Fix #3993: register main-menu gestures as window key bindings

NativeMenuItem.Gesture is display-only when NativeMenuBar renders the
menu inline on Windows/Linux: the managed fallback binds it to
MenuItem.InputGesture, which never handles input. Only macOS's system
menu bar actually executes its key equivalents, so Ctrl+O, Ctrl+S and
F5 showed in the menu but did nothing. The Avalonia docs call this out
explicitly: InputGesture only displays the text and must be paired with
a KeyBinding for the shortcut to function.

Assisted-by: Claude:claude-fable-5:Claude Code

ILSpy.Tests/MainWindow/MainMenuTests.cs

@@ -95,6 +95,48 @@ public class MainMenuTests
 		openItem.Gesture!.Should().Be(expected);
 	}
 
+	// NativeMenuItem.Gesture is display-only when NativeMenuBar renders the menu inline
+	// (the managed fallback binds it to MenuItem.InputGesture, which never handles input),
+	// so every menu gesture must also be registered as a window-level KeyBinding or the
+	// shortcut silently does nothing on Windows / Linux (issue #3993: Ctrl+O, Ctrl+S, F5).
+	[AvaloniaTest]
+	public void Menu_Gestures_Are_Registered_As_Window_KeyBindings()
+	{
+		var window = AppComposition.Current.GetExport<MainWindow>();
+		window.Show();
+
+		var nativeMenu = NativeMenu.GetMenu(window)
+			?? throw new InvalidOperationException("MainMenu.Attach should have set NativeMenu on the window");
+
+		var gestureItems = new System.Collections.Generic.List<(string Path, NativeMenuItem Item)>();
+		CollectItemsWithGesture(nativeMenu, parentPath: "", gestureItems);
+
+		gestureItems.Should().NotBeEmpty("File > Open (Ctrl+O), Reload (F5) and Save (Ctrl+S) declare InputGestureText");
+
+		foreach (var (path, item) in gestureItems)
+		{
+			window.KeyBindings.Should().Contain(
+				kb => Equals(kb.Gesture, item.Gesture) && ReferenceEquals(kb.Command, item.Command),
+				$"the gesture {item.Gesture} shown on '{path}' must actually invoke the item's command");
+		}
+	}
+
+	static void CollectItemsWithGesture(NativeMenu menu, string parentPath, System.Collections.Generic.List<(string, NativeMenuItem)> result)
+	{
+		foreach (var element in menu.Items)
+		{
+			if (element is NativeMenuItemSeparator || element is not NativeMenuItem item)
+				continue;
+			var path = string.IsNullOrEmpty(parentPath) ? (item.Header ?? "<unnamed>") : $"{parentPath} > {item.Header}";
+			// Mirrors RegisterGestureKeyBindings: only items with BOTH a gesture and a command
+			// get a key binding, so a display-only gesture must not fail the assertion.
+			if (item.Gesture != null && item.Command != null)
+				result.Add((path, item));
+			if (item.Menu is { Items.Count: > 0 } sub)
+				CollectItemsWithGesture(sub, path, result);
+		}
+	}
+
 	// Avalonia's macOS NativeMenu bridge maps NativeMenuItem to NSMenuItem and sets
 	// NSMenuItem.action ONLY when Command != null. Without it, NSMenuValidation marks
 	// the item disabled (greyed out) and no click ever reaches managed code - which

ILSpy/Views/MainMenu.axaml.cs

@@ -76,9 +76,43 @@ public static class MainMenu
 			PromoteHelpToMacAppMenu(menu, topLevelByTag);
 		}
 
+		RegisterGestureKeyBindings(window, menu);
 		NativeMenu.SetMenu(window, menu);
 	}
 
+	// NativeMenuItem.Gesture is display-only when NativeMenuBar renders the menu inline:
+	// the managed fallback binds it to MenuItem.InputGesture, which never handles input.
+	// So each gesture is registered as a window-level KeyBinding too - that is what makes
+	// Ctrl+O / Ctrl+S / F5 actually fire on Windows and Linux. On macOS the system menu
+	// bar consumes its key equivalents before they reach the window, so these bindings
+	// stay dormant there. Runs after TranslateGesturesForMacOS so the bound gesture always
+	// matches the one the menu displays. Duplicates of the KeyBindings declared in
+	// MainWindow.axaml (e.g. Alt+Left) are harmless: KeyboardDevice stops dispatching
+	// once a binding marks the event handled, so only the first match executes.
+	static void RegisterGestureKeyBindings(Window window, NativeMenu menu)
+	{
+		foreach (var element in menu.Items)
+		{
+			if (element is NativeMenuItemSeparator || element is not NativeMenuItem item)
+				continue;
+			if (item.Gesture is { } gesture && item.Command is { } command)
+			{
+				var keyBinding = new KeyBinding {
+					Gesture = gesture,
+					Command = command,
+				};
+				// CommandParameter must track the item's property, not snapshot it: for
+				// IProvideParameterBinding commands the item's parameter is itself a binding
+				// that only resolves once the menu lives in a visual tree, so a value copied
+				// here would be null when the shortcut fires.
+				keyBinding.Bind(KeyBinding.CommandParameterProperty, item.GetObservable(NativeMenuItem.CommandParameterProperty));
+				window.KeyBindings.Add(keyBinding);
+			}
+			if (item.Menu != null)
+				RegisterGestureKeyBindings(window, item.Menu);
+		}
+	}
+
 	// macOS convention puts About / Check for Updates under the bold app-named menu
 	// next to the Apple logo, not under a separate "Help" top-level. The Cocoa exporter
 	// samples Application.Current's NativeMenu ONCE at startup (before this window exists)