feat(v2): complete v2 reimplementation

backend/src/backup_tool/observability/health.py

@@ -0,0 +1,39 @@
+"""Readiness checks shared by HTTP and background process roles."""
+
+from __future__ import annotations
+
+import os
+
+from backup_tool.cli import build_alembic_config
+from backup_tool.config import Settings
+from backup_tool.db.engine import assert_schema_current, create_engine
+
+
+class ReadinessError(RuntimeError):
+    """A dependency needed by the selected role is unavailable."""
+
+
+def _require_access(path: object, mode: int) -> None:
+    try:
+        candidate = path if isinstance(path, str) else str(path)
+        if not os.path.isdir(candidate) or not os.access(candidate, mode):
+            raise ReadinessError("required storage is unavailable")
+    except OSError as error:
+        raise ReadinessError("required storage is unavailable") from error
+
+
+async def check_role_readiness(settings: Settings, role: str) -> None:
+    engine = create_engine(settings)
+    try:
+        await assert_schema_current(engine, build_alembic_config(settings))
+    except Exception as error:
+        raise ReadinessError("metadata is unavailable") from error
+    finally:
+        await engine.dispose()
+    if role == "scheduler":
+        return
+    _require_access(settings.data_dir, os.R_OK | os.W_OK | os.X_OK)
+    for root in settings.repository_roots + settings.restore_roots:
+        _require_access(root, os.R_OK | os.W_OK | os.X_OK)
+    for root in settings.local_source_roots:
+        _require_access(root, os.R_OK | os.X_OK)