diff --git a/WheelWizard.Test/Features/Patches/LooseBrsarPatchFileNameTests.cs b/WheelWizard.Test/Features/Patches/LooseBrsarPatchFileNameTests.cs
new file mode 100644
index 000000000..86b6a2964
--- /dev/null
+++ b/WheelWizard.Test/Features/Patches/LooseBrsarPatchFileNameTests.cs
@@ -0,0 +1,29 @@
+using WheelWizard.Features.Patches;
+
+namespace WheelWizard.Test.Features.Patches;
+
+public class LooseBrsarPatchFileNameTests
+{
+    [Theory]
+    [InlineData("[001]sound.BRWSD", "1.brwsd")]
+    [InlineData("[42].BRBNK", "42.brbnk")]
+    [InlineData("[0]name.brwsd", "0.brwsd")]
+    public void TaggedNamesNormalizeIdAndExtension(string name, string expected)
+    {
+        Assert.True(LooseBrsarPatchFileName.TryGetNormalizedFileName(name, out var result));
+        Assert.Equal(expected, result);
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData("[]sound.brwsd")]
+    [InlineData("[-1]sound.brwsd")]
+    [InlineData("[2147483648]sound.brwsd")]
+    [InlineData("[1]sound.szs")]
+    [InlineData("1.brwsd")]
+    public void InvalidNamesAreRejected(string name)
+    {
+        Assert.False(LooseBrsarPatchFileName.TryGetNormalizedFileName(name, out var result));
+        Assert.Empty(result);
+    }
+}
diff --git a/WheelWizard.Test/Features/Patches/ModPatchCompatibilityTests.cs b/WheelWizard.Test/Features/Patches/ModPatchCompatibilityTests.cs
new file mode 100644
index 000000000..cccd9abed
--- /dev/null
+++ b/WheelWizard.Test/Features/Patches/ModPatchCompatibilityTests.cs
@@ -0,0 +1,47 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using Testably.Abstractions.Testing;
+using WheelWizard.Features.Patches;
+using WheelWizard.Models.Mods;
+using WheelWizard.Mods;
+
+namespace WheelWizard.Test.Features.Patches;
+
+public class ModPatchCompatibilityTests
+{
+    [Theory]
+    [InlineData("course.szs", true)]
+    [InlineData("COURSE.SZS", true)]
+    [InlineData("nested/course.szs", true)]
+    [InlineData("revo_kart.brsar", true)]
+    [InlineData("[42]sound.BRWSD", true)]
+    [InlineData("course.tag.szs", false)]
+    [InlineData("notes.txt", false)]
+    [InlineData("sound.brwsd", false)]
+    public void CompatibilityUsesInjectedFilesAndRecognizesConvertibleArchives(string relativePath, bool expected)
+    {
+        var fs = new MockFileSystem();
+        var root = fs.Path.GetFullPath("mods/Test");
+        var file = fs.Path.GetFullPath(fs.Path.Combine(root, relativePath));
+        fs.Directory.CreateDirectory(fs.Path.GetDirectoryName(file)!);
+        fs.File.WriteAllText(file, "archive");
+        var paths = Substitute.For<IModPaths>();
+        paths.GetModDirectoryPath("Test").Returns(root);
+        var service = new ModPatchConversionService(
+            Substitute.For<ISzsPatchConverter>(),
+            NullLogger<ModPatchConversionService>.Instance,
+            fs,
+            paths,
+            Substitute.For<IGameBaselineStore>()
+        );
+        var mod = new Mod { Title = "Test" };
+
+        service.RefreshCompatibility(mod);
+
+        Assert.Equal(expected, mod.HasIncompatibleFiles);
+        Assert.Equal(expected ? new[] { file } : [], service.GetConvertibleArchiveFiles(mod));
+        fs.Directory.Delete(root, recursive: true);
+        service.RefreshCompatibility(mod);
+        Assert.False(mod.HasIncompatibleFiles);
+        Assert.Empty(service.GetConvertibleArchiveFiles(mod));
+    }
+}
diff --git a/WheelWizard.Test/Features/Recomp/RecompPlatformTests.cs b/WheelWizard.Test/Features/Recomp/RecompPlatformTests.cs
new file mode 100644
index 000000000..e5015c0a1
--- /dev/null
+++ b/WheelWizard.Test/Features/Recomp/RecompPlatformTests.cs
@@ -0,0 +1,27 @@
+using System.Runtime.InteropServices;
+using WheelWizard.Recomp;
+
+namespace WheelWizard.Test.Features.Recomp;
+
+public class RecompPlatformTests
+{
+    [Theory]
+    [InlineData("v1.2/../../../release", "v1-2----------release")]
+    [InlineData("", "")]
+    [InlineData("v123", "v123")]
+    public void CachedSetupNameKeepsTagsWithinSingleFileName(string tag, string sanitized)
+    {
+        var result = RecompPlatform.CachedSetupFileName(tag);
+        Assert.Equal($"WiiCompiled-Setup-{sanitized}{Path.GetExtension(RecompPlatform.SetupFileName)}", result);
+        Assert.Equal(result, Path.GetFileName(result));
+        Assert.Equal($"WiiCompiled-Setup-*{Path.GetExtension(result)}", RecompPlatform.CachedSetupSearchPattern);
+    }
+
+    [Theory]
+    [InlineData(Architecture.X64, "WiiCompiled-Setup-x86_64.AppImage")]
+    [InlineData(Architecture.Arm64, "WiiCompiled-Setup-aarch64.AppImage")]
+    [InlineData(Architecture.X86, null)]
+    [InlineData(Architecture.Arm, null)]
+    public void LinuxAssetsMatchSupportedArchitectures(Architecture architecture, string? expected) =>
+        Assert.Equal(expected, RecompPlatform.LinuxReleaseAssetName(architecture));
+}
diff --git a/WheelWizard.Test/Features/Settings/SettingsRecoveryTests.cs b/WheelWizard.Test/Features/Settings/SettingsRecoveryTests.cs
index bcd54e20e..509b462b1 100644
--- a/WheelWizard.Test/Features/Settings/SettingsRecoveryTests.cs
+++ b/WheelWizard.Test/Features/Settings/SettingsRecoveryTests.cs
@@ -28,7 +28,7 @@ public void DolphinEditPreservesExternalValuesAndReloadDoesNotCarryPreviousProfi
         fs.File.WriteAllText("/config/GFX.ini", "[Settings]\nInternalResolution = invalid\n");
         manager.ReloadSettings("/config");
         Assert.Equal(1, resolution.Get());
-        Assert.Equal(false, fps.Get());
+        Assert.False(fps.Get());
         Assert.Contains("invalid", fs.File.ReadAllText("/config/GFX.ini"));
     }
 
@@ -44,10 +44,10 @@ public void RecompReloadMissingKeyUsesDefault()
         manager.LoadSettings("/config/Config.toml");
         fs.File.WriteAllText("/config/Config.toml", "[video]\n");
         manager.ReloadSettings("/config/Config.toml");
-        Assert.Equal(true, setting.Get());
+        Assert.True(setting.Get());
         fs.File.Delete("/config/Config.toml");
         Assert.False(setting.Set(false));
-        Assert.Equal(true, setting.Get());
+        Assert.True(setting.Get());
     }
 
