fix(eigen): reject nonfinite modal validation scales

tests/unit/analysis/solid_frequency_procedure_test.cpp

@@ -276,3 +276,19 @@ TEST(SolidFrequencyProcedure,
   // Original modal Value output is pending. This proves only our independent
   // checks on the supplied input; it is not an external frequency comparison.
 }
+
+TEST(SolidFrequencyProcedure, RejectsOverflowingOriginalPencilValidationScale) {
+  // Every local K entry, eigenvalue, and spectral enclosure is representable.
+  // The all-odd x Walsh mode still overflows the original residual/energy
+  // denominators: finite / infinity must never become passing zero evidence.
+  auto domain = Brick(24U, "", 1.0, 2.0, 3e306);
+  ASSERT_TRUE(domain.HasValue()) << StatusText(domain.GetStatus());
+  const auto result =
+      fesa::SolidFrequencyProcedureExecutor{}.Execute(domain.Value());
+  ASSERT_FALSE(result.HasValue());
+  ASSERT_FALSE(result.GetStatus().Diagnostics().empty());
+  EXPECT_EQ(result.GetStatus().Diagnostics()[0].code,
+            "solid-eigenpair-validation-failed");
+  EXPECT_NE(result.GetStatus().Diagnostics()[0].message.find("nonfinite"),
+            std::string::npos);
+}