test: preserve Dev verification contracts through Refactor APIs

tests/unit/elements/hex8_element_test.cpp

@@ -1180,6 +1180,35 @@ TEST(Hex8Element, MeanVolumeWarpedLowOnlyStateRetainsWeightedCubicEnergy) {
   EXPECT_NEAR(actual_cubic.high, cubic * c * c * c, 1e-11 * c * c * c);
   EXPECT_NE(actual_cubic.high, 0);
 }
+TEST(Hex8Element, BackendOperandRejectionRetainsOriginalStiffnessDiagnostic) {
+  Coordinates coordinates{};
+  for (std::size_t a = 0; a < 8; ++a)
+    for (std::size_t i = 0; i < 3; ++i)
+      coordinates[a][i] = 0.01 * kSigns[a][i];
+  // Original native probe: finite moduli/volume, but mu*gradient overflows.
+  // The failed diagnostic candidate must not become a scalar success fallback.
+  const auto element = Make(coordinates, 1e308, -0.5);
+  ASSERT_FALSE(element.HasValue());
+  EXPECT_EQ(element.GetStatus().Diagnostics()[0].code, "invalid-hex8");
+  EXPECT_EQ(element.GetStatus().Diagnostics()[0].message,
+            "Hex8 reference stiffness is nonfinite.");
+}
+
+TEST(Hex8Element, TensorFailureRetainsPriorityOverEnergyAndTangentOverflow) {
+  Coordinates coordinates{};
+  for (std::size_t a = 0; a < 8; ++a)
+    for (std::size_t i = 0; i < 3; ++i)
+      coordinates[a][i] = 0.01 * kSigns[a][i];
+  const auto element = Make(coordinates, 1e200, -0.5);
+  ASSERT_TRUE(element.HasValue());
+  const auto displacement = Affine(coordinates,
+      Tensor{{{1e100, 0, 0}, {0, 1e100, 0}, {0, 0, 1e100}}});
+  const auto response = element.Value().EvaluateNonlinear(displacement);
+  ASSERT_FALSE(response.HasValue());
+  EXPECT_EQ(response.GetStatus().Diagnostics()[0].code, "invalid-hex8");
+  EXPECT_EQ(response.GetStatus().Diagnostics()[0].message,
+            "Hex8 trial tensor is nonfinite.");
+}
 }  // namespace
 
 TEST(Hex8Element, RejectsNonfiniteCanonicalJacobianActionBeforeFiniteGradients) {