diff --git a/docs/calculation-performance/t4-shell-optimization.md b/docs/calculation-performance/t4-shell-optimization.md
index cb8e908..5043bb3 100644
--- a/docs/calculation-performance/t4-shell-optimization.md
+++ b/docs/calculation-performance/t4-shell-optimization.md
@@ -230,3 +230,60 @@ Source commit c397a147b0e885384da8dee81ef645b9d0b17adb에서 corrected-prefix cl
 Release exe SHA7d3c48351a8b76dbc5274468fc9f205386d28521cde79633dcd970a861321143. Build/native/parent PATH, environment/identity 전후 및 timer facts는 parent constant-shell-native.json/development-constant-shell-before.json/development-constant-shell-after.json/development-constant-shell.json과 해당 run-1/native.json/run.json/stdout/solver log에 보존한다. 최종 HDF5가 없어서 reader/precheck와 blocking U comparator 및 UR warning 비교는 모두 미실행이다. 729node/101frame/schema2 또는 required reference PASS로 표시하지 않는다. 기존 원본이나 최종 H5를 수정하지 않고 현재 partial 파일과 timeout 자료를 보존했다. 추가 micro/profile/whole-run 반복은 하지 않았다.
 
 다음 우선 후보는 profile에서 큰 EvaluateAssembly/EvaluateConstraintOperators 중복을 줄이는 exact true-trial internal constraint subset 재사용이다. False 위치/root 경로 및 external force/rate/acceleration primitive는 유지한다. 구체 context/q/v/direction/request/gate/lifetime 계획과 최소 private friend 범위를 먼저 검토한다. Node-local support6 AD는 support/비용 근거가 충분해진 경우의 비교 후보이며 현재 구현 범위를 확대하지 않는다.
+
+## 완성된 true trial의 내부 constraint 자료 재사용
+
+이 후보는 기존 SW profile의 Assembly/ConstraintOperators 중복 경로를 근거로 한다.
+완성된 true assembly가 이미 계산한 constraint value4, gradient4×24, Hessian24×24
+4개와 방향3차 gradient24 4개만 trial-owned optional에 보관한다. 기존 internal,
+inertia, ordered external/recovery/finite/CSR/hidden-gradient gate가 모두 성공한
+마지막 위치에서 기존 자료를 move한다. False와 initial frame은 저장하지 않는다.
+Accepted frame, reduced history, HDF5에는 이 자료가 붙지 않아 증분마다 누적되는
+구조가 아니다. 기존 Matrix/Vector deep-copy와 move 수명을 사용한다.
+
+소비자는 기존 inventory/null/transverse/node-row gate 뒤의 원래 internal 평가
+자리에서만 재사용을 확인한다. 구성64개 값과 source identity, element/scatter,
+node IDs, q/v, time/frame/increment/iteration 및 directional 요청이 일치해야 한다.
+현재/저장 q/v·구성·time은 finite 확인 뒤 representation 비교하여 ±0도 구별한다.
+Worker 평가 전후와 소비 thread의 masked FP control 및 기존 scope 내부 BLAS1,
+dynamic0이 안정적인 현재 Intel-thread 빌드에 한정한다. Private metadata getter는
+전역 policy를 바꾸지 않고 기존 caller TLS를 원복한다. 불일치/비유한/불명확 key,
+shape/payload 오류는 그 자리의 원래 full 평가와 Status로 돌아간다. 외부 force,
+rate/acceleration primitive, 누적 순서, physics/gates/diagnostic은 그대로 수행한다.
+
+Private element configuration header와 public header의 forward/private friend만
+추가했다. Element가 analysis에 의존하지 않고 vendor 타입을 public에 노출하지 않는다.
+Density는 내부 네 자료의 함수/energy 입력이 아니고 inertia는 매번 평가하므로 키에서
+제외한다. 약13.59MiB는676 shell의 payload 일부 산술 추정이며 객체/allocator/source
+문자열/추가 metadata 및 실제 peak 메모리 실측을 포함하는 상한이 아니다.
+
+독립 source 검토는 최초 bit-only key가 동일 NaN/Inf current+saved key를 수용해
+원래 실패를 생략할 수 있음을 발견했다(needs-fix). 해당 자료와 manifest를 보존한 뒤
+finite key miss를 추가하여 재검토 PASS를 받았다. Source-derived 반례의 native RED는
+미실행이며 실제 RED 관측이라고 기록하지 않는다. 최초 Debug build는 새 raw 자료
+fixture의 Vector3 read-only component 대입 오류로 cmake native2/외부 PowerShell1,
+13.2472474초에 실패했다. 원래 세 좌표를 생성자로 대입하는 test-only 수정으로
+production hash를 유지했고 실패 로그/native/source 자료도 보존했다.
+
+수정 source manifest C4EBD4169D44918E56DECDB0AB1D4AAFABDBA866612874C788DD883CF460C266에서
+정식 Debug 재빌드7 edges native0/6.30초, 새 cache/getter6/6 PASS(native0,
+CTest11.04초/native11.08초), 기존 reduced/initial Newton27/27 PASS(native0,
+CTest6.40초/native6.43초)를 확인했다. 실제 CTest 합33개이며 기존 Constant의33-case
+oracle와 다른 수다. Jet 수식/저장/provenance와 기존 element scope body는 바뀌지
+않아 그 oracle는 이번 슬롯에서 반복하지 않았다. Raw 네 자료/forced-fresh의 strict
+bits, deep copy/move, actual FP/TLS/dynamic miss, serial/TBB, 외부 rates, 동일
+NaN/±Inf q/v key의 실패 진단 전필드와 비유한 time의 fresh 성공을 검사했다.
+
+Corrected-prefix 실제 Ninja deps는 assembly41/reduced operators42/shell26이며
+모두 새 private configuration header를 포함한다. Library SHA
+5108045D88A2439E57934B8D66317DE1B545AFE122BFCF082D60DDB732D20DFE,
+unit SHA CF6D180565FCFDF5AD19EEA26EF627A38C5C8603AE331607031411828700F8BD다.
+Parent artifact의 true-trial-source-vector3.json/patch,
+true-trial-vector3-debug-native.json/built-hashes.json 및 단계별 로그에 실제
+source/compiler/argv/cwd/native/deps/thread/hook을 보존했다. Source10 hash 일치와
+관련 프로세스0 확인 후 CPU를 반환했다.
+
+현재 cache 후보의 Release/원본 shell 실행/실제 call 감소/비용 및 전체 Debug,
+reference/C08/최종100초 합격은 미실행이다. 부분 실행 자료나 이전 source의 PASS를
+이 후보의 전체 성능·물리 검증 완료로 바꾸지 않는다. 다음 bounded 개발 실행은
+0warmup/1회만 수행하고 결과에 따라 다음 최소 후보를 검토한다.
diff --git a/include/fesa/elements/nonlinear_mitc4_shell.h b/include/fesa/elements/nonlinear_mitc4_shell.h
index 9e37076..4359400 100644
--- a/include/fesa/elements/nonlinear_mitc4_shell.h
+++ b/include/fesa/elements/nonlinear_mitc4_shell.h
@@ -15,6 +15,10 @@
 
 namespace fesa {
 
+namespace nonlinear_mitc4_internal {
+struct ConfigurationSnapshot;
+}  // namespace nonlinear_mitc4_internal
+
 /// @brief Stores one four-node nonlinear shell trial in global coordinates.
 struct NonlinearMitc4TrialDofs {
   std::array<Vector3, 4> displacement;
@@ -129,6 +133,8 @@ class NonlinearMitc4Shell {
                                      const Vector3& force_acceleration) const;
 
  private:
+  friend struct nonlinear_mitc4_internal::ConfigurationSnapshot;
+
   /// @brief Retains validated fixed-reference data without analysis ownership.
   NonlinearMitc4Shell(std::array<Vector3, 4> coordinates,
                       std::array<Matrix, 4> initial_frames,
diff --git a/src/fesa/analysis/hht_dynamic_assembly.cpp b/src/fesa/analysis/hht_dynamic_assembly.cpp
index e0ba448..bc60030 100644
--- a/src/fesa/analysis/hht_dynamic_assembly.cpp
+++ b/src/fesa/analysis/hht_dynamic_assembly.cpp
@@ -1,4 +1,5 @@
 #include <algorithm>
+#include <cfenv>
 #include <cmath>
 #include <limits>
 #include <map>
@@ -6,6 +7,10 @@
 #include <string>
 #include <utility>
 