     [Fact]
@@ -66,7 +66,7 @@ public void FailedSaveRollsBackAndCanBeRetried()
         var notifications = 0;
         setting.Changed += _ => notifications++;
         Assert.False(setting.Set(true));
-        Assert.Equal(false, setting.Get());
+        Assert.False(setting.Get());
         Assert.Equal(0, notifications);
         fail = false;
         Assert.True(setting.Set(true));
@@ -86,7 +86,7 @@ public void JsonRetainsExistingKeysAndUnknownValuesAndPreservesCorruptFile()
         var setting = new WhWzSetting<bool>("EnableAnimations", true, s => manager.SaveSettings(path, s));
         manager.RegisterSetting(setting);
         manager.LoadSettings(path);
-        Assert.Equal(false, setting.Get());
+        Assert.False(setting.Get());
         Assert.True(setting.Set(true));
         Assert.Contains("FutureSetting", fs.File.ReadAllText(path));
         Assert.Equal(original, fs.File.ReadAllText(path + ".bak"));
diff --git a/WheelWizard.Test/Shared/IO/PathSafetyTests.cs b/WheelWizard.Test/Shared/IO/PathSafetyTests.cs
new file mode 100644
index 000000000..c755f3800
--- /dev/null
+++ b/WheelWizard.Test/Shared/IO/PathSafetyTests.cs
@@ -0,0 +1,47 @@
+using WheelWizard.Shared.IO;
+
+namespace WheelWizard.Test.Shared.IO;
+
+public class PathSafetyTests
+{
+    [Theory]
+    [InlineData("../outside.bin")]
+    [InlineData("nested/../../outside.bin")]
+    [InlineData("nested\\..\\outside.bin")]
+    [InlineData("/absolute.bin")]
+    [InlineData("C:\\absolute.bin")]
+    [InlineData("C:/absolute.bin")]
+    [InlineData(" ")]
+    public void UnsafeRelativePathsAreRejected(string path)
+    {
+        Assert.False(PathSafety.TryGetPathWithinDirectory(Path.GetTempPath(), path, out var fullPath));
+        Assert.Empty(fullPath);
+    }
+
+    [Fact]
+    public void NestedPathIsNormalizedInsideDirectory()
+    {
+        var root = Path.Combine(Path.GetTempPath(), "PathSafetyTests");
+        Assert.True(PathSafety.TryGetPathWithinDirectory(root, " ./nested\\file.bin ", out var path));
+        Assert.Equal(Path.Combine(root, "nested", "file.bin"), path);
+        Assert.False(PathSafety.IsPathWithinDirectory(root, root + "-sibling/file.bin"));
+        Assert.True(PathSafety.IsPathWithinDirectory(root, root));
+    }
+
+    [Fact]
+    public void ColonInSegmentFollowsPlatformRules()
+    {
+        var accepted = PathSafety.TryGetPathWithinDirectory(Path.GetTempPath(), "nested/data:variant.bin", out _);
+        Assert.Equal(!OperatingSystem.IsWindows(), accepted);
+    }
+
+    [Theory]
+    [InlineData("folder\\mii.bin", "mii.bin")]
+    [InlineData("folder/mii.bin", "mii.bin")]
+    [InlineData("\"mii.bin\"", "mii.bin")]
+    public void SafeFileNameReturnsOnlyLeaf(string input, string expected)
+    {
+        Assert.True(PathSafety.TryGetSafeFileName(input, out var result));
+        Assert.Equal(expected, result);
+    }
+}
diff --git a/WheelWizard.UI.Test/ModInstallOwnerLifetimeTests.cs b/WheelWizard.UI.Test/ModInstallOwnerLifetimeTests.cs
index ff6c374fd..4f23a0777 100644
--- a/WheelWizard.UI.Test/ModInstallOwnerLifetimeTests.cs
+++ b/WheelWizard.UI.Test/ModInstallOwnerLifetimeTests.cs
@@ -4,6 +4,7 @@
 using Avalonia.Interactivity;
 using Avalonia.Threading;
 using NSubstitute;
+using Testably.Abstractions;
 using WheelWizard.GameBanana;
 using WheelWizard.Mods;
 using WheelWizard.Mods.Views.Dialogs;
@@ -47,7 +48,15 @@ public async Task ClosedOwner_CancelsDownloadAndSuppressesLateSuccessOrFailureDi
                 // Deliberately return late instead of honoring cancellation, to exercise the race.
                 return finished.Task;
             });
-        var content = new ModContent(manager, gameBanana, downloads, Substitute.For<IGameBananaMediaService>(), paths, presentation);
+        var content = new ModContent(
+            new RealFileSystem(),
+            manager,
+            gameBanana,
+            downloads,
+            Substitute.For<IGameBananaMediaService>(),
+            paths,
+            presentation
+        );
         var mod = ModTestFixture.CreateMod(123, "Test mod");
         mod.Files = [new() { FileName = "mod.zip", DownloadUrl = "https://example.com/mod.zip" }];
         typeof(ModContent).GetProperty("CurrentMod", BindingFlags.NonPublic | BindingFlags.Instance)!.SetValue(content, mod);
diff --git a/WheelWizard.UI.Test/ModTestFixture.cs b/WheelWizard.UI.Test/ModTestFixture.cs
index 2f9123c31..6f057dffe 100644
--- a/WheelWizard.UI.Test/ModTestFixture.cs
+++ b/WheelWizard.UI.Test/ModTestFixture.cs
@@ -1,4 +1,5 @@
 using NSubstitute;
+using Testably.Abstractions.Testing;
 using WheelWizard.GameBanana;
 using WheelWizard.GameBanana.Domain;
 using WheelWizard.Mods;
@@ -11,6 +12,7 @@ internal static class ModTestFixture
 {
     public static ModContent CreateContent(IGameBananaSingletonService api, IGameBananaMediaService? media = null) =>
         new(
+            new MockFileSystem(),
             Substitute.For<IModManager>(),
             api,
             Substitute.For<IDownloadService>(),
diff --git a/WheelWizard.UI.Test/SharedControlTests.cs b/WheelWizard.UI.Test/SharedControlTests.cs
index aabf211cc..d479f2212 100644
--- a/WheelWizard.UI.Test/SharedControlTests.cs
+++ b/WheelWizard.UI.Test/SharedControlTests.cs
@@ -467,10 +467,11 @@ public void Dropdown_SearchFiltersWithoutChangingSelectionAndShowsEmptyStates()
         Dispatcher.UIThread.RunJobs();
         window.UpdateLayout();
         var popup = dropdown.GetVisualDescendants().OfType<Avalonia.Controls.Primitives.Popup>().Single();
-        var search = popup.Child!.GetVisualDescendants().OfType<InputField>().Single();
-        var empty = popup.Child.GetVisualDescendants().OfType<TextBlock>().Single(x => x.Name == "PART_Empty");
-        var width = popup.Child.Bounds.Width;
-        var height = popup.Child.Bounds.Height;
+        var popupChild = popup.Child!;
+        var search = popupChild.GetVisualDescendants().OfType<InputField>().Single();
+        var empty = popupChild.GetVisualDescendants().OfType<TextBlock>().Single(x => x.Name == "PART_Empty");
+        var width = popupChild.Bounds.Width;
+        var height = popupChild.Bounds.Height;
         Assert.True(width > dropdown.Bounds.Width);
         Dispatcher.UIThread.RunJobs();
         Assert.True(search.IsFocused);
@@ -484,26 +485,26 @@ public void Dropdown_SearchFiltersWithoutChangingSelectionAndShowsEmptyStates()
         Assert.True(dropdown.ContainerFromIndex(0)!.IsVisible);
         Assert.False(dropdown.ContainerFromIndex(1)!.IsVisible);
         Assert.Equal(1, dropdown.SelectedIndex);
-        Assert.Equal(width, popup.Child.Bounds.Width);
-        Assert.True(popup.Child.Bounds.Height < height);
+        Assert.Equal(width, popupChild.Bounds.Width);
+        Assert.True(popupChild.Bounds.Height < height);
         search.Text = "English";
         Dispatcher.UIThread.RunJobs();
         window.UpdateLayout();
-        Assert.Equal(width, popup.Child.Bounds.Width);
-        Assert.True(popup.Child.Bounds.Height < height);
+        Assert.Equal(width, popupChild.Bounds.Width);
+        Assert.True(popupChild.Bounds.Height < height);
         Assert.True(search.IsFocused);
         Assert.True(popup.IsOpen);
         search.Text = "not a language";
         Dispatcher.UIThread.RunJobs();
         window.UpdateLayout();
         Assert.True(empty.IsVisible);
-        Assert.Equal(width, popup.Child.Bounds.Width);
-        Assert.True(popup.Child.Bounds.Height < height);
+        Assert.Equal(width, popupChild.Bounds.Width);
+        Assert.True(popupChild.Bounds.Height < height);
         Assert.Equal("No options found", empty.Text);
         search.Text = "";
         Dispatcher.UIThread.RunJobs();
         window.UpdateLayout();
-        Assert.Equal(height, popup.Child.Bounds.Height);
+        Assert.Equal(height, popupChild.Bounds.Height);
         Assert.False(empty.IsVisible);
         Assert.True(search.IsFocused, "Search lost focus after restoring options.");
         search.Text = "disabled";
@@ -691,7 +692,8 @@ public void Dropdown_OptionsCanMixIconsAndPlainText()
         window.UpdateLayout();
         Assert.Same(iconOption, dropdown.SelectedItem);
         var fieldIcon = Assert.Single(
-            dropdown.GetVisualDescendants().OfType<PathIcon>().Where(icon => icon.Classes.Contains("DropdownOptionIcon"))
+            dropdown.GetVisualDescendants().OfType<PathIcon>(),
+            icon => icon.Classes.Contains("DropdownOptionIcon")
         );
         Assert.Same(iconOption.Icon, fieldIcon.Data);
         Assert.Equal(
@@ -701,7 +703,7 @@ public void Dropdown_OptionsCanMixIconsAndPlainText()
         dropdown.IsDropDownOpen = true;
         window.UpdateLayout();
         var popup = dropdown.GetVisualDescendants().OfType<Avalonia.Controls.Primitives.Popup>().Single();
-        Assert.Single(popup.Child!.GetVisualDescendants().OfType<PathIcon>().Where(icon => icon.Classes.Contains("DropdownOptionIcon")));
+        Assert.Single(popup.Child!.GetVisualDescendants().OfType<PathIcon>(), icon => icon.Classes.Contains("DropdownOptionIcon"));
         Assert.Equal(
             (Color)window.FindResource("Brand300")!,
             Assert.IsAssignableFrom<ISolidColorBrush>(Assert.IsType<DropdownItem>(dropdown.ContainerFromIndex(0)).Foreground).Color
@@ -710,7 +712,7 @@ public void Dropdown_OptionsCanMixIconsAndPlainText()
         dropdown.SelectedIndex = 1;
         window.UpdateLayout();
         Assert.Same(plainOption, dropdown.SelectedItem);
-        Assert.Empty(dropdown.GetVisualDescendants().OfType<PathIcon>().Where(icon => icon.Classes.Contains("DropdownOptionIcon")));
+        Assert.DoesNotContain(dropdown.GetVisualDescendants().OfType<PathIcon>(), icon => icon.Classes.Contains("DropdownOptionIcon"));
         Assert.Contains(dropdown.GetVisualDescendants().OfType<TextBlock>(), text => text.Text == plainOption.Text);
     }
 
