CmdPal: Make settings and app state immutable (#46451)

## Summary
 
 This PR refactors CmdPal settings/state to be immutable end-to-end.
 
 ### Core changes
 - Convert model types to immutable records / init-only properties:
   - `SettingsModel`
   - `AppStateModel`
   - `ProviderSettings`
   - `DockSettings`
   - `RecentCommandsManager`
- supporting settings types (fallback/hotkey/alias/top-level
hotkey/history items, etc.)
- Replace mutable collections with immutable equivalents where
appropriate:
   - `ImmutableDictionary<,>`
   - `ImmutableList<>`
 - Move mutation flow to atomic service updates:
- `ISettingsService.UpdateSettings(Func<SettingsModel, SettingsModel>)`
   - `IAppStateService.UpdateState(Func<AppStateModel, AppStateModel>)`
- Update ViewModels/managers/services to use copy-on-write (`with`)
patterns instead of in-place
mutation.
- Update serialization context + tests for immutable model graph
compatibility.
 
 ## Why
 
Issue #46437 is caused by mutable shared state being updated from
different execution paths/threads,
leading to race-prone behavior during persistence/serialization.
 
By making settings/app state immutable and using atomic swap/update
patterns, we remove in-place
mutation and eliminate this class of concurrency bug.
 
 ## Validation
 
 - Built successfully:
   - `Microsoft.CmdPal.UI.ViewModels`
   - `Microsoft.CmdPal.UI`
   - `Microsoft.CmdPal.UI.ViewModels.UnitTests`
 - Updated unit tests for immutable update patterns.
 
 Fixes #46437

---------

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

src/modules/cmdpal/Microsoft.CmdPal.UI/CommandPaletteContextMenuFactory.cs

@@ -92,7 +92,7 @@ internal sealed partial class CommandPaletteContextMenuFactory : IContextMenuFac
             var providerId = providerContext.ProviderId;
             if (_topLevelCommandManager.LookupProvider(providerId) is CommandProviderWrapper provider)
             {
-                var providerSettings = _settingsService.Settings.GetProviderSettings(provider);
+                var (_, providerSettings) = _settingsService.Settings.GetProviderSettings(provider);
 
                 var alreadyPinnedToTopLevel = providerSettings.PinnedCommandIds.Contains(itemId);
 
@@ -159,7 +159,7 @@ internal sealed partial class CommandPaletteContextMenuFactory : IContextMenuFac
         var providerId = providerContext.ProviderId;
         if (_topLevelCommandManager.LookupProvider(providerId) is CommandProviderWrapper provider)
         {
-            var providerSettings = _settingsService.Settings.GetProviderSettings(provider);
+            var (_, providerSettings) = _settingsService.Settings.GetProviderSettings(provider);
 
             var isPinnedSubCommand = providerSettings.PinnedCommandIds.Contains(itemId);
             if (isPinnedSubCommand)

src/modules/cmdpal/Microsoft.CmdPal.UI/Controls/ShortcutControl/ShortcutControl.xaml.cs

@@ -186,7 +186,7 @@ public sealed partial class ShortcutControl : UserControl, IDisposable, IRecipie
                     _ = _modifierKeysOnEntering.Remove(virtualKey);
                 }
 
-                internalSettings.Win = matchValue;
+                internalSettings = internalSettings with { Win = matchValue };
                 break;
             case VirtualKey.Control:
             case VirtualKey.LeftControl:
@@ -197,7 +197,7 @@ public sealed partial class ShortcutControl : UserControl, IDisposable, IRecipie
                     _ = _modifierKeysOnEntering.Remove(VirtualKey.Control);
                 }
 
-                internalSettings.Ctrl = matchValue;
+                internalSettings = internalSettings with { Ctrl = matchValue };
                 break;
             case VirtualKey.Menu:
             case VirtualKey.LeftMenu:
@@ -208,7 +208,7 @@ public sealed partial class ShortcutControl : UserControl, IDisposable, IRecipie
                     _ = _modifierKeysOnEntering.Remove(VirtualKey.Menu);
                 }
 
