aiohttp's FileResponse uses _sendfile_native on Windows (IOCP-based), which crashes with ov.getresult() when the client disconnects mid-transfer. This happens constantly when users scroll through a gallery of animated previews (video files like .mp4/.webm).
Detect video extensions and stream manually via StreamResponse + chunked reads instead, gracefully handling ConnectionResetError. Images continue using FileResponse (small files, sendfile works fine).
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
- Add `_entry_is_symlink` method to detect symlinks and Windows junctions
- Include first-level symlinks in fingerprint for better cache invalidation
- Re-enable preview path validation for security
- Update tests to verify retargeted symlinks trigger rescan
Temporary workaround for issues #772 and #774 where valid previews
are rejected. Path validation is disabled until proper fix for
preview root path handling is implemented.
