refactor: remove legacy assistant compatibility

backend/services/workflow_engine.py

@@ -9,7 +9,7 @@ from dataclasses import dataclass
 from hashlib import sha256
 from typing import Any
 
-from services.node_specs import normalize_graph
+from services.node_specs import copy_graph
 from services.runtime_variables import DynamicVariableStore
 
 
@@ -37,7 +37,7 @@ class AgentStageConfig:
 
 class WorkflowEngine:
     def __init__(self, graph: dict[str, Any]):
-        self.graph = normalize_graph(graph)
+        self.graph = copy_graph(graph)
         self.revision = self._revision_for(self.graph)
         self.settings = self.graph.get("settings") or {}
         self.nodes: dict[str, dict] = {
@@ -272,7 +272,7 @@ class WorkflowEngine:
         return default if include_default else None
 
     def llm_edges(self, node_id: str) -> list[dict]:
-        """Edges considered by the compatibility dedicated router."""
+        """Edges considered by the dedicated LLM router."""
         return [
             edge
             for edge in self.outgoing(node_id)