feat(output): add GUID-based shared Output pane support

Adds overloads to create/retrieve Output window panes using a caller-supplied GUID, enabling multiple extensions to share a single pane. Updates ExceptionExtensions to always use the well-known GUID for the "Extensions" pane, ensuring idempotency and preventing duplicates. Refactors error handling and removes redundant pane creation logic.

Author: madskristensen

src/toolkit/Community.VisualStudio.Toolkit.Shared/ExtensionMethods/ExceptionExtensions.cs

@@ -203,19 +203,17 @@ private static async Task EnsurePaneAsync()
         {
             if (_pane == null)
             {
-                // Try and get the Extensions pane and if it doesn't exist then create it.
-                _pane = await VS.Windows.GetOutputWindowPaneAsync(_extensionsPaneGuid);
-
-                if (_pane == null)
+                try
+                {
+                    // Always create the pane using the well-known GUID so that all extensions using
+                    // this toolkit share a single "Extensions" pane instead of each creating their own.
+                    // CreatePane in VS is idempotent for a given GUID, so this returns the existing
+                    // pane if one has already been registered under this GUID.
+                    _pane = await VS.Windows.CreateOutputWindowPaneAsync(_paneTitle, _extensionsPaneGuid);
+                }
+                catch (Exception ex)
                 {
-                    try
-                    {
-                        _pane = await VS.Windows.CreateOutputWindowPaneAsync(_paneTitle);
-                    }
-                    catch (Exception ex)
-                    {
-                        Diagnostics.Debug.WriteLine(ex);
-                    }
+                    Diagnostics.Debug.WriteLine(ex);
                 }
             }
 

src/toolkit/Community.VisualStudio.Toolkit.Shared/Helpers/OutputWindowPane.cs

@@ -104,14 +104,30 @@ public string Name
         /// <param name="name">The name (title) of the new pane.</param>
         /// <param name="lazyCreate">Whether to lazily create the pane upon first write.</param>
         /// <returns>A new OutputWindowPane.</returns>
-        public static async Task<OutputWindowPane> CreateAsync(string name, bool lazyCreate = true)
+        public static Task<OutputWindowPane> CreateAsync(string name, bool lazyCreate = true)
+            => CreateAsync(name, Guid.NewGuid(), lazyCreate);
+
+        /// <summary>
+        /// Creates a new Output window pane with the given name and a caller-supplied GUID,
+        /// or returns the existing pane if one with that GUID has already been registered.
+        /// </summary>
+        /// <remarks>
+        /// Use this overload when multiple components or extensions need to share a single pane.
+        /// By providing a stable, well-known GUID, every caller will end up writing to the same
+        /// pane instead of each one creating a new pane with the same name.
+        /// </remarks>
+        /// <param name="name">The name (title) of the pane.</param>
+        /// <param name="guid">The stable unique identifier of the pane.</param>
+        /// <param name="lazyCreate">Whether to lazily create the pane upon first write.</param>
+        /// <returns>A new OutputWindowPane.</returns>
+        public static async Task<OutputWindowPane> CreateAsync(string name, Guid guid, bool lazyCreate = true)
         {
             if (string.IsNullOrEmpty(name))
             {
                 throw new ArgumentException(nameof(name));
             }
 
-            OutputWindowPane pane = new(name, Guid.NewGuid());
+            OutputWindowPane pane = new(name, guid);
 
             if (!lazyCreate)
             {

src/toolkit/Community.VisualStudio.Toolkit.Shared/Windows/Windows.cs

@@ -39,6 +39,23 @@ public enum VSOutputWindowPane
         public Task<OutputWindowPane> CreateOutputWindowPaneAsync(string name, bool lazyCreate = true)
             => OutputWindowPane.CreateAsync(name, lazyCreate);
 
+        /// <summary>
+        /// Creates a new Output window pane with the given name and a caller-supplied GUID,
+        /// or returns the existing pane if one with that GUID has already been registered.
+        /// The pane can be created now or lazily upon the first write to it.
+        /// </summary>
+        /// <remarks>
+        /// Use this overload when multiple components or extensions need to share a single pane.
+        /// By providing a stable, well-known GUID, every caller will end up writing to the same
+        /// pane instead of each one creating a new pane with the same name.
+        /// </remarks>
+        /// <param name="name">The name (title) of the pane.</param>
+        /// <param name="guid">The stable unique identifier of the pane.</param>
+        /// <param name="lazyCreate">Whether to lazily create the pane upon first write.</param>
+        /// <returns>A new OutputWindowPane.</returns>
+        public Task<OutputWindowPane> CreateOutputWindowPaneAsync(string name, Guid guid, bool lazyCreate = true)
+            => OutputWindowPane.CreateAsync(name, guid, lazyCreate);
+
         /// <summary>
         /// Gets an existing Visual Studio Output window pane (General, Build, Debug).
         /// If the General pane does not already exist then it will be created, but that is not the case