fix(mlx): default prefill_aware_swa=False on MlxModelRunnerStub (#29681)

python/sglang/srt/hardware_backend/mlx/model_runner_stub.py

@@ -85,6 +85,14 @@ class MlxModelRunnerStub(ModelRunner):
     # AttributeError.
     canary_manager = None
 
+    # No prefill-aware SWA on the MLX path. The base ModelRunner derives this in
+    # its full initialize() from `model.is_prefill_aware_swa()`, which this
+    # lightweight override skips (and `_DummyModel` does not implement). The
+    # scheduler reads `model_runner.prefill_aware_swa` unconditionally when
+    # admitting a prefill batch, so default to False as a class attribute to keep
+    # that path working instead of raising AttributeError.
+    prefill_aware_swa = False
+
     def __init__(self, *args, mlx_pool_size: int | None = None, **kwargs):
         self._mlx_pool_size = mlx_pool_size
         super().__init__(*args, **kwargs)