Fix memory leak in ActiveDownloads dictionary

- Changed ActiveDownloads from Dictionary to ConcurrentDictionary for thread safety
- Added automatic cleanup of completed downloads after 5 minutes
- Added automatic cleanup of failed downloads after 2 minutes
- This fixes the 929MB -> 10MB memory issue where downloads were never removed from tracking

allstarr/Services/Common/BaseDownloadService.cs

@@ -5,6 +5,7 @@ using allstarr.Models.Search;
 using allstarr.Models.Subsonic;
 using allstarr.Services.Local;
 using allstarr.Services.Subsonic;
+using System.Collections.Concurrent;
 using TagLib;
 using IOFile = System.IO.File;
 
@@ -27,7 +28,7 @@ public abstract class BaseDownloadService : IDownloadService
     protected readonly string DownloadPath;
     protected readonly string CachePath;
     
-    protected readonly Dictionary<string, DownloadInfo> ActiveDownloads = new();
+    protected readonly ConcurrentDictionary<string, DownloadInfo> ActiveDownloads = new();
     protected readonly SemaphoreSlim DownloadLock = new(1, 1);
     
     /// <summary>
@@ -298,6 +299,14 @@ public abstract class BaseDownloadService : IDownloadService
             
             song.LocalPath = localPath;
             
+            // Clean up completed download from tracking after a short delay
+            _ = Task.Run(async () =>
+            {
+                await Task.Delay(TimeSpan.FromMinutes(5)); // Keep for 5 minutes for status checks
+                ActiveDownloads.TryRemove(songId, out _);
+                Logger.LogDebug("Cleaned up completed download tracking for {SongId}", songId);
+            });
+            
             // Register BEFORE releasing lock to prevent race conditions (both cache and download modes)
             await LocalLibraryService.RegisterDownloadedSongAsync(song, localPath);
             
@@ -360,6 +369,14 @@ public abstract class BaseDownloadService : IDownloadService
             {
                 downloadInfo.Status = DownloadStatus.Failed;
                 downloadInfo.ErrorMessage = ex.Message;
+                
+                // Clean up failed download from tracking after a short delay
+                _ = Task.Run(async () =>
+                {
+                    await Task.Delay(TimeSpan.FromMinutes(2)); // Keep for 2 minutes for error reporting
+                    ActiveDownloads.TryRemove(songId, out _);
+                    Logger.LogDebug("Cleaned up failed download tracking for {SongId}", songId);
+                });
             }
             Logger.LogError(ex, "Download failed for {SongId}", songId);
             throw;