+#if defined(_M_X64)
+#include <xmmintrin.h>
+#endif
+
 #include "analysis/hht_dynamic_internal.h"
 #include "math/dense_blas_internal.h"
 #include "fesa/assembly/parallel_for.h"
@@ -14,6 +19,29 @@
 #include "fesa/model/source_target_resolver.h"
 
 namespace fesa::hht_internal {
+
+TrialEvaluationContext ReadTrialEvaluationContext() noexcept {
+  TrialEvaluationContext result{};
+#if defined(_M_X64)
+  result.rounding = std::fegetround();
+  result.mxcsr_control = _mm_getcsr() & 0xFFC0U;
+  result.dense_policy = dense_blas_internal::ReadScopedLocalDensePolicy();
+  result.supported = result.rounding >= 0;
+#endif
+  return result;
+}
+
+bool ReusableTrialContext(const TrialEvaluationContext& before,
+                          const TrialEvaluationContext& after) noexcept {
+  return before.supported && after.supported &&
+         before.rounding == after.rounding &&
+         before.mxcsr_control == after.mxcsr_control &&
+         (before.mxcsr_control & 0x1F80U) == 0x1F80U &&
+         before.dense_policy.blas_max_threads == 1 &&
+         after.dense_policy.blas_max_threads == 1 &&
+         before.dense_policy.dynamic == 0 && after.dense_policy.dynamic == 0;
+}
+
 namespace {
 
 /// @brief Reports a dynamic assembly or equilibrium failure.
@@ -388,6 +416,10 @@ Result<DynamicAssembly> EvaluateAssembly(
   std::vector<std::optional<NonlinearMitc4InertiaEvaluation>> inertia(
       shells.size());
   std::vector<std::optional<Status>> failures(shells.size());
+  const bool retain_constraints =
+      directional_third && !frame.is_initial && std::isfinite(frame.time);
+  std::vector<TrialEvaluationContext> evaluation_contexts(
+      retain_constraints ? shells.size() : 0U);
   parallel_for.Execute(shells.size(), [&](const std::size_t e) {
     const auto q = Gather(frame.generalized_coordinates, shells[e]);
     const auto v = Gather(frame.velocity, shells[e]);
@@ -397,12 +429,18 @@ Result<DynamicAssembly> EvaluateAssembly(
       trial.displacement[node] = Triple(q, 6U * node);
       trial.rotation_vector[node] = Triple(q, 6U * node + 3U);
     }
+    const auto before = retain_constraints ? ReadTrialEvaluationContext()
+                                           : TrialEvaluationContext{};
     auto f = EvaluateInternalResidualAndTangent(
         shells[e].internal, trial, directional_third ? &v : nullptr);
     if (!f.HasValue()) {
       failures[e] = f.GetStatus();
       return;
     }
+    if (retain_constraints) {
+      const auto after = ReadTrialEvaluationContext();
+      if (ReusableTrialContext(before, after)) evaluation_contexts[e] = after;
+    }
     auto m = shells[e].inertia.Evaluate(trial, v, a);
     if (!m.HasValue()) {
       failures[e] = m.GetStatus();
@@ -605,13 +643,52 @@ Result<DynamicAssembly> EvaluateAssembly(
       return Result<DynamicAssembly>::Failure(gradient.GetStatus());
     hidden_gradient = std::move(gradient.Value());
   }
+  std::optional<TrialConstraintData> trial_constraints;
+  if (retain_constraints) {
+    TrialConstraintData data{};
+    data.source_path = domain.SourcePath();
+    data.time = frame.time;
+    data.frame_index = frame.frame_index;
+    data.increment_index = frame.increment_index;
+    data.iteration_count = frame.iteration_count;
+    data.shells.resize(shells.size());
+    for (std::size_t e = 0U; e < shells.size(); ++e) {
+      if (!ReusableTrialContext(evaluation_contexts[e], evaluation_contexts[e]))
+        continue;
+      auto& record = data.shells[e];
+      record.element_index = shells[e].element_index;
+      record.scatter = shells[e].scatter;
+      record.configuration =
+          nonlinear_mitc4_internal::ConfigurationSnapshot::Read(
+              shells[e].internal);
+      record.evaluation_context = evaluation_contexts[e];
+      for (std::size_t i = 0U; i < 24U; ++i) {
+        record.q[i] = frame.generalized_coordinates[shells[e].scatter[i]];
+        record.v[i] = frame.velocity[shells[e].scatter[i]];
+      }
+      for (std::size_t node = 0U; node < 4U; ++node)
+        record.node_source_ids[node] =
+            domain.Nodes()[shells[e].scatter[6U * node] / 6U].source_id;
+      auto& response = *internal[e];
+      record.drilling_constraint = std::move(response.drilling_constraint);
+      record.drilling_constraint_gradient =
+          std::move(response.drilling_constraint_gradient);
+      record.drilling_constraint_hessian =
+          std::move(response.drilling_constraint_hessian);
+      record.drilling_constraint_third_directional_gradient =
+          std::move(response.drilling_constraint_third_directional_gradient);
+      record.directional_internal = true;
+    }
+    trial_constraints = std::move(data);
+  }
   return Result<DynamicAssembly>::Success(
       {std::move(frame), std::move(mass.Value()), std::move(position.Value()),
        std::move(velocity.Value()), std::move(stiffness.Value()),
        std::move(effective.Value()), std::move(metric.Value()),
        std::move(third), std::move(third_scale), std::move(rotations),
        momentum_scale, angular_scale, std::move(hidden_second),
-       std::move(hidden_second_scale), std::move(hidden_gradient)});
+       std::move(hidden_second_scale), std::move(hidden_gradient),
+       std::move(trial_constraints)});
 }
 
 Status CompleteEquilibrium(const Domain& domain, const DofManager& dofs,
diff --git a/src/fesa/analysis/hht_dynamic_internal.h b/src/fesa/analysis/hht_dynamic_internal.h
index da59a70..c199e93 100644
--- a/src/fesa/analysis/hht_dynamic_internal.h
+++ b/src/fesa/analysis/hht_dynamic_internal.h
@@ -2,6 +2,8 @@
 #define FESA_ANALYSIS_HHT_DYNAMIC_INTERNAL_H_
 
 #include <array>
+#include <cstdint>
+#include <filesystem>
 #include <optional>
 #include <vector>
 
@@ -10,6 +12,8 @@
 #include "fesa/elements/nonlinear_mitc4_inertia.h"
 #include "fesa/elements/nonlinear_mitc4_shell.h"
 #include "fesa/math/sparse_matrix.h"
+#include "elements/nonlinear_mitc4_configuration_internal.h"
+#include "math/dense_blas_internal.h"
 
 namespace fesa {
 class LinearSolver;
@@ -25,6 +29,49 @@ struct RuntimeShell {
   NonlinearMitc4Inertia inertia;
 };
 
