fix(cas): fall back from unwritable installation pools

GenHub/GenHub.Core/Interfaces/Common/IStorageWritabilityProbe.cs

@@ -0,0 +1,24 @@
+namespace GenHub.Core.Interfaces.Common;
+
+/// <summary>
+/// Determines whether GenHub can create storage at a filesystem location.
+/// </summary>
+public interface IStorageWritabilityProbe
+{
+    /// <summary>
+    /// Checks whether a directory can be created at, or files written into, the given path.
+    /// </summary>
+    /// <remarks>
+    /// A successful check creates the storage directory when it does not already exist and leaves
+    /// that directory in place. Callers should account for this filesystem side effect.
+    /// </remarks>
+    /// <param name="storagePath">The storage path to check.</param>
+    /// <returns><c>true</c> when the location accepts writes; otherwise, <c>false</c>.</returns>
+    bool CanCreateStorageAt(string storagePath);
+
+    /// <summary>
+    /// Discards any cached result for a storage path so the next check probes the filesystem again.
+    /// </summary>
+    /// <param name="storagePath">The storage path to re-probe, or <c>null</c> to discard every cached result.</param>
+    void Invalidate(string? storagePath = null);
+}

GenHub/GenHub.Core/Interfaces/Storage/ICasPoolResolver.cs

@@ -28,6 +28,12 @@ public interface ICasPoolResolver
     /// <returns>The root path for the appropriate pool.</returns>
     string GetPoolRootPath(ContentType contentType);
 
+    /// <summary>
+    /// Gets the previous installation-pool root retained for read-only lookup.
+    /// </summary>
+    /// <returns>The legacy root, or an empty string when none is configured.</returns>
+    string GetLegacyInstallationPoolRootPath();
+
     /// <summary>
     /// Checks if the installation pool is configured and available.
     /// </summary>

GenHub/GenHub.Core/Interfaces/Storage/IInstallationCasPoolService.cs

@@ -0,0 +1,19 @@
+using GenHub.Core.Models.GameInstallations;
+
+namespace GenHub.Core.Interfaces.Storage;
+
+/// <summary>
+/// Selects and persists an effective installation CAS pool from detected installations.
+/// </summary>
+public interface IInstallationCasPoolService
+{
+    /// <summary>
+    /// Ensures installation-pool settings reflect the currently detected installations.
+    /// </summary>
+    /// <param name="installations">The detected game installations.</param>
+    /// <param name="cancellationToken">A token that can cancel the settings update.</param>
+    /// <returns><c>true</c> when content acquisition may continue; otherwise, <c>false</c>.</returns>
+    Task<bool> EnsurePoolPathAsync(
+        IReadOnlyList<GameInstallation> installations,
+        CancellationToken cancellationToken = default);
+}

GenHub/GenHub.Core/Models/Storage/CasConfiguration.cs

@@ -45,6 +45,18 @@ public TimeSpan GcLockTimeout
     /// </summary>
     public string InstallationPoolRootPath { get; set; } = string.Empty;
 
+    /// <summary>
+    /// Gets or sets a value indicating whether <see cref="InstallationPoolRootPath"/> was
+    /// selected automatically from a detected game installation.
+    /// </summary>
+    public bool IsInstallationPoolRootPathAutoDerived { get; set; }
+
+    /// <summary>
+    /// Gets or sets a previous installation-pool root that remains available for read-only
+    /// object lookup after new writes have fallen back to another pool.
+    /// </summary>
+    public string LegacyInstallationPoolRootPath { get; set; } = string.Empty;
+
     /// <summary>
     /// Gets or sets the hash algorithm to use for content addressing.
     /// </summary>
@@ -133,6 +145,8 @@ public object Clone()
             EnableAutomaticGc = EnableAutomaticGc,
             CasRootPath = CasRootPath,
             InstallationPoolRootPath = InstallationPoolRootPath,
+            IsInstallationPoolRootPathAutoDerived = IsInstallationPoolRootPathAutoDerived,
+            LegacyInstallationPoolRootPath = LegacyInstallationPoolRootPath,
             HashAlgorithm = HashAlgorithm,
             GcGracePeriod = GcGracePeriod,
             MaxCacheSizeBytes = MaxCacheSizeBytes,

GenHub/GenHub.Tests/GenHub.Tests.Core/Common/Services/ConfigurationProviderServiceTests.cs

