Implement diagnostic output opcodes

engine/Age.Engine/Hosting/CaptureHost.cs

@@ -2,6 +2,8 @@ namespace Age.Engine.Hosting;
 public sealed class CaptureHost : IHost
 {
     public List<(int Offset, string Text)> Emitted { get; } = new();
+    public List<DiagnosticMessage> Diagnostics { get; } = new();
+    public void ShowDiagnosticMessage(DiagnosticMessage message) => Diagnostics.Add(message);
     public void ShowText(int offset, string text) => Emitted.Add((offset, text));
     public void WaitForInput() { }
     public void Sleep(long duration) { }

engine/Age.Engine/Hosting/IHost.cs

@@ -28,6 +28,9 @@ public readonly record struct SurfaceRectCopy(
     int SourceSurface, int DestinationSurface, int SourceX, int SourceY,
     int Width, int Height, int DestinationX, int DestinationY);
 
+/// <summary>A synchronous AGE-owned diagnostic prompt after native body/context formatting.</summary>
+public readonly record struct DiagnosticMessage(string Caption, string Text);
+
 public enum SurfaceBlackFadeDirection
 {
     FromBlack,
@@ -38,6 +41,9 @@ public interface IHost
 {
     /// <summary>Report a recoverable runtime discrepancy while allowing script execution to continue.</summary>
     void ReportWarning(string message) => System.Console.Error.WriteLine(message);
+    /// <summary>Present a modal diagnostic and return only after the user dismisses it.</summary>
+    void ShowDiagnosticMessage(DiagnosticMessage message)
+        => System.Console.Error.WriteLine($"{message.Caption}: {message.Text}");
     // Script context is retained for diagnostics/page location; resource operands are universal packed ids.
     void EnterScriptContext(string scriptName) { }
     void ExitScriptContext() { }