fix: use residual stopping for FEAST eigenanalysis

tests/unit/io/hdf5/eigen_hdf5_results_writer_test.cpp

@@ -3,6 +3,8 @@
 #include <gtest/gtest.h>
 #include <hdf5.h>
 
+#include <array>
+#include <cstdint>
 #include <filesystem>
 #include <fstream>
 #include <functional>
@@ -78,6 +80,15 @@ TEST(EigenHdf5ResultsWriter, WritesModalSchemaAndRejectsTamperedState) {
       H5Fopen(path.string().c_str(), H5F_ACC_RDONLY, H5P_DEFAULT);
   ASSERT_GE(file, 0);
   EXPECT_GT(H5Lexists(file, "/steps/Step-1/eigen/modes", H5P_DEFAULT), 0);
+  const hid_t controls =
+      H5Dopen2(file, "/steps/Step-1/eigen/backend/base_fpm", H5P_DEFAULT);
+  ASSERT_GE(controls, 0);
+  std::array<std::int64_t, 128> stored_controls{};
+  ASSERT_GE(H5Dread(controls, H5T_NATIVE_INT64, H5S_ALL, H5S_ALL,
+                    H5P_DEFAULT, stored_controls.data()),
+            0);
+  EXPECT_EQ(stored_controls[5U], 0);
+  EXPECT_GE(H5Dclose(controls), 0);
   EXPECT_GE(H5Fclose(file), 0);
   std::ifstream original_file{path, std::ios::binary};
   const std::string original{std::istreambuf_iterator<char>{original_file}, {}};
@@ -91,6 +102,7 @@ TEST(EigenHdf5ResultsWriter, WritesModalSchemaAndRejectsTamperedState) {
       [](auto& candidate) { candidate.modes[0].cluster_id = 7U; },
       [](auto& candidate) { candidate.constraint_mask[0] = 1U; },
       [](auto& candidate) { candidate.nodal_reduction[0].rcond_inf = 1e-15; },
+      [](auto& candidate) { candidate.backend.base_fpm[5U] = 1; },
       [](auto& candidate) { candidate.eta_gram = 1e-5; }};
   for (const auto& mutate : mutations) {
     auto candidate = state;

tests/unit/solvers/eigen/mkl_feast_eigen_solver_test.cpp

@@ -71,6 +71,8 @@ TEST(MklFeastEigenSolver, SolvesN1AndRetainsBackendEvidence) {
   EXPECT_EQ(result.Value().eigenvectors.Rows(), 1U);
   EXPECT_EQ(result.Value().eigenvectors.Columns(), 1U);
   EXPECT_EQ(result.Value().thread_count, 1U);
+  ASSERT_EQ(result.Value().base_fpm.size(), 128U);
+  EXPECT_EQ(result.Value().base_fpm[5U], 0);
   ASSERT_FALSE(result.Value().backend_calls.empty());
   EXPECT_EQ(result.Value().backend_calls.front().purpose, "total-enclosure");
   EXPECT_EQ(result.Value().backend_calls.back().kind, "solve");