Introduce a service-owned download worker that offloads the full
download-and-finalize pipeline to DownloadService on Android, keeping
downloads alive independently of the Flutter UI process.
Key changes:
- Extract SAF download logic from MainActivity into SafDownloadHandler
- Add NativeDownloadFinalizer for Kotlin-side decryption, format
conversion, metadata embedding, ReplayGain, post-processing, and
history persistence
- Extend DownloadService with native queue management (start, pause,
resume, cancel) using coroutine-based worker with AtomicFile snapshots
- Add Dart-side orchestration: snapshot polling, run-id correlation,
adoption on app restart, and fallback to Dart queue
- Forward embedReplayGain, tidalHighFormat, and postProcessingEnabled
through Go backend DownloadRequest struct
- Add nativeDownloadWorkerEnabled setting with UI toggle
- Make DownloadQueueLookup collections unmodifiable
- Migrate MainActivity from FlutterActivity to FlutterFragmentActivity for SAF picker compatibility
- Add ImpellerAwareFlutterFragment to support Impeller fallback on legacy devices
- Add output_fd support in Go backend for direct file descriptor writes (SAF)
- Add helper functions in output_fd.go for FD-based file operations
- Refactor Tidal/Qobuz/Amazon downloaders to support FD output and skip metadata embedding for SAF (handled by Flutter)
- Add extractQobuzDownloadURLFromBody with unit tests for robust URL parsing
- Add storage mode picker (SAF vs App folder) in download settings for Android
- Fix FFmpeg output path building to avoid same-path conflicts
- Embed metadata to SAF FLAC files via temp file bridge in Flutter
- Upgrade Gradle wrapper to 9.3.1 and add activity-ktx dependency
- Add SAF tree picker and persistent URI storage in settings
- Implement SAF file operations: exists, delete, stat, copy, create
- Update download pipeline to support SAF content URIs
- Add fallback to app-private storage when SAF write fails
- Support SAF in library scan with DocumentFile traversal
- Add history item repair for missing SAF URIs
- Create file_access.dart utilities for abstracted file operations
- Update Tidal/Qobuz/Amazon/Extensions for SAF-aware output
- Add runPostProcessingV2 API for SAF content URIs
- Update screens (album, artist, queue, track) for SAF awareness
Resolves Android 10+ scoped storage permission issues
