Add python_git: a leak-safe GitPython alternative

Every git invocation runs through a single blocking subprocess.run
call in python_git/runner.py that always waits for the process to
exit and closes its pipes before returning, so there is no long-lived
Popen handle for a caller to forget to close (the root cause of
GitPython's known fd/process leaks).

Repo exposes status/log/diff/add/commit/push/pull/fetch, branch and
remote management, and clone, backed by dataclasses in models.py.
Covered by tests/test_repo.py, including an fd-count regression test.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_repo.py

@@ -0,0 +1,119 @@
+import os
+import subprocess
+from pathlib import Path
+
+import pytest
+
+from python_git import GitCommandError, InvalidGitRepositoryError, Repo
+
+
+def _init_repo(path: Path) -> Repo:
+    subprocess.run(["git", "init", "-q", str(path)], check=True)
+    subprocess.run(["git", "-C", str(path), "config", "user.email", "test@example.com"], check=True)
+    subprocess.run(["git", "-C", str(path), "config", "user.name", "Test User"], check=True)
+    return Repo(path)
+
+
+def test_invalid_repository_raises(tmp_path):
+    with pytest.raises(InvalidGitRepositoryError):
+        Repo(tmp_path)
+
+
+def test_missing_path_raises(tmp_path):
+    with pytest.raises(InvalidGitRepositoryError):
+        Repo(tmp_path / "does-not-exist")
+
+
+def test_status_reports_untracked_and_spaced_filenames(tmp_path):
+    repo = _init_repo(tmp_path)
+    (tmp_path / "a file.txt").write_text("hello\n")
+
+    statuses = repo.status()
+
+    assert len(statuses) == 1
+    assert statuses[0].path == "a file.txt"
+    assert statuses[0].index_status == "?"
+
+
+def test_add_commit_log_roundtrip(tmp_path):
+    repo = _init_repo(tmp_path)
+    (tmp_path / "file.txt").write_text("hello\n")
+    repo.add("file.txt")
+    repo.commit("initial commit")
+
+    commits = repo.log()
+
+    assert len(commits) == 1
+    assert commits[0].message == "initial commit"
+    assert commits[0].author_email == "test@example.com"
+    assert not repo.is_dirty()
+
+
+def test_log_on_empty_repo_returns_empty_list(tmp_path):
+    repo = _init_repo(tmp_path)
+    assert repo.log() == []
+
+
+def test_diff_shows_modification(tmp_path):
+    repo = _init_repo(tmp_path)
+    (tmp_path / "file.txt").write_text("hello\n")
+    repo.add("file.txt")
+    repo.commit("initial")
+    (tmp_path / "file.txt").write_text("goodbye\n")
+
+    assert "goodbye" in repo.diff()
+
+
+def test_rename_is_tracked(tmp_path):
+    repo = _init_repo(tmp_path)
+    content = "hello world this is long enough to be detected as a rename\n"
+    (tmp_path / "old.txt").write_text(content)
+    repo.add("old.txt")
+    repo.commit("add old")
+    (tmp_path / "old.txt").rename(tmp_path / "new.txt")
+    repo.add("new.txt", "old.txt")
+
+    renamed = [s for s in repo.status() if s.orig_path]
+
+    assert len(renamed) == 1
+    assert renamed[0].path == "new.txt"
+    assert renamed[0].orig_path == "old.txt"
+
+
+def test_branch_create_and_checkout(tmp_path):
+    repo = _init_repo(tmp_path)
+    (tmp_path / "file.txt").write_text("hello\n")
+    repo.add("file.txt")
+    repo.commit("initial")
+
+    repo.create_branch("feature")
+    repo.checkout("feature")
+
+    assert repo.current_branch() == "feature"
+    branches = {b.name: b.is_current for b in repo.list_branches()}
+    assert branches["feature"] is True
+
+
+def test_git_command_error_on_nonexistent_branch(tmp_path):
+    repo = _init_repo(tmp_path)
+    with pytest.raises(GitCommandError):
+        repo.checkout("does-not-exist")
+
+
+def test_no_fd_leak_across_many_calls(tmp_path):
+    repo = _init_repo(tmp_path)
+    (tmp_path / "file.txt").write_text("hello\n")
+    repo.add("file.txt")
+    repo.commit("initial")
+
+    fd_dir = Path("/proc/self/fd")
+    if not fd_dir.exists():
+        pytest.skip("requires /proc/self/fd (Linux)")
+
+    before = len(os.listdir(fd_dir))
+    for _ in range(200):
+        repo.status()
+        repo.log()
+    after = len(os.listdir(fd_dir))
+
+    assert after <= before