refactor: remove legacy assistant compatibility

backend/routes/assistants.py

@@ -20,7 +20,7 @@ from schemas import (
 )
 from services.auth import require_admin
 from services.masking import mask, resolve_incoming_key
-from services.node_specs import graph_references, normalize_graph, validate_graph
+from services.node_specs import copy_graph, graph_references, validate_graph
 from services.state_expressions import StateExpressionError, validate_update_rules
 from services.system_tools import RESERVED_TOOL_NAMES
 from services.tool_policy import policy_for_tool
@@ -98,9 +98,9 @@ def _validate_workflow(body: AssistantUpsert) -> None:
     if body.graph and str(body.graph.get("specVersion") or "") != "4":
         raise HTTPException(
             400,
-            "Workflow API 仅接受 specVersion=4；旧图请先执行数据库迁移",
+            "Workflow API 仅接受当前 specVersion=4 图结构",
         )
-    body.graph = normalize_graph(body.graph or {})
+    body.graph = copy_graph(body.graph or {})
     errors = validate_graph(body.graph)
     settings = body.graph.get("settings") or {}
     graph_runtime_mode = str(settings.get("runtimeMode") or "pipeline")
@@ -636,7 +636,7 @@ async def _to_out(session: AsyncSession, assistant: Assistant) -> AssistantOut:
         api_key=mask(assistant.api_key),
         app_id=assistant.app_id,
         graph=(
-            normalize_graph(assistant.graph or {})
+            copy_graph(assistant.graph or {})
             if assistant.type == "workflow"
             else {}
         ),