Persist file categories on the index and classify archives and unknown types during idle maintenance.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/Explorer.Domain.Tests/DomainTests.cs

@@ -484,6 +484,108 @@ public class FileClassifierTests
         => FileClassifier.Classify(name, @"C:\Downloads\" + name, isDirectory, isDirectory ? AttributeFlags.Directory : 0, isRepoRoot).Category;
 }
 
+public class EntryCategoryAssignerTests
+{
+    [Fact]
+    public void ApplyAutomatic_sets_extension_category_on_files()
+    {
+        var entry = new IndexEntry
+        {
+            Name = "clip.mkv",
+            NameNorm = "clip.mkv",
+            PathRel = "clip.mkv",
+            Extension = "mkv"
+        };
+        EntryCategoryAssigner.ApplyAutomatic(entry);
+        Assert.Equal(FileCategory.Video, entry.Category);
+        Assert.Equal(CategorySources.Extension, entry.CategorySource);
+        Assert.True(entry.CategoryConfidence >= 80);
+    }
+
+    [Fact]
+    public void User_category_is_not_overwritten()
+    {
+        var entry = new IndexEntry
+        {
+            Name = "clip.mkv",
+            NameNorm = "clip.mkv",
+            PathRel = "clip.mkv",
+            Extension = "mkv"
+        };
+        EntryCategoryAssigner.ApplyUser(entry, FileCategory.Documents, "Manual");
+        EntryCategoryAssigner.ApplyAutomatic(entry);
+        Assert.Equal(FileCategory.Documents, entry.Category);
+        Assert.Equal(CategorySources.User, entry.CategorySource);
+    }
+
+    [Fact]
+    public void Children_majority_sets_folder_or_archive_source()
+    {
+        var folder = new IndexEntry
+        {
+            Name = "Vacation",
+            NameNorm = "vacation",
+            PathRel = "Vacation",
+            IsDirectory = true,
+            Attributes = AttributeFlags.Directory
+        };
+        EntryCategoryAssigner.ApplyAutomatic(
+            folder,
+            childCategories: [FileCategory.Photos, FileCategory.Photos, FileCategory.Photos, FileCategory.Documents]);
+        Assert.Equal(FileCategory.Photos, folder.Category);
+        Assert.Equal(CategorySources.Children, folder.CategorySource);
+
+        var zip = new IndexEntry
+        {
+            Name = "photos.zip",
+            NameNorm = "photos.zip",
+            PathRel = "photos.zip",
+            Extension = "zip"
+        };
+        EntryCategoryAssigner.ApplyAutomatic(
+            zip,
+            childCategories: [FileCategory.Photos, FileCategory.Photos, FileCategory.Photos]);
+        Assert.Equal(FileCategory.Photos, zip.Category);
+        Assert.Equal(CategorySources.ArchiveContents, zip.CategorySource);
+    }
+}
+
+public class OrganizeDestinationsTests
+{
+    [Fact]
+    public void Parses_category_aliases()
+    {
+        Assert.True(OrganizeDestinations.TryParse("photos", out var photos));
+        Assert.Equal(FileCategory.Photos, photos);
+        Assert.True(OrganizeDestinations.TryParse("zip", out var zip));
+        Assert.Equal(FileCategory.Archive, zip);
+        Assert.True(OrganizeDestinations.TryParse("unknown", out var unknown));
+        Assert.Equal(FileCategory.Unknown, unknown);
+        Assert.False(OrganizeDestinations.TryParse("not-a-category", out _));
+    }
+}
+
+public class FileSignatureClassifierTests
+{
+    [Fact]
+    public void Recognizes_common_headers()
+    {
+        Assert.Equal(FileCategory.Photos, Hit([0xFF, 0xD8, 0xFF, 0xE0]));
+        Assert.Equal(FileCategory.Photos, Hit([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]));
+        Assert.Equal(FileCategory.Documents, Hit([0x25, 0x50, 0x44, 0x46]));
+        Assert.Equal(FileCategory.Archive, Hit([0x50, 0x4B, 0x03, 0x04]));
+        Assert.Equal(FileCategory.Archive, Hit([0x37, 0x7A, 0xBC, 0xAF]));
+        Assert.Equal(FileCategory.Installer, Hit([0x4D, 0x5A, 0x90, 0x00]));
+        Assert.Equal(FileCategory.Audio, Hit("RIFF....WAVE"u8.ToArray()));
+        Assert.Equal(FileCategory.Video, Hit("RIFF....AVI "u8.ToArray()));
+        Assert.Null(FileSignatureClassifier.TryClassify([0x00, 0x01, 0x02, 0x03]));
+        Assert.Null(FileSignatureClassifier.TryClassify([0xFF, 0xD8]));
+    }
+
+    private static FileCategory Hit(byte[] header)
+        => FileSignatureClassifier.TryClassify(header)!.Category;
+}
+
 public class GitChangeTests
 {
     [Fact]