+/// @brief Captures only controls used by the current MSVC x64 local evaluator.
+struct TrialEvaluationContext {
+  int rounding{-1};
+  unsigned int mxcsr_control{0U};
+  dense_blas_internal::LocalDensePolicy dense_policy{0, -1};
+  bool supported{false};
+};
+
+/// @brief Queries metadata without changing FP controls or the restored TLS.
+TrialEvaluationContext ReadTrialEvaluationContext() noexcept;
+
+/// @brief Allows only masked, stable, single-worker nondynamic local policy.
+bool ReusableTrialContext(const TrialEvaluationContext& before,
+                          const TrialEvaluationContext& after) noexcept;
+
+/// @brief Owns only complete directional constraint data for one local trial.
+struct DirectionalShellConstraintData {
+  EntityIndex element_index{0U};
+  std::array<std::size_t, 24> scatter{};
+  std::array<SourceEntityId, 4> node_source_ids{};
+  nonlinear_mitc4_internal::ConfigurationSnapshot configuration;
+  std::array<double, 24> q{};
+  std::array<double, 24> v{};
+  TrialEvaluationContext evaluation_context;
+  bool directional_internal{false};
+  Vector drilling_constraint{0U};
+  Matrix drilling_constraint_gradient{0U, 0U};
+  std::array<Matrix, 4> drilling_constraint_hessian{
+      Matrix{0U, 0U}, Matrix{0U, 0U}, Matrix{0U, 0U}, Matrix{0U, 0U}};
+  std::array<Vector, 4> drilling_constraint_third_directional_gradient{
+      Vector{0U}, Vector{0U}, Vector{0U}, Vector{0U}};
+};
+
+/// @brief Travels with one complete assembly, never accepted frame/history.
+struct TrialConstraintData {
+  std::filesystem::path source_path;
+  double time{0.0};
+  std::uint32_t frame_index{0U};
+  std::uint32_t increment_index{0U};
+  std::uint32_t iteration_count{0U};
+  std::vector<DirectionalShellConstraintData> shells;
+};
+
 /// @brief Stores a complete trial with independently assembled operators.
 struct DynamicAssembly {
   DynamicAcceptedFrameState frame;
@@ -43,6 +90,7 @@ struct DynamicAssembly {
   Vector hidden_second_scale{0U};
   // Canonical scalar drilling-constraint derivative, indexed by global node.
   std::optional<SparseMatrix> hidden_gradient;
+  std::optional<TrialConstraintData> trial_constraints;
 };
 
 /// @brief Builds checked shell evaluators in stable source order.
diff --git a/src/fesa/analysis/hht_reduced_operators.cpp b/src/fesa/analysis/hht_reduced_operators.cpp
index 3ff4cfd..a34cb5a 100644
--- a/src/fesa/analysis/hht_reduced_operators.cpp
+++ b/src/fesa/analysis/hht_reduced_operators.cpp
@@ -60,6 +60,88 @@ Vector Local(const Vector& full,
   return local;
 }
 
+/// @brief Preserves the exact floating representation, including signed zero.
+bool SameBits(const double left, const double right) {
+  return std::memcmp(&left, &right, sizeof(double)) == 0;
+}
+
+/// @brief Compares semantic and original source identity without object keys.
+bool SameSource(const SourceEntityId& left, const SourceEntityId& right) {
+  return left.instance_name == right.instance_name &&
+         left.source_label == right.source_label &&
+         left.source_label_text == right.source_label_text;
+}
+
+/// @brief Finds only the current complete directional response, otherwise miss.
+const hht_internal::DirectionalShellConstraintData* MatchingConstraints(
+    const Domain& domain, const hht_internal::RuntimeShell& shell,
+    const hht_internal::DynamicAssembly& assembly, const std::size_t index,
+    const std::size_t shell_count, const Vector& q, const Vector& v) {
+  if (assembly.frame.is_initial || !assembly.trial_constraints.has_value())
+    return nullptr;
+  const auto& owner = *assembly.trial_constraints;
+  const auto& frame = assembly.frame;
+  if (owner.shells.size() != shell_count || index >= owner.shells.size() ||
+      owner.source_path != domain.SourcePath() ||
+      !std::isfinite(owner.time) || !std::isfinite(frame.time) ||
+      !SameBits(owner.time, frame.time) ||
+      owner.frame_index != frame.frame_index ||
+      owner.increment_index != frame.increment_index ||
+      owner.iteration_count != frame.iteration_count)
+    return nullptr;
+  const auto& record = owner.shells[index];
+  if (!record.directional_internal ||
+      record.element_index != shell.element_index ||
+      record.scatter != shell.scatter ||
+      !hht_internal::ReusableTrialContext(
+          record.evaluation_context,
+          hht_internal::ReadTrialEvaluationContext()))
+    return nullptr;
+  const auto configuration =
+      nonlinear_mitc4_internal::ConfigurationSnapshot::Read(shell.internal);
+  if (record.configuration.source.file != configuration.source.file ||
+      record.configuration.source.line != configuration.source.line ||
+      record.configuration.identity != configuration.identity)
+    return nullptr;
+  for (std::size_t i = 0U; i < configuration.values.size(); ++i)
+    if (!std::isfinite(record.configuration.values[i]) ||
+        !std::isfinite(configuration.values[i]) ||
+        !SameBits(record.configuration.values[i], configuration.values[i]))
+      return nullptr;
+  for (std::size_t i = 0U; i < 24U; ++i)
+    if (!std::isfinite(record.q[i]) || !std::isfinite(q[i]) ||
+        !std::isfinite(record.v[i]) || !std::isfinite(v[i]) ||
+        !SameBits(record.q[i], q[i]) || !SameBits(record.v[i], v[i]))
+      return nullptr;
+  for (std::size_t node = 0U; node < 4U; ++node) {
+    const auto global_node = shell.scatter[6U * node] / 6U;
+    if (global_node >= domain.Nodes().size() ||
+        !SameSource(record.node_source_ids[node],
+                    domain.Nodes()[global_node].source_id))
+      return nullptr;
+  }
+  if (record.drilling_constraint.Size() != 4U ||
+      record.drilling_constraint_gradient.Rows() != 4U ||
+      record.drilling_constraint_gradient.Columns() != 24U)
+    return nullptr;
+  for (std::size_t node = 0U; node < 4U; ++node) {
+    const auto& hessian = record.drilling_constraint_hessian[node];
+    const auto& third =
+        record.drilling_constraint_third_directional_gradient[node];
+    if (hessian.Rows() != 24U || hessian.Columns() != 24U ||
+        third.Size() != 24U || !std::isfinite(record.drilling_constraint[node]))
+      return nullptr;
+    for (std::size_t i = 0U; i < 24U; ++i) {
+      if (!std::isfinite(record.drilling_constraint_gradient(node, i)) ||
+          !std::isfinite(third[i]))
+        return nullptr;
+      for (std::size_t j = 0U; j < 24U; ++j)
+        if (!std::isfinite(hessian(i, j))) return nullptr;
+    }
+  }
+  return &record;
+}
+
 NonlinearMitc4TrialDofs Trial(const Vector& local) {
   NonlinearMitc4TrialDofs trial{};
   for (std::size_t node = 0U; node < 4U; ++node) {
@@ -443,32 +525,46 @@ Result<ConstraintOperators> EvaluateConstraintOperators(
     node_row[chart.null_nodes[row]] = row;
   }
   std::vector<bool> external_done(domain.Nodes().size(), false);
+  std::size_t shell_index = 0U;
   for (const auto& shell : shells) {
     const auto q = Local(assembly.frame.generalized_coordinates, shell);
     const auto v = Local(assembly.frame.velocity, shell);
-    const auto internal = EvaluateInternalResidualAndTangent(shell.internal,
-                                                              Trial(q), &v);
-    if (!internal.HasValue())
-      return Result<ConstraintOperators>::Failure(internal.GetStatus());
+    const auto* saved = MatchingConstraints(domain, shell, assembly,
+                                            shell_index++, shells.size(), q, v);
+    std::optional<NonlinearMitc4InternalEquilibrium> fresh;
+    if (saved == nullptr) {
+      auto internal =
+          EvaluateInternalResidualAndTangent(shell.internal, Trial(q), &v);
+      if (!internal.HasValue())
+        return Result<ConstraintOperators>::Failure(internal.GetStatus());
+      fresh = std::move(internal.Value());
+    }
+    const auto& constraint = saved != nullptr ? saved->drilling_constraint
+                                              : fresh->drilling_constraint;
+    const auto& gradient_data = saved != nullptr
+                                    ? saved->drilling_constraint_gradient
+                                    : fresh->drilling_constraint_gradient;
+    const auto& third_data =
+        saved != nullptr
+            ? saved->drilling_constraint_third_directional_gradient
+            : fresh->drilling_constraint_third_directional_gradient;
+    const auto& hessian_data = saved != nullptr
+                                   ? saved->drilling_constraint_hessian
+                                   : fresh->drilling_constraint_hessian;
     for (std::size_t local_node = 0U; local_node < 4U; ++local_node) {
       const auto global_node = shell.scatter[6U * local_node] / 6U;
       if (global_node >= node_row.size() || node_row[global_node] == rows)
         continue;
       const auto row = node_row[global_node];
-      result.rows[row].value +=
-          internal.Value().drilling_constraint[local_node];
+      result.rows[row].value += constraint[local_node];
       for (std::size_t i = 0U; i < 24U; ++i) {
         const auto global_i = shell.scatter[i];
-        const double gradient =
-            internal.Value().drilling_constraint_gradient(local_node, i);
-        const double third = internal.Value()
-                                 .drilling_constraint_third_directional_gradient
-                                 [local_node][i];
+        const double gradient = gradient_data(local_node, i);
+        const double third = third_data[local_node][i];
         if (gradient != 0.0) gradients[row][global_i] += gradient;
         if (third != 0.0) third_gradients[row][global_i] += third;
         for (std::size_t j = 0U; j < 24U; ++j) {
-          const double hessian =
-              internal.Value().drilling_constraint_hessian[local_node](i, j);
+          const double hessian = hessian_data[local_node](i, j);
           if (hessian != 0.0)
             hessians[row][{global_i, shell.scatter[j]}] += hessian;
         }
diff --git a/src/fesa/elements/nonlinear_mitc4_configuration_internal.h b/src/fesa/elements/nonlinear_mitc4_configuration_internal.h
new file mode 100644
index 0000000..618eebc
--- /dev/null
+++ b/src/fesa/elements/nonlinear_mitc4_configuration_internal.h
@@ -0,0 +1,24 @@
+#ifndef FESA_SRC_FESA_ELEMENTS_NONLINEAR_MITC4_CONFIGURATION_INTERNAL_H_
+#define FESA_SRC_FESA_ELEMENTS_NONLINEAR_MITC4_CONFIGURATION_INTERNAL_H_
+
+#include <array>
+#include <string>
+
+#include "fesa/elements/nonlinear_mitc4_shell.h"
+
+namespace fesa::nonlinear_mitc4_internal {
+
+/// @brief Owns reference values without depending on an analysis or identity
+/// key.
+struct ConfigurationSnapshot {
+  std::array<double, 64> values{};
+  SourceLocation source{};
+  std::string identity;
+
+  /// @brief Copies all immutable inputs of the internal equilibrium evaluator.
+  static ConfigurationSnapshot Read(const NonlinearMitc4Shell& element);
+};
+
+}  // namespace fesa::nonlinear_mitc4_internal
+
+#endif  // FESA_SRC_FESA_ELEMENTS_NONLINEAR_MITC4_CONFIGURATION_INTERNAL_H_
diff --git a/src/fesa/elements/nonlinear_mitc4_shell.cpp b/src/fesa/elements/nonlinear_mitc4_shell.cpp
index c025157..e88ea3b 100644
--- a/src/fesa/elements/nonlinear_mitc4_shell.cpp
+++ b/src/fesa/elements/nonlinear_mitc4_shell.cpp
@@ -10,9 +10,34 @@
 #include <utility>
 
