feat(linux): add graphical platform services

2026-07-27 11:54:59 +02:00 · 2026-07-27 11:54:59 +02:00 · 66f114b258
commit 66f114b258
parent 1628d9f587
28 changed files with 1328 additions and 155 deletions
--- a/.github/workflows/headless-portability.yml
+++ b/.github/workflows/headless-portability.yml
@ -11,11 +11,16 @@ on:
      - "src/AcDream.Plugin.Abstractions/**"
      - "src/AcDream.Runtime/**"
      - "src/AcDream.Headless/**"
+      - "src/AcDream.App/**"
+      - "src/AcDream.UI.Abstractions/**"
+      - "src/AcDream.UI.ImGui/**"
      - "tests/AcDream.Core.Tests/**"
      - "tests/AcDream.Core.Net.Tests/**"
      - "tests/AcDream.Content.Tests/**"
      - "tests/AcDream.Runtime.Tests/**"
      - "tests/AcDream.Headless.Tests/**"
+      - "tests/AcDream.App.Tests/**"
+      - "tests/AcDream.UI.Abstractions.Tests/**"
  push:
    paths:
      - ".github/workflows/headless-portability.yml"
@ -26,11 +31,16 @@ on:
      - "src/AcDream.Plugin.Abstractions/**"
      - "src/AcDream.Runtime/**"
      - "src/AcDream.Headless/**"
+      - "src/AcDream.App/**"
+      - "src/AcDream.UI.Abstractions/**"
+      - "src/AcDream.UI.ImGui/**"
      - "tests/AcDream.Core.Tests/**"
      - "tests/AcDream.Core.Net.Tests/**"
      - "tests/AcDream.Content.Tests/**"
      - "tests/AcDream.Runtime.Tests/**"
      - "tests/AcDream.Headless.Tests/**"
+      - "tests/AcDream.App.Tests/**"
+      - "tests/AcDream.UI.Abstractions.Tests/**"
  workflow_dispatch:

 permissions:
@ -95,3 +105,67 @@ jobs:
          Set-Content -LiteralPath headless-k0.json -Value '{"version":1,"sessions":[]}'
          dotnet run --project src/AcDream.Headless/AcDream.Headless.csproj -c Release -- validate --config headless-k0.json
          if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
+
+  linux-graphical:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Install .NET 10
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: "10.0.x"
+
+      - name: Build and publish Linux graphical client
+        shell: pwsh
+        run: |
+          dotnet build src/AcDream.App/AcDream.App.csproj -c Release -r linux-x64
+          if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
+          dotnet publish src/AcDream.App/AcDream.App.csproj `
+            -c Release `
+            -r linux-x64 `
+            --self-contained false `
+            -o artifacts/acdream-linux-x64
+          if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
+
+      - name: Test portable graphical boundary
+        shell: pwsh
+        run: |
+          dotnet test `
+            tests/AcDream.UI.Abstractions.Tests/AcDream.UI.Abstractions.Tests.csproj `
+            -c Release
+          if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
+          dotnet test `
+            tests/AcDream.App.Tests/AcDream.App.Tests.csproj `
+            -c Release `
+            --filter "FullyQualifiedName~LinuxMonotonicFramePacingWaiterTests|FullyQualifiedName~LinuxPlatformBoundaryTests|FullyQualifiedName~GraphicalHostPlatformServicesTests|FullyQualifiedName~GraphicalLegacyConfigurationMigratorTests"
+          if ($LASTEXITCODE -ne 0) { exit $LASTEXITCODE }
+
+      - name: Verify Linux package contract
+        shell: bash
+        run: |
+          set -euo pipefail
+          root=artifacts/acdream-linux-x64
+          test -x "$root/AcDream.App"
+          test -f "$root/AcDream.App.dll"
+          test -f "$root/libglfw.so.3"
+          test -f "$root/libopenal.so"
+          test -f "$root/libcimgui.so"
+          test -f "$root/Rendering/Shaders/mesh_modern.vert"
+          test -f "$root/plugins/AcDream.Plugins.Smoke/AcDream.Plugins.Smoke.dll"
+          test -f "$root/plugins/AcDream.Plugins.Smoke/plugin.json"
+
+          test "$(grep -RIl --include='*.cs' 'LibraryImport(\"kernel32.dll\"' \
+            src/AcDream.App | wc -l)" -eq 1
+          grep -q 'WindowsHighResolutionFramePacingWaiter.cs' < <(
+            grep -RIl --include='*.cs' 'LibraryImport(\"kernel32.dll\"' \
+              src/AcDream.App)
+          ! grep -RIn --include='*.cs' 'LocalApplicationData' \
+            src/AcDream.App src/AcDream.UI.Abstractions
+          ! grep -RIn --include='*.cs' \
+            'WindowsHighResolutionFramePacingWaiter.Create()' \
+            src/AcDream.App \
+            --exclude='FramePacingWaiterFactory.cs' \
+            --exclude='WindowsHighResolutionFramePacingWaiter.cs'
--- a/src/AcDream.App/AcDream.App.csproj
+++ b/src/AcDream.App/AcDream.App.csproj
@ -63,18 +63,42 @@
      <SkipGetTargetFrameworkProperties>true</SkipGetTargetFrameworkProperties>
    </ProjectReference>
  </ItemGroup>
-  <Target Name="CopySmokePluginToPluginsDir" AfterTargets="Build">
+  <Target
+    Name="CopySmokePluginToBuildOutput"
+    AfterTargets="Build"
+    Condition="'$(IsCrossTargetingBuild)' != 'true'">
    <PropertyGroup>
-      <_SmokePluginSourceDir>..\AcDream.Plugins.Smoke\bin\$(Configuration)\net10.0</_SmokePluginSourceDir>
-      <_SmokePluginDestDir>$(OutputPath)plugins\AcDream.Plugins.Smoke</_SmokePluginDestDir>
+      <_SmokePluginSourceDir>$(MSBuildProjectDirectory)/../AcDream.Plugins.Smoke/bin/$(Configuration)/$(TargetFramework)</_SmokePluginSourceDir>
+      <_SmokePluginSourceDir Condition="'$(RuntimeIdentifier)' != ''">$(_SmokePluginSourceDir)/$(RuntimeIdentifier)</_SmokePluginSourceDir>
+      <_SmokePluginDestDir>$(OutputPath)plugins/AcDream.Plugins.Smoke</_SmokePluginDestDir>
    </PropertyGroup>
    <MakeDir Directories="$(_SmokePluginDestDir)" />
    <Copy
-      SourceFiles="$(_SmokePluginSourceDir)\AcDream.Plugins.Smoke.dll"
+      SourceFiles="$(_SmokePluginSourceDir)/AcDream.Plugins.Smoke.dll"
      DestinationFolder="$(_SmokePluginDestDir)"
      SkipUnchangedFiles="true" />
    <WriteLinesToFile
-      File="$(_SmokePluginDestDir)\plugin.json"
+      File="$(_SmokePluginDestDir)/plugin.json"
+      Overwrite="true"
+      Lines="{ &quot;id&quot;: &quot;acdream.smoke&quot;, &quot;displayName&quot;: &quot;Smoke Plugin&quot;, &quot;version&quot;: &quot;0.1.0&quot;, &quot;entryDll&quot;: &quot;AcDream.Plugins.Smoke.dll&quot;, &quot;apiVersion&quot;: 1 }" />
+  </Target>
+
+  <Target
+    Name="CopySmokePluginToPublishOutput"
+    AfterTargets="Publish"
+    Condition="'$(IsCrossTargetingBuild)' != 'true'">
+    <PropertyGroup>
+      <_SmokePluginPublishSourceDir>$(MSBuildProjectDirectory)/../AcDream.Plugins.Smoke/bin/$(Configuration)/$(TargetFramework)</_SmokePluginPublishSourceDir>
+      <_SmokePluginPublishSourceDir Condition="'$(RuntimeIdentifier)' != ''">$(_SmokePluginPublishSourceDir)/$(RuntimeIdentifier)</_SmokePluginPublishSourceDir>
+      <_SmokePluginPublishDestDir>$(PublishDir)plugins/AcDream.Plugins.Smoke</_SmokePluginPublishDestDir>
+    </PropertyGroup>
+    <MakeDir Directories="$(_SmokePluginPublishDestDir)" />
+    <Copy
+      SourceFiles="$(_SmokePluginPublishSourceDir)/AcDream.Plugins.Smoke.dll"
+      DestinationFolder="$(_SmokePluginPublishDestDir)"
+      SkipUnchangedFiles="true" />
+    <WriteLinesToFile
+      File="$(_SmokePluginPublishDestDir)/plugin.json"
      Overwrite="true"
      Lines="{ &quot;id&quot;: &quot;acdream.smoke&quot;, &quot;displayName&quot;: &quot;Smoke Plugin&quot;, &quot;version&quot;: &quot;0.1.0&quot;, &quot;entryDll&quot;: &quot;AcDream.Plugins.Smoke.dll&quot;, &quot;apiVersion&quot;: 1 }" />
  </Target>
--- a/src/AcDream.App/Composition/WorldRenderComposition.cs
+++ b/src/AcDream.App/Composition/WorldRenderComposition.cs
@ -54,6 +54,7 @@ internal sealed record WorldRenderDependencies(
    IGpuResourceRetirementQueue ResourceRetirement,
    ResidencyBudgetOptions ResidencyBudgets,
    uint InitialCenterLandblockId,
+    string DiagnosticsDirectory,
    Action<string> Log);

