[refactor] Separate noise filtering from filesystem semantics

[paul-fresquet]

Summary

Refactor the current file filtering system to clearly separate two distinct concerns:

1. Filesystem semantics — OS-level file attributes (system flag, offline, etc.) — not user-configurable
2. Noise filtering — Application-level exclusion of clutter files (.DS_Store, thumbs.db) — user-configurable

Background

Currently, FileSystemInspector.IsSystem() mixes both concerns:

public bool IsSystem(FileInfo fileInfo)
{
    // Noise filtering (application-level)
    var isCommon = fileInfo.Name.In("desktop.ini", "thumbs.db", ".desktop.ini", ".thumbs.db", ".DS_Store");
    
    // Filesystem semantics (OS-level)
    var isSystem = (fileInfo.Attributes & FileAttributes.System) == FileAttributes.System;
    
    return isCommon || isSystem;
}

This conflation makes it hard to:

• Understand what's being filtered and why
• Extend the noise file list
• Allow future user customization of noise filtering

Proposed Design

New Interface Methods

public interface IFileSystemInspector
{
    // Filesystem semantics (non-configurable, OS-level)
    bool HasSystemAttribute(FileInfo fileInfo);  // Windows FileAttributes.System
    bool IsOffline(FileInfo fileInfo);
    bool IsRecallOnDataAccess(FileInfo fileInfo);
    
    // Noise filtering (application-level, potentially configurable)
    bool IsNoiseFile(FileInfo fileInfo);
}

Separate Noise File Detection

Create a dedicated component or static helper for noise file detection:

public static class NoiseFileDetector
{
    private static readonly HashSet<string> KnownNoiseFileNames = new(StringComparer.OrdinalIgnoreCase)
    {
        // Windows
        "desktop.ini",
        "thumbs.db",
        "ehthumbs.db",
        "ehthumbs_vista.db",
        
        // macOS
        ".DS_Store",
        ".AppleDouble",
        ".LSOverride",
        ".Spotlight-V100",
        ".Trashes",
        ".fseventsd",
        ".TemporaryItems",
        ".VolumeIcon.icns",
        
        // Linux
        ".directory"
    };
    
    public static bool IsNoiseFile(string fileName)
    {
        return KnownNoiseFileNames.Contains(fileName);
    }
}

Acceptance Criteria

• Rename IsSystem() to HasSystemAttribute() (or similar) for clarity
• Create IsNoiseFile() method with extended file list
• Update InventoryBuilder to call both methods separately
• Maintain backward compatibility in SessionSettings.ExcludeSystemFiles behavior
• Document each noise file and its origin (Windows/macOS/Linux)
• Unit tests for noise file detection (case sensitivity, all listed files)

Extended Noise File List

File	Platform	Purpose
desktop.ini	Windows	Folder customization
thumbs.db	Windows	Thumbnail cache
ehthumbs.db	Windows	Media Center thumbnails
ehthumbs_vista.db	Windows	Vista Media Center
.DS_Store	macOS	Finder metadata
.AppleDouble	macOS	Resource forks
.LSOverride	macOS	Launch Services
.Spotlight-V100	macOS	Spotlight index
.Trashes	macOS	Trash folder
.fseventsd	macOS	File system events
.TemporaryItems	macOS	Temporary files
.VolumeIcon.icns	macOS	Volume icon
.directory	Linux (KDE)	Folder metadata

Priority

Important — Improves code clarity and prepares for future extensibility.