 #include "fesa/elements/finite_rotation.h"
+#include "elements/nonlinear_mitc4_configuration_internal.h"
 #include "math/dense_blas_internal.h"
 
 namespace fesa {
+
+nonlinear_mitc4_internal::ConfigurationSnapshot
+nonlinear_mitc4_internal::ConfigurationSnapshot::Read(
+    const NonlinearMitc4Shell& element) {
+  ConfigurationSnapshot result{};
+  std::size_t index = 0U;
+  for (const auto& coordinates : element.coordinates_)
+    for (std::size_t c = 0U; c < 3U; ++c)
+      result.values[index++] = coordinates[c];
+  for (const auto& frame : element.initial_frames_)
+    for (std::size_t i = 0U; i < 3U; ++i)
+      for (std::size_t j = 0U; j < 3U; ++j)
+        result.values[index++] = frame(i, j);
+  for (const auto& director : element.initial_directors_)
+    for (std::size_t c = 0U; c < 3U; ++c) result.values[index++] = director[c];
+  result.values[index++] = element.thickness_;
+  result.values[index++] = element.youngs_modulus_;
+  result.values[index++] = element.poisson_ratio_;
+  result.values[index] = element.drilling_stiffness_;
+  result.source = element.source_location_;
+  result.identity = element.identity_;
+  return result;
+}
+
 namespace {
 
 constexpr std::size_t kNodeCount = 4U;
diff --git a/src/fesa/math/dense_blas_internal.cpp b/src/fesa/math/dense_blas_internal.cpp
index a544715..ed5de9d 100644
--- a/src/fesa/math/dense_blas_internal.cpp
+++ b/src/fesa/math/dense_blas_internal.cpp
@@ -40,6 +40,11 @@ ScopedLocalDenseThreads::~ScopedLocalDenseThreads() {
   if (restore_default_) static_cast<void>(mkl_set_num_threads_local(0));
 }
 
+LocalDensePolicy ReadScopedLocalDensePolicy() noexcept {
+  const ScopedLocalDenseThreads scope{};
+  return {mkl_domain_get_max_threads(MKL_DOMAIN_BLAS), mkl_get_dynamic()};
+}
+
 bool CholeskyLowerAndInverse(const Matrix& matrix, Matrix& lower,
                              Matrix& inverse_lower, CholeskyFailure* failure) {
   if (failure != nullptr) *failure = CholeskyFailure::kNone;
diff --git a/src/fesa/math/dense_blas_internal.h b/src/fesa/math/dense_blas_internal.h
index ea3b107..b2d4481 100644
--- a/src/fesa/math/dense_blas_internal.h
+++ b/src/fesa/math/dense_blas_internal.h
@@ -1,10 +1,10 @@
 #ifndef FESA_SRC_FESA_MATH_DENSE_BLAS_INTERNAL_H_
 #define FESA_SRC_FESA_MATH_DENSE_BLAS_INTERNAL_H_
 
-#include <mkl.h>
-
 #include <cstddef>
 
+#include <mkl.h>
+
 #include "fesa/core/status.h"
 #include "fesa/math/matrix.h"
 #include "fesa/math/vector.h"
@@ -40,6 +40,16 @@ class ScopedLocalDenseThreads {
   bool restore_default_{false};
 };
 
+/// @brief Records requested backend policy, without claiming actual threads.
+struct LocalDensePolicy {
+  int blas_max_threads;
+  int dynamic;
+};
+
+/// @brief Reads BLAS policy inside the same restored scope as local elements.
+/// @note No process-wide policy is changed; positive caller TLS is retained.
+LocalDensePolicy ReadScopedLocalDensePolicy() noexcept;
+
 /// @brief Converts a dense storage length to the private MKL integer type.
 /// @return The converted length or an uncategorized overflow failure.
 Result<MKL_INT> ToMklSize(std::size_t size);
diff --git a/tests/unit/analysis/hht_reduced_shell_test.cpp b/tests/unit/analysis/hht_reduced_shell_test.cpp
index 57f29a0..d8ce519 100644
--- a/tests/unit/analysis/hht_reduced_shell_test.cpp
+++ b/tests/unit/analysis/hht_reduced_shell_test.cpp
@@ -5,6 +5,8 @@
 #include <cmath>
 #include <cfenv>
 #include <cstddef>
+#include <cstring>
+#include <functional>
 #include <iostream>
 #include <memory>
 #include <limits>
@@ -19,6 +21,7 @@
 #endif
 