 internal interface IGameWindowWorldRenderPublication
@ -114,6 +115,7 @@ internal interface IWorldRenderCompositionFactory
        IDatReaderWriter dats,
        BindlessSupport bindless,
        IGpuResourceRetirementQueue retirement,
+        string diagnosticsDirectory,
        ResidencyBudgetOptions budgets);
    void RegisterResidencySources(
        ResidencyManager manager,
@ -293,8 +295,15 @@ internal sealed class RetailWorldRenderCompositionFactory
        IDatReaderWriter dats,
        BindlessSupport bindless,
        IGpuResourceRetirementQueue retirement,
+        string diagnosticsDirectory,
        ResidencyBudgetOptions budgets) =>
-        new(gl, dats, bindless, retirement, budgets);
+        new(
+            gl,
+            dats,
+            bindless,
+            retirement,
+            diagnosticsDirectory,
+            budgets);

    public void RegisterResidencySources(
        ResidencyManager manager,
@ -527,6 +536,7 @@ internal sealed class WorldRenderCompositionPhase
                    content.Dats,
                    bindless,
                    _dependencies.ResourceRetirement,
+                    _dependencies.DiagnosticsDirectory,
                    residency.Budgets),
                _publication.PublishTextureCache,
                WorldRenderCompositionPoint.TextureCachePublished);
--- a/src/AcDream.App/Platform/GraphicalHostPlatformServices.cs
+++ b/src/AcDream.App/Platform/GraphicalHostPlatformServices.cs
@ -0,0 +1,102 @@
+using System.Runtime.InteropServices;
+using AcDream.App.Rendering;
+using AcDream.Runtime.Platform;
+
+namespace AcDream.App.Platform;
+
+internal enum GraphicalHostOperatingSystem
+{
+    Windows,
+    Linux,
+}
+
+internal sealed record GraphicalNativeDependency(
+    string Feature,
+    string PublishedFileName);
+
+internal sealed record GraphicalHostPlatformServices(
+    GraphicalHostOperatingSystem OperatingSystem,
+    Architecture ProcessArchitecture,
+    string RuntimeIdentifier,
+    ApplicationPathSet Paths,
+    IFramePacingWaiterFactory FramePacingWaiters,
+    IReadOnlyList<GraphicalNativeDependency> NativeDependencies)
+{
+    internal static GraphicalHostPlatformServices Resolve()
+    {
+        GraphicalHostOperatingSystem operatingSystem =
+            DetectOperatingSystem();
+        Architecture architecture = RuntimeInformation.ProcessArchitecture;
+        string runtimeIdentifier = ResolveRuntimeIdentifier(
+            operatingSystem,
+            architecture);
+
+        return new GraphicalHostPlatformServices(
+            operatingSystem,
+            architecture,
+            runtimeIdentifier,
+            ApplicationPathSet.Resolve(),
+            new PlatformFramePacingWaiterFactory(operatingSystem),
+            ResolveNativeDependencies(operatingSystem));
+    }
+
+    internal static GraphicalHostOperatingSystem DetectOperatingSystem()
+    {
+        if (System.OperatingSystem.IsWindows())
+            return GraphicalHostOperatingSystem.Windows;
+        if (System.OperatingSystem.IsLinux())
+            return GraphicalHostOperatingSystem.Linux;
+
+        throw new PlatformNotSupportedException(
+            "acdream graphical hosting supports Windows and Linux.");
+    }
+
+    private static string ResolveRuntimeIdentifier(
+        GraphicalHostOperatingSystem operatingSystem,
+        Architecture architecture)
+    {
+        string architectureName = architecture switch
+        {
+            Architecture.X64 => "x64",
+            Architecture.Arm64 => "arm64",
+            Architecture.X86 => "x86",
+            Architecture.Arm => "arm",
+            _ => throw new PlatformNotSupportedException(
+                $"Unsupported graphical process architecture {architecture}."),
+        };
+
+        if (operatingSystem == GraphicalHostOperatingSystem.Linux
+            && architecture != Architecture.X64)
+        {
+            throw new PlatformNotSupportedException(
+                "The first acdream Linux graphical package supports linux-x64 only.");
+        }
+
+        string operatingSystemName =
+            operatingSystem == GraphicalHostOperatingSystem.Windows
+                ? "win"
+                : "linux";
+        return $"{operatingSystemName}-{architectureName}";
+    }
+
+    private static IReadOnlyList<GraphicalNativeDependency>
+        ResolveNativeDependencies(
+            GraphicalHostOperatingSystem operatingSystem) =>
+        operatingSystem switch
+        {
+            GraphicalHostOperatingSystem.Windows =>
+            [
+                new("window/input", "glfw3.dll"),
+                new("developer UI", "cimgui.dll"),
+                new("audio", "soft_oal.dll"),
+            ],
+            GraphicalHostOperatingSystem.Linux =>
+            [
+                new("window/input", "libglfw.so.3"),
+                new("developer UI", "libcimgui.so"),
+                new("audio", "libopenal.so"),
+            ],
+            _ => throw new ArgumentOutOfRangeException(
+                nameof(operatingSystem)),
+        };
+}
--- a/src/AcDream.App/Platform/GraphicalLegacyConfigurationMigrator.cs
+++ b/src/AcDream.App/Platform/GraphicalLegacyConfigurationMigrator.cs
@ -0,0 +1,50 @@
+using AcDream.Runtime.Platform;
+
+namespace AcDream.App.Platform;
+
+internal static class GraphicalLegacyConfigurationMigrator
+{
+    private static readonly string[] FileNames =
+    [
+        "settings.json",
+        "keybinds.json",
+    ];
+
+    internal static IReadOnlyList<string> Migrate(
+        ApplicationPathSet paths)
+    {
+        ArgumentNullException.ThrowIfNull(paths);
+        if (paths.LegacyConfigDirectory is not { } legacyDirectory
+            || PathsEqual(legacyDirectory, paths.ConfigDirectory))
+        {
+            return [];
+        }
+
+        List<string>? migrated = null;
+        foreach (string fileName in FileNames)
+        {
+            string source = Path.Combine(legacyDirectory, fileName);
+            string destination = Path.Combine(
+                paths.ConfigDirectory,
+                fileName);
+            if (!File.Exists(source) || File.Exists(destination))
+                continue;
+
+            Directory.CreateDirectory(paths.ConfigDirectory);
+            File.Copy(source, destination, overwrite: false);
+            (migrated ??= []).Add(destination);
+        }
+
+        return migrated ?? [];
+    }
+
+    private static bool PathsEqual(string left, string right) =>
+        string.Equals(
+            Path.TrimEndingDirectorySeparator(
+                Path.GetFullPath(left)),
+            Path.TrimEndingDirectorySeparator(
+                Path.GetFullPath(right)),
+            OperatingSystem.IsWindows()
+                ? StringComparison.OrdinalIgnoreCase
+                : StringComparison.Ordinal);
+}
--- a/src/AcDream.App/Program.cs
+++ b/src/AcDream.App/Program.cs
@ -1,13 +1,23 @@
 using AcDream.App;
 using AcDream.App.Plugins;
+using AcDream.App.Platform;
 using AcDream.App.Rendering;
 using AcDream.Core.Plugins;
+using AcDream.Runtime.Platform;
 using Serilog;

+GraphicalHostPlatformServices graphicalPlatform =
+    GraphicalHostPlatformServices.Resolve();
+ApplicationPathSet applicationPaths = graphicalPlatform.Paths;
+IReadOnlyList<string> migratedConfigurationFiles =
+    GraphicalLegacyConfigurationMigrator.Migrate(applicationPaths);
+
 if (args.Length >= 1 && args[0] == "ui-studio")
 {
    var so = AcDream.App.Studio.StudioOptions.Parse(args[1..]);
-    using var sw = new AcDream.App.Studio.StudioWindow(so);
+    using var sw = new AcDream.App.Studio.StudioWindow(
+        so,
+        applicationPaths);
    sw.Run();
    return 0;
 }
@ -16,6 +26,20 @@ Log.Logger = new LoggerConfiguration()
    .MinimumLevel.Debug()
    .WriteTo.Console()
    .CreateLogger();
+foreach (string migratedConfigurationFile in migratedConfigurationFiles)
+{
+    Log.Information(
+        "migrated legacy graphical configuration to {Path}",
+        migratedConfigurationFile);
+}
+Log.Information(
+    "graphical platform {RuntimeIdentifier}; native closure: {NativeDependencies}",
+    graphicalPlatform.RuntimeIdentifier,
+    string.Join(
+        ", ",
+        graphicalPlatform.NativeDependencies.Select(
+            dependency =>
+                $"{dependency.Feature}={dependency.PublishedFileName}")));

 var datDir = args.FirstOrDefault() ?? Environment.GetEnvironmentVariable("ACDREAM_DAT_DIR");
 if (string.IsNullOrWhiteSpace(datDir))
@ -36,7 +60,8 @@ using var window = new GameWindow(
    runtimeOptions,
    worldGameState,
    worldEvents,
-    uiRegistry);
+    uiRegistry,
+    graphicalPlatform);
 var host = new AppPluginHost(
    new SerilogAdapter(Log.Logger),
    worldGameState,
@ -44,27 +69,65 @@ var host = new AppPluginHost(
    window.Selection,
    uiRegistry);

