feat: add eigen2 frequency pipeline and fail-closed validation

Implement MITC4 mass, constrained whitening, MKL FEAST, modal HDF5, and deterministic Value comparison. MSVC Debug builds; 394 of 395 tests pass. Original-model all-c residual and the documented S3 static contract conflict remain unresolved; this is an implementation checkpoint, not feature acceptance.

include/fesa/model/domain.h

@@ -4,6 +4,7 @@
 #include <cstddef>
 #include <filesystem>
 #include <memory>
+#include <optional>
 #include <string>
 #include <vector>
 
@@ -47,7 +48,7 @@ class DomainCollectionView {
   std::vector<const T*> entries_;
 };
 
-/// @brief Owns one immutable static-step semantic definition.
+/// @brief Owns one immutable static or frequency-step semantic definition.
 /// @note Loads retain source order and are owned polymorphically by unique
 /// pointers.
 class StepDefinition {
@@ -84,6 +85,12 @@ class StepDefinition {
   /// @brief Reports whether this step uses the nonlinear static procedure.
   bool IsNonlinearStatic() const noexcept;
 
+  /// @brief Reports whether this step defines the frequency procedure.
+  bool IsFrequency() const noexcept;
+
+  /// @brief Returns frequency source semantics when this is a frequency step.
+  const FrequencyStepDefinition* Frequency() const noexcept;
+
   /// @brief Reports the source NLGEOM setting for this static step.
   bool UsesNonlinearGeometry() const noexcept;
 
@@ -108,6 +115,9 @@ class StepDefinition {
   /// @brief Converts one parsed static-step record to owned semantic objects.
   explicit StepDefinition(StaticStepDefinition definition);
 
+  /// @brief Converts one parsed frequency-step record to owned semantics.
+  explicit StepDefinition(FrequencyStepDefinition definition);
+
   std::string name_;
   std::vector<std::unique_ptr<BoundaryCondition>> boundary_conditions_;
   BoundaryConditionView boundary_conditions_view_;
@@ -124,6 +134,7 @@ class StepDefinition {
   double minimum_increment_;
   double maximum_increment_;
   SourceLocation location_;
+  std::optional<FrequencyStepDefinition> frequency_;
 };
 
 /// @brief Owns the complete immutable semantic model definition.
@@ -184,9 +195,15 @@ class Domain {
   /// @brief Returns assembly element surfaces in stable declaration order.
   const std::vector<ElementSurfaceDefinition>& ElementSurfaces() const noexcept;
 
-  /// @brief Returns static steps in stable declaration order.
+  /// @brief Returns procedure steps in stable declaration order.
   const DomainCollectionView<StepDefinition>& Steps() const noexcept;
 
+  /// @brief Returns resolved density records in stable material-index order.
+  const std::vector<MaterialDensityDefinition>& Densities() const noexcept;
+
+  /// @brief Returns the sole frequency source definition when present.
+  const FrequencyStepDefinition* Frequency() const noexcept;
+
   /// @brief Returns sorted nonfatal mapping diagnostics.
   const std::vector<Diagnostic>& Warnings() const noexcept;
 

