Connect MITC4 drilling evidence across analysis procedures

src/fesa/analysis/hht_dynamic_internal.h

@@ -97,6 +97,9 @@ struct DynamicAssembly {
   std::optional<SparseMatrix> hidden_gradient;
   std::optional<TrialConstraintData> trial_constraints;
   std::array<std::vector<hht_field_convergence::FluxOccurrence>, 2> field_flux;
+  // Source-ordered scalar primitive, including the external term exactly once.
+  // Empty when directional primitives were not evaluated; never a zero fallback.
+  Vector hidden_constraint{0U};
 };
 
 /// @brief Builds checked shell evaluators in stable source order.