 #include "analysis/hht_reduced_internal.h"
+#include "math/dense_blas_internal.h"
 #include "fesa/analysis/analysis_model.h"
 #include "fesa/analysis/hht_time_integration.h"
 #include "fesa/assembly/parallel_for.h"
@@ -26,6 +29,71 @@
 
 namespace {
 
+class RestoreTrialEnvironment {
+ public:
+  RestoreTrialEnvironment()
+      : rounding_(std::fegetround()),
+        dynamic_(mkl_get_dynamic()),
+        tls_(mkl_set_num_threads_local(0)) {
+#if defined(_M_X64)
+    mxcsr_ = _mm_getcsr();
+    _mm_setcsr((_mm_getcsr() | 0x1F80U) & ~0x8040U);
+#endif
+    static_cast<void>(std::fesetround(FE_TONEAREST));
+    mkl_set_dynamic(0);
+  }
+  ~RestoreTrialEnvironment() {
+    mkl_set_dynamic(dynamic_);
+    static_cast<void>(mkl_set_num_threads_local(tls_));
+    static_cast<void>(std::fesetround(rounding_));
+#if defined(_M_X64)
+    _mm_setcsr(mxcsr_);
+#endif
+  }
+
+ private:
+  int rounding_;
+  int dynamic_;
+  int tls_;
+#if defined(_M_X64)
+  unsigned int mxcsr_;
+#endif
+};
+
+void ExpectSameBits(const double left, const double right) {
+  EXPECT_EQ(std::memcmp(&left, &right, sizeof(double)), 0);
+}
+
+void ExpectSameOperators(
+    const fesa::hht_reduced_internal::ConstraintOperators& left,
+    const fesa::hht_reduced_internal::ConstraintOperators& right) {
+  ASSERT_EQ(left.rows.size(), right.rows.size());
+  for (std::size_t row = 0U; row < left.rows.size(); ++row) {
+    const auto& a = left.rows[row];
+    const auto& b = right.rows[row];
+    ExpectSameBits(a.value, b.value);
+    ExpectSameBits(a.value_scale, b.value_scale);
+    ExpectSameBits(a.time_first, b.time_first);
+    ExpectSameBits(a.time_second, b.time_second);
+    for (const auto& pair : {std::make_pair(&a.gradient, &b.gradient),
+                             std::make_pair(&a.time_gradient, &b.time_gradient),
+                             std::make_pair(&a.third_directional_gradient,
+                                            &b.third_directional_gradient)}) {
+      ASSERT_EQ(pair.first->size(), pair.second->size());
+      for (std::size_t i = 0U; i < pair.first->size(); ++i) {
+        EXPECT_EQ((*pair.first)[i].dof, (*pair.second)[i].dof);
+        ExpectSameBits((*pair.first)[i].value, (*pair.second)[i].value);
+      }
+    }
+    ASSERT_EQ(a.hessian.size(), b.hessian.size());
+    for (std::size_t i = 0U; i < a.hessian.size(); ++i) {
+      EXPECT_EQ(a.hessian[i].row, b.hessian[i].row);
+      EXPECT_EQ(a.hessian[i].column, b.hessian[i].column);
+      ExpectSameBits(a.hessian[i].value, b.hessian[i].value);
+    }
+  }
+}
+
 struct Fixture {
   std::unique_ptr<fesa::Domain> domain;
   fesa::DofManager dofs;
@@ -394,6 +462,480 @@ TEST(HhtReducedChart, InvertibleGraphDoesNotCertifySelectorTransversality) {
       assembly, chart.Value(), solver).HasValue());
 }
 