diff --git a/WheelWizard/Features/CustomDistributions/RetroRewindBeta.cs b/WheelWizard/Features/CustomDistributions/RetroRewindBeta.cs
index 80ea10f49..fb7f90ee4 100644
--- a/WheelWizard/Features/CustomDistributions/RetroRewindBeta.cs
+++ b/WheelWizard/Features/CustomDistributions/RetroRewindBeta.cs
@@ -261,7 +261,9 @@ private static bool IsBadPasswordException(Exception ex)
     private bool TryGetRelativeExtractionPath(string normalizedPath, out string relativePath)
     {
         relativePath = string.Empty;
-        var archivePath = normalizedPath.Replace(Path.DirectorySeparatorChar, '/').Replace(Path.AltDirectorySeparatorChar, '/');
+        var archivePath = normalizedPath
+            .Replace(_fileSystem.Path.DirectorySeparatorChar, '/')
+            .Replace(_fileSystem.Path.AltDirectorySeparatorChar, '/');
 
         if (archivePath.Equals(FolderName, StringComparison.OrdinalIgnoreCase))
         {
@@ -271,7 +273,10 @@ private bool TryGetRelativeExtractionPath(string normalizedPath, out string rela
 
         if (archivePath.StartsWith($"{FolderName}/", StringComparison.OrdinalIgnoreCase))
         {
-            relativePath = Path.Combine(FolderName, archivePath.Substring(FolderName.Length + 1).Replace('/', Path.DirectorySeparatorChar));
+            relativePath = _fileSystem.Path.Combine(
+                FolderName,
+                archivePath.Substring(FolderName.Length + 1).Replace('/', _fileSystem.Path.DirectorySeparatorChar)
+            );
             return true;
         }
 
@@ -283,9 +288,9 @@ private bool TryGetRelativeExtractionPath(string normalizedPath, out string rela
 
         if (archivePath.StartsWith($"{XMLFolderName}/", StringComparison.OrdinalIgnoreCase))
         {
-            relativePath = Path.Combine(
+            relativePath = _fileSystem.Path.Combine(
                 XMLFolderName,
-                archivePath.Substring(XMLFolderName.Length + 1).Replace('/', Path.DirectorySeparatorChar)
+                archivePath.Substring(XMLFolderName.Length + 1).Replace('/', _fileSystem.Path.DirectorySeparatorChar)
             );
             return true;
         }
@@ -331,16 +336,18 @@ private OperationResult<List<string>> MoveExtractedFiles(string tempExtractionPa
         return Ok(manifestEntries);
     }
 
-    private static bool IsRiivolutionPath(string relativePath)
+    private bool IsRiivolutionPath(string relativePath)
     {
-        var normalized = relativePath.Replace(Path.DirectorySeparatorChar, '/').Replace(Path.AltDirectorySeparatorChar, '/');
+        var normalized = relativePath
+            .Replace(_fileSystem.Path.DirectorySeparatorChar, '/')
+            .Replace(_fileSystem.Path.AltDirectorySeparatorChar, '/');
         return normalized.StartsWith("riivolution/", StringComparison.OrdinalIgnoreCase)
             || normalized.Equals("riivolution", StringComparison.OrdinalIgnoreCase);
     }
 
-    private static bool IsBetaRiivolutionFile(string relativePath)
+    private bool IsBetaRiivolutionFile(string relativePath)
     {
-        var fileName = Path.GetFileName(relativePath);
+        var fileName = _fileSystem.Path.GetFileName(relativePath);
         return fileName.StartsWith("RRBeta", StringComparison.OrdinalIgnoreCase);
     }
 
diff --git a/WheelWizard/Features/Launching/RetroRewindLaunchDescriptor.cs b/WheelWizard/Features/Launching/RetroRewindLaunchDescriptor.cs
index e05d9dc7e..3992b2d28 100644
--- a/WheelWizard/Features/Launching/RetroRewindLaunchDescriptor.cs
+++ b/WheelWizard/Features/Launching/RetroRewindLaunchDescriptor.cs
@@ -110,9 +110,9 @@ private static List<OptionConfig> BuildOptions(string sectionName, int myStuffCh
         return options;
     }
 
-    private static (string SectionName, int MyStuffChoice, bool EnableSeparateSave) GetLaunchInfo(string xmlFilePath)
+    private (string SectionName, int MyStuffChoice, bool EnableSeparateSave) GetLaunchInfo(string xmlFilePath)
     {
-        var fileName = Path.GetFileName(xmlFilePath);
+        var fileName = fileSystem.Path.GetFileName(xmlFilePath);
         if (fileName.Equals("RRBeta.xml", StringComparison.OrdinalIgnoreCase))
             return ("Retro Rewind Beta", 0, true);
 
diff --git a/WheelWizard/Features/MiiRendering/Services/NativeMiiRenderer.cs b/WheelWizard/Features/MiiRendering/Services/NativeMiiRenderer.cs
index e7e0b7cf5..f50bf3f25 100644
--- a/WheelWizard/Features/MiiRendering/Services/NativeMiiRenderer.cs
+++ b/WheelWizard/Features/MiiRendering/Services/NativeMiiRenderer.cs
@@ -413,7 +413,7 @@ private static int MapExpression(MiiImageSpecifications.FaceExpression expressio
             _ => FflNativeInterop.FflExpressionNormal,
         };
 
-    private static OperationResult<CachedHeadDrawParams> GetOrCreateCachedHeadDrawParams(
+    private OperationResult<CachedHeadDrawParams> GetOrCreateCachedHeadDrawParams(
         ManagedFflResourceArchive archive,
         FflNativeInterop.FFLiCharInfo charInfo,
         NativeMiiRenderRequest request,
@@ -502,10 +502,10 @@ private static void EvictHeadDrawCacheIfNeeded_NoLock()
         }
     }
 
-    private static string BuildHeadDrawCacheKey(string studioData, int expressionId, int width, string resourcePath)
+    private string BuildHeadDrawCacheKey(string studioData, int expressionId, int width, string resourcePath)
     {
         var resolutionBucket = width <= 384 ? 256 : 512;
-        return $"{Path.GetFullPath(resourcePath)}|{resolutionBucket}|{expressionId}|{studioData}";
+        return $"{fileSystem.Path.GetFullPath(resourcePath)}|{resolutionBucket}|{expressionId}|{studioData}";
     }
 
     private static List<DecodedDrawMesh> BuildDecodedDrawMeshes(IReadOnlyList<FflNativeInterop.FFLDrawParam> drawParams)
diff --git a/WheelWizard/Features/Mods/Views/Dialogs/ModContent.axaml.cs b/WheelWizard/Features/Mods/Views/Dialogs/ModContent.axaml.cs
index e2864ec49..62f772285 100644
--- a/WheelWizard/Features/Mods/Views/Dialogs/ModContent.axaml.cs
+++ b/WheelWizard/Features/Mods/Views/Dialogs/ModContent.axaml.cs
@@ -1,3 +1,4 @@
+using System.IO.Abstractions;
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Interactivity;
@@ -15,6 +16,8 @@ namespace WheelWizard.Mods.Views.Dialogs;
 
 public partial class ModContent : UserControl
 {
+    private readonly IFileSystem fileSystem;
+
     private IModManager ModManager { get; }
 
     private IGameBananaSingletonService GameBananaService { get; }
@@ -33,6 +36,7 @@ public partial class ModContent : UserControl
     private string? OverrideDownloadUrl { get; set; }
 
     public ModContent(
+        IFileSystem fileSystem,
         IModManager modManager,
         IGameBananaSingletonService gameBananaService,
         IDownloadService downloads,
@@ -41,6 +45,7 @@ public ModContent(
         IModOperationPresentation modPresentation
     )
     {
+        this.fileSystem = fileSystem;
         ModManager = modManager;
         GameBananaService = gameBananaService;
         Downloads = downloads;
@@ -332,7 +337,7 @@ CancellationToken cancellationToken
 
         var url = downloadUrls.First();
         var fileName = GetFileNameFromUrl(url);
-        var filePath = Path.Combine(ModPaths.DownloadFolderPath, fileName);
+        var filePath = fileSystem.Path.Combine(ModPaths.DownloadFolderPath, fileName);
         OperationResult<string?> downloadResult;
         try
         {
@@ -354,7 +359,7 @@ CancellationToken cancellationToken
             return Ok();
         }
 
