fix(hht): preserve metric association and complete MKL actions

src/fesa/analysis/hht_dynamic_internal.h

@@ -95,6 +95,11 @@ std::vector<std::size_t> NullNodes(
     const DofManager& dofs,
     const std::vector<DynamicRotationKinematics>& rotations);
 
+/// @brief Contracts a nodal metric with original left-associated products.
+/// @note Nonfinite products remain for the caller's existing validity gate.
+double OrderedNullMetric(const SparseMatrix& metric, std::size_t node,
+                         const Vector3& direction);
+
 /// @brief Solves the positive-mass and differentiated-null initial equations.
 ///
 /// The returned candidate is finite and exact-zero at constrained DOFs. Its