diff --git a/SysManager/SysManager/Helpers/ObservableCollectionExtensions.cs b/SysManager/SysManager/Helpers/ObservableCollectionExtensions.cs
index d705bff..8be9eef 100644
--- a/SysManager/SysManager/Helpers/ObservableCollectionExtensions.cs
+++ b/SysManager/SysManager/Helpers/ObservableCollectionExtensions.cs
@@ -12,7 +12,7 @@ namespace SysManager.Helpers;
 /// An <see cref="ObservableCollection{T}"/> that supports bulk replacement
 /// with a single <see cref="NotifyCollectionChangedAction.Reset"/> notification.
 /// </summary>
-public class BulkObservableCollection<T> : ObservableCollection<T>
+public sealed class BulkObservableCollection<T> : ObservableCollection<T>
 {
     private bool _suppressNotifications;
 
diff --git a/SysManager/SysManager/Services/ActivityLogService.cs b/SysManager/SysManager/Services/ActivityLogService.cs
index a831d00..8f3e476 100644
--- a/SysManager/SysManager/Services/ActivityLogService.cs
+++ b/SysManager/SysManager/Services/ActivityLogService.cs
@@ -26,7 +26,7 @@ public sealed class ActivityLogService
     public IReadOnlyList<ActivityEntry> GetRecent(int count = 5)
     {
         lock (_lock)
-            return _entries.Take(count).ToList();
+            return _entries.Take(count).ToArray();
     }
 
     public void Log(string action, string detail)
diff --git a/SysManager/SysManager/Services/DnsService.cs b/SysManager/SysManager/Services/DnsService.cs
index 1465ffa..04ab411 100644
--- a/SysManager/SysManager/Services/DnsService.cs
+++ b/SysManager/SysManager/Services/DnsService.cs
@@ -114,7 +114,7 @@ public async Task<IReadOnlyList<string>> CaptureCurrentServersAsync(Cancellation
                 .Select(r => r?.ToString())
                 .Where(s => !string.IsNullOrWhiteSpace(s) && IPAddress.TryParse(s, out _))
                 .Select(s => s!)
-                .ToList();
+                .ToArray();
         }
         finally { _gate.Release(); }
     }
diff --git a/SysManager/SysManager/Services/LargeFileScanner.cs b/SysManager/SysManager/Services/LargeFileScanner.cs
index df70e60..0c675ac 100644
--- a/SysManager/SysManager/Services/LargeFileScanner.cs
+++ b/SysManager/SysManager/Services/LargeFileScanner.cs
@@ -133,7 +133,7 @@ private static IReadOnlyList<LargeFileEntry> Scan(
         }
 
         progress?.Report(new LargeFileProgress(scanned, bytesScanned, "Done"));
-        return heap.Reverse().Select(h => meta[h.Path]).ToList();
+        return heap.Reverse().Select(h => meta[h.Path]).ToArray();
     }
 
     private static bool ShouldSkip(string path)
diff --git a/SysManager/SysManager/Services/PingMonitorService.cs b/SysManager/SysManager/Services/PingMonitorService.cs
index e3f0b5b..8a0f411 100644
--- a/SysManager/SysManager/Services/PingMonitorService.cs
+++ b/SysManager/SysManager/Services/PingMonitorService.cs
@@ -91,7 +91,7 @@ static TimeSpan Clamp(TimeSpan t) =>
             foreach (var target in active)
                 _ = PingOnceAsync(target, ct);
 
-            try { await Task.Delay(Clamp(Interval), ct); }
+            try { await Task.Delay(Clamp(Interval), ct).ConfigureAwait(false); }
             catch (OperationCanceledException) { return; }
         }
     }
diff --git a/SysManager/SysManager/Services/SpeedTestService.cs b/SysManager/SysManager/Services/SpeedTestService.cs
index 911318e..be9e28c 100644
--- a/SysManager/SysManager/Services/SpeedTestService.cs
+++ b/SysManager/SysManager/Services/SpeedTestService.cs
@@ -95,7 +95,7 @@ private static async Task<double> MeasureDownloadAsync(
             }
         });
 
-        await Task.WhenAll(tasks);
+        await Task.WhenAll(tasks).ConfigureAwait(false);
         sw.Stop();
 
         var downloaded = Interlocked.Read(ref totalBytes);
diff --git a/SysManager/SysManager/Services/TracerouteMonitorService.cs b/SysManager/SysManager/Services/TracerouteMonitorService.cs
index 15b7bd8..879757b 100644
--- a/SysManager/SysManager/Services/TracerouteMonitorService.cs
+++ b/SysManager/SysManager/Services/TracerouteMonitorService.cs
@@ -100,7 +100,7 @@ private async Task PumpAsync(CancellationToken ct)
                 catch (InvalidOperationException) { /* traceroute failed for this target — skip */ }
             }
 
-            try { await Task.Delay(Interval, ct); }
+            try { await Task.Delay(Interval, ct).ConfigureAwait(false); }
             catch (OperationCanceledException) { return; }
         }
     }