[BugFix][PCP] Handle missing DP metadata in one-sided EP (#54016)

Signed-off-by: LopezCastroRoberto <robertol.c510@gmail.com>
Co-authored-by: Lucas Wilkinson <lwilkins@redhat.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

vllm/model_executor/layers/fused_moe/prepare_finalize/flashinfer_nvlink_one_sided.py

@@ -13,9 +13,10 @@ from vllm.model_executor.layers.fused_moe.utils import moe_kernel_quantize_input
 from vllm.utils.flashinfer import nvfp4_block_scale_interleave
 
 
-def get_local_sizes():
+def get_local_sizes() -> list[int] | None:
     dp_metadata = get_forward_context().dp_metadata
-    assert dp_metadata is not None
+    if dp_metadata is None:  # PCP with DP=1
+        return None
     return dp_metadata.get_chunk_sizes_across_dp_rank()