From c15becf529a352272da22748465f464e0fd2b199 Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:42:13 +0800
Subject: [PATCH 01/14] feat: Complete traits for operation-level atomicity

---
 src/policy/handler.cppm | 44 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/src/policy/handler.cppm b/src/policy/handler.cppm
index bacf8eb..bc74ce1 100644
--- a/src/policy/handler.cppm
+++ b/src/policy/handler.cppm
@@ -1,5 +1,6 @@
 module;
 
+#include <atomic>
 #include <concepts>
 #include <expected>
 #include <optional>
@@ -84,6 +85,8 @@ namespace concurrency {
 struct injection {
   bool fence_before = false;
   bool fence_after = false;
+  std::memory_order order_before = std::memory_order_seq_cst;
+  std::memory_order order_after = std::memory_order_seq_cst;
 };
 
 template <typename Policy, typename OpTag, typename CommonRep,
@@ -94,6 +97,17 @@ struct handler {
   using result_type = std::expected<CommonRep, ErrorPayload>;
 
   static constexpr auto inject() noexcept -> injection_type { return {}; }
+
+  static constexpr auto load(CommonRep const &) noexcept -> CommonRep {
+    return CommonRep{};
+  }
+
+  static constexpr auto store(CommonRep &, CommonRep) noexcept -> void {}
+
+  static constexpr auto compare_exchange(CommonRep &, CommonRep &,
+                                         CommonRep) noexcept -> bool {
+    return false;
+  }
 };
 
 template <typename Policy, typename OpTag, typename CommonRep,
@@ -126,6 +140,36 @@ concept handler_available = requires {
   requires handler_protocol<Policy, OpTag, CommonRep, ErrorPayload>;
 };
 
+template <typename Policy, typename CommonRep,
+          typename ErrorPayload = error::kind>
+concept handler_access_protocol = requires {
+  requires concurrency_policy<Policy>;
+  {
+    handler<Policy, void, CommonRep, ErrorPayload>::enabled
+  } -> std::convertible_to<bool>;
+  requires handler<Policy, void, CommonRep, ErrorPayload>::enabled;
+  {
+    handler<Policy, void, CommonRep, ErrorPayload>::load(
+        std::declval<CommonRep const &>())
+  } noexcept -> std::same_as<CommonRep>;
+  {
+    handler<Policy, void, CommonRep, ErrorPayload>::store(
+        std::declval<CommonRep &>(), std::declval<CommonRep>())
+  } noexcept -> std::same_as<void>;
+  {
+    handler<Policy, void, CommonRep, ErrorPayload>::compare_exchange(
+        std::declval<CommonRep &>(), std::declval<CommonRep &>(),
+        std::declval<CommonRep>())
+  } noexcept -> std::same_as<bool>;
+};
+
+template <typename Policy, typename CommonRep,
+          typename ErrorPayload = error::kind>
+concept handler_access_available = requires {
+  requires handler<Policy, void, CommonRep, ErrorPayload>::enabled;
+  requires handler_access_protocol<Policy, CommonRep, ErrorPayload>;
+};
+
 } // namespace concurrency
 
 namespace type {

From 239c448692c83c9d2ea174f8323c0f624d5cb65f Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:43:06 +0800
Subject: [PATCH 02/14] feat: Refine memory order concurrency strategy and
 implement traits

---
 src/policy/impl.cppm | 193 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 188 insertions(+), 5 deletions(-)

diff --git a/src/policy/impl.cppm b/src/policy/impl.cppm
index 5888221..82bd674 100644
--- a/src/policy/impl.cppm
+++ b/src/policy/impl.cppm
@@ -1,4 +1,5 @@
 module;
+#include <atomic>
 #include <concepts>
 #include <exception>
 #include <expected>
@@ -6,7 +7,6 @@ module;
 #include <string>
 #include <type_traits>
 
-
 export module mcpplibs.primitives.policy.impl;
 
 import mcpplibs.primitives.operations.traits;
@@ -37,7 +37,10 @@ struct terminate {};
 
 namespace concurrency {
 struct none {};
-struct atomic {};
+struct fenced {};
+struct fenced_relaxed {};
+struct fenced_acq_rel {};
+struct fenced_seq_cst {};
 } // namespace concurrency
 
 template <> struct traits<value::checked> {
@@ -100,8 +103,26 @@ template <> struct traits<concurrency::none> {
   static constexpr auto kind = category::concurrency;
 };
 
-template <> struct traits<concurrency::atomic> {
-  using policy_type = concurrency::atomic;
+template <> struct traits<concurrency::fenced> {
+  using policy_type = concurrency::fenced;
+  static constexpr bool enabled = true;
+  static constexpr auto kind = category::concurrency;
+};
+
+template <> struct traits<concurrency::fenced_relaxed> {
+  using policy_type = concurrency::fenced_relaxed;
+  static constexpr bool enabled = true;
+  static constexpr auto kind = category::concurrency;
+};
+
+template <> struct traits<concurrency::fenced_acq_rel> {
+  using policy_type = concurrency::fenced_acq_rel;
+  static constexpr bool enabled = true;
+  static constexpr auto kind = category::concurrency;
+};
+
+template <> struct traits<concurrency::fenced_seq_cst> {
+  using policy_type = concurrency::fenced_seq_cst;
   static constexpr bool enabled = true;
   static constexpr auto kind = category::concurrency;
 };
@@ -189,7 +210,7 @@ struct concurrency::handler<concurrency::none, OpTag, CommonRep, ErrorPayload> {
 
 template <operations::operation OpTag, typename CommonRep,
           typename ErrorPayload>
-struct concurrency::handler<concurrency::atomic, OpTag, CommonRep,
+struct concurrency::handler<concurrency::fenced, OpTag, CommonRep,
                             ErrorPayload> {
   static constexpr bool enabled = true;
   static constexpr bool requires_external_sync = true;
@@ -200,10 +221,172 @@ struct concurrency::handler<concurrency::atomic, OpTag, CommonRep,
     injection_type out{};
     out.fence_before = true;
     out.fence_after = true;
+    out.order_before = std::memory_order_seq_cst;
+    out.order_after = std::memory_order_seq_cst;
     return out;
   }
 };
 