@@ -3,6 +3,7 @@
 using GenHub.Core.Interfaces.Common;
 using GenHub.Core.Models.Common;
 using GenHub.Core.Models.Enums;
+using GenHub.Core.Models.Storage;
 using Microsoft.Extensions.Logging;
 using Moq;
 
@@ -84,6 +85,30 @@ public void Constructor_WithNullLogger_ThrowsArgumentNullException()
                 null!));
     }
 
+    /// <summary>
+    /// Preserves every CAS option when applying the default primary pool path.
+    /// </summary>
+    [Fact]
+    public void GetCasConfiguration_WhenPrimaryPathIsEmpty_PreservesGcLockTimeout()
+    {
+        var expectedTimeout = TimeSpan.FromSeconds(91);
+        var settings = new UserSettings
+        {
+            CasConfiguration = new CasConfiguration
+            {
+                CasRootPath = string.Empty,
+                GcLockTimeout = expectedTimeout,
+            },
+        };
+        _mockUserSettings.Setup(service => service.Get()).Returns(settings);
+        var provider = CreateProvider();
+
+        var result = provider.GetCasConfiguration();
+
+        Assert.Equal(expectedTimeout, result.GcLockTimeout);
+        Assert.False(string.IsNullOrWhiteSpace(result.CasRootPath));
+    }
+
     /// <summary>
     /// Verifies that GetWorkspacePath returns user setting when it's valid and directory exists.
     /// </summary>

GenHub/GenHub.Tests/GenHub.Tests.Core/Common/Services/StorageLocationServiceTests.cs

@@ -5,6 +5,7 @@
 using GenHub.Core.Models.Common;
 using GenHub.Core.Models.Enums;
 using GenHub.Core.Models.GameInstallations;
+using GenHub.Core.Models.Storage;
 using Microsoft.Extensions.Logging;
 using Moq;
 
@@ -21,6 +22,7 @@ public sealed class StorageLocationServiceTests : IDisposable
     private readonly Mock<IConfigurationProviderService> _configurationProviderService = new();
     private readonly Mock<IGameInstallationService> _gameInstallationService = new();
     private readonly string _applicationDataPath;
+    private readonly string _primaryCasPath;
     private readonly string _tempPath;
 
     /// <summary>
@@ -30,9 +32,75 @@ public StorageLocationServiceTests()
     {
         _tempPath = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString("N"));
         _applicationDataPath = Path.Combine(_tempPath, "AppData");
+        _primaryCasPath = Path.Combine(_applicationDataPath, DirectoryNames.CasPool);
         Directory.CreateDirectory(_applicationDataPath);
 
         _configurationProviderService.Setup(service => service.GetApplicationDataPath()).Returns(_applicationDataPath);
+        _configurationProviderService
+            .Setup(service => service.GetCasConfiguration())
+            .Returns(new CasConfiguration { CasRootPath = _primaryCasPath });
+    }
+
+    /// <summary>
+    /// Reports the effective primary CAS path when installation-adjacent storage is unavailable.
+    /// </summary>
+    [Fact]
+    public void GetCasPoolPath_WhenAdjacentPathIsUnavailable_UsesPrimaryPool()
+    {
+        var settings = new UserSettings { UseInstallationAdjacentStorage = true };
+        _userSettingsService.Setup(service => service.Get()).Returns(settings);
+        var installationPath = Path.Combine(_tempPath, "Game");
+        var installation = new GameInstallation(installationPath, GameInstallationType.Retail);
+        var adjacentPath = Path.Combine(installationPath, DirectoryNames.GenHubCasPool);
+        var probe = new Mock<IStorageWritabilityProbe>();
+        probe.Setup(service => service.CanCreateStorageAt(adjacentPath)).Returns(false);
+        var service = CreateService(probe.Object);
+
+        var result = service.GetCasPoolPath(installation);
+
+        Assert.Equal(_primaryCasPath, result);
+    }
+
+    /// <summary>
+    /// Reports a writable user-configured installation CAS path.
+    /// </summary>
+    [Fact]
+    public void GetCasPoolPath_WhenConfiguredPathIsWritable_UsesConfiguredPool()
+    {
+        var configuredPath = Path.Combine(_tempPath, "CustomCas");
+        var settings = new UserSettings
+        {
+            CasConfiguration = new CasConfiguration { InstallationPoolRootPath = configuredPath },
+        };
+        _userSettingsService.Setup(service => service.Get()).Returns(settings);
+        var probe = new Mock<IStorageWritabilityProbe>();
+        probe.Setup(service => service.CanCreateStorageAt(configuredPath)).Returns(true);
+        var service = CreateService(probe.Object);
+        var installation = new GameInstallation(Path.Combine(_tempPath, "Game"), GameInstallationType.Retail);
+
+        var result = service.GetCasPoolPath(installation);
+
+        Assert.Equal(configuredPath, result);
+    }
+
+    /// <summary>
+    /// Keeps a dotted installation directory intact when resolving adjacent CAS storage.
+    /// </summary>
+    [Fact]
+    public void GetCasPoolPath_WhenInstallationDirectoryContainsDot_UsesFullDirectory()
+    {
+        var settings = new UserSettings { UseInstallationAdjacentStorage = true };
+        _userSettingsService.Setup(service => service.Get()).Returns(settings);
+        var installationPath = Path.Combine(_tempPath, "ZeroHour v1.04");
+        var installation = new GameInstallation(installationPath, GameInstallationType.Retail);
+        var adjacentPath = Path.Combine(installationPath, DirectoryNames.GenHubCasPool);
+        var probe = new Mock<IStorageWritabilityProbe>();
+        probe.Setup(service => service.CanCreateStorageAt(adjacentPath)).Returns(true);
+        var service = CreateService(probe.Object);
+
+        var result = service.GetCasPoolPath(installation);
+
+        Assert.Equal(adjacentPath, result);
     }
 
