feat(result-contract-completion): step 0 — beam-element-end-recovery

include/fesa/elements/beam/beam3d2.hpp

@@ -2,22 +2,34 @@
 
 #include <array>
 #include <optional>
+#include <span>
 #include <vector>
 
 #include <fesa/core/diagnostic.hpp>
 #include <fesa/core/vec3.hpp>
 #include <fesa/fem/beam_frame.hpp>
 #include <fesa/model/beam_section.hpp>
+#include <fesa/model/ids.hpp>
 #include <fesa/model/material.hpp>
 
 namespace fesa {
 
 struct Beam3D2Input final {
     std::array<Vec3, 2> coordinates;
+    std::array<NodeId, 2> node_ids;
     IsotropicElastic material;
     BeamSection section;
 };
 
+struct BeamSectionResult final {
+    double xi;
+    NodeId end_node;
+    std::array<double, 6> section_strain;
+    std::array<double, 6> section_force;
+    double centroid_sigma_xx;
+    std::vector<double> sigma_xx;
+};
+
 struct Beam3D2Contribution final {
     Matrix12 local_stiffness;
     Matrix12 global_stiffness;
@@ -32,4 +44,9 @@ struct BeamKernelResult final {
 [[nodiscard]] BeamKernelResult compute_beam3d2(
     const Beam3D2Input& input);
 
+[[nodiscard]] std::vector<BeamSectionResult> recover_beam3d2(
+    const Beam3D2Input& input,
+    std::span<const double, 12> element_displacement,
+    std::span<const std::array<double, 2>> recovery_points);
+
 }  // namespace fesa