-var pluginsDir = Path.Combine(AppContext.BaseDirectory, "plugins");
-Log.Information("scanning plugins in {PluginsDir}", pluginsDir);
-
 var loaded = new List<LoadedPlugin>();
+var loadedPluginIds = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+StringComparer pathComparer =
+    graphicalPlatform.OperatingSystem
+        == GraphicalHostOperatingSystem.Windows
+        ? StringComparer.OrdinalIgnoreCase
+        : StringComparer.Ordinal;
+string[] pluginRoots =
+[
+    .. new[]
+    {
+        Path.Combine(AppContext.BaseDirectory, "plugins"),
+        applicationPaths.PluginsDirectory,
+    }.Distinct(pathComparer),
+];
+
+foreach (string pluginsDir in pluginRoots)
+{
+    Log.Information("scanning plugins in {PluginsDir}", pluginsDir);
    foreach (var result in PluginDiscovery.Scan(pluginsDir))
    {
        if (!result.Success)
        {
-        Log.Warning("plugin discovery failed for {Dir}: {Error}", result.PluginDirectory, result.Error);
+            Log.Warning(
+                "plugin discovery failed for {Dir}: {Error}",
+                result.PluginDirectory,
+                result.Error);
            continue;
        }

-    var loadResult = PluginLoader.Load(result.PluginDirectory, result.Manifest!, host);
+        if (loadedPluginIds.Contains(result.Manifest!.Id))
+        {
+            Log.Warning(
+                "skipping duplicate plugin id {Id} from {Dir}",
+                result.Manifest.Id,
+                result.PluginDirectory);
+            continue;
+        }
+
+        var loadResult = PluginLoader.Load(
+            result.PluginDirectory,
+            result.Manifest,
+            host);
        if (!loadResult.Success)
        {
-        Log.Warning("plugin load failed for {Id}: {Error}", result.Manifest!.Id, loadResult.Error);
+            Log.Warning(
+                "plugin load failed for {Id}: {Error}",
+                result.Manifest.Id,
+                loadResult.Error);
            continue;
        }

+        loadedPluginIds.Add(result.Manifest.Id);
        loaded.Add(loadResult);
-    Log.Information("loaded plugin {Id} ({DisplayName})", result.Manifest!.Id, result.Manifest.DisplayName);
+        Log.Information(
+            "loaded plugin {Id} ({DisplayName})",
+            result.Manifest.Id,
+            result.Manifest.DisplayName);
+    }
 }

 try
--- a/src/AcDream.App/Rendering/DisplayFramePacingController.cs
+++ b/src/AcDream.App/Rendering/DisplayFramePacingController.cs
@ -72,6 +72,17 @@ internal sealed class DisplayFramePacingController : IDisposable
    {
    }

+    internal DisplayFramePacingController(
+        bool uncappedRendering,
+        FrameProfiler profiler,
+        IFramePacingWaiterFactory waiterFactory)
+        : this(
+            uncappedRendering,
+            profiler,
+            new FramePacingController(waiterFactory))
+    {
+    }
+
    internal DisplayFramePacingController(
        bool uncappedRendering,
        FrameProfiler profiler,
--- a/src/AcDream.App/Rendering/FramePacingController.cs
+++ b/src/AcDream.App/Rendering/FramePacingController.cs
@ -25,9 +25,17 @@ internal sealed class FramePacingController : IDisposable
    private bool _disposed;

    public FramePacingController()
+        : this(PlatformFramePacingWaiterFactory.ForCurrentProcess())
+    {
+    }
+
+    internal FramePacingController(
+        IFramePacingWaiterFactory waiterFactory)
        : this(
            StopwatchFramePacingClock.Instance,
-            WindowsHighResolutionFramePacingWaiter.Create(),
+            (waiterFactory
+                ?? throw new ArgumentNullException(nameof(waiterFactory)))
+                .Create(),
            ownsWaiter: true)
    {
    }
--- a/src/AcDream.App/Rendering/FramePacingWaiterFactory.cs
+++ b/src/AcDream.App/Rendering/FramePacingWaiterFactory.cs
@ -0,0 +1,38 @@
+using AcDream.App.Platform;
+
+namespace AcDream.App.Rendering;
+
+internal interface IFramePacingWaiterFactory
+{
+    IFramePacingWaiter Create();
+}
+
+/// <summary>
+/// The sole startup-time platform selector for software frame waits.
+/// Frame policy and deadline behavior remain platform-neutral.
+/// </summary>
+internal sealed class PlatformFramePacingWaiterFactory
+    : IFramePacingWaiterFactory
+{
+    private readonly GraphicalHostOperatingSystem _operatingSystem;
+
+    internal PlatformFramePacingWaiterFactory(
+        GraphicalHostOperatingSystem operatingSystem)
+    {
+        _operatingSystem = operatingSystem;
+    }
+
+    internal static PlatformFramePacingWaiterFactory ForCurrentProcess() =>
+        new(GraphicalHostPlatformServices.DetectOperatingSystem());
+
+    public IFramePacingWaiter Create() =>
+        _operatingSystem switch
+        {
+            GraphicalHostOperatingSystem.Windows =>
+                WindowsHighResolutionFramePacingWaiter.Create(),
+            GraphicalHostOperatingSystem.Linux =>
+                LinuxMonotonicFramePacingWaiter.Create(),
+            _ => throw new ArgumentOutOfRangeException(
+                nameof(_operatingSystem)),
+        };
+}
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@ -4,9 +4,11 @@ using AcDream.App.Physics;
 using AcDream.App.Rendering.Scene;
 using AcDream.App.Rendering.Wb;
 using AcDream.App.Settings;
+using AcDream.App.Platform;
 using AcDream.App.World;
 using AcDream.Content;
 using AcDream.Runtime;
+using AcDream.Runtime.Platform;
 using AcDream.Runtime.Entities;
 using AcDream.Runtime.Gameplay;
 using AcDream.Runtime.Session;
@ -498,16 +500,19 @@ public sealed class GameWindow :
        _runtimeDiagnosticCommands = new();
    private readonly AcDream.App.Combat.LiveCombatModeCommandSlot
        _liveCombatModeCommands = new();
-    // K.1c: load user-customized bindings from %LOCALAPPDATA%\acdream\keybinds.json,
+    // K.1c/L0: load user-customized bindings from the canonical per-platform
+    // configuration path,
    // falling back to the retail-faithful defaults if the file is missing
    // or corrupt. This is THE single source of truth for the keymap at
    // startup — no other call to RetailDefaults() / AcdreamCurrentDefaults()
    // should land in the GameWindow construction path.
-    private readonly AcDream.UI.Abstractions.Input.KeyBindings _keyBindings = LoadStartupKeyBindings();
+    private readonly AcDream.UI.Abstractions.Input.KeyBindings _keyBindings;
+    private readonly GraphicalHostPlatformServices _platformServices;
+    private readonly ApplicationPathSet _applicationPaths;

