Fix for duplicated dockbands (#46438)

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## Summary of the Pull Request

CommandProviderWrapper.PinDockBand had no duplicate check and it blindly
called .Add() on the settings list every time. This allowed the same
extension to be pinned multiple times to the dock. Once duplicates
existed in settings, LoadTopLevelCommands would faithfully re-create all
of them on every CommandsChanged reload, making edit-mode unpin appear
broken (unpin removes one, reload brings them all back).

 **Fix**
- CommandProviderWrapper.PinDockBand: Check all three band lists
(Start/Center/End) for an existing (ProviderId, CommandId) match before
adding; early-return if already pinned.
- CommandProviderWrapper.LoadTopLevelCommands: Track seen command IDs in
a HashSet when iterating AllPinnedCommands; skip duplicates so they
never materialize in the UI even if present in settings.
  
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---------

Co-authored-by: Jiří Polášek <me@jiripolasek.com>

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/CommandProviderWrapper.cs

@@ -301,8 +301,19 @@ public sealed class CommandProviderWrapper : ICommandProviderContext
         var dockSettings = settings.DockSettings;
         var allPinnedCommands = dockSettings.AllPinnedCommands;
         var pinnedBandsForThisProvider = allPinnedCommands.Where(c => c.ProviderId == ProviderId);
+
+        // Track which command IDs we've already added to avoid duplicates
+        // from settings that were pinned multiple times.
+        HashSet<string> seenCommandIds = new(bands.Select(b => b.Id));
+
         foreach (var (providerId, commandId) in pinnedBandsForThisProvider)
         {
+            if (!seenCommandIds.Add(commandId))
+            {
+                Logger.LogWarning($"Skipping duplicate pinned dock band command {commandId} for provider {providerId}");
+                continue;
+            }
+
             Logger.LogDebug($"Looking for pinned dock band command {commandId} for provider {providerId}");
 
             // First, try to lookup the command as one of this provider's
@@ -440,6 +451,17 @@ public sealed class CommandProviderWrapper : ICommandProviderContext
     {
         var settingsService = serviceProvider.GetRequiredService<ISettingsService>();
         var settings = settingsService.Settings;
+        var dockSettings = settings.DockSettings;
+
+        // Prevent duplicate pins — check all sections
+        if (dockSettings.StartBands.Any(b => b.CommandId == commandId && b.ProviderId == this.ProviderId) ||
+            dockSettings.CenterBands.Any(b => b.CommandId == commandId && b.ProviderId == this.ProviderId) ||
+            dockSettings.EndBands.Any(b => b.CommandId == commandId && b.ProviderId == this.ProviderId))
+        {
+            Logger.LogDebug($"Dock band '{commandId}' from provider '{this.ProviderId}' is already pinned; skipping.");
+            return;
+        }
+
         var bandSettings = new DockBandSettings
         {
             CommandId = commandId,

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Dock/DockViewModel.cs

@@ -21,6 +21,7 @@ public sealed partial class DockViewModel
     private readonly IContextMenuFactory _contextMenuFactory;
 
     private DockSettings _settings;
+    private bool _isEditing;
 
     public TaskScheduler Scheduler { get; }
 
@@ -52,6 +53,12 @@ public sealed partial class DockViewModel
 
     private void DockBands_CollectionChanged(object? sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
     {
+        if (_isEditing)
+        {
+            Logger.LogDebug("Skipping DockBands_CollectionChanged during edit mode");
+            return;
+        }
+
         Logger.LogDebug("Starting DockBands_CollectionChanged");
         SetupBands();
         Logger.LogDebug("Ended DockBands_CollectionChanged");
@@ -302,7 +309,12 @@ public sealed partial class DockViewModel
         _snapshotCenterBands = null;
         _snapshotEndBands = null;
         _snapshotBandViewModels = null;
-        _settingsService.Save();
+
+        // Save without hotReload to avoid triggering SettingsChanged → SetupBands,
+        // which could race with stale DockBands_CollectionChanged work items and
+        // re-add bands that were just unpinned.
+        _settingsService.Save(hotReload: false);
+        _isEditing = false;
         Logger.LogDebug("Saved band order to settings");
     }
 
@@ -317,6 +329,8 @@ public sealed partial class DockViewModel
     /// </summary>
     public void SnapshotBandOrder()
     {
+        _isEditing = true;
+
         var dockSettings = _settingsService.Settings.DockSettings;
         _snapshotStartBands = dockSettings.StartBands.Select(b => b.Clone()).ToList();
         _snapshotCenterBands = dockSettings.CenterBands.Select(b => b.Clone()).ToList();
@@ -391,6 +405,7 @@ public sealed partial class DockViewModel
         _snapshotCenterBands = null;
         _snapshotEndBands = null;
         _snapshotBandViewModels = null;
+        _isEditing = false;
         Logger.LogDebug("Restored band order from snapshot");
     }