[BugFix] Fix Qwen3-Next PP (vllm-project#24709)

Signed-off-by: Nick Hill <nhill@redhat.com>

Author: njhill

vllm/model_executor/models/qwen3_next.py

@@ -2,6 +2,7 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 """Inference-only Qwen3Next model."""
 from collections.abc import Iterable
+from itertools import islice
 from typing import Optional
 
 import torch
@@ -917,8 +918,11 @@ def get_layer(prefix: str):
             make_empty_intermediate_tensors_factory(
                 ["hidden_states", "residual"], config.hidden_size))
 
-        self.norm = Qwen3NextRMSNorm(config.hidden_size,
-                                     eps=config.rms_norm_eps)
+        if get_pp_group().is_last_rank:
+            self.norm = Qwen3NextRMSNorm(config.hidden_size,
+                                         eps=config.rms_norm_eps)
+        else:
+            self.norm = PPMissingLayer()
 
     def get_input_embeddings(self, input_ids: torch.Tensor) -> torch.Tensor:
         return self.embed_tokens(input_ids)
@@ -941,7 +945,7 @@ def forward(
             hidden_states = intermediate_tensors["hidden_states"]
             residual = intermediate_tensors["residual"]
 
-        for layer in self.layers:
+        for layer in islice(self.layers, self.start_layer, self.end_layer):
             hidden_states, residual = layer(
                 positions=positions,
                 hidden_states=hidden_states,