+template <operations::operation OpTag, typename CommonRep,
+          typename ErrorPayload>
+struct concurrency::handler<concurrency::fenced_relaxed, OpTag, CommonRep,
+                            ErrorPayload> {
+  static constexpr bool enabled = true;
+  static constexpr bool requires_external_sync = true;
+  using injection_type = concurrency::injection;
+  using result_type = std::expected<CommonRep, ErrorPayload>;
+
+  static constexpr auto inject() noexcept -> injection_type {
+    injection_type out{};
+    out.fence_before = true;
+    out.fence_after = true;
+    out.order_before = std::memory_order_relaxed;
+    out.order_after = std::memory_order_relaxed;
+    return out;
+  }
+};
+
+template <operations::operation OpTag, typename CommonRep,
+          typename ErrorPayload>
+struct concurrency::handler<concurrency::fenced_acq_rel, OpTag, CommonRep,
+                            ErrorPayload> {
+  static constexpr bool enabled = true;
+  static constexpr bool requires_external_sync = true;
+  using injection_type = concurrency::injection;
+  using result_type = std::expected<CommonRep, ErrorPayload>;
+
+  static constexpr auto inject() noexcept -> injection_type {
+    injection_type out{};
+    out.fence_before = true;
+    out.fence_after = true;
+    out.order_before = std::memory_order_acquire;
+    out.order_after = std::memory_order_release;
+    return out;
+  }
+};
+
+template <operations::operation OpTag, typename CommonRep,
+          typename ErrorPayload>
+struct concurrency::handler<concurrency::fenced_seq_cst, OpTag, CommonRep,
+                            ErrorPayload> {
+  static constexpr bool enabled = true;
+  static constexpr bool requires_external_sync = true;
+  using injection_type = concurrency::injection;
+  using result_type = std::expected<CommonRep, ErrorPayload>;
+
+  static constexpr auto inject() noexcept -> injection_type {
+    injection_type out{};
+    out.fence_before = true;
+    out.fence_after = true;
+    out.order_before = std::memory_order_seq_cst;
+    out.order_after = std::memory_order_seq_cst;
+    return out;
+  }
+};
+
+template <typename CommonRep, typename ErrorPayload>
+struct concurrency::handler<concurrency::fenced, void, CommonRep,
+                            ErrorPayload> {
+  static constexpr bool enabled = std::is_trivially_copyable_v<CommonRep>;
+  using injection_type = concurrency::injection;
+  using result_type = std::expected<CommonRep, ErrorPayload>;
+
+  static auto load(CommonRep const &value) noexcept -> CommonRep {
+    std::atomic_ref<CommonRep const> ref(value);
+    return ref.load(std::memory_order_seq_cst);
+  }
+
+  static auto store(CommonRep &value, CommonRep desired) noexcept -> void {
+    std::atomic_ref<CommonRep> ref(value);
+    ref.store(desired, std::memory_order_seq_cst);
+  }
+
+  static auto compare_exchange(CommonRep &value, CommonRep &expected,
+                               CommonRep desired) noexcept -> bool {
+    std::atomic_ref<CommonRep> ref(value);
+    return ref.compare_exchange_strong(expected, desired,
+                                       std::memory_order_seq_cst,
+                                       std::memory_order_seq_cst);
+  }
+};
+
+template <typename CommonRep, typename ErrorPayload>
+struct concurrency::handler<concurrency::fenced_relaxed, void, CommonRep,
+                            ErrorPayload> {
+  static constexpr bool enabled = std::is_trivially_copyable_v<CommonRep>;
+  using injection_type = concurrency::injection;
+  using result_type = std::expected<CommonRep, ErrorPayload>;
+
+  static auto load(CommonRep const &value) noexcept -> CommonRep {
+    std::atomic_ref<CommonRep const> ref(value);
+    return ref.load(std::memory_order_relaxed);
+  }
+
+  static auto store(CommonRep &value, CommonRep desired) noexcept -> void {
+    std::atomic_ref<CommonRep> ref(value);
+    ref.store(desired, std::memory_order_relaxed);
+  }
+
+  static auto compare_exchange(CommonRep &value, CommonRep &expected,
+                               CommonRep desired) noexcept -> bool {
+    std::atomic_ref<CommonRep> ref(value);
+    return ref.compare_exchange_strong(expected, desired,
+                                       std::memory_order_relaxed,
+                                       std::memory_order_relaxed);
+  }
+};
+
+template <typename CommonRep, typename ErrorPayload>
+struct concurrency::handler<concurrency::fenced_acq_rel, void, CommonRep,
+                            ErrorPayload> {
+  static constexpr bool enabled = std::is_trivially_copyable_v<CommonRep>;
+  using injection_type = concurrency::injection;
+  using result_type = std::expected<CommonRep, ErrorPayload>;
+
+  static auto load(CommonRep const &value) noexcept -> CommonRep {
+    std::atomic_ref<CommonRep const> ref(value);
+    return ref.load(std::memory_order_acquire);
+  }
+
+  static auto store(CommonRep &value, CommonRep desired) noexcept -> void {
+    std::atomic_ref<CommonRep> ref(value);
+    ref.store(desired, std::memory_order_release);
+  }
+
+  static auto compare_exchange(CommonRep &value, CommonRep &expected,
+                               CommonRep desired) noexcept -> bool {
+    std::atomic_ref<CommonRep> ref(value);
+    return ref.compare_exchange_strong(expected, desired,
+                                       std::memory_order_acq_rel,
+                                       std::memory_order_acquire);
+  }
+};
+
+template <typename CommonRep, typename ErrorPayload>
+struct concurrency::handler<concurrency::fenced_seq_cst, void, CommonRep,
+                            ErrorPayload> {
+  static constexpr bool enabled = std::is_trivially_copyable_v<CommonRep>;
+  using injection_type = concurrency::injection;
+  using result_type = std::expected<CommonRep, ErrorPayload>;
+
+  static auto load(CommonRep const &value) noexcept -> CommonRep {
+    return concurrency::handler<concurrency::fenced, void, CommonRep,
+                                ErrorPayload>::load(value);
+  }
+
+  static auto store(CommonRep &value, CommonRep desired) noexcept -> void {
+    concurrency::handler<concurrency::fenced, void, CommonRep,
+                         ErrorPayload>::store(value, desired);
+  }
+
+  static auto compare_exchange(CommonRep &value, CommonRep &expected,
+                               CommonRep desired) noexcept -> bool {
+    return concurrency::handler<concurrency::fenced, void, CommonRep,
+                                ErrorPayload>::compare_exchange(value, expected,
+                                                                desired);
+  }
+};
+
 template <operations::operation OpTag, typename CommonRep,
           typename ErrorPayload>
 struct value::handler<value::checked, OpTag, CommonRep, ErrorPayload> {

