diff --git a/CMakeLists.txt b/CMakeLists.txt
index 91c2b015..bc2fe715 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,12 +18,20 @@ option(WITH_ASCEND "Enable Ascend backend" OFF)
 
 option(WITH_TORCH "Enable PyTorch C++ backend" OFF)
 
-# Default OFF until CANN's `extract_host_stub.py` path handling is fixed for
-# `scikit-build-core` temp-dir builds (triggers `KeyError` on the preprocessed
-# object path). Enable explicitly with `-DBUILD_CUSTOM_KERNEL=ON` when the
-# toolchain is compatible or when building via the standalone
-# `src/ascend/custom/build.sh` script.
-option(BUILD_CUSTOM_KERNEL "Build custom AscendC kernel PyTorch extension (requires `torch_npu`)" OFF)
+# Custom `AscendC` kernels under `src/native/ascend/custom/`. `ON` by default
+# so CI and routine dev builds always exercise `implementation_index=1/2`
+# for `RmsNorm` / `AddRmsNorm`.  Gated by `WITH_ASCEND` in
+# `src/CMakeLists.txt`, so non-Ascend builds ignore it. Pass
+# `-DBUILD_ASCEND_CUSTOM=OFF` to skip the `ccec` build on Ascend
+# machines where the custom kernels aren't needed.
+#
+# When `ON`, `src/CMakeLists.txt` drives the standalone
+# `src/native/ascend/custom/build.sh` via a build-phase custom command. This
+# sidesteps a `CANN` `extract_host_stub.py` path bug that breaks in-tree
+# `ascendc_library()` under `scikit-build-core` temp-dir builds, then links
+# the produced `libno_workspace_kernel.a` into the `ops` module with
+# `--whole-archive`. Requires `torch_npu` and the `AscendC` toolchain (`ccec`).
+option(BUILD_ASCEND_CUSTOM "Build custom AscendC kernels" ON)
 
 option(AUTO_DETECT_DEVICES "Automatically detect available devices" OFF)
 option(AUTO_DETECT_BACKENDS "Automatically detect available backends" OFF)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index ce888b4b..924a4576 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -241,8 +241,70 @@ if(WITH_ASCEND)
     list(APPEND DEVICE_LIST "ascend")
 
