test(rendering): name transient parity differences

When counts diverge, preserve ordered comparison and report the first concrete extra or differing payload. Include retained-classification state in downstream mismatch logs so reveal-edge lifecycle failures can be attributed without weakening the referee.

src/AcDream.App/Rendering/Scene/RenderScenePViewFrameProduct.cs

@@ -420,7 +420,8 @@ internal sealed class RenderScenePViewFrameProductController :
                 _classifiedOutputFirstMismatch = mismatch;
                 _log?.Invoke(
                     "[render-classified-output] first mismatch: "
-                    + mismatch);
+                    + mismatch
+                    + $" classification={_packedClassification}");
             }
         }
 
@@ -458,7 +459,8 @@ internal sealed class RenderScenePViewFrameProductController :
                 _selectionOutputFirstMismatch = selectionMismatch;
                 _log?.Invoke(
                     "[render-selection-output] first mismatch: "
-                    + selectionMismatch);
+                    + selectionMismatch
+                    + $" classification={_packedClassification}");
             }
         }
 
@@ -480,8 +482,22 @@ internal sealed class RenderScenePViewFrameProductController :
     {
         if (expected.Count != actual.Count)
         {
+            int shared = Math.Min(expected.Count, actual.Count);
+            for (int index = 0; index < shared; index++)
+            {
+                if (expected[index] != actual[index])
+                {
+                    return $"field=draw index={index} "
+                        + $"expected={expected[index]} "
+                        + $"actual={actual[index]}";
+                }
+            }
+
+            string extra = expected.Count > actual.Count
+                ? $"firstExtraExpected={expected[shared]}"
+                : $"firstExtraActual={actual[shared]}";
             return $"field=drawCount expected={expected.Count} "
-                + $"actual={actual.Count}";
+                + $"actual={actual.Count} {extra}";
         }
 
         for (int index = 0; index < expected.Count; index++)
@@ -503,8 +519,22 @@ internal sealed class RenderScenePViewFrameProductController :
     {
         if (expected.Count != actual.Count)
         {
+            int shared = Math.Min(expected.Count, actual.Count);
+            for (int index = 0; index < shared; index++)
+            {
+                if (expected[index] != actual[index])
+                {
+                    return $"field=part index={index} "
+                        + $"expected={expected[index]} "
+                        + $"actual={actual[index]}";
+                }
+            }
+
+            string extra = expected.Count > actual.Count
+                ? $"firstExtraExpected={expected[shared]}"
+                : $"firstExtraActual={actual[shared]}";
             return $"field=partCount expected={expected.Count} "
-                + $"actual={actual.Count}";
+                + $"actual={actual.Count} {extra}";
         }
 
         for (int index = 0; index < expected.Count; index++)
@@ -728,8 +758,24 @@ internal sealed class RenderScenePViewFrameProductController :
         }
         if (_packedExpected.Count != _packedActual.Count)
         {
+            int shared = Math.Min(
+                _packedExpected.Count,
+                _packedActual.Count);
+            for (int index = 0; index < shared; index++)
+            {
+                if (_packedExpected[index] != _packedActual[index])
+                {
+                    return $"field=meshPart index={index} "
+                        + $"expected={_packedExpected[index]} "
+                        + $"actual={_packedActual[index]}";
+                }
+            }
+
+            string extra = _packedExpected.Count > _packedActual.Count
+                ? $"firstExtraExpected={_packedExpected[shared]}"
+                : $"firstExtraActual={_packedActual[shared]}";
             return $"field=count expected={_packedExpected.Count} "
-                + $"actual={_packedActual.Count}";
+                + $"actual={_packedActual.Count} {extra}";
         }
 
         for (int index = 0; index < _packedExpected.Count; index++)
@@ -759,8 +805,22 @@ internal sealed class RenderScenePViewFrameProductController :
     {
         if (_expected.Count != _actual.Count)
         {
+            int shared = Math.Min(_expected.Count, _actual.Count);
+            for (int index = 0; index < shared; index++)
+            {
+                if (_expected[index] != _actual[index])
+                {
+                    return $"field=candidate index={index} "
+                        + $"expected={_expected[index]} "
+                        + $"actual={_actual[index]}";
+                }
+            }
+
+            string extra = _expected.Count > _actual.Count
+                ? $"firstExtraExpected={_expected[shared]}"
+                : $"firstExtraActual={_actual[shared]}";
             return $"field=count expected={_expected.Count} "
-                + $"actual={_actual.Count}";
+                + $"actual={_actual.Count} {extra}";
         }
 
         for (int i = 0; i < _expected.Count; i++)