feat(a2a): worker-thread ADV host + blocking wait-for-input + headless self-test

SELFTEST OK: 186 lines match vm0 trace; real SemaphoreSlim gate + CallDeferred exercised headless.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

godot/GodotAdvHost.cs

@@ -0,0 +1,34 @@
+using System.Collections.Generic;
+using System.Threading;
+using Age.Engine.Hosting;
+
+public sealed class GodotAdvHost : IHost
+{
+    private readonly Main _main;
+    private readonly SemaphoreSlim _gate = new(0, 1);
+    public volatile bool IsWaiting;
+    public readonly List<(int Offset, string Text)> Captured = new();
+
+    public GodotAdvHost(Main main) => _main = main;
+
+    public void ShowText(int offset, string text)
+    {
+        Captured.Add((offset, text));
+        _main.CallDeferred("AppendLine", text);
+    }
+
+    public void WaitForInput()
+    {
+        _main.CallDeferred("PageBreak");
+        IsWaiting = true;
+        _gate.Wait();
+        IsWaiting = false;
+        _main.CallDeferred("ClearPage");
+    }
+
+    // called from the main thread (click) or the selftest auto-clicker
+    public void SignalInput() { if (_gate.CurrentCount == 0) _gate.Release(); }
+
+    public void CallScript(long id) { }
+    public void OnStub(int opcode) { }
+}

godot/Main.cs

@@ -1,14 +1,88 @@
+using System.Collections.Generic;
+using System.Text.Json;
+using System.Threading.Tasks;
 using Godot;
 using Age.Engine.Sys4;
+using Age.Engine.Vm;
 
 public partial class Main : Godot.Control
 {
+    private Label _text = null!;
+    private Label _status = null!;
+    private VirtualMachine _vm = null!;
+    private GodotAdvHost _host = null!;
+    private volatile bool _done;
+    private bool _ended;
+    private bool _selftest;
+
     public override void _Ready()
     {
+        _text = new Label { AutowrapMode = TextServer.AutowrapMode.WordSmart };
+        _text.SetAnchorsAndOffsetsPreset(LayoutPreset.FullRect);
+        _text.OffsetLeft = 40; _text.OffsetTop = 40; _text.OffsetRight = -40; _text.OffsetBottom = -80;
+        AddChild(_text);
+        _status = new Label();
+        _status.SetAnchorsAndOffsetsPreset(LayoutPreset.BottomWide);
+        _status.OffsetLeft = 40; _status.OffsetTop = -60;
+        AddChild(_status);
+
+        _selftest = System.Array.IndexOf(OS.GetCmdlineUserArgs(), "--selftest") >= 0;
+
         var table = OpcodeTableJson.Load(Paths.OpcodesJson);
         var script = Sys4Loader.Load(Paths.Scripts()["SC0000.BIN"], table);
-        GD.Print($"SMOKE repo={Paths.Repo}");
-        GD.Print($"SMOKE SC0000 instrs={script.Instructions.Count} strings={script.Strings.Count}");
-        GetTree().Quit(0);
+        _host = new GodotAdvHost(this);
+        _vm = new VirtualMachine(script, table, _host);
+        _ = Task.Run(() => { _vm.Run(); _done = true; });
+
+        if (_selftest)
+            _ = Task.Run(async () => { while (!_done) { if (_host.IsWaiting) _host.SignalInput(); await Task.Delay(1); } });
+    }
+
+    public override void _Process(double delta)
+    {
+        if (_done && !_ended)
+        {
+            _ended = true;
+            ShowEnd();
+            if (_selftest) RunSelfTest();
+        }
+    }
+
+    public override void _UnhandledInput(InputEvent e)
+    {
+        if (_selftest) return;
+        if (e.IsActionPressed("ui_accept") ||
+            (e is InputEventMouseButton mb && mb.Pressed && mb.ButtonIndex == MouseButton.Left))
+            _host.SignalInput();
+    }
+
+    public override void _ExitTree() { _host?.SignalInput(); }
+
+    // ---- UI methods invoked on the main thread via CallDeferred ----
+    public void AppendLine(string text) => _text.Text += text + "\n";
+    public void PageBreak() => _status.Text = "▼ click / Enter";
+    public void ClearPage() { _text.Text = ""; _status.Text = ""; }
+    public void ShowEnd() => _status.Text = "— end —";
+
+    private void RunSelfTest()
+    {
+        var expected = LoadExpected("SC0000.BIN");
+        var actual = _host.Captured.ConvertAll(c => c.Offset);
+        bool ok = expected != null && actual.Count == expected.Count;
+        for (int i = 0; ok && i < actual.Count; i++) ok = actual[i] == expected![i];
+        if (ok) GD.Print($"SELFTEST OK: {actual.Count} lines match vm0 trace");
+        else GD.Print($"SELFTEST FAIL: cs={actual.Count} expected={(expected?.Count.ToString() ?? "n/a")}");
+        GetTree().Quit(ok ? 0 : 1);
+    }
+
+    private static List<int>? LoadExpected(string scene)
+    {
+        string p = System.IO.Path.Combine(Paths.Build, "vm0-trace.json");
+        if (!System.IO.File.Exists(p)) return null;
+        using var doc = JsonDocument.Parse(System.IO.File.ReadAllText(p));
+        if (!doc.RootElement.TryGetProperty(scene, out var e)) return null;
+        var list = new List<int>();
+        foreach (var x in e.GetProperty("offsets").EnumerateArray()) list.Add(x.GetInt32());
+        return list;
     }
 }