fix(db): 假值系统配置落库而非删除记录，布尔开关关闭态可持久化（#6309）

SystemConfigOper.set/async_set 原先对假值（False/0/None/空容器）执行删除记录，
读取端以「无记录」表示未配置并回落默认值，导致「挂载盘删除空目录」等布尔开关
关闭后刷新自动弹回开启。现改为假值同样落库更新，显式删除仍走 delete 方法。

app/db/systemconfig_oper.py

@@ -41,10 +41,9 @@ class SystemConfigOper(DbOper, metaclass=Singleton):
             conf = SystemConfig.get_by_key(self._db, key)
             if conf:
                 if old_value != value:
-                    if value:
-                        conf.update(self._db, {"value": value})
-                    else:
-                        conf.delete(self._db, conf.id)
+                    # 假值（False/0/None/空容器）同样落库而不是删除记录：
+                    # 读取端以「无记录」表示未配置并回落默认值，删除会使布尔开关的关闭态无法持久化
+                    conf.update(self._db, {"value": value})
                     return True
                 return None
             else:
@@ -77,10 +76,9 @@ class SystemConfigOper(DbOper, metaclass=Singleton):
                 return None
             # 执行数据库更新
             if conf:
-                if value:
-                    await conf.async_update(self._db, {"value": value})
-                else:
-                    await conf.async_delete(self._db, conf.id)
+                # 假值（False/0/None/空容器）同样落库而不是删除记录：
+                # 读取端以「无记录」表示未配置并回落默认值，删除会使布尔开关的关闭态无法持久化
+                await conf.async_update(self._db, {"value": value})
             else:
                 conf = SystemConfig(key=key, value=value)
                 await conf.async_create(self._db)

tests/test_systemconfig_oper.py

@@ -1,8 +1,24 @@
 import threading
+import uuid
 from concurrent.futures import ThreadPoolExecutor
 
+import pytest
+
+from app.db.models.systemconfig import SystemConfig
 from app.db.systemconfig_oper import SystemConfigOper
 from app.schemas.types import SystemConfigKey
+from app.utils.singleton import Singleton
+
+
+def _unique_key() -> str:
+    """生成独立测试键，避免用例间相互污染。"""
+    return f"__test__{uuid.uuid4().hex}"
+
+
+def _fresh_oper() -> SystemConfigOper:
+    """重置单例并从数据库重新加载配置缓存。"""
+    Singleton._instances.pop((SystemConfigOper, (), frozenset()), None)
+    return SystemConfigOper()
 
 
 def test_increment_serializes_concurrent_counter_updates(monkeypatch):
@@ -49,3 +65,76 @@ def test_increment_supports_custom_step(monkeypatch):
 
     assert result == 7
     assert stored_value["value"] == 7
+
+
+def test_set_creates_record_for_falsy_value():
+    """无记录时写入假值应创建记录，而不是丢弃配置。"""
+    key = _unique_key()
+    oper = _fresh_oper()
+
+    assert oper.set(key, False) is True
+    assert oper.get(key) is False
+    assert SystemConfig.get_by_key(oper._db, key) is not None
+
+
+def test_set_persists_falsy_value_on_existing_record():
+    """已存在记录时写入假值应更新记录，而不是删除记录回落默认值。"""
+    key = _unique_key()
+    oper = _fresh_oper()
+
+    oper.set(key, True)
+    assert oper.set(key, False) is True
+    assert oper.get(key) is False
+    assert SystemConfig.get_by_key(oper._db, key).value is False
+
+
+@pytest.mark.asyncio
+async def test_async_set_persists_falsy_value_on_existing_record():
+    """异步写入假值同样应更新记录而不是删除记录。"""
+    key = _unique_key()
+    oper = _fresh_oper()
+
+    oper.set(key, True)
+    assert await oper.async_set(key, False) is True
+    assert oper.get(key) is False
+    assert SystemConfig.get_by_key(oper._db, key).value is False
+
+
+@pytest.mark.asyncio
+async def test_async_set_creates_record_for_falsy_value():
+    """异步写入假值且无记录时应创建记录。"""
+    key = _unique_key()
+    oper = _fresh_oper()
+
+    assert await oper.async_set(key, 0) is True
+    assert oper.get(key) == 0
+    assert SystemConfig.get_by_key(oper._db, key).value == 0
+
+
+def test_delete_removes_record_explicitly():
+    """显式 delete 仍是删除配置的唯一途径。"""
+    key = _unique_key()
+    oper = _fresh_oper()
+
+    oper.set(key, False)
+    assert oper.delete(key) is True
+    assert oper.get(key) is None
+    assert SystemConfig.get_by_key(oper._db, key) is None
+
+
+def test_mounted_local_disk_delete_empty_dirs_off_is_persisted():
+    """回归：挂载盘删除空目录开关关闭后，读取端不应回落默认开启（issue #6309）。"""
+    key = SystemConfigKey.MountedLocalDiskDeleteEmptyDirs.value
+    oper = _fresh_oper()
+
+    # 模拟前端保存关闭：已有记录（开启）→ 关闭
+    oper.set(key, True)
+    oper.set(key, False)
+    # 复刻 app/chain/transfer.py 的读取语义：无记录视为默认开启
+    assert (oper.get(key) is not False) is False
+
+    # 模拟全新安装首次保存关闭：无记录 → 创建关闭记录
+    Singleton._instances.pop((SystemConfigOper, (), frozenset()), None)
+    oper.delete(key)
+    _fresh_oper().set(key, False)
+    assert _fresh_oper().get(key) is False