diff --git a/backend/app/services/tasks/worker.py b/backend/app/services/tasks/worker.py
index c40c5de1..3b0bc97a 100644
--- a/backend/app/services/tasks/worker.py
+++ b/backend/app/services/tasks/worker.py
@@ -207,13 +207,14 @@ def _finalize_completed(task_type: TaskType, user_id) -> None:
 def _finalize_dead_letter(
     task_type: TaskType, payload: dict, user_id, *, error: Exception
 ) -> None:
-    """終端ステータス（dead_letter）への更新と失敗通知をまとめて行う。"""
+    """終端ステータス（dead_letter）への更新と失敗通知を行う。
 
-    def work(db: Session) -> None:
-        _mark_dead_letter(db, task_type, payload, error=error)
-        _notify_if_real_user(db, task_type, user_id, "failed")
-
-    _run_in_new_session(work)
+    ``_mark_dead_letter`` は DB エラーを握りつぶす（rollback しない）ため、commit 失敗時に
+    セッションが失効状態のまま残りうる。通知作成が汚染セッションを再利用しないよう、
+    状態更新と通知はそれぞれ独立した新規セッションで実行する。
+    """
+    _run_in_new_session(lambda db: _mark_dead_letter(db, task_type, payload, error=error))
+    _run_in_new_session(lambda db: _notify_if_real_user(db, task_type, user_id, "failed"))
 
 
 def _finalize_retrying(
diff --git a/backend/tests/test_worker/test_github_link.py b/backend/tests/test_worker/test_github_link.py
index c50af5c2..add2dc9f 100644
--- a/backend/tests/test_worker/test_github_link.py
+++ b/backend/tests/test_worker/test_github_link.py
@@ -199,6 +199,7 @@ def test_contribution_calendar_persisted_in_result(
 
         db_session.refresh(cache)
         assert cache.status == "completed"
+        assert cache.result is not None
         assert cache.result["contribution_calendar"]["total_contributions"] == 7
         assert cache.result["contribution_calendar"]["weeks"][0][0]["level"] == 2
         assert cache.warning_message is None
@@ -242,6 +243,7 @@ def test_contribution_fetch_failure_sets_warning(
 
         db_session.refresh(cache)
         assert cache.status == "completed"
+        assert cache.result is not None
         assert cache.result["contribution_calendar"] is None
         assert cache.warning_message is not None
 
diff --git a/frontend/src/components/forms/CareerFormEditors/ClientEditor.tsx b/frontend/src/components/forms/CareerFormEditors/ClientEditor.tsx
index 3600cb23..5c5b1aa0 100644
--- a/frontend/src/components/forms/CareerFormEditors/ClientEditor.tsx
+++ b/frontend/src/components/forms/CareerFormEditors/ClientEditor.tsx
@@ -229,7 +229,7 @@ export function ClientEditor({
         className="danger"
         onClick={() => onRemoveClient(expIndex, clientIndex)}
       >
-        取引先を削除
+        {client.is_vacation ? "休業を削除" : "取引先を削除"}
       </button>
     </div>
   );