Add bounded fully coupled second-order trial correction and frozen screen

libmeanfield/interface/solver/newton.cppm

@@ -268,6 +268,9 @@ export namespace mean_field::solver::nonlinear {
         // A curved trial path cannot recover its Newton tangent by dividing
         // the candidate displacement by alpha. Observers borrow it directly.
         std::span<const mfem::real_t> normalizedDirection{};
+        // Auxiliary trial solves must remain distinct from the Newton report.
+        // Like the state spans, this diagnostic view is borrowed for the callback.
+        const NumericalStrategyDiagnostics *numericalStrategies{nullptr};
     };
 
     struct AfterIteration final {