[ROCm] Define the DSA head-gate graph helpers on HIP (#37118)

Co-authored-by: Zhang, Jiejing <jiejing.zhang@amd.com>

test/registered/unit/layers/attention/test_dsa_head_gate_guard.py

@@ -0,0 +1,42 @@
+import unittest
+
+from sglang.srt.utils import is_cuda, is_hip
+from sglang.test.ci.ci_register import register_cpu_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_cpu_ci(est_time=1, suite="base-a-test-cpu")
+
+HELPERS = ("logits_head_gate_graph", "scale_head_gate_graph")
+
+
+class TestDsaHeadGateGuard(CustomTestCase):
+    """The head-gate helpers are defined in one module and imported in another.
+
+    Both sides carry their own platform condition, so the two can drift: widen
+    the import without widening the definition and every DSA model fails to
+    import on the platform in between. That is a startup failure far from its
+    cause, and no CUDA runner can see it.
+    """
+
+    def test_definition_and_import_agree(self):
+        from sglang.srt.layers.attention.dsa import dsa_indexer, dsa_prefill_cuda_graph
+
+        for name in HELPERS:
+            with self.subTest(helper=name):
+                self.assertEqual(
+                    hasattr(dsa_prefill_cuda_graph, name),
+                    hasattr(dsa_indexer, name),
+                    f"{name} is defined on one side of the guard but not the other",
+                )
+
+    def test_helpers_exist_on_cuda_and_hip(self):
+        from sglang.srt.layers.attention.dsa import dsa_prefill_cuda_graph
+
+        expected = is_cuda() or is_hip()
+        for name in HELPERS:
+            with self.subTest(helper=name):
+                self.assertEqual(hasattr(dsa_prefill_cuda_graph, name), expected)
+
+
+if __name__ == "__main__":
+    unittest.main()