feat(solid): add Hex8 input and three-DOF semantics

include/fesa/loads/concentrated_nodal_load.h

@@ -3,6 +3,8 @@
 
 #include <array>
 #include <cstddef>
+#include <optional>
+#include <string>
 
 #include "fesa/core/diagnostic.h"
 #include "fesa/loads/load.h"
@@ -21,7 +23,10 @@ class ConcentratedNodalLoad final : public Load {
   /// @brief Creates one parsed CLOAD component while preserving diagnostics.
   ConcentratedNodalLoad(SourceTargetQuery target, int source_dof,
                         double magnitude, std::size_t source_order,
-                        SourceLocation location);
+                        SourceLocation location,
+                        std::optional<EntityIndex> amplitude_index = {},
+                        std::string amplitude_name_raw = {},
+                        SourceLocation amplitude_location = {});
 
   /// @brief Computes target-major, component-minor full-DOF contributions.
   Result<std::vector<LoadContribution>> ComputeContributions(
@@ -39,12 +44,28 @@ class ConcentratedNodalLoad final : public Load {
   /// @brief Returns the source location used by structured diagnostics.
   const SourceLocation& Location() const noexcept;
 
+  /// @brief Returns a model-level amplitude index when one was specified.
+  std::optional<EntityIndex> AmplitudeIndex() const noexcept {
+    return amplitude_index_;
+  }
+  /// @brief Returns preserved CLOAD amplitude option spelling.
+  const std::string& AmplitudeName() const noexcept {
+    return amplitude_name_raw_;
+  }
+  /// @brief Returns the source location of the CLOAD amplitude option.
+  const SourceLocation& AmplitudeLocation() const noexcept {
+    return amplitude_location_;
+  }
+
  private:
   SourceTargetQuery target_;
   std::array<double, 6> global_components_{};
   std::size_t source_order_;
   SourceLocation location_{};
   int source_dof_{0};
+  std::optional<EntityIndex> amplitude_index_;
+  std::string amplitude_name_raw_;
+  SourceLocation amplitude_location_;
 };
 
 }  // namespace fesa

include/fesa/loads/load.h

@@ -26,6 +26,8 @@ struct LoadContext {
   const Domain& domain;
   const DofManager& dof_manager;
   const SourceTargetResolver& target_resolver;
+  /// @brief Supplies the actual dynamic endpoint time for amplitude sampling.
+  double step_time{0.0};
 };
 
 /// @brief Produces local ordered load contributions without global mutation.