From 880cada3674e9d9c480159eb9babd7f47773b00d Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:45:02 +0800
Subject: [PATCH 03/14] feat: Add concurrent access interface to primitive type

---
 src/primitive/impl.cppm | 79 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/src/primitive/impl.cppm b/src/primitive/impl.cppm
index 5c0d682..d0a16aa 100644
--- a/src/primitive/impl.cppm
+++ b/src/primitive/impl.cppm
@@ -6,18 +6,97 @@ export module mcpplibs.primitives.primitive.impl;
 
 import mcpplibs.primitives.underlying.traits;
 import mcpplibs.primitives.policy.traits;
+import mcpplibs.primitives.policy.impl;
+import mcpplibs.primitives.policy.handler;
 
 export namespace mcpplibs::primitives {
 
+namespace details {
+
+template <policy::policy_type... Policies> struct count_concurrency_policies;
+
+template <> struct count_concurrency_policies<> {
+  static constexpr std::size_t value = 0;
+};
+
+template <policy::policy_type First, policy::policy_type... Rest>
+struct count_concurrency_policies<First, Rest...> {
+  static constexpr bool is_match =
+      policy::traits<First>::kind == policy::category::concurrency;
+  static constexpr std::size_t value =
+      count_concurrency_policies<Rest...>::value + (is_match ? 1u : 0u);
+};
+
+template <policy::policy_type... Policies> struct resolve_concurrency_policy;
+
+template <> struct resolve_concurrency_policy<> {
+  using type = policy::defaults::concurrency;
+};
+
+template <policy::policy_type First, policy::policy_type... Rest>
+struct resolve_concurrency_policy<First, Rest...> {
+  using type = std::conditional_t<
+      policy::traits<First>::kind == policy::category::concurrency, First,
+      typename resolve_concurrency_policy<Rest...>::type>;
+};
+
+template <policy::policy_type... Policies>
+using resolve_concurrency_policy_t =
+    typename resolve_concurrency_policy<Policies...>::type;
+
+} // namespace details
+
 template <underlying_type T, policy::policy_type... Policies> class primitive {
 public:
   using value_type = T;
   using policies = std::tuple<Policies...>;
+  using concurrency_policy = details::resolve_concurrency_policy_t<Policies...>;
+
+  static_assert(details::count_concurrency_policies<Policies...>::value <= 1,
+                "Multiple concurrency policies are not allowed");
+
   constexpr explicit primitive(value_type v) noexcept : value_(v) {}
   constexpr value_type &value() noexcept { return value_; }
   [[nodiscard]] constexpr value_type const &value() const noexcept { return value_; }
   constexpr explicit operator value_type() const noexcept { return value_; }
 
+  [[nodiscard]] auto load() const noexcept -> value_type {
+    using access_handler_t =
+        policy::concurrency::handler<concurrency_policy, void, value_type,
+                                     policy::error::kind>;
+    static_assert(
+        policy::concurrency::handler_access_available<concurrency_policy,
+                                                      value_type>,
+        "Selected concurrency policy does not provide primitive "
+        "load/store/CAS support");
+    return access_handler_t::load(value_);
+  }
+
+  auto store(value_type desired) noexcept -> void {
+    using access_handler_t =
+        policy::concurrency::handler<concurrency_policy, void, value_type,
+                                     policy::error::kind>;
+    static_assert(
+        policy::concurrency::handler_access_available<concurrency_policy,
+                                                      value_type>,
+        "Selected concurrency policy does not provide primitive "
+        "load/store/CAS support");
+    access_handler_t::store(value_, desired);
+  }
+
+  auto compare_exchange(value_type &expected, value_type desired) noexcept
+      -> bool {
+    using access_handler_t =
+        policy::concurrency::handler<concurrency_policy, void, value_type,
+                                     policy::error::kind>;
+    static_assert(
+        policy::concurrency::handler_access_available<concurrency_policy,
+                                                      value_type>,
+        "Selected concurrency policy does not provide primitive "
+        "load/store/CAS support");
+    return access_handler_t::compare_exchange(value_, expected, desired);
+  }
+
 private:
   value_type value_;
 };

From 371bb529dce7680687a2b869bd9ed8517b065ac8 Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:45:22 +0800
Subject: [PATCH 04/14] style: Fmt code

---
 src/primitive/impl.cppm | 84 +++++++++++++++++++++--------------------
 1 file changed, 44 insertions(+), 40 deletions(-)

diff --git a/src/primitive/impl.cppm b/src/primitive/impl.cppm
index d0a16aa..45ae186 100644
--- a/src/primitive/impl.cppm
+++ b/src/primitive/impl.cppm
@@ -1,6 +1,8 @@
 module;
+#include <cstddef>
 #include <cstdint>
 #include <tuple>
+#include <type_traits>
 
 export module mcpplibs.primitives.primitive.impl;
 
@@ -57,7 +59,9 @@ public:
 
   constexpr explicit primitive(value_type v) noexcept : value_(v) {}
   constexpr value_type &value() noexcept { return value_; }
-  [[nodiscard]] constexpr value_type const &value() const noexcept { return value_; }
+  [[nodiscard]] constexpr value_type const &value() const noexcept {
+    return value_;
+  }
   constexpr explicit operator value_type() const noexcept { return value_; }
 
   [[nodiscard]] auto load() const noexcept -> value_type {
@@ -101,44 +105,44 @@ private:
   value_type value_;
 };
 
