Module thumbnail 

Thumbnail generation and caching service

Follows a modified freedesktop.org thumbnail spec:

• Thumbnails stored on the drive itself for portability
• Named by SHA256 hash of file path
• Stored as JPEG for smaller size
• Three sizes: 128, 256, 512

Performance strategy (matches production photo apps):

1. Extract embedded EXIF thumbnail first (~2ms vs ~200-500ms for full decode)
2. Fall back to bounded full decode when no adequate embedded preview exists
3. Per-image timeout to prevent stuck queue from corrupt/huge images
4. Priority-aware concurrency so visible cells beat background prewarm

Structs

ThumbnailEntry

Cached thumbnail entry.

ThumbnailService

Thumbnail service with LRU cache management

Enums

ThumbnailSize

Thumbnail size variants