diff --git a/application/workflows/co4e_workflow_service.py b/application/workflows/co4e_workflow_service.py
index 549c18e..3b2d3cb 100644
--- a/application/workflows/co4e_workflow_service.py
+++ b/application/workflows/co4e_workflow_service.py
@@ -35,6 +35,8 @@ service này.
 """
 from __future__ import annotations
 
+from ...infrastructure.persistence.json.atomic_json_file import AtomicJsonFile
+
 import json
 import os
 from datetime import datetime
@@ -174,10 +176,10 @@ class Co4EWorkflowService:
         payload = {"runs": [r.to_dict() for r in runs]}
         try:
             self._history_path_value.parent.mkdir(parents=True, exist_ok=True)
-            tmp = self._history_path_value.with_suffix(".json.tmp")
-            tmp.write_text(json.dumps(payload, ensure_ascii=False, indent=2),
-                           encoding="utf-8")
-            tmp.replace(self._history_path_value)   # atomic — khong bao gio de lai file ghi do dang
+            # AtomicJsonFile thay cho tmp+replace tự viết: bản cũ thiếu fsync
+            # (dữ liệu có thể còn trong bộ đệm khi mất điện) và dùng thẳng
+            # Path.replace, vốn thỉnh thoảng bị Defender từ chối trên Windows.
+            AtomicJsonFile(self._history_path_value).write(payload)
         except OSError:
             # Giu dung hanh vi cu (core/co4e_run_manager.py::_save_history):
             # mot lan luu that bai (day dia, mat quyen...) KHONG duoc phep
diff --git a/core/co4e.py b/core/co4e.py
index e0337c4..46e3682 100644
--- a/core/co4e.py
+++ b/core/co4e.py
@@ -18,6 +18,8 @@ existing ``core/skills.py`` registry.
 """
 from __future__ import annotations
 
+from ..infrastructure.persistence.json.atomic_json_file import AtomicJsonFile
+
 import json
 from dataclasses import asdict, dataclass, field
 from pathlib import Path
@@ -233,7 +235,9 @@ def save_workflow(wf: Workflow, directory: Optional[Path] = None) -> Path:
     directory = directory or WORKFLOWS_DIR
     directory.mkdir(parents=True, exist_ok=True)
     path = directory / f"{wf.id}.json"
-    path.write_text(json.dumps(workflow_to_dict(wf), ensure_ascii=False, indent=2), encoding="utf-8")
+    # Tiêu chí nghiệm thu A: mọi thao tác ghi tệp đi qua AtomicJsonFile. Trước
+    # đây ghi thẳng, nên tắt máy giữa lúc lưu là mất luôn workflow.
+    AtomicJsonFile(path).write(workflow_to_dict(wf))
     return path
 
 
@@ -307,7 +311,7 @@ def save_custom_agent(agent: CustomAgent, directory: Optional[Path] = None) -> P
     directory = directory or AGENTS_DIR
     directory.mkdir(parents=True, exist_ok=True)
     path = directory / f"{agent.id}.json"
-    path.write_text(json.dumps(agent_to_dict(agent), ensure_ascii=False, indent=2), encoding="utf-8")
+    AtomicJsonFile(path).write(agent_to_dict(agent))
     return path
 
 
diff --git a/core/co4e_run_manager.py b/core/co4e_run_manager.py
index c92662f..1695401 100644
--- a/core/co4e_run_manager.py
+++ b/core/co4e_run_manager.py
@@ -13,6 +13,8 @@ the run that is currently open.
 """
 from __future__ import annotations
 
+from ..infrastructure.persistence.json.atomic_json_file import AtomicJsonFile
+
 import json
 from pathlib import Path
 from typing import Dict, List, Optional
@@ -152,10 +154,10 @@ class Co4ERunManager(QObject):
         payload = {"runs": [h.to_record() for h in runs]}
         try:
             path.parent.mkdir(parents=True, exist_ok=True)
-            tmp = path.with_suffix(".json.tmp")
-            tmp.write_text(json.dumps(payload, ensure_ascii=False, indent=2),
-                           encoding="utf-8")
-            tmp.replace(path)         # atomic — never leaves a half-written file
+            # AtomicJsonFile thay cho tmp+replace tự viết: bản cũ thiếu fsync
+            # (dữ liệu có thể còn trong bộ đệm khi mất điện) và dùng thẳng
+            # Path.replace, vốn thỉnh thoảng bị Defender từ chối trên Windows.
+            AtomicJsonFile(path).write(payload)
         except OSError:
             pass