-        if (!File.Exists(downloadedFilePath))
+        if (!fileSystem.File.Exists(downloadedFilePath))
             return Fail(t("message_warning.unable_download_mod.extra"));
 
         var popup = new TextInputWindow()
@@ -377,7 +382,7 @@ CancellationToken cancellationToken
             return Fail("Mod name cannot be empty.");
         }
 
-        var invalidChars = Path.GetInvalidFileNameChars();
+        var invalidChars = fileSystem.Path.GetInvalidFileNameChars();
         if (modName.Any(c => invalidChars.Contains(c)))
         {
             TryDeleteTempModsFolder();
@@ -402,10 +407,10 @@ private async Task<OperationResult> PrepareToDownloadFile()
         try
         {
             var tempFolder = ModPaths.DownloadFolderPath;
-            if (Directory.Exists(tempFolder))
-                Directory.Delete(tempFolder, true);
+            if (fileSystem.Directory.Exists(tempFolder))
+                fileSystem.Directory.Delete(tempFolder, true);
 
-            Directory.CreateDirectory(tempFolder);
+            fileSystem.Directory.CreateDirectory(tempFolder);
             await Task.CompletedTask;
             return Ok();
         }
@@ -419,8 +424,8 @@ private OperationResult TryDeleteTempModsFolder()
     {
         try
         {
-            if (Directory.Exists(ModPaths.DownloadFolderPath))
-                Directory.Delete(ModPaths.DownloadFolderPath, true);
+            if (fileSystem.Directory.Exists(ModPaths.DownloadFolderPath))
+                fileSystem.Directory.Delete(ModPaths.DownloadFolderPath, true);
 
             return Ok();
         }
@@ -450,9 +455,9 @@ CancellationToken cancellationToken
     /// <summary>
     /// Extracts the file name from a URL.
     /// </summary>
-    private static string GetFileNameFromUrl(string url)
+    private string GetFileNameFromUrl(string url)
     {
-        return Path.GetFileName(new Uri(url).AbsolutePath);
+        return fileSystem.Path.GetFileName(new Uri(url).AbsolutePath);
     }
 
     /// <summary>
diff --git a/WheelWizard/Features/Patches/LooseBrsarPatchFileName.cs b/WheelWizard/Features/Patches/LooseBrsarPatchFileName.cs
index 932eaf2b1..78be165da 100644
--- a/WheelWizard/Features/Patches/LooseBrsarPatchFileName.cs
+++ b/WheelWizard/Features/Patches/LooseBrsarPatchFileName.cs
@@ -2,6 +2,8 @@ namespace WheelWizard.Features.Patches;
 
 public static class LooseBrsarPatchFileName
 {
+    private static readonly System.IO.Abstractions.IPath NativePath = new Testably.Abstractions.RealFileSystem().Path;
+
     public static bool TryGetNormalizedFileName(string fileName, out string normalizedFileName)
     {
         normalizedFileName = string.Empty;
@@ -17,7 +19,7 @@ public static bool TryGetNormalizedFileName(string fileName, out string normaliz
         if (!idText.All(char.IsDigit) || !int.TryParse(idText, out var fileId))
             return false;
 
-        var extension = Path.GetExtension(fileName);
+        var extension = NativePath.GetExtension(fileName);
         if (
             !extension.Equals(".brwsd", StringComparison.OrdinalIgnoreCase)
             && !extension.Equals(".brbnk", StringComparison.OrdinalIgnoreCase)
diff --git a/WheelWizard/Features/Patches/ModPatchConversionService.cs b/WheelWizard/Features/Patches/ModPatchConversionService.cs
index b289a8719..03893c2e1 100644
--- a/WheelWizard/Features/Patches/ModPatchConversionService.cs
+++ b/WheelWizard/Features/Patches/ModPatchConversionService.cs
@@ -92,8 +92,12 @@ public async Task<OperationResult<ModPatchConversionResult>> ConvertToPatchesAsy
             return new ModPatchConversionResult();
         }
 
-        var tempRoot = Path.Combine(Path.GetTempPath(), "WheelWizardPatchConversion", $"{mod.Title}-{Guid.NewGuid():N}");
-        var tempModDirectory = Path.Combine(tempRoot, mod.Title);
+        var tempRoot = fileSystem.Path.Combine(
+            fileSystem.Path.GetTempPath(),
+            "WheelWizardPatchConversion",
+            $"{mod.Title}-{Guid.NewGuid():N}"
+        );
+        var tempModDirectory = fileSystem.Path.Combine(tempRoot, mod.Title);
         progress?.Report(new(ModOperationStage.Converting, 0, TotalFiles: sourceFiles.Count));
 
         try
@@ -114,7 +118,7 @@ public async Task<OperationResult<ModPatchConversionResult>> ConvertToPatchesAsy
                     {
                         cancellationToken.ThrowIfCancellationRequested();
                         var file = tempFiles[index];
-                        var fileName = Path.GetFileName(file);
+                        var fileName = fileSystem.Path.GetFileName(file);
 
                         progress?.Report(
                             new(
@@ -129,7 +133,7 @@ public async Task<OperationResult<ModPatchConversionResult>> ConvertToPatchesAsy
                         {
                             AddArchiveBundleEntry(
                                 archiveBundles,
-                                Path.Combine(Path.GetDirectoryName(file)!, $"{archivePrefix}.revo_kart.szs"),
+                                fileSystem.Path.Combine(fileSystem.Path.GetDirectoryName(file)!, $"{archivePrefix}.revo_kart.szs"),
                                 normalizedPatchFileName,
                                 fileSystem.File.ReadAllBytes(file)
                             );
@@ -160,13 +164,19 @@ public async Task<OperationResult<ModPatchConversionResult>> ConvertToPatchesAsy
 
                         if (TryGetBundleTarget(conversion.Analysis, out var bundleTarget))
                         {
-                            var bundleDestination = Path.Combine(Path.GetDirectoryName(file)!, $"{archivePrefix}.{bundleTarget}.szs");
+                            var bundleDestination = fileSystem.Path.Combine(
+                                fileSystem.Path.GetDirectoryName(file)!,
+                                $"{archivePrefix}.{bundleTarget}.szs"
+                            );
                             foreach (var entry in conversion.Analysis.Entries)
                             {
                                 if (IsDeletionPatchEntry(entry))
                                 {
-                                    var deletionDestination = Path.Combine(Path.GetDirectoryName(file)!, entry.ExportPath);
-                                    fileSystem.Directory.CreateDirectory(Path.GetDirectoryName(deletionDestination)!);
+                                    var deletionDestination = fileSystem.Path.Combine(
+                                        fileSystem.Path.GetDirectoryName(file)!,
+                                        entry.ExportPath
+                                    );
+                                    fileSystem.Directory.CreateDirectory(fileSystem.Path.GetDirectoryName(deletionDestination)!);
                                     fileSystem.File.WriteAllBytes(deletionDestination, entry.Bytes);
                                     writtenPatchCount++;
                                     continue;
@@ -182,8 +192,8 @@ public async Task<OperationResult<ModPatchConversionResult>> ConvertToPatchesAsy
                         {
                             foreach (var entry in conversion.Analysis.Entries)
                             {
-                                var destination = Path.Combine(Path.GetDirectoryName(file)!, entry.ExportPath);
-                                var destinationDirectory = Path.GetDirectoryName(destination)!;
+                                var destination = fileSystem.Path.Combine(fileSystem.Path.GetDirectoryName(file)!, entry.ExportPath);
+                                var destinationDirectory = fileSystem.Path.GetDirectoryName(destination)!;
                                 if (!fileSystem.Directory.Exists(destinationDirectory))
                                     fileSystem.Directory.CreateDirectory(destinationDirectory);
                                 fileSystem.File.WriteAllBytes(destination, entry.Bytes);
@@ -236,11 +246,11 @@ private OperationResult<ArchiveConversion> ConvertArchiveFile(string file)
         try
         {
             var fileBytes = fileSystem.File.ReadAllBytes(file);
-            var baseline = SelectBaseline(Path.GetFileName(file), fileBytes);
+            var baseline = SelectBaseline(fileSystem.Path.GetFileName(file), fileBytes);
             if (baseline == null)
                 return new ArchiveConversion(null, new PatchConversionAnalysis());
 
-            var analysisResult = AnalyzeArchive(baseline, Path.GetFileName(file), fileBytes);
+            var analysisResult = AnalyzeArchive(baseline, fileSystem.Path.GetFileName(file), fileBytes);
             if (analysisResult.IsFailure)
                 return analysisResult.Error;
 
@@ -289,16 +299,16 @@ private int EstimateDifference(BaselineEntry baseline, byte[] fileBytes) =>
     private IReadOnlyList<string> GetConvertibleArchiveFilesInDirectory(string directory) =>
         fileSystem.Directory.EnumerateFiles(directory, "*", SearchOption.AllDirectories).Where(IsConvertibleArchiveFile).ToArray();
 