-    private static AcDream.UI.Abstractions.Input.KeyBindings LoadStartupKeyBindings()
+    private static AcDream.UI.Abstractions.Input.KeyBindings LoadStartupKeyBindings(
+        string path)
    {
-        var path = AcDream.UI.Abstractions.Input.KeyBindings.DefaultPath();
        var bindings = AcDream.UI.Abstractions.Input.KeyBindings.LoadOrDefault(path);
        Console.WriteLine($"keybinds: loaded {bindings.All.Count} bindings from {path}");
        return bindings;
@ -571,8 +576,28 @@ public sealed class GameWindow :
        WorldGameState worldGameState,
        WorldEvents worldEvents,
        AcDream.App.Plugins.BufferedUiRegistry? uiRegistry = null)
+        : this(
+            options,
+            worldGameState,
+            worldEvents,
+            uiRegistry,
+            GraphicalHostPlatformServices.Resolve())
+    {
+    }
+
+    internal GameWindow(
+        AcDream.App.RuntimeOptions options,
+        WorldGameState worldGameState,
+        WorldEvents worldEvents,
+        AcDream.App.Plugins.BufferedUiRegistry? uiRegistry,
+        GraphicalHostPlatformServices platformServices)
    {
        _options = options ?? throw new System.ArgumentNullException(nameof(options));
+        _platformServices = platformServices
+            ?? throw new ArgumentNullException(nameof(platformServices));
+        _applicationPaths = _platformServices.Paths;
+        _keyBindings = LoadStartupKeyBindings(
+            _applicationPaths.KeyBindingsFile);
        _runtime = new GameRuntime(new GameRuntimeDependencies(
            _combatAttackOperations,
            _combatTargetOperations,
@ -611,10 +636,11 @@ public sealed class GameWindow :
        _worldEvents = worldEvents;
        _displayFramePacing = new DisplayFramePacingController(
            options.UncappedRendering,
-            _frameProfiler);
+            _frameProfiler,
+            _platformServices.FramePacingWaiters);
        _runtimeSettings = new RuntimeSettingsController(
            new JsonRuntimeSettingsStorage(
-                AcDream.UI.Abstractions.Panels.Settings.SettingsStore.DefaultPath()),
+                _applicationPaths.SettingsFile),
            log: Console.WriteLine);
        _animationDiagnostics = AnimationPresentationDiagnostics.FromEnvironment();
        _uiRegistry = uiRegistry;
@ -1209,7 +1235,9 @@ public sealed class GameWindow :
                        devToolsFrameDiagnostics);
                    IRuntimeKeyBindingTarget? keyBindingTarget =
                        hostInputCamera.InputDispatcher is { } settingsDispatcher
-                            ? new RuntimeKeyBindingTarget(settingsDispatcher)
+                            ? new RuntimeKeyBindingTarget(
+                                settingsDispatcher,
+                                _applicationPaths.KeyBindingsFile)
                            : null;
                    optionalDevTools = new SettingsDevToolsOptionalDependencies(
                        devToolsFacts,
@ -1249,6 +1277,7 @@ public sealed class GameWindow :
                        _gpuFrameFlights!,
                        _options.ResidencyBudgets,
                        initialCenterLandblockId,
+                        _applicationPaths.DiagnosticsDirectory,
                        Console.WriteLine),
                    this).Compose(platformResult, contentEffectsAudio, settingsDevTools);
                Console.WriteLine(
--- a/src/AcDream.App/Rendering/LinuxMonotonicFramePacingWaiter.cs
+++ b/src/AcDream.App/Rendering/LinuxMonotonicFramePacingWaiter.cs
@ -0,0 +1,151 @@
+using System.ComponentModel;
+using System.Runtime.InteropServices;
+
+namespace AcDream.App.Rendering;
+
+/// <summary>
+/// Low-CPU Linux frame wait using an absolute CLOCK_MONOTONIC deadline.
+/// EINTR resumes against the original deadline, so signals cannot shorten or
+/// cumulatively extend a normal presentation wait.
+/// </summary>
+internal sealed partial class LinuxMonotonicFramePacingWaiter
+    : IFramePacingWaiter,
+      IDisposable
+{
+    private const int ClockMonotonic = 1;
+    private const int TimerAbsolute = 1;
+    private const int Interrupted = 4;
+    private const long NanosecondsPerSecond = 1_000_000_000L;
+    private bool _disposed;
+
+    private LinuxMonotonicFramePacingWaiter()
+    {
+    }
+
+    internal static LinuxMonotonicFramePacingWaiter Create()
+    {
+        if (!OperatingSystem.IsLinux())
+        {
+            throw new PlatformNotSupportedException(
+                "The monotonic Linux frame waiter requires Linux.");
+        }
+
+        return new LinuxMonotonicFramePacingWaiter();
+    }
+
+    public void Wait(long durationTicks, long clockFrequency)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        if (durationTicks <= 0 || clockFrequency <= 0)
+            return;
+
+        int result = ClockGetTime(ClockMonotonic, out Timespec now);
+        if (result != 0)
+        {
+            throw new Win32Exception(
+                Marshal.GetLastPInvokeError(),
+                "Could not read the Linux monotonic clock.");
+        }
+
+        long durationNanoseconds = ConvertTicksToNanoseconds(
+            durationTicks,
+            clockFrequency);
+        Timespec deadline = AddNanoseconds(now, durationNanoseconds);
+        do
+        {
+            result = ClockNanosleep(
+                ClockMonotonic,
+                TimerAbsolute,
+                in deadline,
+                0);
+        }
+        while (result == Interrupted);
+
+        if (result != 0)
+        {
+            throw new Win32Exception(
+                result,
+                "Waiting on the Linux monotonic frame deadline failed.");
+        }
+    }
+
+    internal static long ConvertTicksToNanoseconds(
+        long durationTicks,
+        long clockFrequency)
+    {
+        if (durationTicks <= 0)
+            throw new ArgumentOutOfRangeException(nameof(durationTicks));
+        if (clockFrequency <= 0)
+            throw new ArgumentOutOfRangeException(nameof(clockFrequency));
+
+        long wholeSeconds = Math.DivRem(
+            durationTicks,
+            clockFrequency,
+            out long remainder);
+        if (wholeSeconds >= long.MaxValue / NanosecondsPerSecond)
+            return long.MaxValue;
+
+        long wholeNanoseconds = wholeSeconds * NanosecondsPerSecond;
+        long fractionalNanoseconds = checked((long)Math.Ceiling(
+            remainder * (double)NanosecondsPerSecond / clockFrequency));
+        if (wholeNanoseconds > long.MaxValue - fractionalNanoseconds)
+            return long.MaxValue;
+
+        return Math.Max(1L, wholeNanoseconds + fractionalNanoseconds);
+    }
+
+    private static Timespec AddNanoseconds(
+        Timespec timestamp,
+        long nanoseconds)
+    {
+        long seconds = nanoseconds / NanosecondsPerSecond;
+        long remainder = nanoseconds % NanosecondsPerSecond;
+        long resultSeconds = timestamp.Seconds > long.MaxValue - seconds
+            ? long.MaxValue
+            : timestamp.Seconds + seconds;
+        if (resultSeconds == long.MaxValue)
+        {
+            return new Timespec(
+                long.MaxValue,
+                NanosecondsPerSecond - 1L);
+        }
+
+        long resultNanoseconds = timestamp.Nanoseconds + remainder;
+        if (resultNanoseconds >= NanosecondsPerSecond)
+        {
+            if (resultSeconds == long.MaxValue)
+            {
+                return new Timespec(
+                    long.MaxValue,
+                    NanosecondsPerSecond - 1L);
+            }
+
+            resultSeconds++;
+            resultNanoseconds -= NanosecondsPerSecond;
+        }
+
+        return new Timespec(resultSeconds, resultNanoseconds);
+    }
+
+    public void Dispose() => _disposed = true;
+
+    [StructLayout(LayoutKind.Sequential)]
+    private readonly record struct Timespec(
+        long Seconds,
+        long Nanoseconds);
+
+    [LibraryImport(
+        "libc",
+        EntryPoint = "clock_gettime",
+        SetLastError = true)]
+    private static partial int ClockGetTime(
+        int clockId,
+        out Timespec timestamp);
+
+    [LibraryImport("libc", EntryPoint = "clock_nanosleep")]
+    private static partial int ClockNanosleep(
+        int clockId,
+        int flags,
+        in Timespec request,
+        nint remainder);
+}
--- a/src/AcDream.App/Rendering/RenderBootstrap.cs
+++ b/src/AcDream.App/Rendering/RenderBootstrap.cs
@ -124,7 +124,8 @@ public sealed record RenderStack(

 /// <summary>Options for <see cref="RenderBootstrap.Create"/>.</summary>
 public sealed record RenderBootstrapOptions(
-    AcDream.UI.Abstractions.Settings.QualitySettings Quality);
+    AcDream.UI.Abstractions.Settings.QualitySettings Quality,
+    string DiagnosticsDirectory);

 /// <summary>
 /// Constructs the UI Studio's render stack from the production classes,
@ -164,7 +165,12 @@ public static class RenderBootstrap

        // --- TextureCache (GameWindow ~1774) ---
        var frameFlights = new GpuFrameFlightController(gl);
-        var textureCache = new TextureCache(gl, dats, bindless, frameFlights);
+        var textureCache = new TextureCache(
+            gl,
+            dats,
+            bindless,
+            frameFlights,
+            opts.DiagnosticsDirectory);

        // --- AnimLoader (GameWindow ~1240) ---
        var animLoader = new AcDream.Content.Vfx.RetailAnimationLoader(dats);
--- a/src/AcDream.App/Rendering/TextureCache.cs
+++ b/src/AcDream.App/Rendering/TextureCache.cs
@ -18,6 +18,7 @@ public sealed unsafe class TextureCache
 {
    private readonly GL _gl;
    private readonly IDatReaderWriter _dats;
+    private readonly string _diagnosticsDirectory;
    // Handle and decoded dimensions are one atomic cache entry. Keeping them
    // in separate dictionaries allowed GetOrUpload(surfaceId) followed by the
    // sized overload to upload a second GL texture and orphan the first.
@ -86,7 +87,15 @@ public sealed unsafe class TextureCache
    private bool _surfaceHistogramAlreadyDumped;

    public TextureCache(GL gl, IDatReaderWriter dats, Wb.BindlessSupport? bindless = null)
-        : this(gl, dats, bindless, ImmediateGpuResourceRetirementQueue.Instance)
+        : this(
+            gl,
+            dats,
+            bindless,
+            ImmediateGpuResourceRetirementQueue.Instance,
+            Path.Combine(
+                Path.GetTempPath(),
+                "acdream",
+                "diagnostics"))
    {
    }

