feat(nonlinear-static-newton-raphson): step 9 - nonlinear-hdf5-schema-v1-writer

include/fesa/io/hdf5/nonlinear_hdf5_results_writer.h

@@ -0,0 +1,22 @@
+#ifndef FESA_IO_HDF5_NONLINEAR_HDF5_RESULTS_WRITER_H_
+#define FESA_IO_HDF5_NONLINEAR_HDF5_RESULTS_WRITER_H_
+
+#include "fesa/results/nonlinear_results_writer.h"
+
+namespace fesa {
+
+/// @brief Writes authoritative schema-v1 nonlinear HDF5 results atomically.
+/// @note HDF5 and platform types remain private to the implementation.
+class NonlinearHdf5ResultsWriter final : public NonlinearResultsWriter {
+ public:
+  /// @brief Writes and self-checks committed nonlinear frames before publish.
+  /// @return Success only after atomic replacement or structured output failure.
+  /// @note Factor-zero state remains metadata and is not an accepted frame.
+  Status Write(const std::filesystem::path& output_path,
+               const Domain& domain, const NonlinearAnalysisState& state,
+               const std::vector<Diagnostic>& diagnostics) override;
+};
+
+}  // namespace fesa
+
+#endif  // FESA_IO_HDF5_NONLINEAR_HDF5_RESULTS_WRITER_H_