-    namespace types {
-        template <policy::policy_type... Policies>
-        using Bool = primitive<bool, Policies...>;
-
-        template <policy::policy_type... Policies>
-        using UChar = primitive<unsigned char, Policies...>;
-        template <policy::policy_type... Policies>
-        using Char8 = primitive<char8_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using Char16 = primitive<char16_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using Char32 = primitive<char32_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using WChar = primitive<wchar_t, Policies...>;
-
-        template <policy::policy_type... Policies>
-        using U8 = primitive<std::uint8_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using U16 = primitive<std::uint16_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using U32 = primitive<std::uint32_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using U64 = primitive<std::uint64_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using I8 = primitive<std::int8_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using I16 = primitive<std::int16_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using I32 = primitive<std::int32_t, Policies...>;
-        template <policy::policy_type... Policies>
-        using I64 = primitive<std::int64_t, Policies...>;
-
-        template <policy::policy_type... Policies>
-        using F32 = primitive<float, Policies...>;
-        template <policy::policy_type... Policies>
-        using F64 = primitive<double, Policies...>;
-        template <policy::policy_type... Policies>
-        using F80 = primitive<long double, Policies...>;
-    }
+namespace types {
+template <policy::policy_type... Policies>
+using Bool = primitive<bool, Policies...>;
+
+template <policy::policy_type... Policies>
+using UChar = primitive<unsigned char, Policies...>;
+template <policy::policy_type... Policies>
+using Char8 = primitive<char8_t, Policies...>;
+template <policy::policy_type... Policies>
+using Char16 = primitive<char16_t, Policies...>;
+template <policy::policy_type... Policies>
+using Char32 = primitive<char32_t, Policies...>;
+template <policy::policy_type... Policies>
+using WChar = primitive<wchar_t, Policies...>;
+
+template <policy::policy_type... Policies>
+using U8 = primitive<std::uint8_t, Policies...>;
+template <policy::policy_type... Policies>
+using U16 = primitive<std::uint16_t, Policies...>;
+template <policy::policy_type... Policies>
+using U32 = primitive<std::uint32_t, Policies...>;
+template <policy::policy_type... Policies>
+using U64 = primitive<std::uint64_t, Policies...>;
+template <policy::policy_type... Policies>
+using I8 = primitive<std::int8_t, Policies...>;
+template <policy::policy_type... Policies>
+using I16 = primitive<std::int16_t, Policies...>;
+template <policy::policy_type... Policies>
+using I32 = primitive<std::int32_t, Policies...>;
+template <policy::policy_type... Policies>
+using I64 = primitive<std::int64_t, Policies...>;
+
+template <policy::policy_type... Policies>
+using F32 = primitive<float, Policies...>;
+template <policy::policy_type... Policies>
+using F64 = primitive<double, Policies...>;
+template <policy::policy_type... Policies>
+using F80 = primitive<long double, Policies...>;
+} // namespace types
 
 } // namespace mcpplibs::primitives

From c087af73d7ae03f13ca230bce42cfd5327621a7b Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:46:41 +0800
Subject: [PATCH 05/14] refactor: Remove hard-coded code in the memory barrier
 injection logic

---
 src/operations/invoker.cppm | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/operations/invoker.cppm b/src/operations/invoker.cppm
index db1788b..0772329 100644
--- a/src/operations/invoker.cppm
+++ b/src/operations/invoker.cppm
@@ -365,13 +365,14 @@ constexpr auto make_div_zero(char const *reason)
   return make_error<CommonRep>(policy::error::kind::divide_by_zero, reason);
 }
 
-constexpr auto apply_runtime_fence(bool enabled) noexcept -> void {
+constexpr auto apply_runtime_fence(bool enabled,
+                                   std::memory_order order) noexcept -> void {
   if (!enabled) {
     return;
   }
 
   if (!std::is_constant_evaluated()) {
-    std::atomic_thread_fence(std::memory_order_seq_cst);
+    std::atomic_thread_fence(order);
   }
 }
 
@@ -660,12 +661,12 @@ constexpr auto run_value(CommonRep lhs, CommonRep rhs,
       op_binding_available<OpTag, ValuePolicy, CommonRep>,
       "Missing operation binding specialization for this OpTag/common type");
 
-  details::apply_runtime_fence(injection.fence_before);
+  details::apply_runtime_fence(injection.fence_before, injection.order_before);
 
   auto decision = op_binding<OpTag, ValuePolicy, CommonRep>::apply(lhs, rhs);
   auto finalized = ValueHandler::finalize(std::move(decision), injection);
 
-  details::apply_runtime_fence(injection.fence_after);
+  details::apply_runtime_fence(injection.fence_after, injection.order_after);
   return finalized;
 }
 

From d7920c2c0c0d8918083b874757e4ae4f55441d20 Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:47:06 +0800
Subject: [PATCH 06/14] refactor: Use new tag name

---
 src/policy/utility.cppm | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/policy/utility.cppm b/src/policy/utility.cppm
index 51de8c7..4ec0eff 100644
--- a/src/policy/utility.cppm
+++ b/src/policy/utility.cppm
@@ -64,7 +64,7 @@ template <> struct priority_error<void> {
 };
 
 template <> struct priority_concurrency<void> {
-  using type = std::tuple<concurrency::atomic, concurrency::none>;
+  using type = std::tuple<concurrency::fenced, concurrency::none>;
 };
 
 template <typename... Ps> struct common_policies {

From 9b18fb1df173176ed922913e126a1313659ff314 Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:48:12 +0800
Subject: [PATCH 07/14] test: Complete the traits tests for the concurrency
 strategy

---
 tests/basic/test_policies.cpp | 65 ++++++++++++++++++++++++++++++-----
 1 file changed, 57 insertions(+), 8 deletions(-)

diff --git a/tests/basic/test_policies.cpp b/tests/basic/test_policies.cpp
index 763073f..aa26f08 100644
--- a/tests/basic/test_policies.cpp
+++ b/tests/basic/test_policies.cpp
@@ -1,3 +1,4 @@
+#include <atomic>
 #include <gtest/gtest.h>
 #include <type_traits>
 import mcpplibs.primitives;
@@ -43,8 +44,20 @@ TEST(PolicyTraitsTest, BuiltinPoliciesHaveCategories) {
   EXPECT_EQ(policy::traits<policy::concurrency::none>::kind,
             policy::category::concurrency);
 
-  EXPECT_TRUE((policy::traits<policy::concurrency::atomic>::enabled));
-  EXPECT_EQ(policy::traits<policy::concurrency::atomic>::kind,
+  EXPECT_TRUE((policy::traits<policy::concurrency::fenced>::enabled));
+  EXPECT_EQ(policy::traits<policy::concurrency::fenced>::kind,
+            policy::category::concurrency);
+
+  EXPECT_TRUE((policy::traits<policy::concurrency::fenced_relaxed>::enabled));
+  EXPECT_EQ(policy::traits<policy::concurrency::fenced_relaxed>::kind,
+            policy::category::concurrency);
+
+  EXPECT_TRUE((policy::traits<policy::concurrency::fenced_acq_rel>::enabled));
+  EXPECT_EQ(policy::traits<policy::concurrency::fenced_acq_rel>::kind,
+            policy::category::concurrency);
+
+  EXPECT_TRUE((policy::traits<policy::concurrency::fenced_seq_cst>::enabled));
+  EXPECT_EQ(policy::traits<policy::concurrency::fenced_seq_cst>::kind,
             policy::category::concurrency);
 
