refactor: 收口 V3 分层架构与插件兼容边界

app/application/database.py

@@ -0,0 +1,37 @@
+"""数据库连通性应用服务。"""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+from typing import Optional
+
+
+DatabaseProbe = Callable[[], Optional[str]]
+
+
+class DatabaseHealthService:
+    """为模块和诊断入口提供不暴露会话实现的数据库探测能力。"""
+
+    def __init__(self, probe: DatabaseProbe) -> None:
+        """保存由组合根提供的数据库探测端口。"""
+        self._probe = probe
+
+    def test(self) -> Optional[str]:
+        """执行数据库探测，成功返回空值，失败返回说明。"""
+        return self._probe()
+
+
+_configured_database_health: DatabaseHealthService | None = None
+
+
+def configure_database_health(service: DatabaseHealthService) -> None:
+    """由启动组合根登记数据库探测服务。"""
+    global _configured_database_health
+    _configured_database_health = service
+
+
+def get_configured_database_health() -> DatabaseHealthService:
+    """返回启动阶段登记的数据库探测服务。"""
+    if _configured_database_health is None:
+        raise RuntimeError("数据库探测服务尚未配置")
+    return _configured_database_health