     # Custom `AscendC` kernels (PyTorch extension, requires `torch_npu`).
-    if(BUILD_CUSTOM_KERNEL)
-        add_subdirectory(native/ascend/custom)
+    if(BUILD_ASCEND_CUSTOM)
+        # In-tree `ascendc_library()` trips the `CANN` `extract_host_stub.py`
+        # path-handling bug under `scikit-build-core`'s temp-dir builds
+        # (`KeyError` on `/./workspace/...` paths in `$<TARGET_OBJECTS>`).
+        # Work around it by driving the standalone `src/native/ascend/custom/build.sh`;
+        # that script invokes a separate `cmake` with
+        # `src/native/ascend/custom/` as its `SOURCE_DIR`, avoiding the buggy
+        # path shape.  The produced `.a` is imported and linked into
+        # `ops` with `--whole-archive`.
+        set(_custom_build_dir "${CMAKE_SOURCE_DIR}/build/build_ascend_custom")
+        set(_custom_lib "${_custom_build_dir}/lib/libno_workspace_kernel.a")
+        set(_custom_source_dir "${CMAKE_CURRENT_BINARY_DIR}/ascend_custom_source")
+
+        if(NOT DEFINED SOC_VERSION OR "${SOC_VERSION}" STREQUAL "")
+            include(${CMAKE_CURRENT_SOURCE_DIR}/native/ascend/custom/cmake/detect_soc.cmake)
+            infiniops_detect_soc(SOC_VERSION)
+        endif()
+
+        # Drive `build.sh` as a build-phase target with explicit source
+        # dependencies so that editing any `op_host/` or `op_kernel/`
+        # source re-triggers the build (plain `execute_process` at
+        # configure time would only gate on file existence and leave
+        # stale `.a` files in place).
+        file(GLOB_RECURSE _custom_srcs CONFIGURE_DEPENDS
+            "${CMAKE_CURRENT_SOURCE_DIR}/native/ascend/custom/*.cpp"
+            "${CMAKE_CURRENT_SOURCE_DIR}/native/ascend/custom/*.h"
+            "${CMAKE_CURRENT_SOURCE_DIR}/native/ascend/custom/build.sh")
+
+        # Scrub env inherited from the outer `scikit-build-core` invocation
+        # before handing control to `build.sh`: `CMAKE_GENERATOR` /
+        # `CMAKE_EXPORT_COMPILE_COMMANDS` leaking into the inner `cmake`
+        # change the path format passed to `ninja`'s `_host_cpp` rule and
+        # re-trigger the `CANN` `extract_host_stub.py` `KeyError`
+        # (`/./workspace/...`) that standalone `build.sh` avoids.
+        #
+        # `pip install` MUST be invoked with `--no-build-isolation` on
+        # Ascend; otherwise pip's build-isolation overlay shadows system
+        # `torch` (via `PYTHONPATH`) and the inner `cmake`'s
+        # `import torch` in `config_envs.cmake` fails with
+        # `ModuleNotFoundError`.
+        add_custom_command(
+            OUTPUT ${_custom_lib}
+            COMMAND ${CMAKE_COMMAND} -E rm -f "${_custom_source_dir}"
+            COMMAND ${CMAKE_COMMAND} -E create_symlink
+                    "${CMAKE_CURRENT_SOURCE_DIR}/native/ascend/custom"
+                    "${_custom_source_dir}"
+            COMMAND ${CMAKE_COMMAND} -E env
+                    --unset=CMAKE_GENERATOR
+                    --unset=CMAKE_EXPORT_COMPILE_COMMANDS
+                    --unset=CMAKE_BUILD_PARALLEL_LEVEL
+                    "BUILD_DIR=${_custom_build_dir}"
+                    "MAIN_SRC_DIR=${CMAKE_CURRENT_SOURCE_DIR}"
+                    bash ${_custom_source_dir}/build.sh ${SOC_VERSION}
+            WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/native/ascend/custom
+            DEPENDS ${_custom_srcs}
+            COMMENT "Building custom AscendC kernels (SOC_VERSION=${SOC_VERSION})"
+            VERBATIM)
+
+        add_custom_target(no_workspace_kernel_build ALL DEPENDS ${_custom_lib})
+
+        add_library(no_workspace_kernel STATIC IMPORTED GLOBAL)
+        set_target_properties(no_workspace_kernel PROPERTIES
+            IMPORTED_LOCATION "${_custom_lib}")
+        add_dependencies(no_workspace_kernel no_workspace_kernel_build)
 
         # Link the compiled `AscendC` kernel objects into `infiniops` so that
         # custom kernel implementations (e.g. `RmsNorm` index 1) can call
@@ -379,9 +441,17 @@ if(GENERATE_PYTHON_BINDINGS)
     # The `Operator<..., 1>` template instantiations that call
     # `aclrtlaunch_*` live in `ops.cc`, so link here with
     # `--whole-archive` to ensure all launch functions are available.
-    if(BUILD_CUSTOM_KERNEL)
+    # `$<TARGET_FILE>` works for both real `ascendc_library()` targets and
+    # `IMPORTED` targets pointing at a pre-built `.a`.  The
+    # `no_workspace_kernel` target is only created inside the
+    # `WITH_ASCEND` block above, so this branch must mirror that gate;
+    # otherwise non-Ascend builds error out with "No target
+    # no_workspace_kernel".
+    if(WITH_ASCEND AND BUILD_ASCEND_CUSTOM)
         target_link_libraries(ops PRIVATE
-            -Wl,--whole-archive no_workspace_kernel -Wl,--no-whole-archive)
+            -Wl,--whole-archive $<TARGET_FILE:no_workspace_kernel> -Wl,--no-whole-archive)
+        # `ops` link step must wait for `build.sh` to produce the `.a`.
+        add_dependencies(ops no_workspace_kernel_build)
     endif()
 
     set_target_properties(infiniops PROPERTIES INSTALL_RPATH "$ORIGIN")
diff --git a/src/native/ascend/custom/CMakeLists.txt b/src/native/ascend/custom/CMakeLists.txt
index ca6e6883..154720aa 100644
--- a/src/native/ascend/custom/CMakeLists.txt
+++ b/src/native/ascend/custom/CMakeLists.txt
@@ -30,8 +30,8 @@ else()
 endif()
 
 set(PROJECT_OP_SRC_BASE ${PROJECT_SOURCE_DIR})
-set(PROJECT_BUILD_PATH ${PROJECT_SOURCE_DIR}/build)
-set(PROJECT_OUTPUT_PATH ${PROJECT_SOURCE_DIR}/output)
+set(MAIN_SRC_DIR "${PROJECT_OP_SRC_BASE}/../.." CACHE PATH
+    "Main InfiniOps source directory.")
 