-    private static bool IsConvertibleArchiveFile(string filePath)
+    private bool IsConvertibleArchiveFile(string filePath)
     {
-        var fileName = Path.GetFileName(filePath);
+        var fileName = fileSystem.Path.GetFileName(filePath);
         if (LooseBrsarPatchFileName.TryGetNormalizedFileName(fileName, out _))
             return true;
 
         if (IsBrsarFileName(fileName))
             return true;
 
-        return Path.GetExtension(filePath).Equals(".szs", StringComparison.OrdinalIgnoreCase)
+        return fileSystem.Path.GetExtension(filePath).Equals(".szs", StringComparison.OrdinalIgnoreCase)
             && !IsModdingArchiveFile(fileName)
             && !KartSzsAllowList.IsAllowedFullCharacterOrKart(fileName);
     }
@@ -358,10 +368,12 @@ private int WriteArchiveBundles(Dictionary<string, Dictionary<string, byte[]>> a
             if (members.Count == 0)
                 continue;
 
-            fileSystem.Directory.CreateDirectory(Path.GetDirectoryName(bundlePath)!);
+            fileSystem.Directory.CreateDirectory(fileSystem.Path.GetDirectoryName(bundlePath)!);
             if (fileSystem.File.Exists(bundlePath))
             {
-                warnings.Add($"{Path.GetFileName(bundlePath)} already existed and was replaced with the converted archive bundle.");
+                warnings.Add(
+                    $"{fileSystem.Path.GetFileName(bundlePath)} already existed and was replaced with the converted archive bundle."
+                );
                 fileSystem.File.Delete(bundlePath);
             }
 
@@ -372,12 +384,12 @@ private int WriteArchiveBundles(Dictionary<string, Dictionary<string, byte[]>> a
         return writtenCount;
     }
 
-    private static bool IsModdingArchiveFile(string fileName)
+    private bool IsModdingArchiveFile(string fileName)
     {
         if (!fileName.EndsWith(".szs", StringComparison.OrdinalIgnoreCase))
             return false;
 
-        var nameWithoutExtension = Path.GetFileNameWithoutExtension(fileName);
+        var nameWithoutExtension = fileSystem.Path.GetFileNameWithoutExtension(fileName);
         var tagSeparator = nameWithoutExtension.LastIndexOf('.');
         return tagSeparator > 0 && tagSeparator + 1 < nameWithoutExtension.Length;
     }
@@ -398,14 +410,16 @@ private void CopyDirectory(string sourceDirectory, string destinationDirectory,
         foreach (var directory in fileSystem.Directory.EnumerateDirectories(sourceDirectory, "*", SearchOption.AllDirectories))
         {
             cancellationToken.ThrowIfCancellationRequested();
-            fileSystem.Directory.CreateDirectory(Path.Combine(destinationDirectory, Path.GetRelativePath(sourceDirectory, directory)));
+            fileSystem.Directory.CreateDirectory(
+                fileSystem.Path.Combine(destinationDirectory, fileSystem.Path.GetRelativePath(sourceDirectory, directory))
+            );
         }
 
         foreach (var file in fileSystem.Directory.EnumerateFiles(sourceDirectory, "*", SearchOption.AllDirectories))
         {
             cancellationToken.ThrowIfCancellationRequested();
-            var destination = Path.Combine(destinationDirectory, Path.GetRelativePath(sourceDirectory, file));
-            fileSystem.Directory.CreateDirectory(Path.GetDirectoryName(destination)!);
+            var destination = fileSystem.Path.Combine(destinationDirectory, fileSystem.Path.GetRelativePath(sourceDirectory, file));
+            fileSystem.Directory.CreateDirectory(fileSystem.Path.GetDirectoryName(destination)!);
             fileSystem.File.Copy(file, destination, true);
         }
     }
diff --git a/WheelWizard/Features/Patches/SzsPatchConverter.cs b/WheelWizard/Features/Patches/SzsPatchConverter.cs
index e40d63553..ab73b04c8 100644
--- a/WheelWizard/Features/Patches/SzsPatchConverter.cs
+++ b/WheelWizard/Features/Patches/SzsPatchConverter.cs
@@ -5,6 +5,8 @@ namespace WheelWizard.Features.Patches;
 
 public sealed class SzsPatchConverter(ISzsArchiveDecoder archiveDecoder) : ISzsPatchConverter
 {
+    private static readonly System.IO.Abstractions.IPath NativePath = new Testably.Abstractions.RealFileSystem().Path;
+
     public OperationResult<PatchConversionAnalysis> AnalyzeAgainstBaseline(BaselineEntry baseline, string moddedName, byte[] moddedBytes)
     {
         // #todo: test conversion against real baselines, including changed, added, removed and unsupported archive members.
@@ -197,7 +199,7 @@ private static string BuildTaggedPatchName(string logicalPath, string archiveTag
 
     private static bool IsBlockedLooseRawOverrideExtension(string path)
     {
-        var extension = Path.GetExtension(path);
+        var extension = NativePath.GetExtension(path);
         return extension.Equals(".kcl", StringComparison.OrdinalIgnoreCase)
             || extension.Equals(".kmp", StringComparison.OrdinalIgnoreCase)
             || extension.Equals(".slt", StringComparison.OrdinalIgnoreCase);
@@ -205,7 +207,7 @@ private static bool IsBlockedLooseRawOverrideExtension(string path)
 
     private static string StripExtension(string fileName)
     {
-        var extension = Path.GetExtension(fileName);
+        var extension = NativePath.GetExtension(fileName);
         return string.IsNullOrEmpty(extension) ? fileName : fileName[..^extension.Length];
     }
 }
diff --git a/WheelWizard/Features/Recomp/RecompInstallService.cs b/WheelWizard/Features/Recomp/RecompInstallService.cs
index 633fa1767..3844b2ea2 100644
--- a/WheelWizard/Features/Recomp/RecompInstallService.cs
+++ b/WheelWizard/Features/Recomp/RecompInstallService.cs
@@ -1,4 +1,4 @@
-using System.IO.Abstractions;
+using System.IO.Abstractions;
 using System.Text.Json;
 using Microsoft.Extensions.Logging;
 using WheelWizard.Models.Enums;
@@ -268,7 +268,7 @@ private bool IsInstallationBusy()
     {
         try
         {
-            var installRoot = Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(environment.InstallFolderPath));
+            var installRoot = fileSystem.Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(environment.InstallFolderPath));
             var parentFolderPath = fileSystem.Directory.GetParent(installRoot)?.FullName;
             if (parentFolderPath is null || !fileSystem.Directory.Exists(parentFolderPath))
                 return false;
@@ -846,8 +846,8 @@ private bool PathsMatch(string? first, string? second)
 
         try
         {
-            var normalizedFirst = Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(first));
-            var normalizedSecond = Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(second));
+            var normalizedFirst = fileSystem.Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(first));
+            var normalizedSecond = fileSystem.Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(second));
             return normalizedFirst.Equals(normalizedSecond, StringComparison.OrdinalIgnoreCase);
         }
         catch (Exception exception)
diff --git a/WheelWizard/Features/Recomp/RecompLinuxInstallService.cs b/WheelWizard/Features/Recomp/RecompLinuxInstallService.cs
index 790325488..4871e809a 100644
--- a/WheelWizard/Features/Recomp/RecompLinuxInstallService.cs
+++ b/WheelWizard/Features/Recomp/RecompLinuxInstallService.cs
@@ -807,8 +807,8 @@ private bool PathsMatch(string? first, string? second)
 
         try
         {
-            var normalizedFirst = Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(first));
-            var normalizedSecond = Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(second));
+            var normalizedFirst = fileSystem.Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(first));
+            var normalizedSecond = fileSystem.Path.TrimEndingDirectorySeparator(fileSystem.Path.GetFullPath(second));
             return normalizedFirst.Equals(normalizedSecond, StringComparison.Ordinal);
         }
         catch (Exception exception)
diff --git a/WheelWizard/Features/Recomp/RecompPlatform.cs b/WheelWizard/Features/Recomp/RecompPlatform.cs
index 9414e866e..57bd435ee 100644
--- a/WheelWizard/Features/Recomp/RecompPlatform.cs
+++ b/WheelWizard/Features/Recomp/RecompPlatform.cs
@@ -11,6 +11,8 @@ namespace WheelWizard.Recomp;
 /// </summary>
 public static class RecompPlatform
 {
+    private static readonly System.IO.Abstractions.IPath NativePath = new Testably.Abstractions.RealFileSystem().Path;
+
     /// <summary>
     /// Whether this is a Linux build on an architecture the recomp publishes an AppImage for. The AppImage
     /// is always run unpacked (see <see cref="RecompProcessRunner"/>), so this holds inside a Flatpak
@@ -43,9 +45,9 @@ public static class RecompPlatform
     public static string CachedSetupFileName(string tagName)
     {
         var sanitized = new string(tagName.Select(character => char.IsLetterOrDigit(character) ? character : '-').ToArray());
-        return $"WiiCompiled-Setup-{sanitized}{Path.GetExtension(SetupFileName)}";
+        return $"WiiCompiled-Setup-{sanitized}{NativePath.GetExtension(SetupFileName)}";
     }
 
