[Bugfix] Fix DeepSeek V4 MTP HC state handling

vllm/model_executor/models/deepseek_v4.py

@@ -1203,10 +1203,10 @@ def forward(
         x: torch.Tensor,
         positions: torch.Tensor,
         input_ids: torch.Tensor | None,
-        post_mix: torch.Tensor | None,
-        res_mix: torch.Tensor | None,
-        residual: torch.Tensor | None,
-    ) -> torch.Tensor:
+        post_mix: torch.Tensor | None = None,
+        res_mix: torch.Tensor | None = None,
+        residual: torch.Tensor | None = None,
+    ) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor, torch.Tensor]:
         if residual is None:
             # Run standalone hc_pre on first layer
             residual = x

vllm/model_executor/models/deepseek_v4_mtp.py

@@ -141,9 +141,12 @@ def forward(
         hidden_states = self.h_proj(previous_hidden_states) + self.e_proj(
             inputs_embeds
         ).unsqueeze(-2)
-        hidden_states = self.mtp_block(
+        hidden_states, residual, post_mix, res_mix = self.mtp_block(
             positions=positions, x=hidden_states, input_ids=None
         )
+        hidden_states = self.mtp_block.hc_post(
+            hidden_states, residual, post_mix, res_mix
+        )
         # Return the flat pre-hc_head residual so it can be re-fed as the
         # next spec step's `previous_hidden_states` when
         # num_speculative_tokens > 1. hc_head is deferred to compute_logits.