+TEST(HhtReducedOperators,
+     CompleteTrialConstraintDataMatchesFreshAndOwnsCopies) {
+  RestoreTrialEnvironment restore;
+  const auto fixture = MakeFixture(false, true);
+  const auto shells =
+      fesa::hht_internal::BuildRuntimeShells(*fixture.domain, fixture.dofs);
+  ASSERT_TRUE(shells.HasValue());
+  const fesa::Vector zero(fixture.dofs.FullDofCount());
+  auto q = zero;
+  auto v = zero;
+  auto force = zero;
+  auto rate = zero;
+  auto acceleration = zero;
+  for (std::size_t i = 0U; i < zero.Size(); ++i) {
+    q[i] = 0.001 * static_cast<double>((i % 5U) + 1U);
+    v[i] = 0.002 * static_cast<double>((i % 7U) + 1U);
+    if (i % 6U >= 3U) {
+      force[i] = 0.03;
+      rate[i] = -0.02;
+      acceleration[i] = 0.01;
+    }
+  }
+  auto assembled = Assemble(fixture, shells.Value(), q, v, zero, force, true);
+  ASSERT_TRUE(assembled.HasValue());
+  ASSERT_TRUE(assembled.Value().trial_constraints.has_value());
+  ASSERT_EQ(assembled.Value().trial_constraints->shells.size(),
+            shells.Value().size());
+  const auto chart = fesa::hht_reduced_internal::BuildFixedChart(
+      fixture.dofs, assembled.Value().rotations);
+  ASSERT_TRUE(chart.HasValue());
+  for (std::size_t e = 0U; e < shells.Value().size(); ++e) {
+    const auto& saved = assembled.Value().trial_constraints->shells[e];
+    ASSERT_TRUE(saved.directional_internal);
+    fesa::NonlinearMitc4TrialDofs trial{};
+    fesa::Vector direction{24U};
+    for (std::size_t node = 0U; node < 4U; ++node) {
+      const auto first = 6U * node;
+      trial.displacement[node] =
+          fesa::Vector3{saved.q[first], saved.q[first + 1U], saved.q[first + 2U]};
+      trial.rotation_vector[node] = fesa::Vector3{
+          saved.q[first + 3U], saved.q[first + 4U], saved.q[first + 5U]};
+    }
+    for (std::size_t i = 0U; i < 24U; ++i) direction[i] = saved.v[i];
+    const auto response = fesa::EvaluateInternalResidualAndTangent(
+        shells.Value()[e].internal, trial, &direction);
+    ASSERT_TRUE(response.HasValue());
+    for (std::size_t node = 0U; node < 4U; ++node) {
+      ExpectSameBits(saved.drilling_constraint[node],
+                     response.Value().drilling_constraint[node]);
+      for (std::size_t i = 0U; i < 24U; ++i) {
+        ExpectSameBits(saved.drilling_constraint_gradient(node, i),
+                       response.Value().drilling_constraint_gradient(node, i));
+        ExpectSameBits(
+            saved.drilling_constraint_third_directional_gradient[node][i],
+            response.Value()
+                .drilling_constraint_third_directional_gradient[node][i]);
+        for (std::size_t j = 0U; j < 24U; ++j)
+          ExpectSameBits(
+              saved.drilling_constraint_hessian[node](i, j),
+              response.Value().drilling_constraint_hessian[node](i, j));
+      }
+    }
+  }
+  const auto evaluate = [&](const fesa::hht_internal::DynamicAssembly& value) {
+    return fesa::hht_reduced_internal::EvaluateConstraintOperators(
+        *fixture.domain, fixture.dofs, shells.Value(), value, chart.Value(),
+        rate, acceleration);
+  };
+  auto fresh = assembled.Value();
+  fresh.trial_constraints.reset();
+  const auto reference = evaluate(fresh);
+  const auto reused = evaluate(assembled.Value());
+  ASSERT_TRUE(reference.HasValue());
+  ASSERT_TRUE(reused.HasValue());
+  ExpectSameOperators(reused.Value(), reference.Value());
+  auto copy = assembled.Value();
+  copy.trial_constraints->shells[0U].drilling_constraint[0U] += 7.0;
+  // Test-only finite marker proves the selected route actually reads its owner.
+  const auto marker = evaluate(copy);
+  ASSERT_TRUE(marker.HasValue());
+  EXPECT_NE(marker.Value().rows[0U].value, reused.Value().rows[0U].value);
+  EXPECT_NE(
+      copy.trial_constraints->shells[0U].drilling_constraint[0U],
+      assembled.Value().trial_constraints->shells[0U].drilling_constraint[0U]);
+  auto moved = std::move(assembled.Value());
+  const auto moved_result = evaluate(moved);
+  ASSERT_TRUE(moved_result.HasValue());
+  ExpectSameOperators(moved_result.Value(), reference.Value());
+  fesa::DynamicAcceptedFrameState frame{};
+  frame.generalized_coordinates = q;
+  frame.velocity = v;
+  frame.acceleration = zero;
+  frame.algorithmic_acceleration = zero;
+  frame.external_force = force;
+  const auto parameters = fesa::MakeHhtParameters(-0.05);
+  ASSERT_TRUE(parameters.HasValue());
+  fesa::TbbParallelFor parallel;
+  const auto tbb = fesa::hht_internal::EvaluateAssembly(
+      *fixture.domain, fixture.dofs, shells.Value(), frame, zero, 0.1,
+      parameters.Value(), parallel, true);
+  ASSERT_TRUE(tbb.HasValue());
+  const auto tbb_result = evaluate(tbb.Value());
+  ASSERT_TRUE(tbb_result.HasValue());
+  ExpectSameOperators(tbb_result.Value(), reference.Value());
+}
+
+TEST(HhtReducedOperators,
+     ChangedTrialConstraintContextFallsBackInOriginalPosition) {
+  RestoreTrialEnvironment restore;
+  const auto fixture = MakeFixture(false);
+  const auto shells =
+      fesa::hht_internal::BuildRuntimeShells(*fixture.domain, fixture.dofs);
+  ASSERT_TRUE(shells.HasValue());
+  const fesa::Vector zero(fixture.dofs.FullDofCount());
+  const auto assembled =
+      Assemble(fixture, shells.Value(), zero, zero, zero, zero, true);
+  ASSERT_TRUE(assembled.HasValue());
+  ASSERT_TRUE(assembled.Value().trial_constraints.has_value());
+  ASSERT_TRUE(
+      assembled.Value().trial_constraints->shells[0U].directional_internal);
+  const auto chart = fesa::hht_reduced_internal::BuildFixedChart(
+      fixture.dofs, assembled.Value().rotations);
+  ASSERT_TRUE(chart.HasValue());
+  const auto evaluate = [&](const fesa::hht_internal::DynamicAssembly& value) {
+    return fesa::hht_reduced_internal::EvaluateConstraintOperators(
+        *fixture.domain, fixture.dofs, shells.Value(), value, chart.Value(),
+        zero, zero);
+  };
+  using Assembly = fesa::hht_internal::DynamicAssembly;
+  std::vector<std::function<void(Assembly&)>> changes{
+      [](Assembly& a) { a.frame.generalized_coordinates[2U] = 0.001; },
+      [](Assembly& a) { a.frame.velocity[3U] = 0.003; },
+      [](Assembly& a) { a.frame.time = 0.1; },
+      [](Assembly& a) { ++a.frame.frame_index; },
+      [](Assembly& a) { ++a.frame.increment_index; },
+      [](Assembly& a) { ++a.frame.iteration_count; },
+      [](Assembly& a) { a.frame.is_initial = true; },
+      [](Assembly& a) { a.trial_constraints->source_path = "different.inp"; },
+      [](Assembly& a) { ++a.trial_constraints->shells[0U].element_index; },
+      [](Assembly& a) { ++a.trial_constraints->shells[0U].scatter[0U]; },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].directional_internal = false;
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].node_source_ids[0U].instance_name +=
+            "x";
+      },
+      [](Assembly& a) {
+        ++a.trial_constraints->shells[0U].node_source_ids[0U].source_label;
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].node_source_ids[0U].source_label_text +=
+            "x";
+      },
+      [](Assembly& a) {
+        ++a.trial_constraints->shells[0U].configuration.source.line;
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].configuration.source.file =
+            "different.inp";
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].configuration.identity += "x";
+      },
+      [](Assembly& a) { a.trial_constraints->shells[0U].q[0U] = -0.0; },
+      [](Assembly& a) { a.trial_constraints->shells[0U].v[0U] = -0.0; },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].drilling_constraint_gradient =
+            fesa::Matrix{0U, 0U};
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].drilling_constraint_hessian[2U] =
+            fesa::Matrix{0U, 0U};
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U]
+            .drilling_constraint_third_directional_gradient[1U] =
+            fesa::Vector{0U};
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].drilling_constraint_hessian[0U](
+            0U, 0U) = std::numeric_limits<double>::infinity();
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U]
+            .evaluation_context.dense_policy.blas_max_threads = 2;
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U]
+            .evaluation_context.dense_policy.dynamic = 1;
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U]
+            .evaluation_context.dense_policy.dynamic = -1;
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].evaluation_context.mxcsr_control ^=
+            0x8000U;
+      },
+      [](Assembly& a) {
+        a.trial_constraints->shells[0U].evaluation_context.supported = false;
+      }};
+  for (std::size_t i = 0U; i < 64U; ++i)
+    changes.push_back([i](Assembly& a) {
+      a.trial_constraints->shells[0U].configuration.values[i] += 0.125;
+    });
+  for (const double invalid : {std::numeric_limits<double>::quiet_NaN(),
+                                std::numeric_limits<double>::infinity(),
+                                -std::numeric_limits<double>::infinity()})
+    changes.push_back([invalid](Assembly& a) {
+      a.trial_constraints->shells[0U].configuration.values[60U] = invalid;
+    });
+  for (std::size_t i = 0U; i < changes.size(); ++i) {
+    SCOPED_TRACE(i);
+    auto candidate = assembled.Value();
+    candidate.trial_constraints->shells[0U].drilling_constraint[0U] = 17.0;
+    changes[i](candidate);
+    auto fresh = candidate;
+    fresh.trial_constraints.reset();
+    const auto reference = evaluate(fresh);
+    const auto actual = evaluate(candidate);
+    ASSERT_TRUE(reference.HasValue());
+    ASSERT_TRUE(actual.HasValue());
+    ExpectSameOperators(actual.Value(), reference.Value());
+  }
+  for (std::size_t kind = 0U; kind < 2U; ++kind) {
+    auto candidate = assembled.Value();
+    if (kind == 0U) candidate.trial_constraints->shells.clear();
+    if (kind == 1U) candidate.trial_constraints.reset();
+    auto fresh = assembled.Value();
+    fresh.trial_constraints.reset();
+    const auto reference = evaluate(fresh);
+    const auto actual = evaluate(candidate);
+    ASSERT_TRUE(reference.HasValue());
+    ASSERT_TRUE(actual.HasValue());
+    ExpectSameOperators(actual.Value(), reference.Value());
+  }
+  // Change the actual consumer environment, preserving the original fallback.
+  for (std::size_t mode = 0U; mode < 5U; ++mode) {
+    SCOPED_TRACE(mode);
+    auto candidate = assembled.Value();
+    candidate.trial_constraints->shells[0U].drilling_constraint[0U] = 17.0;
+    auto fresh = candidate;
+    fresh.trial_constraints.reset();
+#if defined(_M_X64)
+    const auto csr = _mm_getcsr();
+    if (mode == 0U) _mm_setcsr(csr ^ 0x8000U);
+    if (mode == 1U) _mm_setcsr(csr ^ 0x0040U);
+#endif
+    const int rounding = std::fegetround();
+    if (mode == 2U) static_cast<void>(std::fesetround(FE_DOWNWARD));
+    if (mode == 3U) static_cast<void>(mkl_set_num_threads_local(2));