include/fesa/model/model_types.h

@@ -117,18 +117,15 @@ struct StaticStepDefinition {
       std::vector<PrescribedDisplacementDefinition> step_boundaries,
       std::vector<NodalLoad> step_loads,
       std::vector<SurfacePressureLoadDefinition> step_surface_pressure_loads,
-      StaticProcedureKind step_procedure_kind,
-      bool step_nlgeom,
-      double step_initial_increment,
-      double step_time_period,
-      double step_minimum_increment,
-      double step_maximum_increment,
+      StaticProcedureKind step_procedure_kind, bool step_nlgeom,
+      double step_initial_increment, double step_time_period,
+      double step_minimum_increment, double step_maximum_increment,
       SourceLocation step_location)
-        : name{std::move(step_name)},
-          boundaries{std::move(step_boundaries)},
-          loads{std::move(step_loads)},
-          surface_pressure_loads{std::move(step_surface_pressure_loads)},
-          procedure_kind{step_procedure_kind},
+      : name{std::move(step_name)},
+        boundaries{std::move(step_boundaries)},
+        loads{std::move(step_loads)},
+        surface_pressure_loads{std::move(step_surface_pressure_loads)},
+        procedure_kind{step_procedure_kind},
         nlgeom{step_nlgeom},
         initial_increment{step_initial_increment},
         time_period{step_time_period},
@@ -141,35 +138,30 @@ struct StaticStepDefinition {
       std::string step_name,
       std::vector<PrescribedDisplacementDefinition> step_boundaries,
       std::vector<NodalLoad> step_loads,
-      StaticProcedureKind step_procedure_kind,
-      bool step_nlgeom,
-      double step_initial_increment,
-      double step_time_period,
-      double step_minimum_increment,
-      double step_maximum_increment,
+      StaticProcedureKind step_procedure_kind, bool step_nlgeom,
+      double step_initial_increment, double step_time_period,
+      double step_minimum_increment, double step_maximum_increment,
       SourceLocation step_location)
-      : StaticStepDefinition(
-            std::move(step_name), std::move(step_boundaries),
-            std::move(step_loads), {}, step_procedure_kind, step_nlgeom,
-            step_initial_increment, step_time_period, step_minimum_increment,
-            step_maximum_increment, std::move(step_location)) {}
+      : StaticStepDefinition(std::move(step_name), std::move(step_boundaries),
+                             std::move(step_loads), {}, step_procedure_kind,
+                             step_nlgeom, step_initial_increment,
+                             step_time_period, step_minimum_increment,
+                             step_maximum_increment, std::move(step_location)) {
+  }
 
   /// @brief Creates a legacy linear static step definition.
   StaticStepDefinition(
       std::string step_name,
       std::vector<PrescribedDisplacementDefinition> step_boundaries,
-      std::vector<NodalLoad> step_loads,
-      double step_initial_increment,
-      double step_time_period,
-      double step_minimum_increment,
-      double step_maximum_increment,
-      SourceLocation step_location)
-      : StaticStepDefinition(
-            std::move(step_name), std::move(step_boundaries),
-            std::move(step_loads),
-            StaticProcedureKind::kLinearSmallDisplacement, false,
-            step_initial_increment, step_time_period, step_minimum_increment,
-            step_maximum_increment, std::move(step_location)) {}
+      std::vector<NodalLoad> step_loads, double step_initial_increment,
+      double step_time_period, double step_minimum_increment,
+      double step_maximum_increment, SourceLocation step_location)
+      : StaticStepDefinition(std::move(step_name), std::move(step_boundaries),
+                             std::move(step_loads),
+                             StaticProcedureKind::kLinearSmallDisplacement,
+                             false, step_initial_increment, step_time_period,
+                             step_minimum_increment, step_maximum_increment,
+                             std::move(step_location)) {}
 
   std::string name;
   std::vector<PrescribedDisplacementDefinition> boundaries;
@@ -184,6 +176,38 @@ struct StaticStepDefinition {
   SourceLocation location;
 };
 
+/// @brief Identifies the accepted source eigensolver selection.
+enum class FrequencyEigensolver { kLanczos };
+
+/// @brief Identifies the accepted modal normalization selection.
+enum class FrequencyNormalization { kMass };
+
+/// @brief Stores one resolved constant material mass density.
+struct MaterialDensityDefinition {
+  EntityIndex material_index;
+  double rho;
+  SourceLocation location;
+};
+
+/// @brief Stores the sole supported frequency-step source semantics.
+struct FrequencyStepDefinition {
+  std::string source_step_name_raw;
+  std::string source_step_name_canonical;
+  SourceLocation step_location;
+  SourceLocation frequency_location;
+  SourceLocation data_location;
+  std::int64_t requested_mode_count;
+  bool nlgeom_explicit;
+  bool perturbation_explicit;
+  bool eigensolver_explicit;
+  bool sim_explicit;
+  bool acoustic_coupling_explicit;
+  bool normalization_explicit;
+  FrequencyEigensolver eigensolver;
+  FrequencyNormalization normalization;
+  std::vector<PrescribedDisplacementDefinition> boundaries;
+};
+
 /// @brief Stores a stable resolved node-set membership list.
 struct NodeSet {
   std::string name;
@@ -245,6 +269,8 @@ struct ModelDefinition {
   std::vector<InstanceDefinition> instances;
   std::vector<ElementSurfaceDefinition> element_surfaces;
   std::vector<StaticStepDefinition> steps;
+  std::vector<MaterialDensityDefinition> densities;
+  std::optional<FrequencyStepDefinition> frequency_step;
   std::vector<Diagnostic> warnings;
 };