 include(cmake/config_envs.cmake)
 include(cmake/config_ascend.cmake)
@@ -43,13 +43,15 @@ if(CCACHE_PROGRAM)
     set(CMAKE_C_COMPILER_LAUNCHER "${CCACHE_PROGRAM}")
 endif()
 
-# Shared library output location.
-set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${PROJECT_OUTPUT_PATH})
+# `CMAKE_LIBRARY_OUTPUT_DIRECTORY` is set by `build.sh` so that the
+# standalone `libascend_kernel.so` lands next to `libno_workspace_kernel.a`
+# under `<repo>/build/build_ascend_custom/output/`.
 
 # Host-side files.
 file(GLOB OP_SRCS
     ${PROJECT_OP_SRC_BASE}/torch_binding.cpp
     ${PROJECT_OP_SRC_BASE}/rms_norm/op_host/rms_norm.cpp
+    ${PROJECT_OP_SRC_BASE}/add_rms_norm/op_host/add_rms_norm.cpp
 )
 
 # Shared library name — consumed by `kernel_custom.h` variants and by the
@@ -58,9 +60,19 @@ set(OP_PLUGIN_NAME ascend_kernel)
 
 # Kernel-side files (device code compiled by the `AscendC` toolchain).
 ascendc_library(no_workspace_kernel STATIC
-    ${PROJECT_OP_SRC_BASE}/rms_norm/op_kernel/rms_norm.cpp
+    rms_norm/op_kernel/rms_norm.cpp
+    add_rms_norm/op_kernel/add_rms_norm.cpp
 )
 
+# The kernel translation units include `"data_type_enum.h"` from the main
+# project's `src/` so that launcher and device code share one `DataType`
+# enum.  `ascendc_library` forwards the interface target's `INCLUDES`
+# property to the nested `ExternalProject_Add` (see
+# `${ASCEND_HOME_PATH}/tools/tikcpp/ascendc_kernel_cmake/legacy_modules/function.cmake`),
+# so append the main `src/` dir here.
+set_property(TARGET no_workspace_kernel_interface APPEND PROPERTY
+    INCLUDES ${MAIN_SRC_DIR})
+
 # Create the shared library `libascend_kernel.so`.
 add_library(${OP_PLUGIN_NAME} SHARED ${OP_SRCS})
 
diff --git a/src/native/ascend/custom/build.sh b/src/native/ascend/custom/build.sh
index 258a88e4..f7e1cf68 100755
--- a/src/native/ascend/custom/build.sh
+++ b/src/native/ascend/custom/build.sh
@@ -1,5 +1,10 @@
 #!/bin/bash
-# Build custom `AscendC` kernels into `libascend_kernel.so`.
+# Build custom `AscendC` kernels into `libno_workspace_kernel.a` (+ the
+# standalone `libascend_kernel.so`).
+#
+# Intermediate artifacts default to `<repo>/build/build_ascend_custom/`
+# so the source tree under `src/` stays free of build output. Override
+# via `BUILD_DIR=<abs-path> bash build.sh <soc>` if needed.
 set -e
 
 SOC_VERSION="${1:-Ascend910_9382}"
@@ -10,20 +15,26 @@ source "${_CANN_TOOLKIT_INSTALL_PATH}/set_env.sh"
 echo "CANN: ${ASCEND_TOOLKIT_HOME}"
 
 ASCEND_INCLUDE_DIR=${ASCEND_TOOLKIT_HOME}/$(arch)-linux/include
-CURRENT_DIR=$(pwd)
-OUTPUT_DIR=${CURRENT_DIR}/output
-mkdir -p "${OUTPUT_DIR}"
 
