PlaylistDetailScreen zeigt die Songs einer Playlist (watchPlaylistSongs),
erlaubt Entfernen einzelner Songs und Umsortieren per Drag & Drop
(ReorderableListView.builder). Tippen auf einen Song spielt die Playlist
ab dieser Stelle. Leer-Zustand mit Hinweistext.
Da bestehende position-Werte nach Einfügereihenfolge lückenhaft sein
können, schreibt das Umsortieren nicht nur den verschobenen Song um,
sondern vergibt für die gesamte Playlist neue lückenlose Positionen
(0..N-1): MeloDb.reorderAllPlaylistSongs (in einer Transaktion) +
PlaylistService.reorderAll als dünner Wrapper.
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
## Critical Fixes
- Fix CRITICAL-1: Empty scans no longer delete entire library
- Use timestamp-based tombstone logic instead of path-based
- Only mark missing if livePaths is not empty
- Fix CRITICAL-2: Re-scanned files now return from deleted state
- Add deleted=false to SongsCompanion.insert in both scanners
## High Priority Fixes
- HIGH-1: Fix SQLite variable limit crash on large libraries
- Replace isNotIn() with timestamp comparison (O(1) not O(n))
- HIGH-2: Fix UI freezing during scan
- Throttle progress updates (every 50 files or end of scan)
- HIGH-3: Add error handling for scan failures
- Wrap scanFolders/scanAndroidMediaStore in try/catch
- Display scanError banner in LibraryScreen
- HIGH-4: Add error handling for playback failures
- Wrap loadPlaylist in try/catch
## Medium Priority Fixes
- MEDIUM-1: Replace ! with ?? to handle unknown ProcessingState
- MEDIUM-2: Escape LIKE wildcards in search queries
- MEDIUM-4: Display StreamBuilder errors instead of treating as empty
- MEDIUM-8: Add tooltips to all IconButtons for accessibility
- Add doc comments to public database APIs
## Testing
- Add regression tests for CRITICAL-1 and CRITICAL-2
- All 9 existing tests pass
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
