docs: record sdpa backend import binding

CHANGELOG.md

@@ -33,6 +33,10 @@
 
 ## [Unreleased]
 
+### Changed
+- sdpa `PLATFORM.md` 补记多算子 perf registry 顺序加载时的顶层
+  `reference` 遮蔽约束；backend 导入回归测试同步覆盖 P800 与 MLU
+
 ### Fixed
 - P800 性能门禁多算子加载时，`ops.sdpa` backend 的裸 `reference`
   导入可能命中 `sdpa_math.reference` 等同名顶层模块，导致

ops/sdpa/PLATFORM.md

@@ -94,6 +94,13 @@ kernel/backends/
 
 合并流程与后续平台扩展仍按 [MERGE.md](MERGE.md) 执行。
 
+多算子同进程/perf registry 会按 provider 顺序加载多个 `reference.py`。
+backend 内不允许裸 `from reference import ...` 作为首选路径：一旦其他
+算子的顶层 `reference` 已进入 `sys.modules`，该导入会解析到错误模块。
+正确顺序是包态相对导入优先（如 `from ...reference import ...`），仅
+单算子脚本模式 fallback 到顶层 `reference`。该问题已在
+`tests/unit/test_sdpa_backend_import.py` 固化，实测记录见 PR #22。
+
 ## 6. 引用防误用
 
 函数名**有意**保持 `sdpa_triton`（公共 API 稳定）。平台区分靠三层：

tests/unit/test_sdpa_backend_import.py

@@ -5,7 +5,17 @@
 import types
 
 
-def test_p800_backend_survives_foreign_top_level_reference(monkeypatch):
+import pytest
+
+
+@pytest.mark.parametrize(
+    ("module_name",),
+    [
+        ("ops.sdpa.kernel.backends.p800_kunlunxin",),
+        ("ops.sdpa.kernel.backends.mlu590",),
+    ],
+)
+def test_backend_survives_foreign_top_level_reference(module_name, monkeypatch):
     """Guard the multi-operator perf-registry import order.
 
     Earlier standalone operators can leave their own ``reference`` module in
@@ -15,9 +25,11 @@ def test_p800_backend_survives_foreign_top_level_reference(monkeypatch):
     foreign = types.ModuleType("reference")
     monkeypatch.setitem(sys.modules, "reference", foreign)
 
-    module = importlib.import_module(
-        "ops.sdpa.kernel.backends.p800_kunlunxin"
-    )
+    module = importlib.import_module(module_name)
+    # Package scanning may have imported this backend before this test. Reload
+    # after installing the foreign top-level module so the test always covers
+    # the import statements rather than a cached module object.
     module = importlib.reload(module)
 
     assert module.sdpa_reference.__module__ == "ops.sdpa.reference"
+    assert callable(module.sdpa_reference)