[LoRA][Spec Decode] Support LoRA for Nemotron-H MTP models (#32265)

Signed-off-by: Daniel Serebrenik <daserebrenik@nvidia.com>
Co-authored-by: Jee Jee Li <pandaleefree@gmail.com>

vllm/model_executor/models/interfaces.py

@@ -521,6 +521,8 @@ class SupportsLoRA(Protocol):
     # are empty by default.
     embedding_modules: ClassVar[dict[str, str]] = {}
     packed_modules_mapping: dict[str, list[str]] = {}
+    # Module prefixes to skip during LoRA loading (e.g., ["mtp."] for MTP layers)
+    lora_skip_prefixes: ClassVar[list[str]] = []
 
 
 # We can't use runtime_checkable with ClassVar for issubclass checks

vllm/model_executor/models/nemotron_h.py

@@ -771,6 +771,9 @@ class NemotronHForCausalLM(
         "lm_head": "output_embeddings",
     }
 
+    # Skip MTP (Multi-Token Prediction) layers during LoRA loading
+    lora_skip_prefixes = ["mtp."]
+
     @classmethod
     def get_mamba_state_dtype_from_config(
         cls,