diff --git a/docs/dashboard-overview-api.md b/docs/dashboard-overview-api.md
index 3c07c38cf..e8e001e5b 100644
--- a/docs/dashboard-overview-api.md
+++ b/docs/dashboard-overview-api.md
@@ -29,7 +29,7 @@
 - red/yellow/green 状态变化输出 `market.<region>.status`。
 - change item 的 quality 取 current/previous 两份快照中较差的一侧；任一侧 partial 会降低整个 what_changed 块，任一侧 unavailable 不生成可靠变化项。
 - 没有第二份有效快照时，返回 `previous_completed_snapshot_unavailable`；部分 region 缺基线时整个块标记为 `partial`，并追加 `previous_completed_snapshot_unavailable:<region>`，避免把“缺少基线”误解为“没有变化”。不会临时拉行情或生成一份“当前”快照冒充基线。
-- 历史详情读取失败，或投影出的 `context_snapshot` 不是 JSON object（例如损坏的 JSON 字符串）时，不再把其余更旧记录提升为 current/latest；对应快照和变化对比保持不可用并返回 limitation。
+- 历史详情读取失败、投影出的 `context_snapshot` 不是 JSON object，或其中已存在的 `market_light_snapshots` 不是 object（例如损坏的 JSON 字符串/数组）时，不再把其余更旧记录提升为 current/latest；对应快照和变化对比保持不可用并返回 limitation。
 - 快照校验失败时仍保留其 `trade_date` 的目标位置：最新日期无有效快照时不回退到更旧 current，最近更早日期无有效快照时不越过它继续寻找更旧 previous。同一目标日期存在其他有效重跑快照时，仍可使用该日期的有效版本。
 - 外层市场键必须与快照内部 `region` 一致；例如 `cn` 键下的 `region=us` 快照会按无效快照处理，不能进入 A 股的 current/previous 或变化项。
 - 历史扫描被截断等 market limitations 会同步进入 what_changed；剩余快照不能在来源历史不完整时被标记为 fresh。
diff --git a/src/services/dashboard_overview_service.py b/src/services/dashboard_overview_service.py
index 728242991..cc23e71a4 100644
--- a/src/services/dashboard_overview_service.py
+++ b/src/services/dashboard_overview_service.py
@@ -88,6 +88,10 @@ class DashboardOverviewService:
                     if not isinstance(context_snapshot, dict):
                         detail_failure_count += 1
                         continue
+                    snapshot_container = context_snapshot.get("market_light_snapshots")
+                    if snapshot_container is not None and not isinstance(snapshot_container, dict):
+                        detail_failure_count += 1
+                        continue
                     raw_snapshots = self._extract_snapshots(context_snapshot)
                     for region, raw_snapshot in raw_snapshots.items():
                         raw_trade_date = str(raw_snapshot.get("trade_date") or "").strip()
diff --git a/tests/test_dashboard_overview_api.py b/tests/test_dashboard_overview_api.py
index e110468e6..6a46d1ccf 100644
--- a/tests/test_dashboard_overview_api.py
+++ b/tests/test_dashboard_overview_api.py
@@ -296,6 +296,26 @@ def test_malformed_projected_context_does_not_promote_older_snapshots() -> None:
     assert "latest_completed_snapshot_unavailable" in payload["market"]["meta"]["limitations"]
 
 
+def test_malformed_nested_snapshot_container_does_not_promote_older_snapshots() -> None:
+    dependencies = _dependencies()
+    original_detail = dependencies["history_service"].get_history_detail_by_id.side_effect
+
+    def detail_with_malformed_container(record_id: int) -> dict:
+        if record_id == 1:
+            return {"context_snapshot": {"market_light_snapshots": "{invalid-json"}}
+        return original_detail(record_id)
+
+    dependencies["history_service"].get_history_detail_by_id.side_effect = detail_with_malformed_container
+
+    payload = DashboardOverviewService(**dependencies).get_overview()
+
+    assert payload["market"]["data"]["latest_snapshots"] == {}
+    assert payload["what_changed"]["data"]["current_trade_dates"] == {}
+    assert payload["what_changed"]["data"]["items"] == []
+    assert "market_review_detail_partial" in payload["market"]["meta"]["limitations"]
+    assert "latest_completed_snapshot_unavailable" in payload["market"]["meta"]["limitations"]
+
+
 def test_invalid_latest_snapshot_does_not_promote_an_older_trade_date() -> None:
     dependencies = _dependencies()
     reviews = [