diff --git a/backend/app/services/ar_overdue_alert.py b/backend/app/services/ar_overdue_alert.py
index 26f96484..dd21218f 100644
--- a/backend/app/services/ar_overdue_alert.py
+++ b/backend/app/services/ar_overdue_alert.py
@@ -706,7 +706,7 @@ def compute(
         unit_total = _dec(r.get("total_amt"))
         pct = (float(c["overdue_amt"] / unit_total) if unit_total > 0 else None)
         msg = _clip(
-            "【应收账款逾期】%s（%s）%s 期末逾期 %d 天以上 ¥%s，占该户应收 %s%%｜建议：%s｜责任人：%s"
+            "【应收账款逾期】%s（%s）%s 账龄最老 %d 天，逾期合计 ¥%s（占该户 %s%%）｜建议：%s｜责任人：%s"
             % (
                 r.get("unit_name"), r.get("unit_code"), period, c["oldest_days"],
                 _fmt_money(c["overdue_amt"]), _fmt_pct(pct), action or "见规则配置", who["name"],
diff --git a/backend/tests/test_ar_aging_overdue_20261020.py b/backend/tests/test_ar_aging_overdue_20261020.py
index 0fa5cf9a..90746639 100644
--- a/backend/tests/test_ar_aging_overdue_20261020.py
+++ b/backend/tests/test_ar_aging_overdue_20261020.py
@@ -232,6 +232,36 @@ def test_single_overdue_red_and_yellow_households(staff: Session):
         assert "｜责任人：" in c["alert_message"]
 
 
+def test_single_customer_message_wording_hkjj120_20261021(aging: Session):
+    """D2（2026-10-21）：单户文案须把「最老账龄」与「逾期合计」分开写清。
+
+    样例 = 生产 HKJJ120 逐档实数（借方应收户口径，只读复核）：
+      total 352,494.00 = 52,374 + 34,549 + 35,799 + 80,191 + 84,466 + 65,115
+      31 天以上逾期合计 = 300,120.00（占该户 85.14%），150+ 档 = 65,115.00。
+    旧文案「期末逾期 151 天以上 ¥300,120.00」会被读成「最老档就是 30 万」，
+    故本用例硬断言旧措辞不再出现、新措辞逐字出现，且判据字段（金额/天数/占比）零变化。
+    """
+    _reset_table(aging)
+    _add(aging, "2026-09", "HKJJ120", "西安酣君品创贸易有限责任公司", 352494.00,
+         [52374.00, 34549.00, 35799.00, 80191.00, 84466.00, 65115.00])
+    p = json.loads(json.dumps(BASE_PARAMS))
+    p["assignee_by_unit"] = {"HKJJ120": "李世昌"}
+    res = ar_overdue_alert.compute(aging, ENT, "2026-09", p)
+    c = {x["unit_code"]: x for x in res["per_customer"]}["HKJJ120"]
+    # 判据字段（禁随文案改动）
+    assert c["level"] == "red"
+    assert c["oldest_days"] == 151
+    assert c["overdue_amt"] == pytest.approx(300120.00)
+    assert c["total_amt"] == pytest.approx(352494.00)
+    assert c["pct_of_unit"] == pytest.approx(0.851419, abs=1e-6)
+    # 文案口径
+    assert "账龄最老 151 天，逾期合计 ¥300,120.00（占该户 85.14%）" in c["alert_message"]
+    assert "期末逾期" not in c["alert_message"]
+    assert c["alert_message"].count("｜建议：") == 1
+    assert c["alert_message"].endswith("｜责任人：李世昌")
+    assert len(c["alert_message"]) <= 500
+
+
 def test_assignee_chain_salesman_then_dept(staff: Session):
     res = ar_overdue_alert.compute(staff, ENT, "2026-09", BASE_PARAMS)
     by_code = {c["unit_code"]: c for c in res["per_customer"]}