@ -95,12 +104,15 @@ public sealed unsafe class TextureCache
        IDatReaderWriter dats,
        Wb.BindlessSupport? bindless,
        IGpuResourceRetirementQueue retirementQueue,
+        string diagnosticsDirectory,
        ResidencyBudgetOptions? budgets = null)
    {
        budgets ??= ResidencyBudgetOptions.Default;
        _gl = gl;
        _dats = dats;
        _bindless = bindless;
+        ArgumentException.ThrowIfNullOrWhiteSpace(diagnosticsDirectory);
+        _diagnosticsDirectory = diagnosticsDirectory;
        ArgumentNullException.ThrowIfNull(retirementQueue);
        if (bindless is not null)
        {
@ -602,7 +614,8 @@ public sealed unsafe class TextureCache
    ///    pulled in world content (not just sky/UI/font). The original
    ///    frame-only gate fired during the login/handshake phase where
    ///    OnRender ticks at GUI rates but no world has streamed in.
-    /// Output goes to %LOCALAPPDATA%\acdream\n6-surfaces.txt. Zero cost
+    /// Output goes to the host-provided portable diagnostics directory.
+    /// Zero cost
    /// when off. See spec §5 in
    /// docs/superpowers/specs/2026-05-11-phase-n6-slice1-design.md.
    /// </summary>
@ -638,10 +651,10 @@ public sealed unsafe class TextureCache

    private void DumpSurfaceHistogramCore()
    {
-        var localAppData = System.Environment.GetFolderPath(System.Environment.SpecialFolder.LocalApplicationData);
-        var outDir = System.IO.Path.Combine(localAppData, "acdream");
-        System.IO.Directory.CreateDirectory(outDir);
-        var outPath = System.IO.Path.Combine(outDir, "n6-surfaces.txt");
+        System.IO.Directory.CreateDirectory(_diagnosticsDirectory);
+        var outPath = System.IO.Path.Combine(
+            _diagnosticsDirectory,
+            "n6-surfaces.txt");

        var sb = new System.Text.StringBuilder();
        sb.AppendLine($"# acdream surface-format histogram — generated {DateTime.UtcNow:yyyy-MM-ddTHH:mm:ssZ}");
--- a/src/AcDream.App/Settings/RuntimeKeyBindingTarget.cs
+++ b/src/AcDream.App/Settings/RuntimeKeyBindingTarget.cs
@ -20,11 +20,12 @@ internal sealed class RuntimeKeyBindingTarget : IRuntimeKeyBindingTarget

    public RuntimeKeyBindingTarget(
        InputDispatcher dispatcher,
-        string? path = null,
+        string path,
        Action<string>? log = null)
    {
        _dispatcher = dispatcher ?? throw new ArgumentNullException(nameof(dispatcher));
-        _path = path ?? KeyBindings.DefaultPath();
+        ArgumentException.ThrowIfNullOrWhiteSpace(path);
+        _path = path;
        _log = log ?? Console.WriteLine;
    }

--- a/src/AcDream.App/Studio/StudioWindow.cs
+++ b/src/AcDream.App/Studio/StudioWindow.cs
@ -2,6 +2,7 @@ using System.Numerics;
 using AcDream.Content;
 using AcDream.App.Rendering;
 using AcDream.App.UI;
+using AcDream.Runtime.Platform;
 using DatReaderWriter;
 using Silk.NET.Input;
 using Silk.NET.Maths;
@ -36,6 +37,7 @@ namespace AcDream.App.Studio;
 public sealed class StudioWindow : IDisposable
 {
    private readonly StudioOptions _opts;
+    private readonly ApplicationPathSet _applicationPaths;

    // Created in OnLoad, released in OnClosing.
    private IWindow?      _window;
@ -64,8 +66,17 @@ public sealed class StudioWindow : IDisposable
    private bool _screenshotDone;

    public StudioWindow(StudioOptions opts)
+        : this(opts, ApplicationPathSet.Resolve())
+    {
+    }
+
+    internal StudioWindow(
+        StudioOptions opts,
+        ApplicationPathSet applicationPaths)
    {
        _opts = opts ?? throw new ArgumentNullException(nameof(opts));
+        _applicationPaths = applicationPaths
+            ?? throw new ArgumentNullException(nameof(applicationPaths));
    }

    /// <summary>
@ -77,7 +88,7 @@ public sealed class StudioWindow : IDisposable
        // Resolve quality settings the same way GameWindow.Run() does
        // (SettingsStore → QualitySettings.From → WithEnvOverrides).
        var startupStore   = new AcDream.UI.Abstractions.Panels.Settings.SettingsStore(
-            AcDream.UI.Abstractions.Panels.Settings.SettingsStore.DefaultPath());
+            _applicationPaths.SettingsFile);
        var startupDisplay = startupStore.LoadDisplay();
        var startupBase    = AcDream.UI.Abstractions.Settings.QualitySettings.From(startupDisplay.Quality);
        var startupQuality = AcDream.UI.Abstractions.Settings.QualitySettings.WithEnvOverrides(startupBase);
@ -118,12 +129,17 @@ public sealed class StudioWindow : IDisposable
        // Build QualitySettings for RenderBootstrap (same as Run() above — re-read
        // after the GL context is confirmed, mirroring GameWindow.OnLoad).
        var store   = new AcDream.UI.Abstractions.Panels.Settings.SettingsStore(
-            AcDream.UI.Abstractions.Panels.Settings.SettingsStore.DefaultPath());
+            _applicationPaths.SettingsFile);
        var display = store.LoadDisplay();
        var quality = AcDream.UI.Abstractions.Settings.QualitySettings.WithEnvOverrides(
            AcDream.UI.Abstractions.Settings.QualitySettings.From(display.Quality));

-        _stack = RenderBootstrap.Create(gl, _dats, new RenderBootstrapOptions(quality));
+        _stack = RenderBootstrap.Create(
+            gl,
+            _dats,
+            new RenderBootstrapOptions(
+                quality,
+                _applicationPaths.DiagnosticsDirectory));

        if (_opts.Mockup)
            MockupDesktop.Load(_dats, _stack);
--- a/src/AcDream.Headless/Platform/HeadlessPathSet.cs
+++ b/src/AcDream.Headless/Platform/HeadlessPathSet.cs
@ -1,4 +1,5 @@
 using AcDream.Headless.Configuration;
+using AcDream.Runtime.Platform;

 namespace AcDream.Headless.Platform;

@ -14,86 +15,24 @@ internal sealed record HeadlessPathSet(
        ArgumentNullException.ThrowIfNull(overrides);
        platform ??= HeadlessPlatformEnvironment.Instance;

-        string config;
-        string data;
-        string cache;
-        if (platform.IsWindows)
+        try
        {
-            string roaming = RequireFolder(
-                platform,
-                Environment.SpecialFolder.ApplicationData);
-            string local = RequireFolder(
-                platform,
-                Environment.SpecialFolder.LocalApplicationData);
-            config = Path.Combine(roaming, "acdream");
-            data = Path.Combine(local, "acdream");
-            cache = Path.Combine(local, "acdream", "cache");
-        }
-        else
-        {
-            string home = RequireFolder(
-                platform,
-                Environment.SpecialFolder.UserProfile);
-            config = ResolveXdg(
-                platform,
-                "XDG_CONFIG_HOME",
-                Path.Combine(home, ".config"),
-                "acdream");
-            data = ResolveXdg(
-                platform,
-                "XDG_DATA_HOME",
-                Path.Combine(home, ".local", "share"),
-                "acdream");
-            cache = ResolveXdg(
-                platform,
-                "XDG_CACHE_HOME",
-                Path.Combine(home, ".cache"),
-                "acdream");
-        }
-
+            ApplicationPathSet paths = ApplicationPathSet.Resolve(
+                overrides.ConfigDirectory,
+                overrides.DataDirectory,
+                overrides.CacheDirectory,
+                platform);
            return new HeadlessPathSet(
-            Normalize(overrides.ConfigDirectory ?? config, platform),
-            Normalize(overrides.DataDirectory ?? data, platform),
-            Normalize(overrides.CacheDirectory ?? cache, platform));
+                paths.ConfigDirectory,
+                paths.DataDirectory,
+                paths.CacheDirectory);
        }
-
-    private static string ResolveXdg(
-        IHeadlessPlatformEnvironment platform,
-        string variable,
-        string fallback,
-        string leaf)
+        catch (Exception exception)
+            when (exception is ArgumentException
+                or InvalidOperationException
+                or NotSupportedException)
        {
-        string? configured = platform.GetEnvironmentVariable(variable);
-        string root = string.IsNullOrWhiteSpace(configured)
-            ? fallback
-            : configured;
-        return Path.Combine(root, leaf);
-    }
-
-    private static string RequireFolder(
-        IHeadlessPlatformEnvironment platform,
-        Environment.SpecialFolder folder)
-    {
-        string value = platform.GetFolderPath(folder);
-        if (string.IsNullOrWhiteSpace(value))
-        {
-            throw new HeadlessConfigurationException(
-                $"The operating system did not provide {folder}.");
-        }
-        return value;
-    }
-
-    private static string Normalize(
-        string path,
-        IHeadlessPlatformEnvironment platform)
-    {
-        if (string.IsNullOrWhiteSpace(path))
-        {
-            throw new HeadlessConfigurationException(
-                "Headless directories cannot be empty.");
-        }
-
-        return Path.TrimEndingDirectorySeparator(
-            Path.GetFullPath(path, platform.CurrentDirectory));
+            throw new HeadlessConfigurationException(exception.Message);
+        }
    }
 }
--- a/src/AcDream.Headless/Platform/HeadlessPlatformEnvironment.cs
+++ b/src/AcDream.Headless/Platform/HeadlessPlatformEnvironment.cs
@ -1,11 +1,10 @@
+using AcDream.Runtime.Platform;
+
 namespace AcDream.Headless.Platform;

 internal interface IHeadlessPlatformEnvironment
+    : IApplicationPathEnvironment
 {
-    bool IsWindows { get; }
-    string CurrentDirectory { get; }
-    string? GetEnvironmentVariable(string name);
-    string GetFolderPath(Environment.SpecialFolder folder);
 }

