[Diffusion] Use current_platform instead of hardcoded "cuda" in cosmos3 guardrails (#34612)

Co-authored-by: ronnie_zheng <zl19940307@163.com>

docs/cookbook/diffusion/Cosmos/Cosmos3.mdx

@@ -44,6 +44,12 @@ pip install "cosmos-guardrail==0.3.1"
 
 `cosmos-guardrail` downloads gated NVIDIA guardrail weights, so pass a Hugging Face token if your environment needs one. If the package is not installed, SGLang skips Cosmos3 guardrails and logs a warning. To disable Cosmos3 guardrails for local experiments, set `SGLANG_DISABLE_COSMOS3_GUARDRAILS=1` before starting the server.
 
+There may be problems loading the Cosmos-1.0-Guardrail weights on Ascend NPU. If the *_pickle.UnpicklingError* error occurs during startup, you should change ```weight_only=True``` to ```weights_only=False``` parameter in *cosmos_guardrail/cosmos_utils.py*:
+```
+#!/usr/bin/env bash
+COSMOS_GUARDRAIL_DIR="$(dirname "$(python -c 'import cosmos_guardrail; print(cosmos_guardrail.__file__)')")"
+sed -i 's/weights_only=True/weights_only=False/g' "$COSMOS_GUARDRAIL_DIR/cosmos_utils.py"
+```
 ## 3. Serve Cosmos3
 
 Serve `Cosmos3-Nano` directly from the Hugging Face model ID:

python/sglang/multimodal_gen/runtime/pipelines_core/stages/model_specific_stages/cosmos3_guardrails.py

@@ -21,6 +21,7 @@ from sglang.multimodal_gen.runtime.pipelines_core.stages.base import (
     PipelineStage,
     StageParallelismType,
 )
+from sglang.multimodal_gen.runtime.platforms import current_platform
 from sglang.multimodal_gen.runtime.server_args import ServerArgs
 from sglang.multimodal_gen.runtime.utils.logging_utils import init_logger
 
@@ -49,7 +50,7 @@ def _init_guardrails(offload_to_cpu: bool = False) -> None:
         "Initializing Cosmos3 guardrails (offload_to_cpu=%s) ...", offload_to_cpu
     )
     _checker = CosmosSafetyChecker()
-    idle_device = "cpu" if offload_to_cpu else "cuda"
+    idle_device = "cpu" if offload_to_cpu else current_platform.device_type
     for runner in (_checker.text_guardrail, _checker.video_guardrail):
         if runner is None or not hasattr(runner, "models"):
             continue