Implement diagnostic output opcodes

godot/GodotAdvHost.cs

@@ -26,6 +26,7 @@ public sealed class GodotAdvHost : IHost
     private readonly Stack<string> _scriptContexts = new();
     private readonly ScriptPresentationBarrier _presentationBarrier = new();
     private readonly AutoResetEvent _presentationRequestConsumed = new(false);
+    private readonly AutoResetEvent _diagnosticMessageCompleted = new(false);
     private readonly bool _synchronizeExplicitPresentation;
     private long _explicitPresentationRequestGeneration;
     private long _consumedPresentationRequestGeneration;
@@ -117,6 +118,20 @@ public sealed class GodotAdvHost : IHost
 
     public void ReportWarning(string message) => System.Console.Error.WriteLine(message);
 
+    public void ShowDiagnosticMessage(DiagnosticMessage message)
+    {
+        if (_stopping) return;
+        _timeline?.Event("diagnostic-message", new()
+        {
+            ["caption"] = message.Caption,
+            ["text"] = message.Text,
+        });
+        _main.CallDeferred("ShowAgeDiagnostic", message.Text, message.Caption);
+        while (!_stopping && !_diagnosticMessageCompleted.WaitOne(50)) { }
+    }
+
+    public void CompleteDiagnosticMessage() => _diagnosticMessageCompleted.Set();
+
     private string CurrentScene
     {
         get { lock (_scriptContextLock) return _scriptContexts.TryPeek(out var scene) ? scene : _rootScene; }
@@ -950,6 +965,7 @@ public sealed class GodotAdvHost : IHost
         if (_gate.CurrentCount == 0) _gate.Release();
         _inputCallbackSignal.Set();
         _frameSignal.Set();
+        _diagnosticMessageCompleted.Set();
     }
 
     public void ResetSceneContext()

godot/Main.cs

@@ -912,6 +912,22 @@ public partial class Main : Godot.Control
         _ageCursorTexture = null;
     }
 
+    public void ShowAgeDiagnostic(string text, string caption)
+    {
+        try
+        {
+            OS.Alert(text, caption);
+        }
+        catch (System.Exception error)
+        {
+            GD.PushError($"[diagnostic] native alert failed: {error.Message}");
+        }
+        finally
+        {
+            _host?.CompleteDiagnosticMessage();
+        }
+    }
+
     public override void _ExitTree()
     {
         bool vmStopped = true;