Harden movie playback lifecycle and diagnostics

engine/Age.Engine.Tests/GodotTraceSinkTests.cs

@@ -0,0 +1,31 @@
+using Age.Engine.Diagnostics;
+using Age.Engine.Model;
+
+public class GodotTraceSinkTests
+{
+    [Fact]
+    public void SnapshotRetainsCurrentStackAndBoundedRecentSteps()
+    {
+        using var locator = new PageLocatorState("SYSTEM4", null);
+        var sink = new GodotTraceSink(locator);
+        sink.Emit(TraceEvent.FrameEnter("SYSTEM4.BIN", 0, FrameCause.TopScene));
+        sink.Emit(TraceEvent.FrameEnter("BTL.BIN", 1, FrameCause.CallScript, 0x2b10));
+
+        for (int index = 0; index < 140; index++)
+        {
+            var instruction = new Instruction(0x2400 + index, 0x100 + index,
+                                              Array.Empty<Operand>());
+            sink.Emit(TraceEvent.Step(index, instruction, 1));
+        }
+
+        GodotTraceSnapshot snapshot = sink.Snapshot();
+
+        Assert.Equal("BTL.BIN", snapshot.CurrentScript);
+        Assert.Equal(0x2400 + 139, snapshot.CurrentOffset);
+        Assert.Equal(0x100 + 139, snapshot.CurrentOpcode);
+        Assert.Equal(new[] { "SYSTEM4.BIN", "BTL.BIN" }, snapshot.CallStack);
+        Assert.Equal(128, snapshot.RecentSteps.Count);
+        Assert.Equal(0x2400 + 12, snapshot.RecentSteps[0].Offset);
+        Assert.Equal(0x2400 + 139, snapshot.RecentSteps[^1].Offset);
+    }
+}