macOS Quick Look extensions for 48K ZX Spectrum .SNA snapshot files.

• Spacebar Preview: Press spacebar on .SNA files to see full 256×192 decoded image
• Finder Thumbnails: File icons display decoded ZX Spectrum screenshots with correct aspect ratio

• Type: Quick Look Preview (spacebar)
• Entry: PreviewViewController (QLPreviewingController)
• Function: Renders 256×192 bitmap in preview panel
• Note: Uses UIKit coordinate system, full resolution display

• Type: Quick Look Thumbnail (Finder icons)
• Entry: ThumbnailProvider (QLThumbnailProvider)
• Function: Renders scaled thumbnail preserving 4:3 aspect ratio
• Note: Sandboxed XPC extension, scales to icon grid while maintaining aspect

• Extension: .SNA
• Size: 49,179 bytes (fixed, 48K Spectrum snapshot)
• Resolution: 256×192 pixels (4:3 aspect ratio)
• Memory Layout:
  • Bytes 0-26: Registers + state (27 bytes)
  • Bytes 27-6,910: Display memory (32×192 chars = 32×24 chars × 8 pixels)
  • Bytes 6,911-7,678: Attributes (color + brightness per char)

The decoder reconstructs the ZX Spectrum display format:

1. Parse attribute bytes (ink color, paper color, brightness)
2. Iterate 24×32 character grid
3. For each character, unpack 8 pixel rows from display memory
4. Map bits to RGB using decoded color attributes
5. Handle Spectrum's "venetian blinds" memory layout (Y coordinate transformation)

❌ Merged both extensions in one Info.plist array → Broke preview functionality
❌ DRY refactoring with shared SnapshotDecoder.swift → Module compilation errors
❌ Manual pbxproj editing → Too fragile, UUID management errors
❌ Relied on file discovery → Swift files need explicit Build Phase entry or Xcode won't compile
❌ Used only request.maximumSize → Forced thumbnails to square; Finder ignored aspect ratio
✅ Constrained contextSize between minimumSize and maximumSize → Finder respects aspect ratio (per Apple docs & Stack Overflow)

# Build both extensions
xcodebuild build -scheme zxql-host-app

# Reset Quick Look daemon
qlmanage -r

# Test spacebar preview
qlmanage -p /path/to/file.sna

# Or in Finder
open -a Finder /path/to/files
# Press spacebar on .sna file
# Thumbnails auto-display in icon view

For system-wide use (not just development):

cp -r /path/to/zxql-host-app.app /Applications/
# Extensions load automatically

zxql-host-app/
├── Info-generated.plist          # Declares com.hippietrail.sna UTType
└── AppDelegate.swift

zxql-preview-extension/
├── Info.plist                    # Preview extension config
├── PreviewViewController.swift    # QLPreviewingController subclass
├── Base.lproj/
│   └── PreviewViewController.xib # UI (ImageView)
└── *.swift                       # Support code & color decoding

zxql-thumbnail-extension/
├── Info.plist                    # Thumbnail extension config  
└── ThumbnailProvider.swift       # QLThumbnailProvider subclass
                                  # Contains: SNA decoder, color rendering

• zxql-preview-extension/Info.plist - Declares com.apple.quicklook.preview extension point
• zxql-preview-extension/PreviewViewController.swift - Spacebar preview implementation
• zxql-thumbnail-extension/Info.plist - Declares com.apple.quicklook.thumbnail extension point
• zxql-thumbnail-extension/ThumbnailProvider.swift - Finder icon implementation
• zxql-host-app/Info-generated.plist - UTType declaration for .sna files

Checklist for new file type:

1. Create custom UTType in host app's Info.plist
2. Add Preview Extension target (File > New > Target > macOS > Quick Look Preview Extension)
   • Implement QLPreviewingController
   • Add source files to Build Phases > Compile Sources
   • Configure Info.plist with QLSupportedContentTypes
3. Add Thumbnail Extension target (File > New > Target > macOS > Thumbnail Extension)
   • Implement QLThumbnailProvider
   • Add source files to Build Phases > Compile Sources
   • Configure Info.plist with QLSupportedContentTypes + QLThumbnailMinimumDimension
4. Test both via qlmanage -r and spacebar/Finder
5. Install to /Applications/ for system-wide use

See Apple Quick Look Thumbnailing docs