fix: Physics pause points that miss a pre-existing GameObject now log diagnostics for future investigation

Assets/RegressionHarness/PhysicsCallbackExistingInstance/HarnessDomainMarker.cs

@@ -0,0 +1,12 @@
+namespace io.github.hatayama.UnityCliLoop.RegressionHarness
+{
+    // A static readonly value is re-initialized whenever the AppDomain reloads, so comparing this
+    // value before and after a EditorUtility.RequestScriptReload() call is a deterministic way to
+    // detect that the reload has actually completed -- unlike polling for IPC responsiveness alone,
+    // which can observe the pre-reload domain still answering before the reload has even started
+    // (RequestScriptReload queues the reload for a later editor update, it does not run inline).
+    public static class HarnessDomainMarker
+    {
+        public static readonly string Id = System.Guid.NewGuid().ToString();
+    }
+}