   EXPECT_TRUE((policy::traits<policy::value::saturating>::enabled));
@@ -60,24 +73,60 @@ TEST(PolicyTraitsTest, BuiltinPoliciesHaveCategories) {
   EXPECT_TRUE((std::is_same_v<policy::defaults::type, policy::type::strict>));
 }
 
-TEST(PolicyConcurrencyTest, AtomicInjectsFences) {
-  using atomic_handler =
-      policy::concurrency::handler<policy::concurrency::atomic,
+TEST(PolicyConcurrencyTest, FencedInjectsFences) {
+  using fenced_handler =
+      policy::concurrency::handler<policy::concurrency::fenced,
                                    operations::Addition, int,
                                    policy::error::kind>;
   using single_handler = policy::concurrency::handler<policy::concurrency::none,
                                                       operations::Addition, int,
                                                       policy::error::kind>;
 
-  auto const atomic_injection = atomic_handler::inject();
+  auto const fenced_injection = fenced_handler::inject();
   auto const single_injection = single_handler::inject();
 
-  EXPECT_TRUE(atomic_injection.fence_before);
-  EXPECT_TRUE(atomic_injection.fence_after);
+  EXPECT_TRUE(fenced_injection.fence_before);
+  EXPECT_TRUE(fenced_injection.fence_after);
+  EXPECT_EQ(fenced_injection.order_before, std::memory_order_seq_cst);
+  EXPECT_EQ(fenced_injection.order_after, std::memory_order_seq_cst);
   EXPECT_FALSE(single_injection.fence_before);
   EXPECT_FALSE(single_injection.fence_after);
 }
 
+TEST(PolicyConcurrencyTest, FencedVariantsUseExpectedMemoryOrders) {
+  using relaxed_handler =
+      policy::concurrency::handler<policy::concurrency::fenced_relaxed,
+                                   operations::Addition, int,
+                                   policy::error::kind>;
+  using acq_rel_handler =
+      policy::concurrency::handler<policy::concurrency::fenced_acq_rel,
+                                   operations::Addition, int,
+                                   policy::error::kind>;
+
+  auto const relaxed = relaxed_handler::inject();
+  auto const acq_rel = acq_rel_handler::inject();
+
+  EXPECT_EQ(relaxed.order_before, std::memory_order_relaxed);
+  EXPECT_EQ(relaxed.order_after, std::memory_order_relaxed);
+  EXPECT_EQ(acq_rel.order_before, std::memory_order_acquire);
+  EXPECT_EQ(acq_rel.order_after, std::memory_order_release);
+}
+
+TEST(PolicyConcurrencyTest, PrimitiveAccessHandlerProtocolByPolicy) {
+  EXPECT_TRUE((
+      policy::concurrency::handler_access_available<policy::concurrency::fenced,
+                                                    int>));
+  EXPECT_TRUE((policy::concurrency::handler_access_available<
+               policy::concurrency::fenced_relaxed, int>));
+  EXPECT_TRUE((policy::concurrency::handler_access_available<
+               policy::concurrency::fenced_acq_rel, int>));
+  EXPECT_TRUE((policy::concurrency::handler_access_available<
+               policy::concurrency::fenced_seq_cst, int>));
+  EXPECT_FALSE(
+      (policy::concurrency::handler_access_available<policy::concurrency::none,
+                                                     int>));
+}
+
 TEST(PolicyProtocolTest, BuiltinHandlersSatisfyProtocolConcepts) {
   static_assert(policy::type::handler_protocol<policy::type::strict,
                                                operations::Addition, int, int>);

From c89b99a317240be04a6af856aa539b13791dfdb6 Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:49:44 +0800
Subject: [PATCH 08/14] test: Add a new concurrency strategy test and correct
 the original test name

---
 tests/basic/test_operations.cpp | 58 ++++++++++++++++++++++++++++++---
 1 file changed, 53 insertions(+), 5 deletions(-)

diff --git a/tests/basic/test_operations.cpp b/tests/basic/test_operations.cpp
index d8bdf4b..ceb1fcc 100644
--- a/tests/basic/test_operations.cpp
+++ b/tests/basic/test_operations.cpp
@@ -5,7 +5,6 @@
 #include <type_traits>
 #include <vector>
 
-
 import mcpplibs.primitives;
 
 using namespace mcpplibs::primitives;
@@ -87,9 +86,9 @@ TEST(OperationsTest, UncheckedDivisionUsesRawArithmeticWhenValid) {
   EXPECT_EQ(result->value(), 25);
 }
 
-TEST(OperationsTest, AtomicPolicyPathReturnsExpectedValue) {
+TEST(OperationsTest, FencedPolicyPathReturnsExpectedValue) {
   using value_t =
-      primitive<int, policy::value::checked, policy::concurrency::atomic,
+      primitive<int, policy::value::checked, policy::concurrency::fenced,
                 policy::error::expected>;
 
   auto const lhs = value_t{12};
@@ -101,9 +100,9 @@ TEST(OperationsTest, AtomicPolicyPathReturnsExpectedValue) {
   EXPECT_EQ(result->value(), 42);
 }
 
-TEST(OperationsTest, AtomicPolicyConcurrentInvocationsRemainConsistent) {
+TEST(OperationsTest, FencedPolicyConcurrentInvocationsRemainConsistent) {
   using value_t =
-      primitive<int, policy::value::checked, policy::concurrency::atomic,
+      primitive<int, policy::value::checked, policy::concurrency::fenced,
                 policy::error::expected>;
 
   constexpr int kThreadCount = 8;
@@ -148,6 +147,55 @@ TEST(OperationsTest, AtomicPolicyConcurrentInvocationsRemainConsistent) {
   EXPECT_EQ(mismatch_count.load(std::memory_order_relaxed), 0);
 }
 
