Implement system menu guard opcode

engine/Age.Engine.Tests/SystemMenuGuardOpcodeTests.cs

@@ -0,0 +1,66 @@
+using Age.Engine.Model;
+using Age.Engine.Sys4;
+using Age.Engine.Vm;
+
+public class SystemMenuGuardOpcodeTests
+{
+    private static readonly OpcodeTable Table = OpcodeTableJson.Load(Paths.OpcodesJson);
+    private static Operand I(long value) => new(0, value);
+    private static (int, Operand[]) Exit() => (0x2, Array.Empty<Operand>());
+
+    [Fact]
+    public void SetterDefaultsEnabledAndReplacesTheCompleteNativeDword()
+    {
+        Script config = ScriptAssembler.Assemble(Table, "CONFIG.BIN",
+        [
+            (0x142, [I(0)]),
+            (0x142, [I(-7)]),
+            Exit(),
+        ], []);
+        var vm = new VirtualMachine(config, Table, new RecordingHost());
+
+        Assert.Equal(1, vm.SystemMenuActionsEnabled);
+
+        vm.Run();
+
+        Assert.Equal(-7, vm.SystemMenuActionsEnabled);
+    }
+
+    [Fact]
+    public void ConfigEntryAndExitPairRestoresNativeMenuActions()
+    {
+        Script config = ScriptAssembler.Assemble(Table, "CONFIG.BIN",
+        [
+            (0x142, [I(0)]),
+            (0x142, [I(1)]),
+            Exit(),
+        ], []);
+        var vm = new VirtualMachine(config, Table, new RecordingHost());
+
+        vm.Run();
+
+        Assert.Equal(1, vm.SystemMenuActionsEnabled);
+    }
+
+    [Fact]
+    public void RootSceneReloadRestoresTheNativeDefault()
+    {
+        Script system4 = ScriptAssembler.Assemble(Table, "SYSTEM4.BIN",
+        [
+            Exit(),
+        ], []);
+        Script config = ScriptAssembler.Assemble(Table, "CONFIG.BIN",
+        [
+            (0x142, [I(0)]),
+            (0x9, Array.Empty<Operand>()),
+        ], []);
+        var provider = new MapProvider(new Dictionary<long, Script> { [0] = system4 });
+        var host = new RecordingHost();
+        var vm = new VirtualMachine(config, Table, host, provider: provider);
+
+        vm.Run();
+
+        Assert.Equal(1, vm.SystemMenuActionsEnabled);
+        Assert.Equal(1, host.SceneContextResets);
+    }
+}