+    if (mode == 4U) mkl_set_dynamic(1);
+    const auto reference = evaluate(fresh);
+    const auto actual = evaluate(candidate);
+    if (mode == 4U) mkl_set_dynamic(0);
+    if (mode == 3U) EXPECT_EQ(mkl_set_num_threads_local(0), 2);
+    static_cast<void>(std::fesetround(rounding));
+#if defined(_M_X64)
+    _mm_setcsr(csr);
+#endif
+    ASSERT_TRUE(reference.HasValue());
+    ASSERT_TRUE(actual.HasValue());
+    ExpectSameOperators(actual.Value(), reference.Value());
+  }
+  auto failed_trial = assembled.Value();
+  failed_trial.frame.generalized_coordinates[0U] =
+      std::numeric_limits<double>::infinity();
+  auto fresh_failure = failed_trial;
+  fresh_failure.trial_constraints.reset();
+  const auto failed = evaluate(failed_trial);
+  const auto original = evaluate(fresh_failure);
+  ASSERT_FALSE(failed.HasValue());
+  ASSERT_FALSE(original.HasValue());
+  ASSERT_EQ(failed.GetStatus().Diagnostics().size(),
+            original.GetStatus().Diagnostics().size());
+  EXPECT_EQ(failed.GetStatus().Diagnostics()[0U].code,
+            original.GetStatus().Diagnostics()[0U].code);
+  EXPECT_EQ(failed.GetStatus().Diagnostics()[0U].message,
+            original.GetStatus().Diagnostics()[0U].message);
+  const auto rerun = evaluate(assembled.Value());
+  auto fresh = assembled.Value();
+  fresh.trial_constraints.reset();
+  const auto reference = evaluate(fresh);
+  ASSERT_TRUE(rerun.HasValue());
+  ASSERT_TRUE(reference.HasValue());
+  ExpectSameOperators(rerun.Value(), reference.Value());
+}
+
+TEST(HhtReducedOperators, TrialContextControlsAndInitialFalseFailureLifetime) {
+  RestoreTrialEnvironment restore;
+  const auto context = fesa::hht_internal::ReadTrialEvaluationContext();
+  ASSERT_TRUE(fesa::hht_internal::ReusableTrialContext(context, context));
+  for (const unsigned int bit : {0x0040U, 0x8000U, 0x2000U, 0x0080U}) {
+    auto changed = context;
+    changed.mxcsr_control ^= bit;
+    EXPECT_FALSE(fesa::hht_internal::ReusableTrialContext(context, changed));
+  }
+  auto unmasked = context;
+  unmasked.mxcsr_control &= ~0x0080U;
+  EXPECT_FALSE(fesa::hht_internal::ReusableTrialContext(unmasked, unmasked));
+  static_cast<void>(mkl_set_num_threads_local(2));
+  const auto positive = fesa::hht_internal::ReadTrialEvaluationContext();
+  EXPECT_FALSE(fesa::hht_internal::ReusableTrialContext(positive, positive));
+  EXPECT_EQ(mkl_set_num_threads_local(0), 2);
+  mkl_set_dynamic(1);
+  const auto dynamic = fesa::hht_internal::ReadTrialEvaluationContext();
+  EXPECT_FALSE(fesa::hht_internal::ReusableTrialContext(dynamic, dynamic));
+  mkl_set_dynamic(0);
+  const auto fixture = MakeFixture(false);
+  const auto shells =
+      fesa::hht_internal::BuildRuntimeShells(*fixture.domain, fixture.dofs);
+  ASSERT_TRUE(shells.HasValue());
+  const fesa::Vector zero(fixture.dofs.FullDofCount());
+  const auto position =
+      Assemble(fixture, shells.Value(), zero, zero, zero, zero, false);
+  ASSERT_TRUE(position.HasValue());
+  EXPECT_FALSE(position.Value().trial_constraints.has_value());
+  mkl_set_dynamic(1);
+  const auto dynamic_trial =
+      Assemble(fixture, shells.Value(), zero, zero, zero, zero, true);
+  mkl_set_dynamic(0);
+  ASSERT_TRUE(dynamic_trial.HasValue());
+  ASSERT_TRUE(dynamic_trial.Value().trial_constraints.has_value());
+  EXPECT_FALSE(
+      dynamic_trial.Value().trial_constraints->shells[0U].directional_internal);
+  static_cast<void>(mkl_set_num_threads_local(2));
+  const auto positive_trial =
+      Assemble(fixture, shells.Value(), zero, zero, zero, zero, true);
+  EXPECT_EQ(mkl_set_num_threads_local(0), 2);
+  ASSERT_TRUE(positive_trial.HasValue());
+  ASSERT_TRUE(positive_trial.Value().trial_constraints.has_value());
+  EXPECT_FALSE(positive_trial.Value()
+                   .trial_constraints->shells[0U]
+                   .directional_internal);
+  fesa::DynamicAcceptedFrameState frame{};
+  frame.is_initial = true;
+  for (auto* vector :
+       {&frame.generalized_coordinates, &frame.velocity, &frame.acceleration,
+        &frame.algorithmic_acceleration, &frame.external_force})
+    *vector = zero;
+  fesa::SerialParallelFor parallel;
+  const auto parameters = fesa::MakeHhtParameters(-0.05);
+  ASSERT_TRUE(parameters.HasValue());
+  const auto initial = fesa::hht_internal::EvaluateAssembly(
+      *fixture.domain, fixture.dofs, shells.Value(), frame, zero, 0.1,
+      parameters.Value(), parallel, true);
+  ASSERT_TRUE(initial.HasValue());
+  EXPECT_FALSE(initial.Value().trial_constraints.has_value());
+  auto invalid = zero;
+  invalid[0U] = std::numeric_limits<double>::quiet_NaN();
+  const auto failure =
+      Assemble(fixture, shells.Value(), invalid, zero, zero, zero, true);
+  EXPECT_FALSE(failure.HasValue());
+  const auto current =
+      Assemble(fixture, shells.Value(), zero, zero, zero, zero, true);
+  const auto next =
+      Assemble(fixture, shells.Value(), zero, zero, zero, zero, true);
+  ASSERT_TRUE(current.HasValue());
+  ASSERT_TRUE(next.HasValue());
+  ASSERT_EQ(current.Value().trial_constraints->shells.size(),
+            shells.Value().size());
+  ASSERT_EQ(next.Value().trial_constraints->shells.size(),
+            shells.Value().size());
+  EXPECT_NE(&current.Value().trial_constraints->shells[0U],
+            &next.Value().trial_constraints->shells[0U]);
+}
+
+TEST(HhtReducedOperators, NonfiniteMatchingTrialKeysPreserveOriginalFailure) {
+  RestoreTrialEnvironment restore;
+  const auto fixture = MakeFixture(false);
+  const auto shells =
+      fesa::hht_internal::BuildRuntimeShells(*fixture.domain, fixture.dofs);
+  ASSERT_TRUE(shells.HasValue());
+  const fesa::Vector zero(fixture.dofs.FullDofCount());
+  const auto assembled =
+      Assemble(fixture, shells.Value(), zero, zero, zero, zero, true);
+  ASSERT_TRUE(assembled.HasValue());
+  ASSERT_TRUE(assembled.Value().trial_constraints.has_value());
+  ASSERT_TRUE(
+      assembled.Value().trial_constraints->shells[0U].directional_internal);
+  const auto chart = fesa::hht_reduced_internal::BuildFixedChart(
+      fixture.dofs, assembled.Value().rotations);
+  ASSERT_TRUE(chart.HasValue());
+  const auto evaluate = [&](const fesa::hht_internal::DynamicAssembly& value) {
+    return fesa::hht_reduced_internal::EvaluateConstraintOperators(
+        *fixture.domain, fixture.dofs, shells.Value(), value, chart.Value(),
+        zero, zero);
+  };
+  const std::array<double, 3> invalid{std::numeric_limits<double>::quiet_NaN(),
+                                      std::numeric_limits<double>::infinity(),
+                                      -std::numeric_limits<double>::infinity()};
+  for (std::size_t channel = 0U; channel < 2U; ++channel)
+    for (std::size_t i = 0U; i < invalid.size(); ++i) {
+      SCOPED_TRACE(channel);
+      SCOPED_TRACE(i);
+      auto candidate = assembled.Value();
+      auto& saved = candidate.trial_constraints->shells[0U];
+      if (channel == 0U) {
+        candidate.frame.generalized_coordinates[0U] = invalid[i];
+        saved.q[0U] = invalid[i];
+      } else {
+        candidate.frame.velocity[0U] = invalid[i];
+        saved.v[0U] = invalid[i];
+      }
+      auto fresh = candidate;
+      fresh.trial_constraints.reset();
+      const auto original = evaluate(fresh);
+      const auto actual = evaluate(candidate);
+      ASSERT_FALSE(original.HasValue());
+      ASSERT_FALSE(actual.HasValue());
+      EXPECT_EQ(actual.GetStatus().Category(), original.GetStatus().Category());
+      const auto& a = actual.GetStatus().Diagnostics();
+      const auto& b = original.GetStatus().Diagnostics();
+      ASSERT_EQ(a.size(), b.size());
+      for (std::size_t j = 0U; j < a.size(); ++j) {
+        EXPECT_EQ(a[j].severity, b[j].severity);
+        EXPECT_EQ(a[j].code, b[j].code);
+        EXPECT_EQ(a[j].location.file, b[j].location.file);
+        EXPECT_EQ(a[j].location.line, b[j].location.line);
+        EXPECT_EQ(a[j].keyword, b[j].keyword);
+        EXPECT_EQ(a[j].entity_identity, b[j].entity_identity);
+        EXPECT_EQ(a[j].message, b[j].message);
+      }
+    }
+}
+
+TEST(HhtReducedOperators, NonfiniteMatchingTimeKeyMissPreservesFreshSuccess) {
+  RestoreTrialEnvironment restore;
+  const auto fixture = MakeFixture(false);
+  const auto shells =
+      fesa::hht_internal::BuildRuntimeShells(*fixture.domain, fixture.dofs);
+  ASSERT_TRUE(shells.HasValue());
+  const fesa::Vector zero(fixture.dofs.FullDofCount());
+  const auto assembled =
+      Assemble(fixture, shells.Value(), zero, zero, zero, zero, true);
+  ASSERT_TRUE(assembled.HasValue());
+  ASSERT_TRUE(assembled.Value().trial_constraints.has_value());
+  const auto chart = fesa::hht_reduced_internal::BuildFixedChart(
+      fixture.dofs, assembled.Value().rotations);
+  ASSERT_TRUE(chart.HasValue());
+  const auto evaluate = [&](const fesa::hht_internal::DynamicAssembly& value) {
+    return fesa::hht_reduced_internal::EvaluateConstraintOperators(
+        *fixture.domain, fixture.dofs, shells.Value(), value, chart.Value(),
+        zero, zero);
+  };
+  const auto parameters = fesa::MakeHhtParameters(-0.05);
+  ASSERT_TRUE(parameters.HasValue());
+  fesa::SerialParallelFor parallel;
+  for (const double bad_time : {std::numeric_limits<double>::quiet_NaN(),
+                                std::numeric_limits<double>::infinity(),
+                                -std::numeric_limits<double>::infinity()}) {
+    auto candidate = assembled.Value();
+    candidate.frame.time = bad_time;
+    candidate.trial_constraints->time = bad_time;
+    candidate.trial_constraints->shells[0U].drilling_constraint[0U] = 17.0;
+    auto fresh = candidate;
+    fresh.trial_constraints.reset();
+    const auto reference = evaluate(fresh);
+    const auto actual = evaluate(candidate);
+    ASSERT_TRUE(reference.HasValue());
+    ASSERT_TRUE(actual.HasValue());
+    ExpectSameOperators(actual.Value(), reference.Value());
+    const auto producer = fesa::hht_internal::EvaluateAssembly(
+        *fixture.domain, fixture.dofs, shells.Value(), candidate.frame, zero,
+        0.1, parameters.Value(), parallel, true);
+    ASSERT_TRUE(producer.HasValue());
+    EXPECT_FALSE(producer.Value().trial_constraints.has_value());
+    const auto producer_result = evaluate(producer.Value());
+    ASSERT_TRUE(producer_result.HasValue());
+    ExpectSameOperators(producer_result.Value(), reference.Value());
+  }
+}
+
 TEST(HhtReducedOperators, ScatterShellDerivativesByConstraintRow) {
   const auto fixture = MakeFixture(false);
   const auto shells = fesa::hht_internal::BuildRuntimeShells(*fixture.domain,
diff --git a/tests/unit/math/dense_blas_internal_test.cpp b/tests/unit/math/dense_blas_internal_test.cpp
index d3be2a4..7ddfb66 100644
--- a/tests/unit/math/dense_blas_internal_test.cpp
+++ b/tests/unit/math/dense_blas_internal_test.cpp
@@ -11,6 +11,39 @@
 namespace fesa::dense_blas_internal {
 namespace {
 
