Fix CancellationTokenSource leak in ViewModels (#3448)

* Fix CancellationTokenSource leak in ViewModels

Dispose the previous CancellationTokenSource before overwriting it in
IPScanner, PortScanner, Traceroute, PingMonitor, PingMonitorHost and SNMP.
Each Start() created a new instance without disposing the old one, leaking
the WaitHandle allocated by CancellationTokenSource on every run.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Update next-release.md

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: BornToBeRoot

Source/NETworkManager/ViewModels/IPScannerViewModel.cs

@@ -440,6 +440,7 @@ private async Task Start()
 
         DragablzTabItem.SetTabHeader(_tabId, Host);
 
+        _cancellationTokenSource?.Dispose();
         _cancellationTokenSource = new CancellationTokenSource();
 
         // Resolve hostnames

Source/NETworkManager/ViewModels/PingMonitorHostViewModel.cs

@@ -627,6 +627,7 @@ public async Task Start()
         IsStatusMessageDisplayed = false;
         IsRunning = true;
 
+        _cancellationTokenSource?.Dispose();
         _cancellationTokenSource = new CancellationTokenSource();
 
         // Resolve hostnames

Source/NETworkManager/ViewModels/PingMonitorViewModel.cs

@@ -400,6 +400,7 @@ public void Start()
         // Reset chart
         ResetTimeChart();
 
+        _cancellationTokenSource?.Dispose();
         _cancellationTokenSource = new CancellationTokenSource();
 
         var ping = new Ping

Source/NETworkManager/ViewModels/PortScannerViewModel.cs

@@ -390,6 +390,7 @@ private async Task Start()
 
         DragablzTabItem.SetTabHeader(_tabId, Host);
 
+        _cancellationTokenSource?.Dispose();
         _cancellationTokenSource = new CancellationTokenSource();
 
         // Resolve hostnames

Source/NETworkManager/ViewModels/SNMPViewModel.cs

@@ -502,6 +502,7 @@ await DNSClientHelper.ResolveAorAaaaAsync(Host,
             ipAddress = dnsResult.Value;
         }
 
+        _cancellationTokenSource?.Dispose();
         _cancellationTokenSource = new CancellationTokenSource();
 
         // SNMP...

Source/NETworkManager/ViewModels/TracerouteViewModel.cs

@@ -323,6 +323,7 @@ private async Task StartTrace()
 
         DragablzTabItem.SetTabHeader(_tabId, Host);
 
+        _cancellationTokenSource?.Dispose();
         _cancellationTokenSource = new CancellationTokenSource();
 
         // Try to parse the string into an IP-Address

Website/docs/changelog/next-release.md

@@ -110,6 +110,7 @@ Release date: **xx.xx.2025**
 
 ## Dependencies, Refactoring & Documentation
 
+- Fixed `CancellationTokenSource` leak in `IPScanner`, `PortScanner`, `Traceroute`, `PingMonitor`, `PingMonitorHost` and `SNMP` ViewModels. The previous instance was never disposed before being overwritten on each run, leaking the underlying `WaitHandle`. [#3448](https://github.com/BornToBeRoot/NETworkManager/pull/3448)
 - Replace fire-and-forget `.ConfigureAwait(false)` calls with explicit discard assignments (`_ = SomeAsyncOperation()`) across command handlers, startup/load paths and profile callbacks. [#3441](https://github.com/BornToBeRoot/NETworkManager/pull/3441)
 - Code cleanup & refactoring
 - Language files updated via [#transifex](https://github.com/BornToBeRoot/NETworkManager/pulls?q=author%3Aapp%2Ftransifex-integration)