+TEST(OperationsTest, PrimitiveFencedLoadStoreAndCasWork) {
+  using value_t =
+      primitive<int, policy::value::checked, policy::concurrency::fenced,
+                policy::error::expected>;
+
+  auto value = value_t{1};
+  EXPECT_EQ(value.load(), 1);
+
+  value.store(4);
+  EXPECT_EQ(value.load(), 4);
+
+  auto expected = 4;
+  EXPECT_TRUE(value.compare_exchange(expected, 7));
+  EXPECT_EQ(value.load(), 7);
+
+  expected = 9;
+  EXPECT_FALSE(value.compare_exchange(expected, 11));
+  EXPECT_EQ(expected, 7);
+}
+
+TEST(OperationsTest, PrimitiveFencedCasSupportsConcurrentIncrements) {
+  using value_t =
+      primitive<int, policy::value::checked, policy::concurrency::fenced,
+                policy::error::expected>;
+
+  constexpr int kThreadCount = 6;
+  constexpr int kIterationsPerThread = 5000;
+
+  auto counter = value_t{0};
+  std::vector<std::thread> workers;
+  workers.reserve(kThreadCount);
+
+  for (int i = 0; i < kThreadCount; ++i) {
+    workers.emplace_back([&]() {
+      for (int n = 0; n < kIterationsPerThread; ++n) {
+        auto expected = counter.load();
+        while (!counter.compare_exchange(expected, expected + 1)) {
+        }
+      }
+    });
+  }
+
+  for (auto &worker : workers) {
+    worker.join();
+  }
+
+  EXPECT_EQ(counter.load(), kThreadCount * kIterationsPerThread);
+}
+
 TEST(OperationsTest, StrictTypeRejectsMixedTypesAtCompileTime) {
   using lhs_t = primitive<int, policy::value::checked, policy::type::strict,
                           policy::error::expected>;

From 289489a14c35c68a43efcea00de2098e45ffef98 Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:50:20 +0800
Subject: [PATCH 09/14] docs: Update the documentation for the new concurrency
 strategy interface

---
 README.md | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 119a66d..517f89e 100644
--- a/README.md
+++ b/README.md
@@ -51,7 +51,29 @@ auto maybe = x + y; // std::expected<primitive<int, policy::error::expected>, po
 - `policy::value::{checked, unchecked, saturating}`
 - `policy::type::{strict, compatible, transparent}`
 - `policy::error::{throwing, expected, terminate}`
-- `policy::concurrency::{none, atomic}`
+- `policy::concurrency::{none, fenced, fenced_relaxed, fenced_acq_rel, fenced_seq_cst}`
+
+并发策略说明：
+
+- `fenced*` 系列是操作级并发语义，通过策略注入内存序 fence；
+- `primitive` 存储仍保持统一、零开销布局，不引入额外存储层抽象；
+- `primitive::load/store/compare_exchange` 由并发策略的协议实现提供，若策略未实现该协议会在编译期报错。
+
+示例（并发访问 API）：
+
+```cpp
+using shared_t = primitive<int, policy::value::checked,
+                                                     policy::concurrency::fenced_acq_rel,
+                                                     policy::error::expected>;
+
+shared_t v{1};
+v.store(2);
+auto expected = 2;
+if (v.compare_exchange(expected, 3)) {
+    auto now = v.load();
+    (void)now;
+}
+```
 
 默认策略位于 `policy::defaults`：
 

From 78cb06bc2492cb2f210260d5038b47c0122855cd Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:51:12 +0800
Subject: [PATCH 10/14] docs: Add a new concurrency strategy example program

---
 examples/ex05_concurrency_policy.cpp | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/examples/ex05_concurrency_policy.cpp b/examples/ex05_concurrency_policy.cpp
index e4da76a..27a6cc2 100644
--- a/examples/ex05_concurrency_policy.cpp
+++ b/examples/ex05_concurrency_policy.cpp
@@ -2,11 +2,12 @@
  * Example: ex05_concurrency_policy
  *
  * Purpose:
- * Demonstrate the atomic concurrency policy path under multi-threaded
+ * Demonstrate the fenced concurrency policy path under multi-threaded
  * repeated dispatch.
  *
  * Expected results:
  * - Concurrent add operations consistently produce value 42.
+ * - Primitive load/store/CAS APIs work under fenced policy.
  * - mismatch_count remains zero after all worker threads join.
  * - Program prints a success message and exits with code 0.
  */
@@ -21,13 +22,22 @@ import mcpplibs.primitives;
 using namespace mcpplibs::primitives;
 
 int main() {
-  // Point 5: Use atomic concurrency policy and verify concurrent consistency.
-  using atomic_t =
-      primitive<int, policy::value::checked, policy::concurrency::atomic,
+  // Point 5: Use fenced concurrency policy and verify concurrent consistency.
+  using fenced_t =
+      primitive<int, policy::value::checked, policy::concurrency::fenced,
                 policy::error::expected>;
 
-  auto const lhs = atomic_t{12};
-  auto const rhs = atomic_t{30};
+  auto const lhs = fenced_t{12};
+  auto const rhs = fenced_t{30};
+
+  auto concurrent_value = fenced_t{1};
+  concurrent_value.store(2);
+  auto expected = 2;
+  if (!concurrent_value.compare_exchange(expected, 3) ||
+      concurrent_value.load() != 3) {
+    std::cerr << "fenced load/store/CAS mismatch\n";
+    return 1;
+  }
 
   std::atomic<int> mismatch_count{0};
   std::vector<std::thread> workers;
@@ -51,7 +61,7 @@ int main() {
 
   // A non-zero mismatch count indicates unexpected behavior under concurrency.
   if (mismatch_count.load(std::memory_order_relaxed) != 0) {
-    std::cerr << "atomic policy path mismatch\n";
+    std::cerr << "fenced policy path mismatch\n";
     return 1;
   }
 

From 568fcf22a1fb1ddacf8a03994d3ebf947738e8eb Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Thu, 19 Mar 2026 18:52:06 +0800
Subject: [PATCH 11/14] docs: Correct the code for the custom concurrency
 policy in the example program

---
 examples/ex07_custom_policy.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/examples/ex07_custom_policy.cpp b/examples/ex07_custom_policy.cpp
index 0c6e0d1..ef36c13 100644
--- a/examples/ex07_custom_policy.cpp
+++ b/examples/ex07_custom_policy.cpp
@@ -12,10 +12,12 @@
  * - Program prints a success message and exits with code 0.
  */
 
+#include <atomic>
 #include <expected>
 #include <iostream>
 #include <type_traits>
 
+
 import mcpplibs.primitives;
 import mcpplibs.primitives.operations.invoker;
 
@@ -79,6 +81,8 @@ struct mcpplibs::primitives::policy::concurrency::handler<
     injection_type out{};
     out.fence_before = true;
     out.fence_after = false;
+    out.order_before = std::memory_order_acquire;
+    out.order_after = std::memory_order_relaxed;
     return out;
   }
 };

