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

src/fesa/math/dense_blas_internal.h

@@ -31,7 +31,7 @@ class ScopedSingleEquationThreads {
 Result<MKL_INT> ToMklSize(std::size_t size);
 
 /// @brief Computes left-transpose times right through ordinary dense MKL.
-/// @throws std::invalid_argument if the row counts differ.
+/// @throws std::invalid_argument for mismatched rows or nonfinite operands.
 Matrix MultiplyTransposeLeft(const Matrix& left, const Matrix& right);
 
 /// @brief Multiplies a compact diagonal matrix by a vector through MKL.

src/fesa/math/matrix.cpp

@@ -1,5 +1,6 @@
 #include "fesa/math/matrix.h"
 
+#include <cmath>
 #include <mkl.h>
 
 #include <limits>
@@ -107,6 +108,12 @@ Vector Matrix::Multiply(const Vector& rhs) const {
     throw std::invalid_argument{
         "Matrix-vector multiplication has incompatible dimensions."};
   }
+  for (const double value : values_)
+    if (!std::isfinite(value))
+      throw std::invalid_argument{"Matrix product inputs must be finite."};
+  for (std::size_t i = 0; i < rhs.Size(); ++i)
+    if (!std::isfinite(rhs.Data()[i]))
+      throw std::invalid_argument{"Matrix product inputs must be finite."};
 
   Vector result{rows_};
   if (rows_ == 0 || columns_ == 0) {
@@ -126,6 +133,12 @@ Matrix Matrix::Multiply(const Matrix& rhs) const {
     throw std::invalid_argument{
         "Matrix multiplication has incompatible dimensions."};
   }
+  for (const double value : values_)
+    if (!std::isfinite(value))
+      throw std::invalid_argument{"Matrix product inputs must be finite."};
+  for (const double value : rhs.values_)
+    if (!std::isfinite(value))
+      throw std::invalid_argument{"Matrix product inputs must be finite."};
 
   Matrix result{rows_, rhs.columns_};
   if (rows_ == 0 || columns_ == 0 || rhs.columns_ == 0) {