.UnhandledException += (_, e) =>
         {
             if (e.ExceptionObject is Exception ex)

StarterNG/Services/LocalizationService.cs

@@ -3,16 +3,29 @@ using System.Collections.Generic;
 using System.ComponentModel;
 using System.IO;
 using System.Xml;
+using StarterNG.Application.Abstractions;
 
 namespace StarterNG.Services;
 
-public class LocalizationService : INotifyPropertyChanged
+/// <summary>
+/// Loads the translation table from startercfg/lang/*.xml and exposes it as
+/// <see cref="ILocalizedStrings"/>. Stays a change-notifying class because the
+/// XAML binds to it directly as a static source.
+/// </summary>
+public class LocalizationService : INotifyPropertyChanged, ILocalizedStrings
 {
     public static string LangDirectory =>
         Path.Combine(AppContext.BaseDirectory, "startercfg", "lang");
 
+    private readonly IDiagnosticsLog _log;
+
     private Dictionary<string, string> _strings = new();
 
+    public LocalizationService(IDiagnosticsLog log)
+    {
+        _log = log;
+    }
+
     public event PropertyChangedEventHandler? PropertyChanged;
 
     public event Action? LanguageChanged;
@@ -43,7 +56,7 @@ public class LocalizationService : INotifyPropertyChanged
 
             lock (_reportedMisses)
                 if (_reportedMisses.Add(key))
-                    Infrastructure.Diagnostics.Log($"lang/{CurrentLangCode}: missing key \"{key}\"");
+                    _log.Log($"lang/{CurrentLangCode}: missing key \"{key}\"");
 
             return key;
         }
@@ -58,7 +71,7 @@ public class LocalizationService : INotifyPropertyChanged
 
     public readonly record struct LanguageInfo(string Code, string Name, string Path);
 
-    public static IReadOnlyList<LanguageInfo> AvailableLanguages()
+    public static IReadOnlyList<LanguageInfo> AvailableLanguages(IDiagnosticsLog? log = null)
     {
         var list = new List<LanguageInfo>();
         if (!Directory.Exists(LangDirectory))
@@ -74,7 +87,7 @@ public class LocalizationService : INotifyPropertyChanged
             }
             catch (Exception ex)
             {
-                StarterNG.Infrastructure.Diagnostics.Log($"lang/{Path.GetFileName(path)}", ex);
+                log?.Log($"lang/{Path.GetFileName(path)}", ex);
             }
         }
         return list;
@@ -82,7 +95,7 @@ public class LocalizationService : INotifyPropertyChanged
 
     public string Load(string codeOrName)
     {
-        var languages = AvailableLanguages();
+        var languages = AvailableLanguages(_log);
 
         LanguageInfo? match = null;
         foreach (var lang in languages)