feat: add deterministic message interaction stages

backend/services/workflow_engine.py

@@ -190,20 +190,12 @@ class WorkflowEngine:
             sections.append(f"[当前阶段任务]\n{prompt}")
         return "\n\n".join(sections)
 
-    def greeting(self, store: DynamicVariableStore) -> str:
-        return store.render(str(self.data(self.start_id).get("greeting") or ""))
-
     def routing_prompt(self, node_id: str, store: DynamicVariableStore) -> str:
         """Describe the current node to the small LLM edge router."""
         if self.node_type(node_id) == "agent":
             return self.prompt_for(node_id, store)
         data = self.data(node_id)
-        details = (
-            data.get("greeting")
-            or data.get("message")
-            or data.get("target")
-            or ""
-        )
+        details = data.get("message") or data.get("target") or ""
         rendered = store.render(str(details)).strip()
         return f"{self.node_type(node_id) or 'workflow'} 节点：{rendered or self.name(node_id)}"