fix: enforce thermal boundary dof endpoints

include/fesa/analysis/analysis_model.h

@@ -20,8 +20,10 @@ class AnalysisModel {
   /// @brief Returns the non-owned Domain backing this view.
   const Domain& GetDomain() const noexcept;
 
-  /// @brief Returns the sole active static step.
-  const StepDefinition& Step() const noexcept;
+  /// @brief Returns the sole active structural step.
+  /// @throws std::logic_error when this is a thermal view.
+  /// @note Thermal callers must use ThermalStep().
+  const StepDefinition& Step() const;
 
   /// @brief Reports whether this view selects the uncoupled thermal step.
   bool IsThermal() const noexcept;
@@ -56,6 +58,12 @@ class AnalysisModel {
   /// @brief Returns connected thermal node indices in stable Domain order.
   const std::vector<EntityIndex>& ActiveThermalNodes() const noexcept;
 
+  /// @brief Returns thermal-material collection positions in source order.
+  const std::vector<EntityIndex>& ActiveThermalMaterials() const noexcept;
+
+  /// @brief Returns thermal-section collection positions in source order.
+  const std::vector<EntityIndex>& ActiveThermalSections() const noexcept;
+
   /// @brief Returns active surface pressure records without copying Domain data.
   const std::vector<SurfacePressureLoadDefinition>& ActiveSurfacePressureLoads()
       const noexcept;
@@ -74,6 +82,8 @@ class AnalysisModel {
   std::vector<EntityIndex> active_loads_;
   std::vector<EntityIndex> active_thermal_elements_;
   std::vector<EntityIndex> active_thermal_nodes_;
+  std::vector<EntityIndex> active_thermal_materials_;
+  std::vector<EntityIndex> active_thermal_sections_;
   bool is_thermal_{false};
 };
 

include/fesa/elements/ds4_thermal.h

@@ -2,6 +2,7 @@
 #define FESA_ELEMENTS_DS4_THERMAL_H_
 
 #include <array>
+#include <limits>
 #include <utility>
 #include <vector>
 
@@ -14,6 +15,9 @@ namespace fesa {
 /// state.
 class Ds4ThermalDefinition final : public ElementDefinition {
  public:
+  /// @brief Marks that DS4 has no entry in Domain::Properties().
+  static constexpr EntityIndex kNoPropertyIndex =
+      (std::numeric_limits<EntityIndex>::max)();
   Ds4ThermalDefinition(SourceEntityId source_id,
                        std::array<EntityIndex, 4> node_indices,
                        EntityIndex section_index, SourceLocation location);
@@ -74,7 +78,7 @@ inline EntityIndex Ds4ThermalDefinition::MaterialIndex() const noexcept {
 }
 
 inline EntityIndex Ds4ThermalDefinition::PropertyIndex() const noexcept {
-  return section_index_;
+  return kNoPropertyIndex;
 }
 
 inline EntityIndex Ds4ThermalDefinition::ThermalSectionIndex() const noexcept {

include/fesa/model/model_types.h

@@ -239,6 +239,8 @@ struct ThermalMaterialDefinition {
 };
 
 /// @brief Stores one centered homogeneous thermal shell assignment.
+/// @note material_index addresses ModelDefinition::thermal_materials and,
+/// after Domain construction, Domain::ThermalMaterials(), never Properties().
 struct ThermalShellSectionDefinition {
   SourceEntityId source_id;
   std::string name;
@@ -268,6 +270,16 @@ struct ThermalInitialConditionDefinition {
   SourceLocation location;
 };
 
+/// @brief Identifies the fixed bottom-to-top thermal station source DOFs.
+/// @note This is separate from the six-component structural DofComponent.
+enum class ThermalDofComponent : int {
+  kBottom = 11,
+  kLower = 12,
+  kMiddle = 13,
+  kUpper = 14,
+  kTop = 15
+};
+
 /// @brief Stores one prescribed thermal source DOF value.
 struct ThermalBoundaryConditionDefinition {
   EntityIndex node_index;