-BUILD_DIR=build
+# Resolve build directory.  `<script>/../../..` is `<repo>/`.
+SCRIPT_DIR=$(cd "$(dirname "$0")" && pwd)
+REAL_SCRIPT_DIR=$(cd "$(dirname "$(readlink -f "$0")")" && pwd)
+REPO_ROOT=$(cd "${REAL_SCRIPT_DIR}/../../.." && pwd)
+BUILD_DIR="${BUILD_DIR:-${REPO_ROOT}/build/build_ascend_custom}"
+OUTPUT_DIR="${BUILD_DIR}/output"
+MAIN_SRC_DIR="${MAIN_SRC_DIR:-${REPO_ROOT}/src}"
+
 rm -rf "${BUILD_DIR}"
-mkdir -p "${BUILD_DIR}"
+mkdir -p "${BUILD_DIR}" "${OUTPUT_DIR}"
 
 cmake \
     -DASCEND_HOME_PATH="${ASCEND_HOME_PATH}" \
     -DASCEND_INCLUDE_DIR="${ASCEND_INCLUDE_DIR}" \
     -DSOC_VERSION="${SOC_VERSION}" \
+    -DCMAKE_LIBRARY_OUTPUT_DIRECTORY="${OUTPUT_DIR}" \
+    -DMAIN_SRC_DIR="${MAIN_SRC_DIR}" \
     -B "${BUILD_DIR}" \
-    -S .
+    -S "${SCRIPT_DIR}"
 
 cmake --build "${BUILD_DIR}" -j 16
 
diff --git a/src/native/ascend/custom/cmake/config_ascend.cmake b/src/native/ascend/custom/cmake/config_ascend.cmake
index 1772e9e7..29bbee85 100644
--- a/src/native/ascend/custom/cmake/config_ascend.cmake
+++ b/src/native/ascend/custom/cmake/config_ascend.cmake
@@ -9,17 +9,9 @@ set(ASCEND_CANN_PACKAGE_PATH ${ASCEND_HOME_PATH})
 # Auto-detect `SOC_VERSION` from `npu-smi info` if not set externally.
 # Required by `CANN`'s `ascendc.cmake` for `AscendC` kernel compilation.
 if(NOT DEFINED SOC_VERSION OR "${SOC_VERSION}" STREQUAL "")
-    execute_process(
-        COMMAND bash -c "npu-smi info 2>/dev/null | awk '/910B|910A|310/ {for (i=1;i<=NF;i++) if ($i ~ /^(910|310)/) {print \"Ascend\" $i; exit}}'"
-        OUTPUT_VARIABLE _DETECTED_SOC
-        OUTPUT_STRIP_TRAILING_WHITESPACE)
-
-    if(_DETECTED_SOC)
-        set(SOC_VERSION "${_DETECTED_SOC}" CACHE STRING "Ascend SOC version" FORCE)
-    else()
-        set(SOC_VERSION "Ascend910B4" CACHE STRING "Ascend SOC version" FORCE)
-    endif()
-
+    include(${CMAKE_CURRENT_LIST_DIR}/detect_soc.cmake)
+    infiniops_detect_soc(_detected_soc)
+    set(SOC_VERSION "${_detected_soc}" CACHE STRING "Ascend SOC version" FORCE)
     message(STATUS "SOC_VERSION auto-set to ${SOC_VERSION}")
 endif()
 
diff --git a/src/native/ascend/custom/cmake/detect_soc.cmake b/src/native/ascend/custom/cmake/detect_soc.cmake
new file mode 100644
index 00000000..548ead0a
--- /dev/null
+++ b/src/native/ascend/custom/cmake/detect_soc.cmake
@@ -0,0 +1,24 @@
+# Auto-detect the Ascend SOC version from `npu-smi info`.
+#
+# `infiniops_detect_soc(<out_var>)` parses the first `910*` / `310*` entry
+# in `npu-smi info` and writes `Ascend<NNNX>` into the named variable in
+# the caller's scope.  Falls back to `Ascend910B4` when detection fails
+# (no NPU on the host, `npu-smi` missing, output format mismatch).
+#
+# Called from both `src/CMakeLists.txt` (outer `pip install` build, to
+# forward `SOC_VERSION` to the standalone `build.sh` invocation) and
+# `src/native/ascend/custom/cmake/config_ascend.cmake` (the sub-build driven
+# by that `build.sh`).
+
+function(infiniops_detect_soc out_var)
+    execute_process(
+        COMMAND bash -c "npu-smi info 2>/dev/null | awk '/910B|910A|310/ {for (i=1;i<=NF;i++) if ($i ~ /^(910|310)/) {print \"Ascend\" $i; exit}}'"
+        OUTPUT_VARIABLE _detected
+        OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+    if(_detected)
+        set(${out_var} "${_detected}" PARENT_SCOPE)
+    else()
+        set(${out_var} "Ascend910B4" PARENT_SCOPE)
+    endif()
+endfunction()