-                internalSettings.Alt = matchValue;
+                internalSettings = internalSettings with { Alt = matchValue };
                 break;
             case VirtualKey.Shift:
             case VirtualKey.LeftShift:
@@ -219,14 +219,14 @@ public sealed partial class ShortcutControl : UserControl, IDisposable, IRecipie
                     _ = _modifierKeysOnEntering.Remove(VirtualKey.Shift);
                 }
 
-                internalSettings.Shift = matchValue;
+                internalSettings = internalSettings with { Shift = matchValue };
                 break;
             case VirtualKey.Escape:
                 internalSettings = new HotkeySettings();
                 shortcutDialog.IsPrimaryButtonEnabled = false;
                 return;
             default:
-                internalSettings.Code = matchValueCode;
+                internalSettings = internalSettings with { Code = matchValueCode };
                 break;
         }
     }
@@ -276,7 +276,7 @@ public sealed partial class ShortcutControl : UserControl, IDisposable, IRecipie
             else if (internalSettings.Shift && !_modifierKeysOnEntering.Contains(VirtualKey.Shift) && !internalSettings.Win && !internalSettings.Alt && !internalSettings.Ctrl)
             {
                 // This is to reset the shift key press within the control as it was not used within the control but rather was used to leave the hotkey.
-                internalSettings.Shift = false;
+                internalSettings = internalSettings with { Shift = false };
 
                 SendSingleKeyboardInput((short)VirtualKey.Shift, (uint)NativeKeyboardHelper.KeyEventF.KeyDown);
 

src/modules/cmdpal/Microsoft.CmdPal.UI/MainWindow.xaml.cs

@@ -910,8 +910,7 @@ public sealed partial class MainWindow : WindowEx,
             // the last non-dock placement because dock sessions intentionally skip updates.
             if (_currentWindowPosition.IsSizeValid)
             {
-                settings.LastWindowPosition = _currentWindowPosition;
-                settingsService.Save();
+                settingsService.UpdateSettings(s => s with { LastWindowPosition = _currentWindowPosition });
             }
         }
 

src/modules/cmdpal/Microsoft.CmdPal.UI/RunHistoryService.cs

@@ -2,6 +2,7 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Collections.Immutable;
 using Microsoft.CmdPal.Common.Services;
 using Microsoft.CmdPal.UI.ViewModels;
 using Microsoft.CmdPal.UI.ViewModels.Services;
@@ -19,10 +20,13 @@ internal sealed class RunHistoryService : IRunHistoryService
 
     public IReadOnlyList<string> GetRunHistory()
     {
-        if (_appStateService.State.RunHistory.Count == 0)
+        if (_appStateService.State.RunHistory.IsEmpty)
         {
             var history = Microsoft.Terminal.UI.RunHistory.CreateRunHistory();
-            _appStateService.State.RunHistory.AddRange(history);
+            _appStateService.UpdateState(state => state with
+            {
+                RunHistory = history.ToImmutableList(),
+            });
         }
 
         return _appStateService.State.RunHistory;
@@ -30,22 +34,24 @@ internal sealed class RunHistoryService : IRunHistoryService
 
     public void ClearRunHistory()
     {
-        _appStateService.State.RunHistory.Clear();
+        _appStateService.UpdateState(state => state with
+        {
+            RunHistory = ImmutableList<string>.Empty,
+        });
     }
 
     public void AddRunHistoryItem(string item)
     {
-        // insert at the beginning of the list
         if (string.IsNullOrWhiteSpace(item))
         {
-            return; // Do not add empty or whitespace items
+            return;
         }
 
-        _appStateService.State.RunHistory.Remove(item);
-
-        // Add the item to the front of the history
-        _appStateService.State.RunHistory.Insert(0, item);
-
-        _appStateService.Save();
+        _appStateService.UpdateState(state => state with
+        {
+            RunHistory = state.RunHistory
+                .Remove(item)
+                .Insert(0, item),
+        });
     }
 }