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

src/fesa/solvers/eigen/mkl_feast_eigen_solver.cpp

@@ -1194,8 +1194,13 @@ Result<FeastEigenResult> MklFeastEigenSolver::SolveImpl(
     for (std::size_t row = 0; row < n; ++row)
       mode[row] = ordered_vectors(row, right);
     const auto action = mass != nullptr ? mass->Multiply(mode) : std::move(mode);
-    for (std::size_t row = 0; row < n; ++row)
+    for (std::size_t row = 0; row < n; ++row) {
+      if (!std::isfinite(action[row]))
+        return Result<FeastEigenResult>::Failure(
+            TraceFailure("eigenpair-validation-failed", "gram",
+                         "The independent mass action is nonfinite."));
       mass_modes(row, right) = action[row];
+    }
   }
   const auto gram = dense_blas_internal::MultiplyTransposeLeft(ordered_vectors,
                                                               mass_modes);
@@ -1245,6 +1250,10 @@ Result<FeastEigenResult> MklFeastEigenSolver::SolveImpl(
                           solve_upper,
                           upper_search_termination};
   return Result<FeastEigenResult>::Success(std::move(result));
+} catch (const std::invalid_argument&) {
+  return Result<FeastEigenResult>::Failure(
+      Failure("eigenpair-validation-failed", "independent-action",
+              "Modal product inputs must be finite and shape compatible."));
 } catch (const std::length_error&) {
   return Result<FeastEigenResult>::Failure(
       Failure("feast-integer-overflow", "independent-action",