Create custom run ancestors privately

src/format_bench/workflow.py

@@ -49,6 +49,20 @@ def _default_run_dir(root: Path, dataset_id: str) -> Path:
     return root / "runs" / f"{dataset_id}-{stamp}"
 
 
+def _create_missing_private_parents(destination: Path) -> None:
+    missing: list[Path] = []
+    parent = destination.parent
+    while not parent.exists():
+        missing.append(parent)
+        parent = parent.parent
+
+    # LLM contract: EXISTING_ANCESTOR -> PRIVATE_ANCESTORS_READY | FAILED.
+    # Create shallow-to-deep without parents=True so every new level requests
+    # 0700; any mkdir failure stops before the private run leaf is created.
+    for directory in reversed(missing):
+        directory.mkdir(mode=0o700)
+
+
 def _safe_format_component(
     value: object, label: str, *, extension: bool = False
 ) -> str:
@@ -143,11 +157,9 @@ def prepare_run(
     destination = run_dir or _default_run_dir(root, dataset_id)
     if run_dir is None:
         destination.parent.mkdir(mode=0o700, exist_ok=True)
-    destination.mkdir(
-        mode=0o700,
-        parents=run_dir is not None,
-        exist_ok=False,
-    )
+    else:
+        _create_missing_private_parents(destination)
+    destination.mkdir(mode=0o700, exist_ok=False)
     input_dir = destination / "input"
     input_dir.mkdir(mode=0o700)
 

tests/test_workflow.py

@@ -215,6 +215,50 @@ def record_mode(
     assert (run_dir / "manifest.json").is_file()
 
 
+@pytest.mark.skipif(os.name != "posix", reason="POSIX directory-mode contract")
+@pytest.mark.parametrize("mask", (0o002, 0o000))
+def test_prepare_run_creates_each_missing_custom_ancestor_privately(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+    mask: int,
+) -> None:
+    root = Path(__file__).parents[1]
+    existing_parent = tmp_path / "existing"
+    existing_parent.mkdir(mode=0o700)
+    first_ancestor = existing_parent / "first"
+    second_ancestor = first_ancestor / "second"
+    run_dir = second_ancestor / "run"
+    created_levels = (first_ancestor, second_ancestor, run_dir)
+    requested_modes: dict[Path, int] = {}
+    real_mkdir = Path.mkdir
+
+    def record_mode(
+        path: Path,
+        mode: int = 0o777,
+        parents: bool = False,
+        exist_ok: bool = False,
+    ) -> None:
+        if path in created_levels:
+            requested_modes[path] = mode
+            assert parents is False
+        real_mkdir(path, mode=mode, parents=parents, exist_ok=exist_ok)
+
+    monkeypatch.setattr(Path, "mkdir", record_mode)
+
+    previous_mask = os.umask(mask)
+    try:
+        prepared = prepare_run(root, DATASET, run_dir, fixture=True, selected=())
+    finally:
+        os.umask(previous_mask)
+
+    assert prepared == run_dir
+    assert requested_modes == {directory: 0o700 for directory in created_levels}
+    for directory in created_levels:
+        assert stat.S_IMODE(directory.stat().st_mode) == 0o700
+    assert (run_dir / "input" / "manifest.json").is_file()
+    assert (run_dir / "manifest.json").is_file()
+
+
 @pytest.mark.skipif(os.name != "posix", reason="POSIX directory-mode contract")
 @pytest.mark.parametrize("mask", (0o002, 0o000))
 def test_prepare_run_creates_missing_default_parent_privately(