diff --git a/AI.md b/AI.md
index f3be3cc..9fd03f5 100644
--- a/AI.md
+++ b/AI.md
@@ -47,7 +47,7 @@ unfinished work out of `TODO.md` merely because its architecture is documented.
 
 Latest patch marker expected in an up-to-date bundle:
 
-- `0483 nwfs: document NSS namespace bottom-up dependency order`
+- `0484 core: add Linux pthread spinlock backend for NSS runtime`
 
 When a later chat receives a new `mars-nwe-master` bundle, compare `git log -1`
 with this marker.  If the uploaded bundle already contains this commit subject,
@@ -67,23 +67,19 @@ The active line is expected to include:
 
 Last generated patch:
 
-- `0483 nwfs: document NSS namespace bottom-up dependency order`
+- `0484 core: add Linux pthread spinlock backend for NSS runtime`
 
 Purpose of that patch:
 
-- Record the bottom-up dependency order for the real NSS namespace import.
-- Keep `dosNSpace.c` imported but not built until `nameSpace.c` and its real
-  beast/admin-volume/runtime dependencies are present.
-- Identify the next code work as the smallest real NSS runtime base below
-  `comnBeasts.h`: `latch.h`, `xCache.h`, FSM/scheduler/cache headers and their
-  source owners, while reusing existing `include/core` headers instead of
-  duplicating them under `include/nwfs`.
-- Preserve the `_ADMIN` volume policy for the later admin-volume import:
-  `SYS` is volume ID `0`, `_ADMIN` is volume ID `1`, and normal volumes start
-  at `2`; `_ADMIN` may be built before NCP exposure but must remain hidden until
-  the runtime path is ready.
-- Extend the namespace import-layout test so it fails if future patches skip the
-  documented runtime/latch/cache/beast/admin-volume order or reintroduce shims.
+- Add the first real bottom-up NSS runtime primitive in `include/core`: a
+  Linux-userspace spinlock backend backed by POSIX `pthread_spinlock_t`.
+- Keep the backend generic in core because `latch.h`, MPK/scheduler headers and
+  future common-layer imports are not NWFS-specific.
+- Add a local `nwcore.spinlock` CTest that checks init/destroy, lock/unlock and
+  trylock-on-held-lock behavior without enabling namespace or `_ADMIN` at run
+  time.
+- Record that mars-nwe is now a Linux-only userspace target for this NSS runtime
+  import path; no BSD fallback or NWFS-local spinlock shim should be added.
 
 
 Directory/NDS work order before any FLAIM storage conversion:
diff --git a/doc/NSS_NAMESPACE_AUDIT.md b/doc/NSS_NAMESPACE_AUDIT.md
index ae4988d..7ceefaa 100644
--- a/doc/NSS_NAMESPACE_AUDIT.md
+++ b/doc/NSS_NAMESPACE_AUDIT.md
@@ -180,17 +180,21 @@ not add private copies under `src/nwfs/`.
 
 The planned code order is therefore:
 
-1. `nwfs-nss-runtime-base`: the smallest real subset of NSS MPK/scheduler/FSM
+1. `nwcore-nss-spinlock`: Linux-userspace spinlock primitive backed by POSIX
+   `pthread_spinlock_t`.  This is core-owned because the NSS latch/MPK/runtime
+   layer is shared infrastructure, not a filesystem object.  mars-nwe is Linux
+   userspace only for this path; do not add BSD portability scaffolding here.
+2. `nwcore-nss-runtime-base`: the smallest real subset of NSS MPK/scheduler/FSM
    headers and sources needed by `latch.h`/`xCache.h`, with Linux-kernel-only or
    NDPS/DDS-only includes removed or guarded only when the filesystem path does
    not use them.
-2. `nwfs-latch-cache-base`: direct imports for `latch`/cache types required by
-   beast structures.
-3. `nwfs-beast-base`: beast class and root-beast structure support.
-4. `nwfs-admin-volume`: build the `_ADMIN` virtual volume model, but do not
+3. `nwfs-latch-cache-base`: direct imports for `latch`/cache types required by
+   beast structures once the generic runtime primitives are in core.
+4. `nwfs-beast-base`: beast class and root-beast structure support.
+5. `nwfs-admin-volume`: build the `_ADMIN` virtual volume model, but do not
    expose it through NCP until the runtime path is ready.
-5. `nwfs-namespace-registry`: `nameSpace.c` and registration state.
-6. DOS namespace activation: build `dosNSpace.c` only after the registry and its
+6. `nwfs-namespace-registry`: `nameSpace.c` and registration state.
+7. DOS namespace activation: build `dosNSpace.c` only after the registry and its
    real dependencies are present.
 