From 168fcefc943ce4c45e3d2dbdc58158202da5ecfe Mon Sep 17 00:00:00 2001
From: FrozenLemonTee <frozenlemontee@gmail.com>
Date: Fri, 20 Mar 2026 00:02:26 +0800
Subject: [PATCH 12/14] refactor: Use helper to extract code

---
 src/policy/impl.cppm | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/src/policy/impl.cppm b/src/policy/impl.cppm
index 82bd674..d4f8814 100644
--- a/src/policy/impl.cppm
+++ b/src/policy/impl.cppm
@@ -148,6 +148,14 @@ inline constexpr bool rejects_arithmetic_for_boolean_or_character_v =
     is_arithmetic_operation_v<OpTag> &&
     (is_boolean_or_character_v<LhsRep> || is_boolean_or_character_v<RhsRep>);
 
+template <typename T>
+auto atomic_ref_load(T const &value, std::memory_order order) noexcept -> T {
+  // libc++ rejects std::atomic_ref<const T>; load through a non-mutating view.
+  auto &mutable_value = const_cast<T &>(value);
+  std::atomic_ref<T> ref(mutable_value);
+  return ref.load(order);
+}
+
 } // namespace details
 
 // Default protocol specializations.
@@ -292,8 +300,7 @@ struct concurrency::handler<concurrency::fenced, void, CommonRep,
   using result_type = std::expected<CommonRep, ErrorPayload>;
 
   static auto load(CommonRep const &value) noexcept -> CommonRep {
-    std::atomic_ref<CommonRep const> ref(value);
-    return ref.load(std::memory_order_seq_cst);
+    return details::atomic_ref_load(value, std::memory_order_seq_cst);
   }
 
   static auto store(CommonRep &value, CommonRep desired) noexcept -> void {
@@ -318,8 +325,7 @@ struct concurrency::handler<concurrency::fenced_relaxed, void, CommonRep,
   using result_type = std::expected<CommonRep, ErrorPayload>;
 
   static auto load(CommonRep const &value) noexcept -> CommonRep {
-    std::atomic_ref<CommonRep const> ref(value);
-    return ref.load(std::memory_order_relaxed);
+    return details::atomic_ref_load(value, std::memory_order_relaxed);
   }
 
   static auto store(CommonRep &value, CommonRep desired) noexcept -> void {
@@ -344,8 +350,7 @@ struct concurrency::handler<concurrency::fenced_acq_rel, void, CommonRep,
   using result_type = std::expected<CommonRep, ErrorPayload>;
 
   static auto load(CommonRep const &value) noexcept -> CommonRep {
-    std::atomic_ref<CommonRep const> ref(value);
-    return ref.load(std::memory_order_acquire);
+    return details::atomic_ref_load(value, std::memory_order_acquire);
   }
 
   static auto store(CommonRep &value, CommonRep desired) noexcept -> void {

From 156439f6fa9051d39cd6a2afd27154f143e05c82 Mon Sep 17 00:00:00 2001
From: FrozenlemonTee <frozenlemontee@gmail.com>
Date: Fri, 20 Mar 2026 19:13:01 +0800
Subject: [PATCH 13/14] refactor: Add and use atomic_ref_compatible checks for
 concurrency handlers

---
 src/policy/impl.cppm | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/src/policy/impl.cppm b/src/policy/impl.cppm
index d4f8814..0ec7c17 100644
--- a/src/policy/impl.cppm
+++ b/src/policy/impl.cppm
@@ -136,6 +136,28 @@ using concurrency = concurrency::none;
 
 namespace details {
 
+template <typename T, bool = std::is_trivially_copyable_v<T>>
+struct atomic_ref_alignment_compatible : std::false_type {};
+
+template <typename T>
+struct atomic_ref_alignment_compatible<T, true>
+    : std::bool_constant<(alignof(T) >=
+                          std::atomic_ref<T>::required_alignment)> {};
+
+template <typename T>
+inline constexpr bool atomic_ref_compatible_v =
+    atomic_ref_alignment_compatible<T>::value;
+
+template <typename T> constexpr void assert_atomic_ref_compatible() {
+  static_assert(std::is_trivially_copyable_v<T>,
+                "concurrency::handler atomic access requires trivially "
+                "copyable CommonRep");
+  static_assert(
+      atomic_ref_alignment_compatible<T>::value,
+      "concurrency::handler atomic access requires alignof(CommonRep) to "
+      "satisfy std::atomic_ref<CommonRep>::required_alignment");
+}
+
 template <typename OpTag>
 inline constexpr bool is_arithmetic_operation_v =
     operations::op_has_capability_v<OpTag, operations::capability::arithmetic>;
@@ -150,6 +172,7 @@ inline constexpr bool rejects_arithmetic_for_boolean_or_character_v =
 
 template <typename T>
 auto atomic_ref_load(T const &value, std::memory_order order) noexcept -> T {
+  assert_atomic_ref_compatible<T>();
   // libc++ rejects std::atomic_ref<const T>; load through a non-mutating view.
   auto &mutable_value = const_cast<T &>(value);
   std::atomic_ref<T> ref(mutable_value);
@@ -295,7 +318,7 @@ struct concurrency::handler<concurrency::fenced_seq_cst, OpTag, CommonRep,
 template <typename CommonRep, typename ErrorPayload>
 struct concurrency::handler<concurrency::fenced, void, CommonRep,
                             ErrorPayload> {
-  static constexpr bool enabled = std::is_trivially_copyable_v<CommonRep>;
+  static constexpr bool enabled = details::atomic_ref_compatible_v<CommonRep>;
   using injection_type = concurrency::injection;
   using result_type = std::expected<CommonRep, ErrorPayload>;
 
@@ -304,12 +327,14 @@ struct concurrency::handler<concurrency::fenced, void, CommonRep,
   }
 
   static auto store(CommonRep &value, CommonRep desired) noexcept -> void {
+    details::assert_atomic_ref_compatible<CommonRep>();
     std::atomic_ref<CommonRep> ref(value);
     ref.store(desired, std::memory_order_seq_cst);
   }
 
   static auto compare_exchange(CommonRep &value, CommonRep &expected,
                                CommonRep desired) noexcept -> bool {
+    details::assert_atomic_ref_compatible<CommonRep>();
     std::atomic_ref<CommonRep> ref(value);
     return ref.compare_exchange_strong(expected, desired,
                                        std::memory_order_seq_cst,
@@ -320,7 +345,7 @@ struct concurrency::handler<concurrency::fenced, void, CommonRep,
 template <typename CommonRep, typename ErrorPayload>
 struct concurrency::handler<concurrency::fenced_relaxed, void, CommonRep,
                             ErrorPayload> {
-  static constexpr bool enabled = std::is_trivially_copyable_v<CommonRep>;
+  static constexpr bool enabled = details::atomic_ref_compatible_v<CommonRep>;
   using injection_type = concurrency::injection;
   using result_type = std::expected<CommonRep, ErrorPayload>;
 
