fix: Use is_speculators_eagle_config for Eagle detection in V1 check

- Import and use is_speculators_eagle_config function for cleaner detection
- This reuses the existing speculators Eagle detection logic
- Still falls back to checking model_type and name patterns if needed
- Fixes issue where speculative_method was None causing V0 fallback

Signed-off-by: rtuli@redhat.com

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Rahul Tuli <rtuli@redhat.com>

Author: rahul-tuli

vllm/engine/arg_utils.py

@@ -44,6 +44,7 @@
 from vllm.usage.usage_lib import UsageContext
 from vllm.utils import (STR_DUAL_CHUNK_FLASH_ATTN_VAL, FlexibleArgumentParser,
                         GiB_bytes, get_ip, is_in_ray_actor)
+from vllm.transformers_utils.configs.speculators_eagle import is_speculators_eagle_config
 
 # yapf: enable
 
@@ -1468,6 +1469,8 @@ def _is_v1_supported_oracle(self, model_config: ModelConfig) -> bool:
         if self.speculative_config is not None:
             # This is supported but experimental (handled below).
             speculative_method = self.speculative_config.get("method")
+            speculative_model = self.speculative_config.get("model")
+            
             if speculative_method:
                 if speculative_method in ("ngram", "[ngram]"):
                     is_ngram_enabled = True
@@ -1476,9 +1479,31 @@ def _is_v1_supported_oracle(self, model_config: ModelConfig) -> bool:
                 elif speculative_method in ("eagle", "eagle3", "deepseek_mtp"):
                     is_eagle_enabled = True
             else:
-                speculative_model = self.speculative_config.get("model")
-                if speculative_model in ("ngram", "[ngram]"):
-                    is_ngram_enabled = True
+                # If method is not set, try to detect from model
+                if speculative_model:
+                    if speculative_model in ("ngram", "[ngram]"):
+                        is_ngram_enabled = True
+                    else:
+                        # Check if it's a speculators Eagle model
+                        if is_speculators_eagle_config(speculative_model):
+                            is_eagle_enabled = True
+                        else:
+                            # Try to check regular model_type
+                            try:
+                                from transformers import PretrainedConfig
+                                config_dict, _ = PretrainedConfig.get_config_dict(
+                                    speculative_model
+                                )
+                                if config_dict.get("model_type") in ["eagle", "eagle3"]:
+                                    is_eagle_enabled = True
+                            except Exception:
+                                # If config loading fails, fall back to name checking
+                                if isinstance(speculative_model, str) and (
+                                    "eagle-" in speculative_model.lower() or 
+                                    "eagle3-" in speculative_model.lower()
+                                ):
+                                    is_eagle_enabled = True
+                        
             if not (is_ngram_enabled or is_eagle_enabled or is_medusa_enabled):
                 # Other speculative decoding methods are not supported yet.
                 _raise_or_fallback(feature_name="Speculative Decoding",