 The `_ADMIN` volume ID policy for that later import is fixed even while the
diff --git a/include/core/spinlock.h b/include/core/spinlock.h
new file mode 100644
index 0000000..7cb0b62
--- /dev/null
+++ b/include/core/spinlock.h
@@ -0,0 +1,54 @@
+#ifndef MARS_NWE_CORE_SPINLOCK_H
+#define MARS_NWE_CORE_SPINLOCK_H
+
+#include <pthread.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Linux userspace backend for NSS runtime spin locks.
+ *
+ * The imported NSS common-layer headers were written for NetWare/NLM and
+ * Linux-kernel style spinlock APIs.  mars-nwe now targets Linux userspace, so
+ * keep the primitive in libnwcore and map it directly to POSIX pthread
+ * spinlocks instead of carrying a fake NWFS-local shim.
+ */
+typedef pthread_spinlock_t spinlock_t;
+
+static inline void
+spin_lock_init(spinlock_t *lock)
+{
+    (void)pthread_spin_init(lock, PTHREAD_PROCESS_PRIVATE);
+}
+
+static inline void
+spin_lock_destroy(spinlock_t *lock)
+{
+    (void)pthread_spin_destroy(lock);
+}
+
+static inline void
+spin_lock(spinlock_t *lock)
+{
+    (void)pthread_spin_lock(lock);
+}
+
+static inline void
+spin_unlock(spinlock_t *lock)
+{
+    (void)pthread_spin_unlock(lock);
+}
+
+static inline int
+spin_trylock(spinlock_t *lock)
+{
+    return pthread_spin_trylock(lock) == 0;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* MARS_NWE_CORE_SPINLOCK_H */
diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
index 78b4fbe..b2215d8 100644
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -63,6 +63,10 @@ configure_file(
     "${CMAKE_SOURCE_DIR}/include/core/que.h"
     "${NWCORE_BUILD_INCLUDE_DIR}/que.h"
     COPYONLY)
+configure_file(
+    "${CMAKE_SOURCE_DIR}/include/core/spinlock.h"
+    "${NWCORE_BUILD_INCLUDE_DIR}/spinlock.h"
+    COPYONLY)
 configure_file(
     "${CMAKE_SOURCE_DIR}/include/core/size_t.h"
     "${NWCORE_BUILD_INCLUDE_DIR}/size_t.h"
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index ed15749..a6fc430 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -17,5 +17,8 @@ if(MARS_NWE_BUILD_TESTS)
 endif()
 
 if(MARS_NWE_BUILD_NWFS_TESTS)
+    if(NOT MARS_NWE_BUILD_TESTS)
+        add_subdirectory(core/spinlock)
+    endif()
     add_subdirectory(nwfs)
 endif()
diff --git a/tests/core/CMakeLists.txt b/tests/core/CMakeLists.txt
index 6e2ec25..daa48f6 100644
--- a/tests/core/CMakeLists.txt
+++ b/tests/core/CMakeLists.txt
@@ -4,6 +4,7 @@
 
 add_subdirectory(ini)
 add_subdirectory(log)
+add_subdirectory(spinlock)
 add_subdirectory(bit)
 add_subdirectory(bitmap)
 add_subdirectory(crc)
diff --git a/tests/core/spinlock/CMakeLists.txt b/tests/core/spinlock/CMakeLists.txt
new file mode 100644
index 0000000..13fe1d5
--- /dev/null
+++ b/tests/core/spinlock/CMakeLists.txt
@@ -0,0 +1,9 @@
+add_executable(test_nwcore_spinlock
+    test_nwcore_spinlock.c)
+
+target_compile_features(test_nwcore_spinlock PRIVATE c_std_99)
+target_include_directories(test_nwcore_spinlock PRIVATE
+    "${CMAKE_SOURCE_DIR}/include/core")
+target_link_libraries(test_nwcore_spinlock PRIVATE mars_nwe::core)
+
+add_test(NAME nwcore.spinlock COMMAND test_nwcore_spinlock)
diff --git a/tests/core/spinlock/test_nwcore_spinlock.c b/tests/core/spinlock/test_nwcore_spinlock.c
new file mode 100644
index 0000000..0de4157
--- /dev/null
+++ b/tests/core/spinlock/test_nwcore_spinlock.c
@@ -0,0 +1,29 @@
+#include "spinlock.h"
+
+#include <pthread.h>
+#include <stdio.h>
+
+#define CHECK(expr) \
+  do { \
+    if (!(expr)) { \
+      fprintf(stderr, "CHECK failed at %s:%d: %s\n", __FILE__, __LINE__, #expr); \
+      return 1; \
+    } \
+  } while (0)
+
+int main(void)
+{
+  spinlock_t lock;
+
+  spin_lock_init(&lock);
+
+  CHECK(spin_trylock(&lock));
+  CHECK(!spin_trylock(&lock));
+  spin_unlock(&lock);
+
+  spin_lock(&lock);
+  spin_unlock(&lock);
+
+  spin_lock_destroy(&lock);
+  return 0;
+}