@@ -329,12 +354,14 @@ struct concurrency::handler<concurrency::fenced_relaxed, void, CommonRep,
   }
 
   static auto store(CommonRep &value, CommonRep desired) noexcept -> void {
+    details::assert_atomic_ref_compatible<CommonRep>();
     std::atomic_ref<CommonRep> ref(value);
     ref.store(desired, std::memory_order_relaxed);
   }
 
   static auto compare_exchange(CommonRep &value, CommonRep &expected,
                                CommonRep desired) noexcept -> bool {
+    details::assert_atomic_ref_compatible<CommonRep>();
     std::atomic_ref<CommonRep> ref(value);
     return ref.compare_exchange_strong(expected, desired,
                                        std::memory_order_relaxed,
@@ -345,7 +372,7 @@ struct concurrency::handler<concurrency::fenced_relaxed, void, CommonRep,
 template <typename CommonRep, typename ErrorPayload>
 struct concurrency::handler<concurrency::fenced_acq_rel, void, CommonRep,
                             ErrorPayload> {
-  static constexpr bool enabled = std::is_trivially_copyable_v<CommonRep>;
+  static constexpr bool enabled = details::atomic_ref_compatible_v<CommonRep>;
   using injection_type = concurrency::injection;
   using result_type = std::expected<CommonRep, ErrorPayload>;
 
@@ -354,12 +381,14 @@ struct concurrency::handler<concurrency::fenced_acq_rel, void, CommonRep,
   }
 
   static auto store(CommonRep &value, CommonRep desired) noexcept -> void {
+    details::assert_atomic_ref_compatible<CommonRep>();
     std::atomic_ref<CommonRep> ref(value);
     ref.store(desired, std::memory_order_release);
   }
 
   static auto compare_exchange(CommonRep &value, CommonRep &expected,
                                CommonRep desired) noexcept -> bool {
+    details::assert_atomic_ref_compatible<CommonRep>();
     std::atomic_ref<CommonRep> ref(value);
     return ref.compare_exchange_strong(expected, desired,
                                        std::memory_order_acq_rel,
@@ -370,7 +399,7 @@ struct concurrency::handler<concurrency::fenced_acq_rel, void, CommonRep,
 template <typename CommonRep, typename ErrorPayload>
 struct concurrency::handler<concurrency::fenced_seq_cst, void, CommonRep,
                             ErrorPayload> {
-  static constexpr bool enabled = std::is_trivially_copyable_v<CommonRep>;
+  static constexpr bool enabled = details::atomic_ref_compatible_v<CommonRep>;
   using injection_type = concurrency::injection;
   using result_type = std::expected<CommonRep, ErrorPayload>;
 

From 6e14d3d22f8942af50a0ac56cb412e7696b4eb03 Mon Sep 17 00:00:00 2001
From: FrozenlemonTee <frozenlemontee@gmail.com>
Date: Fri, 20 Mar 2026 19:13:08 +0800
Subject: [PATCH 14/14] test: Add tests for non-trivially copyable and low
 alignment representations in concurrency policies

---
 tests/basic/test_policies.cpp | 41 +++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/tests/basic/test_policies.cpp b/tests/basic/test_policies.cpp
index aa26f08..7872382 100644
--- a/tests/basic/test_policies.cpp
+++ b/tests/basic/test_policies.cpp
@@ -7,6 +7,15 @@ using namespace mcpplibs::primitives;
 
 namespace {
 struct NullCapabilityProbe {};
+
+struct NonTriviallyCopyableRep {
+  int value{0};
+  ~NonTriviallyCopyableRep() {}
+};
+
+struct LowAlignmentRep {
+  unsigned char bytes[sizeof(std::uint64_t)]{};
+};
 } // namespace
 
 template <> struct operations::traits<NullCapabilityProbe> {
@@ -127,6 +136,38 @@ TEST(PolicyConcurrencyTest, PrimitiveAccessHandlerProtocolByPolicy) {
                                                      int>));
 }
 
+TEST(PolicyConcurrencyTest, PrimitiveAccessRejectsNonTriviallyCopyableRep) {
+  EXPECT_FALSE((
+      policy::concurrency::handler_access_available<policy::concurrency::fenced,
+                                                    NonTriviallyCopyableRep>));
+  EXPECT_FALSE((policy::concurrency::handler_access_available<
+                policy::concurrency::fenced_relaxed, NonTriviallyCopyableRep>));
+  EXPECT_FALSE((policy::concurrency::handler_access_available<
+                policy::concurrency::fenced_acq_rel, NonTriviallyCopyableRep>));
+  EXPECT_FALSE((policy::concurrency::handler_access_available<
+                policy::concurrency::fenced_seq_cst, NonTriviallyCopyableRep>));
+}
+
+TEST(PolicyConcurrencyTest, PrimitiveAccessRespectsAtomicRefAlignmentGate) {
+  constexpr bool requires_stronger_alignment =
+      std::atomic_ref<LowAlignmentRep>::required_alignment >
+      alignof(LowAlignmentRep);
+
+  if constexpr (requires_stronger_alignment) {
+    EXPECT_FALSE((policy::concurrency::handler_access_available<
+                  policy::concurrency::fenced, LowAlignmentRep>));
+    EXPECT_FALSE((policy::concurrency::handler_access_available<
+                  policy::concurrency::fenced_relaxed, LowAlignmentRep>));
+    EXPECT_FALSE((policy::concurrency::handler_access_available<
+                  policy::concurrency::fenced_acq_rel, LowAlignmentRep>));
+    EXPECT_FALSE((policy::concurrency::handler_access_available<
+                  policy::concurrency::fenced_seq_cst, LowAlignmentRep>));
+  } else {
+    GTEST_SKIP() << "platform atomic_ref required_alignment does not exceed "
+                    "alignof(LowAlignmentRep)";
+  }
+}
+
 TEST(PolicyProtocolTest, BuiltinHandlersSatisfyProtocolConcepts) {
   static_assert(policy::type::handler_protocol<policy::type::strict,
                                                operations::Addition, int, int>);