Prevent premature 'downloading' status before actual byte transfer
starts, and cache async provider values to avoid UI flicker during
queue library reloads.
Progress pipeline:
- StartItemProgress now initializes with 'preparing' status instead
of 'downloading'
- SetItemProgress ignores synthetic pre-download progress updates
while status is still 'preparing' (no byte data yet)
- DownloadService reads backend status field and propagates preparing/
downloading/finalizing to native worker item snapshot
- Dart progress stream maps 'preparing' to DownloadStatus.downloading
with progress 0.0 (indeterminate spinner)
Queue tab:
- Add _queueLibraryCountsCache and _queueLibraryPageDataCache to
retain last successful data during FutureProvider refetches
- Prevents empty-state flash when loadedIndexVersion bumps trigger
provider invalidation
- Caches trimmed to max 24 entries via FIFO eviction
zarzet
83d7106e35