 internal sealed class HeadlessPlatformEnvironment
--- a/src/AcDream.Runtime/Platform/ApplicationPathSet.cs
+++ b/src/AcDream.Runtime/Platform/ApplicationPathSet.cs
@ -0,0 +1,171 @@
+namespace AcDream.Runtime.Platform;
+
+/// <summary>
+/// BCL-only view of the process environment used to resolve portable
+/// application paths exactly once at a host composition root.
+/// </summary>
+public interface IApplicationPathEnvironment
+{
+    bool IsWindows { get; }
+
+    string CurrentDirectory { get; }
+
+    string? GetEnvironmentVariable(string name);
+
+    string GetFolderPath(Environment.SpecialFolder folder);
+}
+
+internal sealed class ApplicationPathEnvironment
+    : IApplicationPathEnvironment
+{
+    internal static ApplicationPathEnvironment Instance { get; } = new();
+
+    private ApplicationPathEnvironment()
+    {
+    }
+
+    public bool IsWindows => OperatingSystem.IsWindows();
+
+    public string CurrentDirectory => Environment.CurrentDirectory;
+
+    public string? GetEnvironmentVariable(string name) =>
+        Environment.GetEnvironmentVariable(name);
+
+    public string GetFolderPath(Environment.SpecialFolder folder) =>
+        Environment.GetFolderPath(folder);
+}
+
+/// <summary>
+/// Canonical portable per-user paths shared by graphical and no-window hosts.
+/// Hosts may override the three roots, but feature code only receives the
+/// resolved immutable paths and never reads operating-system state itself.
+/// </summary>
+public sealed record ApplicationPathSet(
+    string ConfigDirectory,
+    string DataDirectory,
+    string CacheDirectory,
+    string? LegacyConfigDirectory)
+{
+    public string SettingsFile =>
+        Path.Combine(ConfigDirectory, "settings.json");
+
+    public string KeyBindingsFile =>
+        Path.Combine(ConfigDirectory, "keybinds.json");
+
+    public string LogsDirectory =>
+        Path.Combine(DataDirectory, "logs");
+
+    public string ScreenshotsDirectory =>
+        Path.Combine(DataDirectory, "screenshots");
+
+    public string PluginsDirectory =>
+        Path.Combine(DataDirectory, "plugins");
+
+    public string DiagnosticsDirectory =>
+        Path.Combine(CacheDirectory, "diagnostics");
+
+    public static ApplicationPathSet Resolve(
+        string? configDirectory = null,
+        string? dataDirectory = null,
+        string? cacheDirectory = null,
+        IApplicationPathEnvironment? platform = null)
+    {
+        platform ??= ApplicationPathEnvironment.Instance;
+
+        string config;
+        string data;
+        string cache;
+        if (platform.IsWindows)
+        {
+            string roaming = RequireFolder(
+                platform,
+                Environment.SpecialFolder.ApplicationData);
+            string local = RequireFolder(
+                platform,
+                Environment.SpecialFolder.LocalApplicationData);
+            config = Path.Combine(roaming, "acdream");
+            data = Path.Combine(local, "acdream");
+            cache = Path.Combine(local, "acdream", "cache");
+        }
+        else
+        {
+            string home = RequireFolder(
+                platform,
+                Environment.SpecialFolder.UserProfile);
+            config = ResolveXdg(
+                platform,
+                "XDG_CONFIG_HOME",
+                Path.Combine(home, ".config"),
+                "acdream");
+            data = ResolveXdg(
+                platform,
+                "XDG_DATA_HOME",
+                Path.Combine(home, ".local", "share"),
+                "acdream");
+            cache = ResolveXdg(
+                platform,
+                "XDG_CACHE_HOME",
+                Path.Combine(home, ".cache"),
+                "acdream");
+        }
+
+        string? legacyConfigDirectory =
+            platform.IsWindows && configDirectory is null
+                ? Path.Combine(
+                    RequireFolder(
+                        platform,
+                        Environment.SpecialFolder.LocalApplicationData),
+                    "acdream")
+                : null;
+
+        return new ApplicationPathSet(
+            Normalize(configDirectory ?? config, platform),
+            Normalize(dataDirectory ?? data, platform),
+            Normalize(cacheDirectory ?? cache, platform),
+            legacyConfigDirectory is null
+                ? null
+                : Normalize(legacyConfigDirectory, platform));
+    }
+
+    private static string ResolveXdg(
+        IApplicationPathEnvironment platform,
+        string variable,
+        string fallback,
+        string leaf)
+    {
+        string? configured = platform.GetEnvironmentVariable(variable);
+        string root = string.IsNullOrWhiteSpace(configured)
+            ? fallback
+            : configured;
+        return Path.Combine(root, leaf);
+    }
+
+    private static string RequireFolder(
+        IApplicationPathEnvironment platform,
+        Environment.SpecialFolder folder)
+    {
+        string value = platform.GetFolderPath(folder);
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            throw new InvalidOperationException(
+                $"The operating system did not provide {folder}.");
+        }
+
+        return value;
+    }
+
+    private static string Normalize(
+        string path,
+        IApplicationPathEnvironment platform)
+    {
+        if (string.IsNullOrWhiteSpace(path))
+        {
+            throw new ArgumentException(
+                "Application directories cannot be empty.",
+                nameof(path));
+        }
+
+        return Path.TrimEndingDirectorySeparator(
+            Path.GetFullPath(path, platform.CurrentDirectory));
+    }
+}
--- a/src/AcDream.UI.Abstractions/Input/KeyBindings.cs
+++ b/src/AcDream.UI.Abstractions/Input/KeyBindings.cs
@ -18,7 +18,7 @@ namespace AcDream.UI.Abstractions.Input;
 /// K.1c: <see cref="RetailDefaults"/> now returns the full retail-faithful
 /// preset (byte-precise to <c>retail-default.keymap.txt</c>);
 /// <see cref="LoadOrDefault"/> + <see cref="SaveToFile"/> persist the
-/// table to JSON under <see cref="DefaultPath"/> with version-based
+/// table to JSON at a host-provided portable path with version-based
 /// migration. <see cref="AcdreamCurrentDefaults"/> is preserved as a
 /// reference for tests pinning the older WASD-only behavior, but is no
 /// longer the GameWindow startup source.
@ -596,11 +596,4 @@ public sealed class KeyBindings
        return result;
    }

-    /// <summary>
-    /// Default path: <c>%LOCALAPPDATA%\acdream\keybinds.json</c>.
-    /// </summary>
-    public static string DefaultPath() => Path.Combine(
-        Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
-        "acdream",
-        "keybinds.json");
 }
--- a/src/AcDream.UI.Abstractions/Panels/Settings/SettingsStore.cs
+++ b/src/AcDream.UI.Abstractions/Panels/Settings/SettingsStore.cs
@ -13,7 +13,8 @@ public readonly record struct UiWindowPosition(float X, float Y);
 /// <summary>
 /// JSON-backed persistence for non-keybind settings (Display today; future
 /// tabs Audio / Gameplay / Chat / Character will be added to the same
-/// file). Path: <c>%LOCALAPPDATA%\acdream\settings.json</c>. Coexists
+/// file). The graphical host supplies a canonical portable configuration
+/// path. Coexists
 /// with <c>keybinds.json</c>, which retains its own
 /// <see cref="Input.KeyBindings.LoadOrDefault"/> path.
 ///
@ -41,12 +42,6 @@ public sealed class SettingsStore
        _path = path ?? throw new ArgumentNullException(nameof(path));
    }