+TEST(DenseBlasInternal, PolicyQueryPreservesDefaultPositiveAndNestedTls) {
+  const int previous = mkl_set_num_threads_local(0);
+  struct Restore {
+    int previous;
+    ~Restore() { static_cast<void>(mkl_set_num_threads_local(previous)); }
+  } restore{previous};
+  const int global = mkl_get_max_threads();
+  const int domain = mkl_domain_get_max_threads(MKL_DOMAIN_BLAS);
+  const int dynamic = mkl_get_dynamic();
+  for (int repeat = 0; repeat < 2; ++repeat) {
+    const auto policy = ReadScopedLocalDensePolicy();
+    EXPECT_EQ(policy.blas_max_threads, 1);
+    EXPECT_EQ(policy.dynamic, dynamic);
+    EXPECT_EQ(mkl_set_num_threads_local(0), 0);
+    EXPECT_EQ(mkl_get_max_threads(), global);
+    EXPECT_EQ(mkl_domain_get_max_threads(MKL_DOMAIN_BLAS), domain);
+    EXPECT_EQ(mkl_get_dynamic(), dynamic);
+  }
+  static_cast<void>(mkl_set_num_threads_local(2));
+  EXPECT_EQ(ReadScopedLocalDensePolicy().blas_max_threads, 2);
+  EXPECT_EQ(mkl_set_num_threads_local(2), 2);
+  static_cast<void>(mkl_set_num_threads_local(0));
+  try {
+    const ScopedLocalDenseThreads outer{};
+    EXPECT_EQ(ReadScopedLocalDensePolicy().blas_max_threads, 1);
+    EXPECT_EQ(mkl_set_num_threads_local(1), 1);
+    throw std::runtime_error{"policy-query-unwind"};
+  } catch (const std::runtime_error&) {
+  }
+  EXPECT_EQ(mkl_set_num_threads_local(0), 0);
+  EXPECT_EQ(mkl_get_dynamic(), dynamic);
+}
+
 TEST(DenseBlasInternal,
      OuterProductUsesRectangularStorageAndPreservesRejection) {
   const std::array<double, 2U> left{2.0, -3.0};