fix(math): preflight finite dense operands at dispatch boundary

src/fesa/analysis/linear_frequency_procedure.cpp

@@ -275,6 +275,10 @@ Result<EigenAnalysisState> ExecuteCandidate(const Domain& domain) {
     std::size_t pivot = 0U;
     for (std::size_t dof = 0; dof < y.Size(); ++dof) {
       physical[dof] = D(dof, length) * y[dof];
+      if (!std::isfinite(physical[dof]))
+        return Result<EigenAnalysisState>::Failure(
+            MetricFailure("initial_modal_mass", physical[dof],
+                          state.backend.column_ids[column]));
       if (std::abs(y[dof]) > std::abs(y[pivot])) pivot = dof;
     }
     Vector mass_times = eigen_internal::MultiplyNodalMass(nodal_mass, physical);
@@ -413,6 +417,10 @@ Result<EigenAnalysisState> LinearFrequencyProcedureExecutor::Execute(
           std::move(diagnostics)));
     }
     return result;
+  } catch (const std::invalid_argument&) {
+    return Result<EigenAnalysisState>::Failure(
+        Failure("invalid-eigenvalue-result", "modal-workspace",
+                "Modal product inputs must be finite and shape compatible."));
   } catch (const std::bad_alloc&) {
     return Result<EigenAnalysisState>::Failure(
         Failure("eigen-allocation-failed", "modal-workspace",