-    /// <summary>Default path: <c>%LOCALAPPDATA%\acdream\settings.json</c>.</summary>
-    public static string DefaultPath() => Path.Combine(
-        Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
-        "acdream",
-        "settings.json");
-
    /// <summary>
    /// Load Display settings. Missing file → <see cref="DisplaySettings.Default"/>.
    /// Missing individual keys fall back to the corresponding default
--- a/tests/AcDream.App.Tests/Composition/WorldRenderCompositionTests.cs
+++ b/tests/AcDream.App.Tests/Composition/WorldRenderCompositionTests.cs
@ -178,6 +178,7 @@ public sealed class WorldRenderCompositionTests
                    ImmediateGpuResourceRetirementQueue.Instance,
                    _budgets,
                    0xA9B4FFFFu,
+                    Path.Combine(Path.GetTempPath(), "acdream-tests"),
                    _ => { }),
                Publication,
                Factory,
@ -297,6 +298,7 @@ public sealed class WorldRenderCompositionTests
            IDatReaderWriter dats,
            BindlessSupport bindless,
            IGpuResourceRetirementQueue retirement,
+            string diagnosticsDirectory,
            ResidencyBudgetOptions budgets)
        {
            TextureBudgets = budgets;
--- a/tests/AcDream.App.Tests/Platform/GraphicalHostPlatformServicesTests.cs
+++ b/tests/AcDream.App.Tests/Platform/GraphicalHostPlatformServicesTests.cs
@ -0,0 +1,56 @@
+using AcDream.App.Platform;
+
+namespace AcDream.App.Tests.Platform;
+
+public sealed class GraphicalHostPlatformServicesTests
+{
+    [Fact]
+    public void CurrentPlatformOwnsPathsPacingAndNativeClosure()
+    {
+        GraphicalHostPlatformServices platform =
+            GraphicalHostPlatformServices.Resolve();
+
+        Assert.NotNull(platform.Paths);
+        Assert.NotNull(platform.FramePacingWaiters);
+        Assert.Equal(3, platform.NativeDependencies.Count);
+        Assert.All(
+            platform.NativeDependencies,
+            dependency =>
+            {
+                Assert.False(string.IsNullOrWhiteSpace(dependency.Feature));
+                Assert.False(string.IsNullOrWhiteSpace(
+                    dependency.PublishedFileName));
+            });
+
+        if (OperatingSystem.IsWindows())
+        {
+            Assert.Equal(
+                GraphicalHostOperatingSystem.Windows,
+                platform.OperatingSystem);
+            Assert.StartsWith(
+                "win-",
+                platform.RuntimeIdentifier,
+                StringComparison.Ordinal);
+            Assert.Contains(
+                platform.NativeDependencies,
+                dependency =>
+                    dependency.PublishedFileName == "glfw3.dll");
+            return;
+        }
+
+        if (OperatingSystem.IsLinux())
+        {
+            Assert.Equal(
+                GraphicalHostOperatingSystem.Linux,
+                platform.OperatingSystem);
+            Assert.Equal("linux-x64", platform.RuntimeIdentifier);
+            Assert.Contains(
+                platform.NativeDependencies,
+                dependency =>
+                    dependency.PublishedFileName == "libglfw.so.3");
+            return;
+        }
+
+        throw new PlatformNotSupportedException();
+    }
+}
--- a/tests/AcDream.App.Tests/Platform/GraphicalLegacyConfigurationMigratorTests.cs
+++ b/tests/AcDream.App.Tests/Platform/GraphicalLegacyConfigurationMigratorTests.cs
@ -0,0 +1,66 @@
+using AcDream.App.Platform;
+using AcDream.Runtime.Platform;
+
+namespace AcDream.App.Tests.Platform;
+
+public sealed class GraphicalLegacyConfigurationMigratorTests
+    : IDisposable
+{
+    private readonly string _root = Path.Combine(
+        Path.GetTempPath(),
+        "acdream-l0-migration-" + Guid.NewGuid().ToString("N"));
+
+    [Fact]
+    public void MissingCanonicalFilesAreCopiedWithoutOverwriting()
+    {
+        string legacy = Path.Combine(_root, "legacy");
+        string canonical = Path.Combine(_root, "canonical");
+        Directory.CreateDirectory(legacy);
+        Directory.CreateDirectory(canonical);
+        File.WriteAllText(
+            Path.Combine(legacy, "settings.json"),
+            "legacy-settings");
+        File.WriteAllText(
+            Path.Combine(legacy, "keybinds.json"),
+            "legacy-keybinds");
+        File.WriteAllText(
+            Path.Combine(canonical, "keybinds.json"),
+            "canonical-keybinds");
+        var paths = new ApplicationPathSet(
+            canonical,
+            Path.Combine(_root, "data"),
+            Path.Combine(_root, "cache"),
+            legacy);
+
+        IReadOnlyList<string> migrated =
+            GraphicalLegacyConfigurationMigrator.Migrate(paths);
+
+        Assert.Single(migrated);
+        Assert.Equal(
+            "legacy-settings",
+            File.ReadAllText(paths.SettingsFile));
+        Assert.Equal(
+            "canonical-keybinds",
+            File.ReadAllText(paths.KeyBindingsFile));
+    }
+
+    [Fact]
+    public void NoLegacyDirectoryProducesNoWrites()
+    {
+        var paths = new ApplicationPathSet(
+            Path.Combine(_root, "canonical"),
+            Path.Combine(_root, "data"),
+            Path.Combine(_root, "cache"),
+            LegacyConfigDirectory: null);
+
+        Assert.Empty(
+            GraphicalLegacyConfigurationMigrator.Migrate(paths));
+        Assert.False(Directory.Exists(paths.ConfigDirectory));
+    }
+
+    public void Dispose()
+    {
+        if (Directory.Exists(_root))
+            Directory.Delete(_root, recursive: true);
+    }
+}
--- a/tests/AcDream.App.Tests/Rendering/LinuxMonotonicFramePacingWaiterTests.cs
+++ b/tests/AcDream.App.Tests/Rendering/LinuxMonotonicFramePacingWaiterTests.cs
@ -0,0 +1,85 @@
+using System.Diagnostics;
+using AcDream.App.Rendering;
+
+namespace AcDream.App.Tests.Rendering;
+
+public sealed class LinuxMonotonicFramePacingWaiterTests
+{
+    [Theory]
+    [InlineData(1L, 1_000_000_000L, 1L)]
+    [InlineData(1L, 3L, 333_333_334L)]
+    [InlineData(15L, 1_000L, 15_000_000L)]
+    [InlineData(6_060L, 1_000_000L, 6_060_000L)]
+    public void TickConversionRoundsUpWithoutReturningZero(
+        long ticks,
+        long frequency,
+        long expected)
+    {
+        Assert.Equal(
+            expected,
+            LinuxMonotonicFramePacingWaiter
+                .ConvertTicksToNanoseconds(ticks, frequency));
+    }
+
+    [Fact]
+    public void PlatformFactorySelectsCurrentOperatingSystem()
+    {
+        IFramePacingWaiter waiter =
+            PlatformFramePacingWaiterFactory
+                .ForCurrentProcess()
+                .Create();
+
+        if (OperatingSystem.IsWindows())
+        {
+            Assert.IsType<WindowsHighResolutionFramePacingWaiter>(
+                waiter);
+            ((IDisposable)waiter).Dispose();
+            return;
+        }
+
+        if (OperatingSystem.IsLinux())
+        {
+            Assert.IsType<LinuxMonotonicFramePacingWaiter>(waiter);
+            ((IDisposable)waiter).Dispose();
+            return;
+        }
+
+        throw new PlatformNotSupportedException();
+    }
+
+    [Fact]
+    public void LinuxWaitBlocksUntilRequestedMonotonicDeadline()
+    {
+        if (!OperatingSystem.IsLinux())
+            return;
+
+        LinuxMonotonicFramePacingWaiter waiter =
+            LinuxMonotonicFramePacingWaiter.Create();
+        long start = Stopwatch.GetTimestamp();
+        waiter.Wait(
+            durationTicks: Stopwatch.Frequency / 200L,
+            clockFrequency: Stopwatch.Frequency);
+        TimeSpan elapsed = Stopwatch.GetElapsedTime(start);
+
+        Assert.True(
+            elapsed >= TimeSpan.FromMilliseconds(4),
+            $"Linux monotonic wait returned after {elapsed.TotalMilliseconds:F3} ms.");
+        Assert.True(
+            elapsed < TimeSpan.FromSeconds(1),
+            $"Linux monotonic wait stalled for {elapsed.TotalMilliseconds:F3} ms.");
+    }
+
+    [Fact]
+    public void LinuxWaiterRejectsUseAfterDisposal()
+    {
+        if (!OperatingSystem.IsLinux())
+            return;
+
+        LinuxMonotonicFramePacingWaiter waiter =
+            LinuxMonotonicFramePacingWaiter.Create();
+        waiter.Dispose();
+
+        Assert.Throws<ObjectDisposedException>(
+            () => waiter.Wait(1, Stopwatch.Frequency));
+    }
+}
--- a/tests/AcDream.App.Tests/Rendering/LinuxPlatformBoundaryTests.cs
+++ b/tests/AcDream.App.Tests/Rendering/LinuxPlatformBoundaryTests.cs
@ -0,0 +1,123 @@
+namespace AcDream.App.Tests.Rendering;
+
+public sealed class LinuxPlatformBoundaryTests
+{
+    [Fact]
+    public void FramePacingSelectsPlatformWaiterOnlyAtFactoryBoundary()
+    {
+        string app = AppSourceRoot();
+        string controller = File.ReadAllText(Path.Combine(
+            app,
+            "Rendering",
+            "FramePacingController.cs"));
+        Assert.Contains(
+            "PlatformFramePacingWaiterFactory.ForCurrentProcess()",
+            controller,
+            StringComparison.Ordinal);
+        Assert.DoesNotContain(
+            "WindowsHighResolutionFramePacingWaiter.Create()",
+            controller,
+            StringComparison.Ordinal);
+
+        string[] windowsImports = Directory
+            .EnumerateFiles(app, "*.cs", SearchOption.AllDirectories)
+            .Where(path => File.ReadAllText(path).Contains(
+                "LibraryImport(\"kernel32.dll\"",
+                StringComparison.Ordinal))
+            .Select(path => Path.GetFileName(path)!)
+            .ToArray();
+
+        Assert.Equal(
+            ["WindowsHighResolutionFramePacingWaiter.cs"],
+            windowsImports);
+    }
+
+    [Fact]
+    public void GraphicalFeatureCodeDoesNotResolveWindowsLocalAppData()
+    {
+        string root = RepositoryRoot();
+        string[] productionFiles =
+        [
+            .. Directory.EnumerateFiles(
+                Path.Combine(root, "src", "AcDream.App"),