     /// <summary>The pattern that matches every cached setup of this platform, for pruning superseded ones.</summary>
-    public static string CachedSetupSearchPattern => $"WiiCompiled-Setup-*{Path.GetExtension(SetupFileName)}";
+    public static string CachedSetupSearchPattern => $"WiiCompiled-Setup-*{NativePath.GetExtension(SetupFileName)}";
 }
diff --git a/WheelWizard/Features/Settings/Views/OtherSettings.axaml.cs b/WheelWizard/Features/Settings/Views/OtherSettings.axaml.cs
index a10332d4e..5ba630c6f 100644
--- a/WheelWizard/Features/Settings/Views/OtherSettings.axaml.cs
+++ b/WheelWizard/Features/Settings/Views/OtherSettings.axaml.cs
@@ -1,3 +1,4 @@
+using System.IO.Abstractions;
 using Avalonia.Controls;
 using Avalonia.Interactivity;
 using WheelWizard.CustomDistributions;
@@ -12,6 +13,8 @@ namespace WheelWizard.Settings.Views;
 
 public partial class OtherSettings : UserControl
 {
+    private readonly IFileSystem fileSystem;
+
     private readonly bool _settingsAreDisabled;
 
     private IFilePickerService FilePicker { get; }
@@ -23,12 +26,14 @@ public partial class OtherSettings : UserControl
     private ISettingsManager SettingsService { get; }
 
     public OtherSettings(
+        IFileSystem fileSystem,
         IFilePickerService filePicker,
         ICustomDistributionPaths distributionPaths,
         ICustomDistributionSingletonService customDistributionSingletonService,
         ISettingsManager settingsService
     )
     {
+        this.fileSystem = fileSystem;
         FilePicker = filePicker;
         DistributionPaths = distributionPaths;
         CustomDistributionSingletonService = customDistributionSingletonService;
@@ -41,7 +46,7 @@ ISettingsManager settingsService
         // controls individually so the recomp switch never becomes trapped behind Dolphin setup.
         LaunchRrOnStartup.IsEnabled = !_settingsAreDisabled;
         DolphinReinstallButton.IsEnabled = !_settingsAreDisabled;
-        OpenGameFolderButton.IsEnabled = !_settingsAreDisabled && Directory.Exists(DistributionPaths.RootFolderPath);
+        OpenGameFolderButton.IsEnabled = !_settingsAreDisabled && fileSystem.Directory.Exists(DistributionPaths.RootFolderPath);
         OpenSaveFolderButton.IsEnabled = !_settingsAreDisabled;
         if (!_settingsAreDisabled)
             LoadSettings();
@@ -57,8 +62,8 @@ private void LoadSettings()
     {
         // Only loads when the settings are not disabled (aka when the paths are set up correctly)
         LaunchRrOnStartup.IsChecked = SettingsService.Get<bool>(SettingsService.LAUNCH_RR_ON_STARTUP);
-        OpenGameFolderButton.IsEnabled = Directory.Exists(DistributionPaths.RootFolderPath);
-        OpenSaveFolderButton.IsEnabled = Directory.Exists(DistributionPaths.SaveFolderPath);
+        OpenGameFolderButton.IsEnabled = fileSystem.Directory.Exists(DistributionPaths.RootFolderPath);
+        OpenSaveFolderButton.IsEnabled = fileSystem.Directory.Exists(DistributionPaths.SaveFolderPath);
     }
 
     private void ForceLoadSettings()
@@ -119,7 +124,7 @@ private void OpenSaveFolder_OnClick(object? sender, RoutedEventArgs e)
 
     private void GameFileFolder_Click(object? sender, RoutedEventArgs e)
     {
-        if (!Directory.Exists(DistributionPaths.RootFolderPath))
+        if (!fileSystem.Directory.Exists(DistributionPaths.RootFolderPath))
             return;
 
         FilePicker.OpenFolderInFileManager(DistributionPaths.RootFolderPath);
diff --git a/WheelWizard/Features/Settings/Views/RecompSettings.axaml.cs b/WheelWizard/Features/Settings/Views/RecompSettings.axaml.cs
index 5f222e689..cc1bfa0e2 100644
--- a/WheelWizard/Features/Settings/Views/RecompSettings.axaml.cs
+++ b/WheelWizard/Features/Settings/Views/RecompSettings.axaml.cs
@@ -1,3 +1,4 @@
+using System.IO.Abstractions;
 using Avalonia.Controls;
 using Avalonia.Interactivity;
 using WheelWizard.Recomp;
@@ -12,6 +13,8 @@ namespace WheelWizard.Settings.Views;
 
 public partial class RecompSettings : UserControl
 {
+    private readonly IFileSystem fileSystem;
+
     private bool _loading;
 
     private IFilePickerService FilePicker { get; }
@@ -29,6 +32,7 @@ public partial class RecompSettings : UserControl
     private IRecompPaths RecompPaths { get; }
 
     public RecompSettings(
+        IFileSystem fileSystem,
         IFilePickerService filePicker,
         ISettingsManager settingsService,
         IRecompSettingManager recompSettingsFile,
@@ -38,6 +42,7 @@ public RecompSettings(
         IRecompInstallService? recompInstallService = null
     )
     {
+        this.fileSystem = fileSystem;
         FilePicker = filePicker;
         SettingsService = settingsService;
         RecompSettingsFile = recompSettingsFile;
@@ -74,7 +79,7 @@ private void LoadSettings()
 
             var installFolder = RecompEnvironment?.InstallFolderPath ?? RecompPaths.InstallFolderPath;
             InstallLocationText.Text = installFolder;
-            OpenInstallFolder.IsEnabled = installed && Directory.Exists(installFolder);
+            OpenInstallFolder.IsEnabled = installed && fileSystem.Directory.Exists(installFolder);
             UninstallButton.IsEnabled = installed;
             WiiCompiledVersionText.Text = t(
                 "helper_text.installed_version",
@@ -90,7 +95,7 @@ private void LoadSettings()
             SharedNandWarningIcon.IsVisible = sharingDolphinData;
 
             var cloneFolder = RecompPaths.NandCopyFolderPath;
-            DolphinCloneStatus.Text = Directory.Exists(cloneFolder)
+            DolphinCloneStatus.Text = fileSystem.Directory.Exists(cloneFolder)
                 ? t("status.recomp_dolphin_clone_available", new { path = cloneFolder })
                 : t("status.recomp_dolphin_clone_missing");
         }
@@ -269,7 +274,7 @@ private async void CloneDolphinData_OnClick(object? sender, RoutedEventArgs e)
         }
 
         var cloneFolder = RecompPaths.NandCopyFolderPath;
-        if (Directory.Exists(cloneFolder))
+        if (fileSystem.Directory.Exists(cloneFolder))
         {
             var overwrite = await new YesNoWindow()
                 .SetMainText(t("question.recomp_overwrite_dolphin_clone.title"))
@@ -329,7 +334,7 @@ private async Task ApplyNandSettingAsync()
     private void OpenInstallFolder_OnClick(object? sender, RoutedEventArgs e)
     {
         var installFolder = RecompEnvironment?.InstallFolderPath ?? RecompPaths.InstallFolderPath;
-        if (Directory.Exists(installFolder))
+        if (fileSystem.Directory.Exists(installFolder))
             FilePicker.OpenFolderInFileManager(installFolder);
     }
 
diff --git a/WheelWizard/Features/Settings/Views/WhWzSettings.axaml.cs b/WheelWizard/Features/Settings/Views/WhWzSettings.axaml.cs
index 7ed71ab4c..5c4f795f3 100644
--- a/WheelWizard/Features/Settings/Views/WhWzSettings.axaml.cs
+++ b/WheelWizard/Features/Settings/Views/WhWzSettings.axaml.cs
@@ -1,3 +1,4 @@
+using System.IO.Abstractions;
 using System.Runtime.InteropServices;
 using Avalonia.Controls;
 using Avalonia.Interactivity;
@@ -24,6 +25,8 @@ namespace WheelWizard.Settings.Views;
 
 public partial class WhWzSettings : UserControl
 {
+    private readonly IFileSystem fileSystem;
+
     // #todo: move settings state and location-change workflows into a view model so this page mostly handles the controls.
     private readonly IApplicationLogFiles _logFiles;
 
