perf(gix): resolve fixed metadata paths from the native Git directory

GitPython asks `--git-path` for `modules` and `COMMIT_EDITMSG`. Git's
`path.c` keeps these fixed leaves in the private Git directory, including
linked worktrees; the location is already available from Gix. Resolve the
repository's canonical Git directory through Gix and append only those two
leaf names. Use the existing `to_native_path_linux()` formatter for Git's
forward-slash output on Windows. This is the native-location adaptation
permitted by `AGENTS.md`.

Keep arbitrary metadata names on Git, since objects, indexes, hooks and other
paths have separate configuration/environment or common-directory rules.
Symlinked metadata leaves also retain CLI canonicalization, including dangling
targets. Do not implement the general Git path resolver in Python.

Each ordinary fixed-path lookup drops from one CLI launch to zero. Regression
tests forbid launches for both names across normal, bare and linked worktrees,
including a bare main repository, and compare all returned paths with Git.
Additional cases require CLI for metadata symlinks and an unconverted path.

Validation: affected metadata/submodule/commit-message tests passed with Gix
first (87 passed in 27.87s), plus 2 fallback cases in 0.16s, then CLI
(81 passed, 1 skipped in 62.10s). After applying the shared path formatter,
the focused checks passed again with Gix first (9 passed in 1.58s), then CLI
(3 passed, 1 skipped in 0.94s). Ruff lint/format and `git diff --check` passed.
The ledger now identifies only the remaining general-resolution requirements.

Author: codex

doc/gix-backend.md

@@ -129,7 +129,7 @@ The historical full-suite counts above predate this correction. A constant
 | `Git.get_object_header`, ODB `info` | Object resolution and native header lookup | Custom storage, unsupported revision grammar |
 | `Git.stream_object_data`, ODB `stream` | Object bytes in an independent stream | Objects larger than 8 MiB; GIX-2 |
 | `Repo` opening/discovery | Native storage, worktree, object format and empty-tree metadata | Repository-format validation, unsupported layouts/environment and native validation gaps; GIX-1/14/19 |
-| `Repo.rev_parse`, `rev_parse` metadata queries | Revision lookup, common directory, object format, bare flag, worktree root | Repository-format validation, message searches and describe forms; GIX-1/14/17 |
+| `Repo.rev_parse`, `rev_parse` metadata queries | Revision lookup, common directory, object format, bare flag, worktree root, fixed `modules`/`COMMIT_EDITMSG` locations | Repository-format validation, other metadata paths, symlinked metadata leaves, message searches and describe forms; GIX-1/14/17/22 |
 | Tree enumeration, `ls_tree` | Native tree entries with modes, names, and object IDs | Other command options |
 | Symbolic reference lookup, `symbolic_ref` | Nonrecursive target lookup | Mutation, missing-reference diagnostics |
 | Reference enumeration, `for_each_ref` | Sorted reference names and literal prefixes, preserving symbolic aliases | Dangling symbolic refs, root refs, glob patterns, other formats/options |
@@ -419,6 +419,7 @@ below use the supplied `pygix` source and its pinned Gitoxide revision.
 | GIX-18 | The tree-diff resource cache reads attributes from the index; Git also consults worktree attributes. Native binary classification with textconv configured can also differ even in `to_git` mode. | Independent attribute-source control and `--no-textconv` parity. Statistics currently fall back for any effective `diff` attribute. |
 | GIX-19 | GixPython opens repositories with `extensions.compatObjectFormat`, but translation and object-write compatibility have not been validated. The installed Git reports `compatibility hash algorithm support requires Rust` when asked to translate an ID. This is an unvalidated capability guard, not evidence of missing native object mappings. | Verify compatibility-format reads, writes and OID translation against a Git build that supports them. All operations use CLI in the meantime. |
 | GIX-21 | Native snapshot overrides for `committer.name`, `committer.email` and `gitoxide.commit.committerDate` resolve correctly. Applying them to the retained repository would expose command-specific identity to other threads. GixPython 0.1.0 has no general independent repository clone: Python `copy`/`deepcopy` fail, while the binding's internal `RepoHandle::clone()` shares its `Arc` state. | Bind a cheap independent native clone with isolated config so native identity resolution can apply per-command overrides, including removal semantics. Reopening isolates state but repeats setup; `with_object_memory()` also changes object-write behavior and is not a general clone API. Keep native process/config identity and CLI for differing command overrides. Do not mutate process environment/shared snapshots or resolve identity fields in Python. Explicit canonical commit inputs may still be adapted to `gix.Signature`. |
+| GIX-22 | The native Git directory is sufficient for the two fixed metadata leaves used here: `modules` and `COMMIT_EDITMSG`. Git's `path.c` applies no special relocation to either, including in linked worktrees. The adapter appends only these names to the canonical native Git directory. | No new binding is needed for these ordinary paths. Other `--git-path` names and symlinked metadata leaves retain CLI resolution; a general resolver must handle config/environment overrides, common/private storage and canonical targets. `Repository.modules_path()` means `.gitmodules`, not the `modules` storage directory. |
 
