feat(cpp-object-oriented-modular-refactoring): step 5 - solver-workflow-google-style

include/fesa/assembly/sparse_assembler.h

@@ -0,0 +1,27 @@
+#ifndef FESA_ASSEMBLY_SPARSE_ASSEMBLER_H_
+#define FESA_ASSEMBLY_SPARSE_ASSEMBLER_H_
+
+#include "fesa/core/status.h"
+#include "fesa/math/sparse_matrix.h"
+
+namespace fesa {
+
+class AnalysisModel;
+class DofManager;
+class ParallelFor;
+
+/// @brief Owns deterministic element-contribution reduction into global CSR.
+class SparseAssembler {
+ public:
+  /// @brief Assembles stiffness in stable source-element and local-entry order.
+  /// @return A validated full-DOF CSR matrix or structured model failure.
+  /// @note Parallel workers produce index-owned local buffers; serial reduction
+  /// remains the sole global CSR writer.
+  static Result<SparseMatrix> AssembleStiffness(
+      const AnalysisModel& model, const DofManager& dofs,
+      const ParallelFor& parallel_for);
+};
+
+}  // namespace fesa
+
+#endif  // FESA_ASSEMBLY_SPARSE_ASSEMBLER_H_