fix: stabilize library scan IDs, pause queue behavior, and scan race condition

- Generate stable SHA-1 based IDs for SAF-scanned library items to prevent null ID crashes on the Dart side
- Suppress false queue-complete notification when user pauses instead of finishing the queue, and break out of parallel loop immediately when paused with no active downloads
- Use SQLite as the single source of truth for library scan results to fix a race condition where auto-scan could fire before provider state finished loading, dropping unchanged rows

android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt

@@ -30,6 +30,7 @@ import org.json.JSONObject
 import java.io.File
 import java.io.FileInputStream
 import java.io.FileOutputStream
+import java.security.MessageDigest
 import java.util.Locale
 
 class MainActivity: FlutterFragmentActivity() {
@@ -111,6 +112,13 @@ class MainActivity: FlutterFragmentActivity() {
         }
     }
 
+    private fun buildStableLibraryId(filePath: String): String {
+        val digest = MessageDigest.getInstance("SHA-1")
+        val bytes = digest.digest(filePath.toByteArray(Charsets.UTF_8))
+        val hex = bytes.joinToString("") { "%02x".format(it) }
+        return "lib_$hex"
+    }
+
     data class SafScanProgress(
         var totalFiles: Int = 0,
         var scannedFiles: Int = 0,
@@ -1263,7 +1271,9 @@ class MainActivity: FlutterFragmentActivity() {
             } else {
                 try {
                     val lastModified = try { doc.lastModified() } catch (_: Exception) { 0L }
-                    metadataObj.put("filePath", doc.uri.toString())
+                    val stableUri = doc.uri.toString()
+                    metadataObj.put("id", buildStableLibraryId(stableUri))
+                    metadataObj.put("filePath", stableUri)
                     metadataObj.put("fileModTime", lastModified)
                     results.put(metadataObj)
                 } catch (_: Exception) {
@@ -1680,7 +1690,9 @@ class MainActivity: FlutterFragmentActivity() {
             } else {
                 try {
                     val safeLastModified = try { doc.lastModified() } catch (_: Exception) { lastModified }
-                    metadataObj.put("filePath", doc.uri.toString())
+                    val stableUri = doc.uri.toString()
+                    metadataObj.put("id", buildStableLibraryId(stableUri))
+                    metadataObj.put("filePath", stableUri)
                     metadataObj.put("fileModTime", safeLastModified)
                     metadataObj.put("lastModified", safeLastModified)
                     results.put(metadataObj)

lib/providers/download_queue_provider.dart

@@ -3248,6 +3248,7 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
     }
     _log.d('Concurrent downloads: ${state.concurrentDownloads}');
     await _processQueueParallel();
+    final stoppedWhilePaused = state.isPaused;
 
     _stopProgressPolling();
 
@@ -3273,7 +3274,7 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
     _log.i(
       'Queue stats - completed: $_completedInSession, failed: $_failedInSession, totalAtStart: $_totalQueuedAtStart',
     );
-    if (_totalQueuedAtStart > 0) {
+    if (!stoppedWhilePaused && _totalQueuedAtStart > 0) {
       await _notificationService.showQueueComplete(
         completedCount: _completedInSession,
         failedCount: _failedInSession,
@@ -3288,13 +3289,17 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
       }
     }
 
-    _log.i('Queue processing finished');
+    if (stoppedWhilePaused) {
+      _log.i('Queue processing paused');
+    } else {
+      _log.i('Queue processing finished');
+    }
     state = state.copyWith(isProcessing: false, currentDownload: null);
 
     final hasQueuedItems = state.items.any(
       (item) => item.status == DownloadStatus.queued,
     );
-    if (hasQueuedItems) {
+    if (hasQueuedItems && !state.isPaused) {
       _log.i(
         'Found queued items after processing finished, restarting queue...',
       );
@@ -3310,8 +3315,15 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
 
     while (true) {
       if (state.isPaused) {
+        if (activeDownloads.isEmpty) {
+          _log.d('Queue is paused and no active downloads remain');
+          break;
+        }
         _log.d('Queue is paused, waiting for active downloads...');
-        await Future.delayed(_queueSchedulingInterval);
+        await Future.any([
+          Future.wait(activeDownloads.values),
+          Future.delayed(_queueSchedulingInterval),
+        ]);
         continue;
       }
 

lib/providers/local_library_provider.dart

@@ -329,6 +329,11 @@ class LocalLibraryNotifier extends Notifier<LocalLibraryState> {
         if (items.isNotEmpty) {
           await _db.upsertBatch(items.map((e) => e.toJson()).toList());
         }
+        final persistedItems =
+            (await _db.getAll())
+                .map(LocalLibraryItem.fromJson)
+                .toList(growable: false)
+              ..sort(_compareLibraryItems);
 
         final now = DateTime.now();
         try {
@@ -341,7 +346,7 @@ class LocalLibraryNotifier extends Notifier<LocalLibraryState> {
         }
 
         state = state.copyWith(
-          items: items,
+          items: persistedItems,
           isScanning: false,
           scanProgress: 100,
           lastScannedAt: now,
@@ -350,11 +355,11 @@ class LocalLibraryNotifier extends Notifier<LocalLibraryState> {
         );
 
         _log.i(
-          'Full scan complete: ${items.length} tracks found, '
+          'Full scan complete: ${persistedItems.length} tracks found, '
           '$skippedDownloads already in downloads',
         );
         await _showScanCompleteNotification(
-          totalTracks: items.length,
+          totalTracks: persistedItems.length,
           excludedDownloadedCount: skippedDownloads,
           errorCount: state.scanErrorCount,
         );
@@ -439,8 +444,14 @@ class LocalLibraryNotifier extends Notifier<LocalLibraryState> {
           '$skippedCount skipped, ${deletedPaths.length} deleted, $totalFiles total',
         );
 
+        // Build the incremental merge base from SQLite, not the current
+        // provider state. Startup auto-scan can fire before `state.items` has
+        // finished loading, which would otherwise drop unchanged rows from the
+        // in-memory library until a manual full rescan.
+        final existingJson = await _db.getAll();
         final currentByPath = <String, LocalLibraryItem>{
-          for (final item in state.items) item.filePath: item,
+          for (final item in existingJson.map(LocalLibraryItem.fromJson))
+            item.filePath: item,
         };
         final existingDownloadedPaths = <String>[];
         currentByPath.removeWhere((path, _) {
@@ -491,8 +502,11 @@ class LocalLibraryNotifier extends Notifier<LocalLibraryState> {
           _log.i('Deleted $deleteCount items from database');
         }
 
-        final items = currentByPath.values.toList(growable: false)
-          ..sort(_compareLibraryItems);
+        final items =
+            (await _db.getAll())
+                .map(LocalLibraryItem.fromJson)
+                .toList(growable: false)
+              ..sort(_compareLibraryItems);
 
         final now = DateTime.now();
         try {