 For GIX-8, at fixture commit `44e0a8ec55c42559dfcdf5117710b26261a7c937`,
 compare `git rev-list HEAD` with

git/_backend.py

@@ -224,6 +224,17 @@ def object_data(command: Any, ref: bytes, *, stream: bool = False) -> Any:
 
 
 def _rev_parse(repo: Any, args: List[str], kwargs: Dict[str, Any]) -> bytes:
+    if args[:2] == ["--path-format=absolute", "--git-path"]:
+        from git.util import to_native_path_linux
+
+        if len(args) != 3 or args[2] not in ("modules", "COMMIT_EDITMSG"):
+            raise _Unsupported("Git metadata path resolution (GIX-22)")
+        # Git keeps these fixed leaves in the private Git directory, including
+        # linked worktrees. Other names have their own config/environment rules.
+        path = os.path.join(_canonical_repository(repo).git_dir(), args[2])
+        if os.path.islink(path):
+            raise _Unsupported("symlinked metadata path (GIX-22)")
+        return os.fsencode(to_native_path_linux(path)) + b"\n"
     if args == ["--path-format=absolute", "--git-common-dir"]:
         return os.fsencode(os.path.abspath(repo.common_dir())) + b"\n"
     if args == ["--is-bare-repository"]:

test/test_gix_backend.py

@@ -191,6 +191,44 @@ def test_native_objects_trees_commits_and_index_reads(repo):
         assert commit.replace(message="changed").message == "changed"
 
 
+def test_native_metadata_paths_match_git_in_each_worktree(repo, tmp_path):
+    repo.index.commit("initial", skip_hooks=True)
+    linked_path = tmp_path / "linked"
+    repo.git.worktree("add", "--detach", str(linked_path))
+    with Repo(linked_path) as linked, Repo.init(tmp_path / "bare", bare=True, object_format=repo.object_format) as bare:
+        bare_linked_path = tmp_path / "bare-linked"
+        bare.git.worktree("add", "--orphan", "-b", "main", str(bare_linked_path))
+        with Repo(bare_linked_path) as bare_linked:
+            for current in (repo, linked, bare, bare_linked):
+                queries = [
+                    ("rev_parse", "--path-format=absolute", "--git-path", name)
+                    for name in ("modules", "COMMIT_EDITMSG")
+                ]
+                with patch.object(_backend, "gix", None):
+                    expected = [current.git._call_process_safe(*query) for query in queries]
+                count = _backend.statistics().get(("Git.execute", "CLI process"), 0)
+                with patch.object(Git, "execute", side_effect=AssertionError("unexpected CLI call")):
+                    assert [current.git._call_process_safe(*query) for query in queries] == expected
+                assert _backend.statistics().get(("Git.execute", "CLI process"), 0) == count
+        assert Path(linked.git_dir, "modules") != Path(repo.common_dir, "modules")
+
+
+def test_metadata_symlinks_retain_git_canonicalization(repo, tmp_path):
+    for name in ("modules", "COMMIT_EDITMSG"):
+        target = tmp_path / name
+        try:
+            Path(repo.git_dir, name).symlink_to(target, target_is_directory=name == "modules")
+        except OSError as exc:
+            pytest.skip(f"symlinks unavailable: {exc}")
+        query = ("rev_parse", "--path-format=absolute", "--git-path", name)
+        with patch.object(_backend, "gix", None):
+            expected = repo.git._call_process_safe(*query)
+        assert Path(expected) == target
+        with patch.object(Git, "execute", autospec=True, side_effect=Git.execute) as cli:
+            assert repo.git._call_process_safe(*query) == expected
+            cli.assert_called_once()
+
+
 def test_native_tree_and_commit_bytes_match_cli(repo):
     actor = Actor("Example", "example@example.invalid")
     Path(repo.working_dir, "file").write_bytes(b"payload\n")
@@ -217,7 +255,8 @@ def test_unknown_command_and_storage_environment_use_cli(repo):
         with repo.git.custom_environment(GIT_INDEX_FILE=".git/index"):
             assert repo.git._call_process_safe("ls_files", "--stage", "-v", "-z", "--full-name") == "fallback"
         assert repo.git._call_process_safe("rev_parse", "--show-ref-format") == "fallback"
-        assert cli.call_count == 3
+        assert repo.git._call_process_safe("rev_parse", "--path-format=absolute", "--git-path", "objects") == "fallback"
+        assert cli.call_count == 4
 
     command = Git(repo.working_dir)
     command._repo = repo.git._repo