feat: add thermal semantic domain model

include/fesa/elements/ds4_thermal.h

@@ -0,0 +1,95 @@
+#ifndef FESA_ELEMENTS_DS4_THERMAL_H_
+#define FESA_ELEMENTS_DS4_THERMAL_H_
+
+#include <array>
+#include <utility>
+#include <vector>
+
+#include "fesa/elements/element_definition.h"
+
+namespace fesa {
+
+/// @brief Defines one four-node uncoupled transient thermal DS4 element.
+/// @note This semantic definition contains no geometry kernel or equation
+/// state.
+class Ds4ThermalDefinition final : public ElementDefinition {
+ public:
+  Ds4ThermalDefinition(SourceEntityId source_id,
+                       std::array<EntityIndex, 4> node_indices,
+                       EntityIndex section_index, SourceLocation location);
+
+  ElementDefinitionKind Kind() const noexcept override;
+  const SourceEntityId& SourceId() const noexcept override;
+  std::string_view SourceElementType() const noexcept override;
+  const std::vector<EntityIndex>& NodeIndices() const noexcept override;
+  EntityIndex MaterialIndex() const noexcept override;
+  EntityIndex PropertyIndex() const noexcept override;
+
+  /// @brief Returns the stable thermal-section collection position.
+  EntityIndex ThermalSectionIndex() const noexcept;
+  /// @brief Returns the source location defining this element.
+  const SourceLocation& Location() const noexcept;
+
+ private:
+  friend class Domain;
+
+  void BindMaterialIndex(EntityIndex material_index) noexcept;
+
+  SourceEntityId source_id_;
+  std::array<EntityIndex, 4> node_indices_;
+  std::vector<EntityIndex> node_indices_view_;
+  EntityIndex section_index_;
+  EntityIndex material_index_{0U};
+  SourceLocation location_;
+};
+
+inline Ds4ThermalDefinition::Ds4ThermalDefinition(
+    SourceEntityId source_id, std::array<EntityIndex, 4> node_indices,
+    EntityIndex section_index, SourceLocation location)
+    : source_id_{std::move(source_id)},
+      node_indices_{node_indices},
+      node_indices_view_{node_indices.begin(), node_indices.end()},
+      section_index_{section_index},
+      location_{std::move(location)} {}
+
+inline ElementDefinitionKind Ds4ThermalDefinition::Kind() const noexcept {
+  return ElementDefinitionKind::kDs4Thermal;
+}
+
+inline const SourceEntityId& Ds4ThermalDefinition::SourceId() const noexcept {
+  return source_id_;
+}
+
+inline std::string_view Ds4ThermalDefinition::SourceElementType() const noexcept {
+  return "DS4";
+}
+
+inline const std::vector<EntityIndex>& Ds4ThermalDefinition::NodeIndices()
+    const noexcept {
+  return node_indices_view_;
+}
+
+inline EntityIndex Ds4ThermalDefinition::MaterialIndex() const noexcept {
+  return material_index_;
+}
+
+inline EntityIndex Ds4ThermalDefinition::PropertyIndex() const noexcept {
+  return section_index_;
+}
+
+inline EntityIndex Ds4ThermalDefinition::ThermalSectionIndex() const noexcept {
+  return section_index_;
+}
+
+inline const SourceLocation& Ds4ThermalDefinition::Location() const noexcept {
+  return location_;
+}
+
+inline void Ds4ThermalDefinition::BindMaterialIndex(
+    EntityIndex material_index) noexcept {
+  material_index_ = material_index;
+}
+
+}  // namespace fesa
+
+#endif  // FESA_ELEMENTS_DS4_THERMAL_H_

include/fesa/elements/element_definition.h

@@ -9,7 +9,7 @@
 namespace fesa {
 
 /// @brief Identifies the supported semantic element-definition kinds.
-enum class ElementDefinitionKind { kEulerBeam3D, kMitc4Shell };
+enum class ElementDefinitionKind { kEulerBeam3D, kMitc4Shell, kDs4Thermal };
 
 /// @brief Provides immutable source identity and topology for one element.
 /// @note Numerical stiffness, recovery, and equation ids are intentionally