Move host transport records to model

engine/Age.Engine/Model/AdvPresentationContracts.cs

@@ -0,0 +1,16 @@
+namespace Age.Engine.Model;
+
+public readonly record struct AdvWaitIndicatorConfig(
+    int LayoutSlot, int X, int Y, int SurfaceSlot,
+    int SourceX, int SourceY, int CellWidth, int CellHeight,
+    int TerminalFrame, long FramePeriodMs)
+{
+    /// <summary>Select the current atlas frame. TerminalFrame is the exclusive native upper bound,
+    /// so SYSTEM4's value 12 addresses the twelve cells 0 through 11.</summary>
+    public int FrameAt(long elapsedMs)
+    {
+        int frameCount = System.Math.Max(1, TerminalFrame);
+        long period = System.Math.Max(1, FramePeriodMs);
+        return (int)(System.Math.Max(0, elapsedMs) / period % frameCount);
+    }
+}

engine/Age.Engine/Model/DiagnosticContracts.cs

@@ -0,0 +1,4 @@
+namespace Age.Engine.Model;
+
+/// <summary>A synchronous AGE-owned diagnostic prompt after native body/context formatting.</summary>
+public readonly record struct DiagnosticMessage(string Caption, string Text);