[AMD] test(sgl-kernel): seed RNG on ROCm in test_moe_topk_sigmoid to fix tie-break flake (#25356)

sgl-kernel/tests/test_moe_topk_sigmoid.py

@@ -5,6 +5,19 @@ import pytest
 import torch
 from sgl_kernel import topk_sigmoid
 
+_IS_HIP = torch.version.hip is not None
+
+
+@pytest.fixture(autouse=True)
+def _deterministic_seed():
+    # AMD/ROCm only: pin RNG so torch.randn produces identical gating scores
+    # across runs. atol=0 indices comparison is otherwise tripped by near-tied
+    # sigmoid scores where hipCUB's tie-break inside torch.topk disagrees with
+    # sgl_kernel.topk_sigmoid. Not observed on CUDA, so leave CUDA behavior
+    # unchanged.
+    if _IS_HIP:
+        torch.manual_seed(0)
+
 
 @pytest.mark.parametrize(
     "num_tokens, num_experts, topk",