@@ -44,6 +47,7 @@ public partial class WhWzSettings : UserControl
     private IDiscImageService DiscImages { get; }
 
     public WhWzSettings(
+        IFileSystem fileSystem,
         IApplicationLogFiles logFiles,
         IFilePickerService filePicker,
         IDolphinPaths dolphinPaths,
@@ -54,6 +58,7 @@ public WhWzSettings(
         IDiscImageService discImages
     )
     {
+        this.fileSystem = fileSystem;
         DiscImages = discImages;
         FilePicker = filePicker;
         DolphinPaths = dolphinPaths;
@@ -166,7 +171,7 @@ private async void DolphinExeBrowse_OnClick(object sender, RoutedEventArgs e)
                 if (string.IsNullOrWhiteSpace(resolvedFolder))
                     return;
 
-                var executablePath = Path.Combine(resolvedFolder, "Contents", "MacOS", "Dolphin");
+                var executablePath = fileSystem.Path.Combine(resolvedFolder, "Contents", "MacOS", "Dolphin");
                 await ApplyLocationSettingAsync(SettingsService.DOLPHIN_LOCATION, ShellQuoting.QuoteUnixArgument(executablePath));
             }
 
@@ -178,7 +183,7 @@ private async void DolphinExeBrowse_OnClick(object sender, RoutedEventArgs e)
         {
             if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
             {
-                if (string.Equals(Path.GetFileName(filePath), "DolphinTool.exe", StringComparison.OrdinalIgnoreCase))
+                if (string.Equals(fileSystem.Path.GetFileName(filePath), "DolphinTool.exe", StringComparison.OrdinalIgnoreCase))
                 {
                     await MessageTranslationHelper.AwaitMessageAsync(MessageTranslation.Warning_DolphinToolSelected);
                     return;
@@ -283,7 +288,7 @@ private async void DolphinUserPathBrowse_OnClick(object sender, RoutedEventArgs
         var currentFolder = (string)SettingsService.USER_FOLDER_PATH.Get();
         var topLevel = TopLevel.GetTopLevel(this);
         // If a current folder exists and is valid, suggest it as the starting location
-        if (!string.IsNullOrEmpty(currentFolder) && Directory.Exists(currentFolder))
+        if (!string.IsNullOrEmpty(currentFolder) && fileSystem.Directory.Exists(currentFolder))
         {
             var folder = await topLevel!.StorageProvider.TryGetFolderFromPathAsync(currentFolder);
             var folders = await FilePicker.SelectFolderAsync("Select Dolphin User Path", folder);
@@ -312,7 +317,7 @@ private async void DolphinUserPathBrowse_OnClick(object sender, RoutedEventArgs
 
     private async Task<bool> ApplyLocationSettingAsync(Setting<string> setting, string path)
     {
-        var normalizedPath = setting == SettingsService.USER_FOLDER_PATH ? Path.TrimEndingDirectorySeparator(path) : path;
+        var normalizedPath = setting == SettingsService.USER_FOLDER_PATH ? fileSystem.Path.TrimEndingDirectorySeparator(path) : path;
 
         if (!SettingsEditing.Set(SettingsService, setting, normalizedPath))
         {
@@ -333,7 +338,7 @@ private void GameLocationOpen_OnClick(object sender, RoutedEventArgs e) =>
 
     private void DolphinUserFolderOpen_OnClick(object sender, RoutedEventArgs e)
     {
-        if (Directory.Exists(DolphinPaths.UserFolderPath))
+        if (!string.IsNullOrWhiteSpace(DolphinPaths.UserFolderPath) && fileSystem.Directory.Exists(DolphinPaths.UserFolderPath))
             FilePicker.OpenFolderInFileManager(DolphinPaths.UserFolderPath);
     }
 
@@ -342,8 +347,8 @@ private void OpenContainingFolder(string filePath)
         try
         {
             var unquotedPath = filePath.Trim().Trim('\'', '"');
-            var folderPath = Path.GetDirectoryName(Path.GetFullPath(unquotedPath));
-            if (!string.IsNullOrWhiteSpace(folderPath) && Directory.Exists(folderPath))
+            var folderPath = fileSystem.Path.GetDirectoryName(fileSystem.Path.GetFullPath(unquotedPath));
+            if (!string.IsNullOrWhiteSpace(folderPath) && fileSystem.Directory.Exists(folderPath))
                 FilePicker.OpenFolderInFileManager(folderPath);
         }
         catch
@@ -354,8 +359,8 @@ private void OpenContainingFolder(string filePath)
 
     private void AppDataLocationOpen_OnClick(object sender, RoutedEventArgs e)
     {
-        if (!Directory.Exists(ApplicationData.DirectoryPath))
-            Directory.CreateDirectory(ApplicationData.DirectoryPath);
+        if (!fileSystem.Directory.Exists(ApplicationData.DirectoryPath))
+            fileSystem.Directory.CreateDirectory(ApplicationData.DirectoryPath);
 
         FilePicker.OpenFolderInFileManager(ApplicationData.DirectoryPath);
     }
@@ -391,7 +396,9 @@ private void UpdateLocationRows()
             DolphinExecutableOpenButton.IsVisible && CanOpenContainingFolder(DolphinPaths.ExecutablePath);
         GameLocationOpenButton.IsEnabled = CanOpenContainingFolder(SettingsService.Get<string>(SettingsService.GAME_LOCATION));
         UpdateGameFileDetails();
-        DolphinUserFolderOpenButton.IsEnabled = Directory.Exists(DolphinPaths.UserFolderPath);
+        DolphinUserFolderOpenButton.IsEnabled = (
+            !string.IsNullOrWhiteSpace(DolphinPaths.UserFolderPath) && fileSystem.Directory.Exists(DolphinPaths.UserFolderPath)
+        );
     }
 
     private static void SetLocationRowState(PathIcon completeIcon, PathIcon warningIcon, SettingsButton changeButton, bool isValid)
@@ -401,13 +408,13 @@ private static void SetLocationRowState(PathIcon completeIcon, PathIcon warningI
         changeButton.Tone = isValid ? ActionButtonTone.Secondary : ActionButtonTone.Brand;
     }
 
-    private static bool CanOpenContainingFolder(string filePath)
+    private bool CanOpenContainingFolder(string filePath)
     {
         try
         {
             var unquotedPath = filePath.Trim().Trim('\'', '"');
-            var folderPath = Path.GetDirectoryName(Path.GetFullPath(unquotedPath));
-            return !string.IsNullOrWhiteSpace(folderPath) && Directory.Exists(folderPath);
+            var folderPath = fileSystem.Path.GetDirectoryName(fileSystem.Path.GetFullPath(unquotedPath));
+            return !string.IsNullOrWhiteSpace(folderPath) && fileSystem.Directory.Exists(folderPath);
         }
         catch
         {
@@ -415,7 +422,8 @@ private static bool CanOpenContainingFolder(string filePath)
         }
     }
 
-    private static bool IsConfiguredExecutableFile(string value) => File.Exists(value.Trim().Trim('\'', '"'));
+    private bool IsConfiguredExecutableFile(string value) =>
+        !string.IsNullOrWhiteSpace(value.Trim().Trim('\'', '"')) && fileSystem.File.Exists(value.Trim().Trim('\'', '"'));
 
     private void UpdateAppDataLocationUi()
     {
@@ -661,7 +669,7 @@ private async void AppDataLocationChange_OnClick(object sender, RoutedEventArgs
         IStorageFolder? suggestedStart = null;
 
         var currentPath = ApplicationData.DirectoryPath;
-        if (!string.IsNullOrWhiteSpace(currentPath) && Directory.Exists(currentPath))
+        if (!string.IsNullOrWhiteSpace(currentPath) && fileSystem.Directory.Exists(currentPath))
             suggestedStart = await topLevel!.StorageProvider.TryGetFolderFromPathAsync(currentPath);
 
         var folders = await FilePicker.SelectFolderAsync("Select Wheel Wizard data folder", suggestedStart);
diff --git a/WheelWizard/Features/WiiManagement/MiiManagement/Views/MiiListPage.axaml.cs b/WheelWizard/Features/WiiManagement/MiiManagement/Views/MiiListPage.axaml.cs
index 43c6b7f12..b15a63caa 100644
--- a/WheelWizard/Features/WiiManagement/MiiManagement/Views/MiiListPage.axaml.cs
+++ b/WheelWizard/Features/WiiManagement/MiiManagement/Views/MiiListPage.axaml.cs
@@ -322,7 +322,7 @@ private void ExportMultipleMiiFiles(Mii[] miis)
 
     public static string ReplaceInvalidFileNameChars(string filename)
     {
-        var invalid = Path.GetInvalidFileNameChars();
+        var invalid = new Testably.Abstractions.RealFileSystem().Path.GetInvalidFileNameChars();
         return string.Join("_", filename.Split(invalid, StringSplitOptions.RemoveEmptyEntries));
     }
 
diff --git a/WheelWizard/Program.cs b/WheelWizard/Program.cs
index 4fd2ef691..1f15a54b2 100644
--- a/WheelWizard/Program.cs
+++ b/WheelWizard/Program.cs
@@ -162,7 +162,8 @@ private static AppBuilder CreateWheelWizardApp(Func<Task<IDesktopStartup>> creat
 
