tests/config(test[duplicates]): cover ordered loader items and writer

why: Drive duplicate-preserving loader and writer work via failing tests and CLI regression coverage.
what:
- assert DuplicateAwareConfigReader exposes ordered top-level items
- add writer regression verifying duplicate sections persist on save
- extend CLI no-merge test expectations and discovery mocks for new loader API

Author: tony

tests/cli/test_add.py

@@ -820,7 +820,10 @@ class NoMergePreservationFixture(t.NamedTuple):
 
 
 @pytest.mark.xfail(
-    reason="vcspull add --no-merge overwrites earlier duplicate workspace sections (data loss bug)",
+    reason=(
+        "vcspull add --no-merge overwrites earlier duplicate workspace sections "
+        "(data loss bug)"
+    ),
 )
 @pytest.mark.parametrize(
     list(NoMergePreservationFixture._fields),
@@ -837,7 +840,7 @@ def test_add_repo_no_merge_preserves_duplicate_sections(
     tmp_path: pathlib.Path,
     monkeypatch: MonkeyPatch,
 ) -> None:
-    """vcspull add should not drop duplicate workspace sections when --no-merge."""
+    """CLI add should not drop duplicate workspace sections when --no-merge."""
     monkeypatch.setenv("HOME", str(tmp_path))
     monkeypatch.chdir(tmp_path)
 
@@ -850,9 +853,11 @@ def test_add_repo_no_merge_preserves_duplicate_sections(
     (
         _initial_config,
         initial_duplicates,
+        initial_items,
     ) = DuplicateAwareConfigReader.load_with_duplicates(config_file)
     assert workspace_label in initial_duplicates
     assert len(initial_duplicates[workspace_label]) == 2
+    assert [key for key, _ in initial_items] == [workspace_label, workspace_label]
 
     add_repo(
         name=new_repo_name,
@@ -867,8 +872,14 @@ def test_add_repo_no_merge_preserves_duplicate_sections(
     (
         _final_config,
         duplicate_sections,
+        final_items,
     ) = DuplicateAwareConfigReader.load_with_duplicates(config_file)
 
+    assert [key for key, _ in final_items] == [
+        workspace_label,
+        workspace_label,
+    ], f"{test_id}: final items unexpectedly merged"
+
     assert workspace_label in duplicate_sections, f"{test_id}: workspace missing"
     workspace_entries = duplicate_sections[workspace_label]
     assert len(workspace_entries) == 2, f"{test_id}: duplicate sections collapsed"

tests/cli/test_discover.py

@@ -441,7 +441,7 @@ def test_discover_config_load_edges(
         if mode == "non_dict":
             monkeypatch.setattr(
                 "vcspull.cli.discover.DuplicateAwareConfigReader.load_with_duplicates",
-                lambda _path: (["invalid"], {}),
+                lambda _path: (["invalid"], {}, []),
             )
         else:  # mode == "exception"
 

tests/test_config_reader.py

@@ -93,3 +93,41 @@ def test_duplicate_aware_reader_passes_through_json(tmp_path: pathlib.Path) -> N
         },
     }
     assert reader.duplicate_sections == {}
+
+
+def test_duplicate_aware_reader_preserves_top_level_item_order(
+    tmp_path: pathlib.Path,
+) -> None:
+    """Loader should expose ordered top-level items so duplicates can be replayed."""
+    yaml_content = textwrap.dedent(
+        """\
+        ~/study/python/:
+          Flexget:
+            repo: git+https://github.com/Flexget/Flexget.git
+        ~/study/python/:
+          bubbles:
+            repo: git+https://github.com/Stiivi/bubbles.git
+        ~/study/python/:
+          cubes:
+            repo: git+https://github.com/Stiivi/cubes.git
+        """,
+    )
+    config_path = _write(tmp_path, "ordered.yaml", yaml_content)
+
+    reader = DuplicateAwareConfigReader.from_file(config_path)
+
+    items = reader.top_level_items
+    assert [key for key, _ in items] == [
+        "~/study/python/",
+        "~/study/python/",
+        "~/study/python/",
+    ]
+    assert items[0][1] == {
+        "Flexget": {"repo": "git+https://github.com/Flexget/Flexget.git"},
+    }
+    assert items[1][1] == {
+        "bubbles": {"repo": "git+https://github.com/Stiivi/bubbles.git"},
+    }
+    assert items[2][1] == {
+        "cubes": {"repo": "git+https://github.com/Stiivi/cubes.git"},
+    }

tests/test_config_writer.py

@@ -0,0 +1,54 @@
+"""Tests for duplicate-preserving config writer utilities."""
+
+from __future__ import annotations
+
+import pathlib
+import textwrap
+import typing as t
+
+import pytest
+
+from vcspull.config import save_config_yaml_with_items
+
+FixtureEntry = tuple[str, dict[str, t.Any]]
+
+
+@pytest.mark.parametrize(
+    ("entries", "expected_yaml"),
+    [
+        (
+            (
+                (
+                    "~/study/python/",
+                    {"Flexget": {"repo": "git+https://github.com/Flexget/Flexget.git"}},
+                ),
+                (
+                    "~/study/python/",
+                    {"bubbles": {"repo": "git+https://github.com/Stiivi/bubbles.git"}},
+                ),
+            ),
+            textwrap.dedent(
+                """\
+                ~/study/python/:
+                  Flexget:
+                    repo: git+https://github.com/Flexget/Flexget.git
+                ~/study/python/:
+                  bubbles:
+                    repo: git+https://github.com/Stiivi/bubbles.git
+                """,
+            ),
+        ),
+    ],
+)
+def test_save_config_yaml_with_items_preserves_duplicate_sections(
+    entries: tuple[FixtureEntry, ...],
+    expected_yaml: str,
+    tmp_path: pathlib.Path,
+) -> None:
+    """Writing duplicates should round-trip without collapsing sections."""
+    config_path = tmp_path / ".vcspull.yaml"
+
+    save_config_yaml_with_items(config_path, list(entries))
+
+    yaml_text = config_path.read_text(encoding="utf-8")
+    assert yaml_text == expected_yaml