+                "*.cs",
+                SearchOption.AllDirectories),
+            .. Directory.EnumerateFiles(
+                Path.Combine(root, "src", "AcDream.UI.Abstractions"),
+                "*.cs",
+                SearchOption.AllDirectories),
+        ];
+
+        string[] offenders = productionFiles
+            .Where(path => File.ReadAllText(path).Contains(
+                "LocalApplicationData",
+                StringComparison.Ordinal))
+            .Select(path => Path.GetRelativePath(root, path))
+            .ToArray();
+
+        Assert.Empty(offenders);
+    }
+
+    [Fact]
+    public void OperatingSystemChecksRemainInsidePlatformOwners()
+    {
+        string app = AppSourceRoot();
+        string[] offenders = Directory
+            .EnumerateFiles(app, "*.cs", SearchOption.AllDirectories)
+            .Where(path => File.ReadAllText(path).Contains(
+                "OperatingSystem.Is",
+                StringComparison.Ordinal))
+            .Where(path =>
+            {
+                string relative = Path.GetRelativePath(app, path)
+                    .Replace('\\', '/');
+                return !relative.StartsWith(
+                        "Platform/",
+                        StringComparison.Ordinal)
+                    && relative is not
+                        "Rendering/FramePacingWaiterFactory.cs"
+                    && relative is not
+                        "Rendering/LinuxMonotonicFramePacingWaiter.cs"
+                    && relative is not
+                        "Rendering/WindowsHighResolutionFramePacingWaiter.cs";
+            })
+            .Select(path => Path.GetRelativePath(app, path))
+            .ToArray();
+
+        Assert.Empty(offenders);
+    }
+
+    [Fact]
+    public void SmokePluginCopyUsesRidAwarePortableBuildAndPublishPaths()
+    {
+        string project = File.ReadAllText(Path.Combine(
+            AppSourceRoot(),
+            "AcDream.App.csproj"));
+
+        Assert.Contains("$(TargetFramework)", project, StringComparison.Ordinal);
+        Assert.Contains("$(RuntimeIdentifier)", project, StringComparison.Ordinal);
+        Assert.Contains("$(OutputPath)plugins/", project, StringComparison.Ordinal);
+        Assert.Contains("$(PublishDir)plugins/", project, StringComparison.Ordinal);
+        Assert.DoesNotContain(
+            @"bin\$(Configuration)\net10.0",
+            project,
+            StringComparison.Ordinal);
+    }
+
+    private static string AppSourceRoot() =>
+        Path.Combine(RepositoryRoot(), "src", "AcDream.App");
+
+    private static string RepositoryRoot()
+    {
+        DirectoryInfo? directory = new(AppContext.BaseDirectory);
+        while (directory is not null)
+        {
+            if (File.Exists(Path.Combine(directory.FullName, "AcDream.slnx")))
+                return directory.FullName;
+            directory = directory.Parent;
+        }
+
+        throw new DirectoryNotFoundException(
+            "Could not locate repository root from test output.");
+    }
+}
--- a/tests/AcDream.Runtime.Tests/Platform/ApplicationPathSetTests.cs
+++ b/tests/AcDream.Runtime.Tests/Platform/ApplicationPathSetTests.cs
@ -0,0 +1,162 @@
+using AcDream.Runtime.Platform;
+
+namespace AcDream.Runtime.Tests.Platform;
+
+public sealed class ApplicationPathSetTests
+{
+    [Fact]
+    public void LinuxUsesXdgRootsAndPublishesFeaturePaths()
+    {
+        string root = Path.GetFullPath(
+            Path.Combine(Path.GetTempPath(), "acdream-runtime-xdg"));
+        var platform = new FixtureEnvironment(isWindows: false)
+        {
+            CurrentDirectoryValue = Path.Combine(root, "work"),
+            UserProfile = Path.Combine(root, "home"),
+            Variables =
+            {
+                ["XDG_CONFIG_HOME"] = Path.Combine(root, "cfg"),
+                ["XDG_DATA_HOME"] = Path.Combine(root, "data"),
+                ["XDG_CACHE_HOME"] = Path.Combine(root, "cache"),
+            },
+        };
+
+        ApplicationPathSet paths = ApplicationPathSet.Resolve(
+            platform: platform);
+
+        Assert.Equal(
+            Path.Combine(root, "cfg", "acdream"),
+            paths.ConfigDirectory);
+        Assert.Equal(
+            Path.Combine(root, "data", "acdream"),
+            paths.DataDirectory);
+        Assert.Equal(
+            Path.Combine(root, "cache", "acdream"),
+            paths.CacheDirectory);
+        Assert.Equal(
+            Path.Combine(paths.ConfigDirectory, "settings.json"),
+            paths.SettingsFile);
+        Assert.Equal(
+            Path.Combine(paths.ConfigDirectory, "keybinds.json"),
+            paths.KeyBindingsFile);
+        Assert.Equal(
+            Path.Combine(paths.DataDirectory, "plugins"),
+            paths.PluginsDirectory);
+        Assert.Equal(
+            Path.Combine(paths.CacheDirectory, "diagnostics"),
+            paths.DiagnosticsDirectory);
+        Assert.Null(paths.LegacyConfigDirectory);
+    }
+
+    [Fact]
+    public void LinuxFallsBackToHomeAndNormalizesOverrides()
+    {
+        string root = Path.GetFullPath(
+            Path.Combine(Path.GetTempPath(), "acdream runtime paths"));
+        var platform = new FixtureEnvironment(isWindows: false)
+        {
+            CurrentDirectoryValue = Path.Combine(root, "work"),
+            UserProfile = Path.Combine(root, "home"),
+        };
+
+        ApplicationPathSet paths = ApplicationPathSet.Resolve(
+            "relative config",
+            "dåta",
+            "cache",
+            platform);
+
+        Assert.Equal(
+            Path.GetFullPath(
+                "relative config",
+                platform.CurrentDirectoryValue),
+            paths.ConfigDirectory);
+        Assert.Equal(
+            Path.GetFullPath("dåta", platform.CurrentDirectoryValue),
+            paths.DataDirectory);
+        Assert.Equal(
+            Path.GetFullPath("cache", platform.CurrentDirectoryValue),
+            paths.CacheDirectory);
+    }
+
+    [Fact]
+    public void WindowsUsesRoamingConfigAndLocalData()
+    {
+        string root = Path.GetFullPath(
+            Path.Combine(Path.GetTempPath(), "acdream-runtime-windows"));
+        var platform = new FixtureEnvironment(isWindows: true)
+        {
+            CurrentDirectoryValue = Path.Combine(root, "work"),
+            ApplicationData = Path.Combine(root, "AppData", "Roaming"),
+            LocalApplicationData =
+                Path.Combine(root, "AppData", "Local"),
+        };
+
+        ApplicationPathSet paths = ApplicationPathSet.Resolve(
+            platform: platform);
+
+        Assert.Equal(
+            Path.Combine(
+                platform.ApplicationData,
+                "acdream"),
+            paths.ConfigDirectory);
+        Assert.Equal(
+            Path.Combine(
+                platform.LocalApplicationData,
+                "acdream"),
+            paths.DataDirectory);
+        Assert.Equal(
+            Path.Combine(
+                platform.LocalApplicationData,
+                "acdream",
+                "cache"),
+            paths.CacheDirectory);
+        Assert.Equal(
+            Path.Combine(
+                platform.LocalApplicationData,
+                "acdream"),
+            paths.LegacyConfigDirectory);
+    }
+
+    private sealed class FixtureEnvironment(bool isWindows)
+        : IApplicationPathEnvironment
+    {
+        public bool IsWindows { get; } = isWindows;
+
+        public string CurrentDirectoryValue { get; init; } =
+            Environment.CurrentDirectory;
+
+        public string CurrentDirectory => CurrentDirectoryValue;
+
+        public string UserProfile { get; init; } =
+            Environment.GetFolderPath(
+                Environment.SpecialFolder.UserProfile);
+
+        public string ApplicationData { get; init; } =
+            Environment.GetFolderPath(
+                Environment.SpecialFolder.ApplicationData);
+
+        public string LocalApplicationData { get; init; } =
+            Environment.GetFolderPath(
+                Environment.SpecialFolder.LocalApplicationData);
+
+        public Dictionary<string, string> Variables { get; } =
+            new(StringComparer.Ordinal);
+
+        public string? GetEnvironmentVariable(string name) =>
+            Variables.TryGetValue(name, out string? value)
+                ? value
+                : null;
+
+        public string GetFolderPath(
+            Environment.SpecialFolder folder) =>
+            folder switch
+            {
+                Environment.SpecialFolder.UserProfile => UserProfile,
+                Environment.SpecialFolder.ApplicationData =>
+                    ApplicationData,
+                Environment.SpecialFolder.LocalApplicationData =>
+                    LocalApplicationData,
+                _ => string.Empty,
+            };
+    }
+}
--- a/tests/AcDream.UI.Abstractions.Tests/Input/KeyBindingsJsonTests.cs
+++ b/tests/AcDream.UI.Abstractions.Tests/Input/KeyBindingsJsonTests.cs
@ -322,11 +322,4 @@ public class KeyBindingsJsonTests
        }
    }

-    [Fact]
-    public void DefaultPath_lives_under_LocalAppData_acdream()
-    {
-        var path = KeyBindings.DefaultPath();
-        Assert.Contains("acdream", path);
-        Assert.EndsWith("keybinds.json", path);
-    }
 }
--- a/tests/AcDream.UI.Abstractions.Tests/Panels/Settings/SettingsStoreTests.cs
+++ b/tests/AcDream.UI.Abstractions.Tests/Panels/Settings/SettingsStoreTests.cs
@ -143,13 +143,6 @@ public sealed class SettingsStoreTests : System.IDisposable
        Assert.Contains("1920x1080", raw);
    }

-    [Fact]
-    public void DefaultPath_is_under_LocalAppData_acdream()
-    {
-        var path = SettingsStore.DefaultPath();
-        Assert.EndsWith("acdream" + Path.DirectorySeparatorChar + "settings.json", path);
-    }
-
    // -- Audio section round-trip ----------------------------------------

    [Fact]