     /// <summary>
@@ -188,9 +256,10 @@ public void Dispose()
         GC.SuppressFinalize(this);
     }
 
-    private StorageLocationService CreateService() => new(
+    private StorageLocationService CreateService(IStorageWritabilityProbe? writabilityProbe = null) => new(
         _userSettingsService.Object,
         _configurationProviderService.Object,
         _gameInstallationService.Object,
+        writabilityProbe ?? new StorageWritabilityProbe(new Mock<ILogger<StorageWritabilityProbe>>().Object),
         new Mock<ILogger<StorageLocationService>>().Object);
 }

GenHub/GenHub.Tests/GenHub.Tests.Core/Common/Services/UserSettingsServiceTests.cs

@@ -4,6 +4,7 @@
 using GenHub.Core.Interfaces.Common;
 using GenHub.Core.Models.Common;
 using GenHub.Core.Models.Enums;
+using GenHub.Core.Models.Storage;
 using Microsoft.Extensions.Logging;
 using Moq;
 
@@ -131,6 +132,37 @@ public async Task LoadSettings_AfterSave_LoadsCorrectData()
         Assert.Equal(NavigationTab.Downloads, loadedSettings.LastSelectedTab);
     }
 
+    /// <summary>
+    /// Verifies that the historical installation-pool provenance marker survives settings persistence.
+    /// </summary>
+    /// <returns>A task representing the asynchronous test operation.</returns>
+    [Fact]
+    public async Task LoadSettings_AfterSave_PreservesInstallationPoolProvenanceMarker()
+    {
+        var settingsPath = Path.Combine(_tempDirectory, "provenance", FileTypes.SettingsFileName);
+        Directory.CreateDirectory(Path.GetDirectoryName(settingsPath)!);
+        var service1 = new TestableUserSettingsService(
+            _mockLogger.Object,
+            CreateAppConfigMock(),
+            settingsPath);
+        service1.Update(settings =>
+        {
+            settings.CasConfiguration.InstallationPoolRootPath = "/historical/installation/.genhub-cas";
+            settings.MarkAsExplicitlySet(nameof(CasConfiguration.InstallationPoolRootPath));
+        });
+        await service1.SaveAsync();
+
+        var service2 = new TestableUserSettingsService(
+            _mockLogger.Object,
+            CreateAppConfigMock(),
+            settingsPath);
+        var loadedSettings = service2.Get();
+
+        Assert.Contains(
+            nameof(CasConfiguration.InstallationPoolRootPath),
+            loadedSettings.ExplicitlySetProperties);
+    }
+
     /// <summary>
     /// Verifies that GetSettings returns default values with corrupted JSON.
     /// </summary>
@@ -394,4 +426,4 @@ public TestableUserSettingsService(ILogger<UserSettingsService> logger, IAppConf
             SetSettingsFilePath(settingsFilePath);
         }
     }
-}
+}