feat(v2): complete v2 reimplementation

tests/fault/test_deletion_failure.py

@@ -0,0 +1,23 @@
+from __future__ import annotations
+
+from datetime import timedelta
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+from backup_tool.gc import purge_repository
+
+
+def test_gc_keeps_manifest_when_unlink_fails(tmp_path: Path) -> None:
+    root = tmp_path / "repository"
+    manifest = root / "manifests" / "deleted.json"
+    manifest.parent.mkdir(parents=True)
+    manifest.write_text('{"entries": []}', encoding="utf-8")
+
+    with (
+        patch("pathlib.Path.unlink", side_effect=OSError("read-only")),
+        pytest.raises(OSError),
+    ):
+        purge_repository(root, {"deleted"}, grace=timedelta(0))
+
+    assert manifest.exists()