now it works

Mlaumcherb.Client.Avalonia/холопы/ErrorHelper.cs

@@ -0,0 +1,36 @@
+using Avalonia.Controls;
+using DTLib.Demystifier;
+using Mlaumcherb.Client.Avalonia.зримое;
+using MsBox.Avalonia;
+using MsBox.Avalonia.Dto;
+using MsBox.Avalonia.Enums;
+using MsBox.Avalonia.Models;
+
+namespace Mlaumcherb.Client.Avalonia.холопы;
+
+public static class ErrorHelper
+{
+    internal static void ShowMessageBox(string context, Exception err) 
+        => ShowMessageBox(context, err.ToStringDemystified());
+
+    internal static async void ShowMessageBox(string context, string err)
+    {
+        LauncherApp.Logger.LogError(context, err);
+        var box = MessageBoxManager.GetMessageBoxCustom(new MessageBoxCustomParams
+            {
+                ButtonDefinitions = new List<ButtonDefinition> { new() { Name = "пон" } },
+                ContentTitle = "ОШИБКА",
+                ContentMessage = err,
+                Icon = Icon.Error,
+                WindowStartupLocation = WindowStartupLocation.CenterOwner,
+                CanResize = true,
+                MaxWidth = 1000,
+                MaxHeight = 1000,
+                SizeToContent = SizeToContent.WidthAndHeight,
+                ShowInCenter = true,
+                Topmost = true
+            }
+        );
+        await box.ShowAsync().ConfigureAwait(false);
+    }
+}

Mlaumcherb.Client.Avalonia/холопы/LZMAHelper.cs

@@ -0,0 +1,26 @@
+namespace Mlaumcherb.Client.Avalonia.холопы;
+
+/// <summary>
+/// https://gist.github.com/ststeiger/cb9750664952f775a341
+/// </summary>
+public static class LZMAHelper
+{
+    public static void Decompress(Stream inputStream, Stream outputStream)
+    {
+        var decoder = new SevenZip.Compression.LZMA.Decoder();
+        var properties = new byte[5];
+        // Read decoder properties
+        if (inputStream.Read(properties, 0, 5) != 5)
+            throw new Exception("lzma stream is too short");
+        decoder.SetDecoderProperties(properties);
+        
+        // Read decompressed data size
+        var fileLengthBytes = new byte[8];
+        if(inputStream.Read(fileLengthBytes, 0, 8) != 8)
+            throw new Exception("lzma stream is too short");
+        long fileLength = BitConverter.ToInt64(fileLengthBytes, 0);
+        
+        // Decode
+        decoder.Code(inputStream, outputStream, -1, fileLength, null);
+    }
+}

Mlaumcherb.Client.Avalonia/холопы/PathHelper.cs

@@ -0,0 +1,57 @@
+using Mlaumcherb.Client.Avalonia.зримое;
+
+namespace Mlaumcherb.Client.Avalonia.холопы;
+
+public static class PathHelper
+{
+    public static IOPath GetRootFullPath() =>
+        System.IO.Path.GetFullPath(new IOPath(LauncherApp.Config.minecraft_dir).ToString());
+    
+    public static IOPath GetAssetsDir() => 
+        Path.Concat(GetRootFullPath(), "assets");
+    
+    public static IOPath GetAssetIndexFilePath(string id) => 
+        Path.Concat(GetAssetsDir(), $"assets/indexes/{id}.json");
+    
+    public static IOPath GetVersionDescriptorPath(string id) => 
+        Path.Concat(GetVersionDir(id), id + ".json");
+
+    public static IOPath GetVersionsDir() => 
+        Path.Concat(GetRootFullPath(), "versions");
+    
+    public static IOPath GetVersionDir(string id) => 
+        Path.Concat(GetVersionsDir(), id);
+
+    public static IOPath GetVersionJarFilePath(string id) =>
+        Path.Concat(GetVersionDir(id), id + ".jar");
+    
+    public static IOPath GetLibrariesDir() => 
+        Path.Concat(GetRootFullPath(), "libraries");
+
+    public static IOPath GetNativeLibrariesDir(string id) =>
+        Path.Concat(GetVersionDir(id), "natives", PlatformHelper.GetOsAndArch());
+    
+    public static IOPath GetJavaRuntimesDir() => 
+        Path.Concat(GetRootFullPath(), "java");
+    
+    
+    public static IOPath GetJavaRuntimeDir(string id) => 
+        Path.Concat(GetJavaRuntimesDir(), PlatformHelper.GetOsAndArch(), id);
+
+    public static IOPath GetJavaBinDir(string id) =>
+        Path.Concat(GetJavaRuntimeDir(id), "bin");
+    public static IOPath GetJavaExecutablePath(string id, bool debug)
+    {
+        string executable_name = "java";
+        if (debug)
+            executable_name += "w";
+        if(OperatingSystem.IsWindows())
+            executable_name += ".exe";
+        return Path.Concat(GetJavaBinDir(id), executable_name);
+    }
+
+    public static string GetLog4jConfigFileName() => "log4j.xml";
+    
+    public static IOPath GetLog4jConfigFilePath() =>
+        Path.Concat(GetAssetsDir(), GetLog4jConfigFileName());
+}

Mlaumcherb.Client.Avalonia/холопы/PlatformHelper.cs

@@ -0,0 +1,55 @@
+using System.Runtime.InteropServices;
+using Mlaumcherb.Client.Avalonia.классы;
+
+// ReSharper disable CollectionNeverUpdated.Global
+
+namespace Mlaumcherb.Client.Avalonia.холопы;
+
+public static class PlatformHelper
+{
+    public static bool CheckOs(Os os) =>
+        os.name switch
+        {
+            null => true,
+            "osx" => OperatingSystem.IsMacOS(),
+            "linux" => OperatingSystem.IsLinux(),
+            "windows" => OperatingSystem.IsWindows(),
+            _ => throw new ArgumentOutOfRangeException(os.name)
+        }
+        && os.arch switch
+        {
+            null => true,
+            "i386" or "x86" => RuntimeInformation.OSArchitecture == Architecture.X86,
+            "x64" => RuntimeInformation.OSArchitecture == Architecture.X64,
+            "arm64" => RuntimeInformation.OSArchitecture == Architecture.Arm64,
+            _ => false
+        };
+
+    public static string GetOs() =>
+        Environment.OSVersion.Platform switch
+        {
+            PlatformID.Win32NT => "windows",
+            PlatformID.Unix => "linux",
+            PlatformID.MacOSX => "osx",
+            _ => throw new PlatformNotSupportedException("OS not supported")
+        };
+    
+    public static string GetArch() =>
+        RuntimeInformation.OSArchitecture switch
+        {
+            Architecture.X86 => "x86",
+            Architecture.X64 => "x64",
+            Architecture.Arm64 => "arm64",
+            _ => throw new PlatformNotSupportedException("OS not supported")
+        };
+    
+    public static string GetArchOld() =>
+        RuntimeInformation.OSArchitecture switch
+        {
+            Architecture.X86 => "32",
+            Architecture.X64 => "64",
+            _ => throw new PlatformNotSupportedException("OS not supported")
+        };
+
+    public static string GetOsAndArch() => GetOs() + '-' + GetArch();
+}