fix(models): reject DeepSeek V4 FP4 tensor parallelism

Fail closed before loading unsupported FP4 MoE tensor-parallel configurations.

Fixes #47528

Co-authored-by: Devin AI <noreply@devin.ai>

Signed-off-by: Sidharth <dumko.raj@gmail.com>
Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Signed-off-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: dumko2001

vllm/models/deepseek_v4/quant_config.py

@@ -140,6 +140,13 @@ def get_quant_method(self, layer, prefix):
             ):
                 return UnquantizedFusedMoEMethod(layer.moe_config)
             if self.expert_dtype == "fp4":
+                parallel_config = get_current_vllm_config().parallel_config
+                if parallel_config.tensor_parallel_size > 1:
+                    raise ValueError(
+                        "DeepSeek V4 FP4 MoE is not supported with tensor "
+                        "parallelism. Use data parallelism with expert "
+                        "parallelism instead."
+                    )
                 if self.moe_quant_algo == "NVFP4":
                     from vllm.model_executor.layers.quantization.modelopt import (
                         ModelOptNvFp4FusedMoE,