     private static void SetupWorkingDirectory()
     {
-        if (new RuntimeEnvironment().IsFlatpakSandboxed(new RealFileSystem()))
+        var fileSystem = new RealFileSystem();
+        if (new RuntimeEnvironment().IsFlatpakSandboxed(fileSystem))
         {
             // In this case, we would not want executable directory-relative paths, since this is in `/app/bin`.
             // We are going to use the home directory instead (this should be the original working directory anyway).
@@ -171,7 +172,7 @@ private static void SetupWorkingDirectory()
         else
         {
             // Resolve all relative paths based on the WheelWizard executable's directory by default
-            var executableDirectory = Path.GetDirectoryName(Environment.ProcessPath);
+            var executableDirectory = fileSystem.Path.GetDirectoryName(Environment.ProcessPath);
             if (!string.IsNullOrWhiteSpace(executableDirectory))
                 Environment.CurrentDirectory = executableDirectory;
         }
@@ -182,7 +183,7 @@ private static void SetupWorkingDirectory()
         var whWzBaseDir = Environment.GetEnvironmentVariable("WW_BASEDIR") ?? string.Empty;
         try
         {
-            var whWzBaseDirAbsolute = Path.GetFullPath(whWzBaseDir);
+            var whWzBaseDirAbsolute = fileSystem.Path.GetFullPath(whWzBaseDir);
             Environment.CurrentDirectory = whWzBaseDirAbsolute;
         }
         catch
diff --git a/WheelWizard/Shared/Desktop/Storage/StoragePaths.cs b/WheelWizard/Shared/Desktop/Storage/StoragePaths.cs
index 94b2dc235..69737eecf 100644
--- a/WheelWizard/Shared/Desktop/Storage/StoragePaths.cs
+++ b/WheelWizard/Shared/Desktop/Storage/StoragePaths.cs
@@ -4,6 +4,8 @@ namespace WheelWizard.Shared.Desktop.Storage;
 
 public static class StoragePaths
 {
+    private static readonly System.IO.Abstractions.IPath NativePath = new Testably.Abstractions.RealFileSystem().Path;
+
     public static string? TryResolveLocalPath(IStorageItem? item)
     {
         if (item == null)
@@ -38,7 +40,7 @@ public static class StoragePaths
             if (uri.IsAbsoluteUri)
                 return null;
             var raw = uri.ToString();
-            if (!string.IsNullOrWhiteSpace(raw) && Path.IsPathRooted(raw))
+            if (!string.IsNullOrWhiteSpace(raw) && NativePath.IsPathRooted(raw))
                 return raw;
         }
 
diff --git a/WheelWizard/Shared/IO/PathSafety.cs b/WheelWizard/Shared/IO/PathSafety.cs
index 33dcf234b..a008a1ed1 100644
--- a/WheelWizard/Shared/IO/PathSafety.cs
+++ b/WheelWizard/Shared/IO/PathSafety.cs
@@ -2,6 +2,8 @@ namespace WheelWizard.Shared.IO;
 
 public static class PathSafety
 {
+    private static readonly System.IO.Abstractions.IPath NativePath = new Testably.Abstractions.RealFileSystem().Path;
+
     public static bool TryGetPathWithinDirectory(string directory, string relativePath, out string fullPath)
     {
         fullPath = string.Empty;
@@ -9,9 +11,9 @@ public static bool TryGetPathWithinDirectory(string directory, string relativePa
         if (!TryNormalizeRelativePath(relativePath, out var normalizedRelativePath))
             return false;
 
-        var destinationPath = Path.Combine(directory, normalizedRelativePath);
-        var fullDirectory = Path.GetFullPath(directory);
-        var candidatePath = Path.GetFullPath(destinationPath);
+        var destinationPath = NativePath.Combine(directory, normalizedRelativePath);
+        var fullDirectory = NativePath.GetFullPath(directory);
+        var candidatePath = NativePath.GetFullPath(destinationPath);
 
         if (!IsPathWithinDirectory(fullDirectory, candidatePath))
             return false;
@@ -25,16 +27,16 @@ public static bool IsPathWithinDirectory(string directory, string path)
         if (string.IsNullOrWhiteSpace(directory) || string.IsNullOrWhiteSpace(path))
             return false;
 
-        var fullDirectory = Path.GetFullPath(directory);
-        var fullPath = Path.GetFullPath(path);
-        var relativePath = Path.GetRelativePath(fullDirectory, fullPath);
+        var fullDirectory = NativePath.GetFullPath(directory);
+        var fullPath = NativePath.GetFullPath(path);
+        var relativePath = NativePath.GetRelativePath(fullDirectory, fullPath);
 
         return relativePath == "."
             || (
-                !Path.IsPathRooted(relativePath)
+                !NativePath.IsPathRooted(relativePath)
                 && !relativePath.Equals("..", StringComparison.Ordinal)
-                && !relativePath.StartsWith($"..{Path.DirectorySeparatorChar}", StringComparison.Ordinal)
-                && !relativePath.StartsWith($"..{Path.AltDirectorySeparatorChar}", StringComparison.Ordinal)
+                && !relativePath.StartsWith($"..{NativePath.DirectorySeparatorChar}", StringComparison.Ordinal)
+                && !relativePath.StartsWith($"..{NativePath.AltDirectorySeparatorChar}", StringComparison.Ordinal)
             );
     }
 
@@ -46,7 +48,12 @@ public static bool TryNormalizeRelativePath(string path, out string normalizedPa
             return false;
 
         var trimmedPath = path.Trim();
-        if (Path.IsPathFullyQualified(trimmedPath) || trimmedPath.StartsWith('/') || trimmedPath.StartsWith('\\'))
+        if (
+            NativePath.IsPathFullyQualified(trimmedPath)
+            || trimmedPath.StartsWith('/')
+            || trimmedPath.StartsWith('\\')
+            || IsWindowsDriveRooted(trimmedPath)
+        )
             return false;
 
         var segments = trimmedPath.Replace('\\', '/').Split('/', StringSplitOptions.RemoveEmptyEntries).Where(segment => segment != ".");
@@ -54,7 +61,7 @@ public static bool TryNormalizeRelativePath(string path, out string normalizedPa
         var safeSegments = new List<string>();
         foreach (var segment in segments)
         {
-            if (segment == ".." || segment.Contains(Path.VolumeSeparatorChar))
+            if (segment == ".." || segment.Contains(NativePath.VolumeSeparatorChar))
                 return false;
 
             safeSegments.Add(segment);
@@ -63,10 +70,14 @@ public static bool TryNormalizeRelativePath(string path, out string normalizedPa
         if (safeSegments.Count == 0)
             return false;
 
-        normalizedPath = Path.Combine(safeSegments.ToArray());
+        normalizedPath = NativePath.Combine(safeSegments.ToArray());
         return true;
     }
 
+    // Windows drive paths are rejected on every platform, even where ':' is a valid filename character.
+    private static bool IsWindowsDriveRooted(string path) =>
+        path.Length >= 2 && char.IsAsciiLetter(path[0]) && path[1] == ':' && (path.Length == 2 || path[2] is '/' or '\\');
+
     public static bool TryGetSafeFileName(string fileName, out string safeFileName)
     {
         safeFileName = string.Empty;
@@ -78,7 +89,7 @@ public static bool TryGetSafeFileName(string fileName, out string safeFileName)
         if (string.IsNullOrWhiteSpace(leafName) || leafName is "." or "..")
             return false;
 
-        if (leafName.IndexOfAny(Path.GetInvalidFileNameChars()) >= 0)
+        if (leafName.IndexOfAny(NativePath.GetInvalidFileNameChars()) >= 0)
             return false;
 
         safeFileName = leafName;
diff --git a/WheelWizard/Views/Shell/Layout.axaml.cs b/WheelWizard/Views/Shell/Layout.axaml.cs
index 0072958b4..bf2416c88 100644
--- a/WheelWizard/Views/Shell/Layout.axaml.cs
+++ b/WheelWizard/Views/Shell/Layout.axaml.cs
@@ -442,7 +442,7 @@ private void UpdateLiveAlert(LiveStatusService sender)
             if (this.FindControl<PathIcon>("LiveStatusIcon") is { } pathIcon)
             {
                 // Parse the SVG path data
-                var geometry = Geometry.Parse(sender.Status.Icon!);
+                var geometry = Geometry.Parse(sender.Status!.Icon!);
                 pathIcon.Data = geometry;
 
                 // Apply custom color if provided, otherwise use a default
@@ -461,7 +461,7 @@ private void UpdateLiveAlert(LiveStatusService sender)
             LiveStatusIcon.ClearValue(PathIcon.DataProperty);
             LiveStatusIcon.ClearValue(PathIcon.ForegroundProperty);
             // Use variant-based styling
-            LiveStatusBorder.Classes.Add(sender.Status.Variant.ToString()!);
+            LiveStatusBorder.Classes.Add(sender.Status!.Variant.ToString()!);
         }
     }