CmdPal: Fix RDP extension rejecting host:port connections (#45740)

## Summary

Fixes #45100

Uri.CheckHostName does not accept host:port strings (e.g.
localhost:3389), returning UriHostNameType.Unknown. This causes the RDP
extension to show an invalid hostname error when connecting to a local
forwarded port.

## Changes

- OpenRemoteDesktopCommand.cs - Strip port suffix before
Uri.CheckHostName validation. The full host:port is still passed to
mstsc /v:.
- FallbackRemoteDesktopItem.cs - Same port-aware validation so the
fallback correctly recognizes host:port queries and displays them in the
title.
- FallbackRemoteDesktopItemTests.cs - Added tests for localhost:3389 and
192.168.1.100:3390 inputs.

## Validation

Port detection uses LastIndexOf(':') + ushort.TryParse to safely
identify a trailing port number without affecting IPv6 addresses or
plain hostnames.

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/modules/cmdpal/Tests/Microsoft.CmdPal.Ext.RemoteDesktop.UnitTests/FallbackRemoteDesktopItemTests.cs

@@ -98,6 +98,48 @@ public class FallbackRemoteDesktopItemTests
         Assert.IsNull(command);
     }
 
+    [TestMethod]
+    public void UpdateQuery_WhenQueryIsHostnameWithPort_UsesFullHostPort()
+    {
+        // Arrange
+        var setup = CreateFallback();
+        var fallback = setup.Fallback;
+        const string hostPort = "localhost:3389";
+
+        // Act
+        fallback.UpdateQuery(hostPort);
+
+        // Assert
+        var expectedTitle = string.Format(CultureInfo.CurrentCulture, OpenHostCompositeFormat, hostPort);
+        Assert.AreEqual(expectedTitle, fallback.Title);
+        Assert.AreEqual(Resources.remotedesktop_title, fallback.Subtitle);
+
+        var command = fallback.Command as OpenRemoteDesktopCommand;
+        Assert.IsNotNull(command);
+        Assert.AreEqual(hostPort, GetCommandHost(command));
+    }
+
+    [TestMethod]
+    public void UpdateQuery_WhenQueryIsIPWithPort_UsesFullHostPort()
+    {
+        // Arrange
+        var setup = CreateFallback();
+        var fallback = setup.Fallback;
+        const string hostPort = "192.168.1.100:3390";
+
+        // Act
+        fallback.UpdateQuery(hostPort);
+
+        // Assert
+        var expectedTitle = string.Format(CultureInfo.CurrentCulture, OpenHostCompositeFormat, hostPort);
+        Assert.AreEqual(expectedTitle, fallback.Title);
+        Assert.AreEqual(Resources.remotedesktop_title, fallback.Subtitle);
+
+        var command = fallback.Command as OpenRemoteDesktopCommand;
+        Assert.IsNotNull(command);
+        Assert.AreEqual(hostPort, GetCommandHost(command));
+    }
+
     private static string GetCommandHost(OpenRemoteDesktopCommand command)
     {
         var field = typeof(OpenRemoteDesktopCommand).GetField("_rdpHost", BindingFlags.NonPublic | BindingFlags.Instance);

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.RemoteDesktop/Commands/FallbackRemoteDesktopItem.cs

@@ -60,18 +60,34 @@ internal sealed partial class FallbackRemoteDesktopItem : FallbackCommandItem
             Title = connectionName;
             Subtitle = string.Format(CultureInfo.CurrentCulture, RemoteDesktopOpenHostFormat, connectionName);
         }
-        else if (ValidUriHostNameTypes.Contains(Uri.CheckHostName(query)))
-        {
-            var connectionName = query.Trim();
-            Command = new OpenRemoteDesktopCommand(connectionName);
-            Title = string.Format(CultureInfo.CurrentCulture, RemoteDesktopOpenHostFormat, connectionName);
-            Subtitle = Resources.remotedesktop_title;
-        }
         else
         {
-            Title = string.Empty;
-            Subtitle = string.Empty;
-            Command = _emptyCommand;
+            // Strip port suffix (e.g. "localhost:3389") before validation,
+            // since Uri.CheckHostName does not accept host:port strings.
+            var hostForValidation = query.Trim();
+            var lastColon = hostForValidation.LastIndexOf(':');
+            if (lastColon > 0 && lastColon < hostForValidation.Length - 1)
+            {
+                var portPart = hostForValidation.Substring(lastColon + 1);
+                if (ushort.TryParse(portPart, out _))
+                {
+                    hostForValidation = hostForValidation.Substring(0, lastColon);
+                }
+            }
+
+            if (ValidUriHostNameTypes.Contains(Uri.CheckHostName(hostForValidation)))
+            {
+                var connectionName = query.Trim();
+                Command = new OpenRemoteDesktopCommand(connectionName);
+                Title = string.Format(CultureInfo.CurrentCulture, RemoteDesktopOpenHostFormat, connectionName);
+                Subtitle = Resources.remotedesktop_title;
+            }
+            else
+            {
+                Title = string.Empty;
+                Subtitle = string.Empty;
+                Command = _emptyCommand;
+            }
         }
     }
 }

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.RemoteDesktop/Commands/OpenRemoteDesktopCommand.cs

@@ -46,7 +46,20 @@ internal sealed partial class OpenRemoteDesktopCommand : BaseObservable, IInvoka
         if (!string.IsNullOrWhiteSpace(_rdpHost))
         {
             // validate that _rdpHost is a proper hostname or IP address
-            if (Uri.CheckHostName(_rdpHost) == UriHostNameType.Unknown)
+            // Strip port suffix (e.g. "localhost:3389") before validation,
+            // since Uri.CheckHostName does not accept host:port strings.
+            var hostForValidation = _rdpHost;
+            var lastColon = _rdpHost.LastIndexOf(':');
+            if (lastColon > 0 && lastColon < _rdpHost.Length - 1)
+            {
+                var portPart = _rdpHost.Substring(lastColon + 1);
+                if (ushort.TryParse(portPart, out _))
+                {
+                    hostForValidation = _rdpHost.Substring(0, lastColon);
+                }
+            }
+
+            if (Uri.CheckHostName(hostForValidation) == UriHostNameType.Unknown)
             {
                 return CommandResult.ShowToast(new ToastArgs()
                 {