diff --git a/api/core/plugin/impl/model_runtime.py b/api/core/plugin/impl/model_runtime.py
index 7d0f7fd5ba..51df79b7ea 100644
--- a/api/core/plugin/impl/model_runtime.py
+++ b/api/core/plugin/impl/model_runtime.py
@@ -298,6 +298,8 @@ class PluginModelRuntime(ModelRuntime):
         LLMResultWithStructuredOutput
         | Generator[LLMResultChunkWithStructuredOutput, None, None]
     ): 
+        # TODO: added to pass type check.
+        # it is a new method from upstream that is not invoked at all.
         raise NotImplementedError
 
     def get_llm_num_tokens(
diff --git a/api/services/workflow_draft_variable_service.py b/api/services/workflow_draft_variable_service.py
index fa0b6fa3fa..aed3819f18 100644
--- a/api/services/workflow_draft_variable_service.py
+++ b/api/services/workflow_draft_variable_service.py
@@ -5,7 +5,7 @@ from collections.abc import Mapping, Sequence
 from concurrent.futures import ThreadPoolExecutor
 from datetime import datetime
 from enum import StrEnum
-from typing import Any, ClassVar, NotRequired, TypedDict, cast
+from typing import Any, ClassVar, NotRequired, TypedDict
 
 from sqlalchemy import Engine, delete, orm, select
 from sqlalchemy.dialects.mysql import insert as mysql_insert
@@ -32,7 +32,7 @@ from graphon.file import File
 from graphon.nodes import BuiltinNodeTypes
 from graphon.nodes.variable_assigner.common.helpers import get_updated_variables
 from graphon.variable_loader import VariableLoader
-from graphon.variables import Segment, StringSegment, VariableBase
+from graphon.variables import Segment, StringSegment, Variable, VariableBase
 from graphon.variables.consts import SELECTORS_LENGTH
 from graphon.variables.segments import (
     ArrayFileSegment,
@@ -162,7 +162,7 @@ class DraftVarLoader(VariableLoader):
 
         return list(variable_by_selector.values())
 
-    def _load_offloaded_variable(self, draft_var: WorkflowDraftVariable) -> tuple[tuple[str, str], VariableBase]:
+    def _load_offloaded_variable(self, draft_var: WorkflowDraftVariable) -> tuple[tuple[str, str], Variable]:
         # This logic is closely tied to `WorkflowDraftVaribleService._try_offload_large_variable`
         # and must remain synchronized with it.
         # Ideally, these should be co-located for better maintainability.