fix(git_helper): remove comfyui_manager import to fix Windows subprocess crash (#2703)

git_helper.py is spawned as a standalone subprocess on Windows
(manager_core.py:1342). The import of comfyui_manager.common.timestamp_utils
triggered comfyui_manager/__init__.py which imports from comfy.cli_args —
unavailable in the subprocess environment, causing ModuleNotFoundError.

Inline get_backup_branch_name() using only stdlib (time, uuid), preserving
the original collision-detection and UUID-fallback semantics. Add 9 tests
covering standalone subprocess loading, behavioral equivalence, edge cases
(repo.heads exception, 99-suffix exhaustion with UUID fallback).

tests/common/test_git_helper.py

@@ -0,0 +1,173 @@
+"""Minimal tests for git_helper standalone execution and get_backup_branch_name.
+
+git_helper.py runs as a subprocess on Windows and must NOT import comfyui_manager.
+Tests validate: (1) no forbidden imports via AST, (2) subprocess-level standalone
+execution, (3) get_backup_branch_name behavioural correctness.
+"""
+
+import ast
+import pathlib
+import subprocess
+import sys
+import textwrap
+
+import pytest
+
+_GIT_HELPER_PATH = pathlib.Path(__file__).resolve().parents[2] / "comfyui_manager" / "common" / "git_helper.py"
+
+
+# ---------------------------------------------------------------------------
+# 1. No comfyui_manager imports (AST check — no execution)
+# ---------------------------------------------------------------------------
+
+def test_no_comfyui_manager_import():
+    """git_helper.py must be free of comfyui_manager imports (Windows subprocess safety)."""
+    tree = ast.parse(_GIT_HELPER_PATH.read_text(encoding="utf-8"))
+    for node in ast.walk(tree):
+        if isinstance(node, ast.ImportFrom) and node.module and "comfyui_manager" in node.module:
+            pytest.fail(f"Forbidden import at line {node.lineno}: from {node.module}")
+
+
+# ---------------------------------------------------------------------------
+# 2. Standalone subprocess execution (mirrors the actual Windows bug scenario)
+# ---------------------------------------------------------------------------
+
+def test_standalone_subprocess_can_load(tmp_path):
+    """git_helper.py must load in a subprocess without comfyui_manager on sys.path."""
+    (tmp_path / "folder_paths.py").touch()
+
+    # Run git_helper.py in a clean subprocess with stripped sys.path.
+    # git_helper.py has a module-level sys.argv dispatcher that calls sys.exit,
+    # so we set argv to --check with a dummy path to avoid IndexError, then
+    # catch the SystemExit to verify the function loaded successfully.
+    script = textwrap.dedent(f"""\
+        import sys, os
+        sys.path = [p for p in sys.path
+                    if "comfyui_manager" not in p and "comfyui-manager" not in p]
+        os.environ["COMFYUI_PATH"] = {str(tmp_path)!r}
+
+        import importlib.util
+        spec = importlib.util.spec_from_file_location("git_helper", {str(_GIT_HELPER_PATH)!r})
+        mod = importlib.util.module_from_spec(spec)
+
+        # Intercept sys.exit from module-level argv dispatcher
+        real_exit = sys.exit
+        exit_code = [None]
+        def fake_exit(code=0):
+            exit_code[0] = code
+            raise SystemExit(code)
+        sys.exit = fake_exit
+
+        try:
+            spec.loader.exec_module(mod)
+        except SystemExit:
+            pass
+        finally:
+            sys.exit = real_exit
+
+        # The function must be defined regardless of argv dispatcher outcome
+        assert hasattr(mod, "get_backup_branch_name"), "Function not defined"
+        name = mod.get_backup_branch_name()
+        assert name.startswith("backup_"), f"Bad name: {{name}}"
+        print(f"OK: {{name}}")
+    """)
+
+    result = subprocess.run(
+        [sys.executable, "-c", script],
+        capture_output=True, text=True, timeout=30,
+    )
+    assert result.returncode == 0, f"stderr: {result.stderr}"
+    assert "OK: backup_" in result.stdout
+
+
+# ---------------------------------------------------------------------------
+# 3. get_backup_branch_name behavioural tests (function extracted via AST)
+# ---------------------------------------------------------------------------
+
+@pytest.fixture(scope="module")
+def _get_backup_branch_name():
+    """Extract and compile get_backup_branch_name from git_helper.py source."""
+    source = _GIT_HELPER_PATH.read_text(encoding="utf-8")
+    tree = ast.parse(source)
+
+    for node in ast.walk(tree):
+        if isinstance(node, ast.FunctionDef) and node.name == "get_backup_branch_name":
+            func_source = ast.get_source_segment(source, node)
+            assert func_source is not None
+            ns = {}
+            exec(compile(ast.parse(func_source), "<test>", "exec"), ns)  # noqa: S102
+            return ns["get_backup_branch_name"]
+
+    pytest.fail("get_backup_branch_name not found in git_helper.py")
+
+
+class _FakeHead:
+    def __init__(self, name):
+        self.name = name
+
+
+class _FakeRepo:
+    def __init__(self, branch_names):
+        self.heads = [_FakeHead(n) for n in branch_names]
+
+
+def test_basic_name_format(_get_backup_branch_name):
+    import time
+    name = _get_backup_branch_name()
+    assert name.startswith("backup_")
+    expected = f"backup_{time.strftime('%Y%m%d_%H%M%S')}"
+    assert name == expected
+
+
+def test_no_collision(_get_backup_branch_name):
+    repo = _FakeRepo(["main", "dev"])
+    name = _get_backup_branch_name(repo)
+    assert name.startswith("backup_")
+
+
+def test_single_collision(_get_backup_branch_name):
+    import time
+    ts = time.strftime("%Y%m%d_%H%M%S")
+    repo = _FakeRepo(["main", f"backup_{ts}"])
+    name = _get_backup_branch_name(repo)
+    assert name == f"backup_{ts}_1"
+
+
+def test_multi_collision(_get_backup_branch_name):
+    import time
+    ts = time.strftime("%Y%m%d_%H%M%S")
+    repo = _FakeRepo([f"backup_{ts}", f"backup_{ts}_1", f"backup_{ts}_2"])
+    name = _get_backup_branch_name(repo)
+    assert name == f"backup_{ts}_3"
+
+
+def test_repo_none_returns_base(_get_backup_branch_name):
+    name = _get_backup_branch_name(None)
+    assert name.startswith("backup_")
+
+
+def test_repo_heads_exception_returns_base(_get_backup_branch_name):
+    """When repo.heads raises, fall back to base name without suffix."""
+
+    class _BrokenRepo:
+        @property
+        def heads(self):
+            raise RuntimeError("simulated git error")
+
+    name = _get_backup_branch_name(_BrokenRepo())
+    assert name.startswith("backup_")
+    assert "_1" not in name  # no suffix — exception path returns base
+
+
+def test_uuid_fallback_on_full_collision(_get_backup_branch_name):
+    """When all 99 suffixes are taken, fall back to UUID."""
+    import time
+    ts = time.strftime("%Y%m%d_%H%M%S")
+    # All names from backup_TS through backup_TS_99 are taken
+    taken = [f"backup_{ts}"] + [f"backup_{ts}_{i}" for i in range(1, 100)]
+    repo = _FakeRepo(taken)
+    name = _get_backup_branch_name(repo)
+    assert name.startswith(f"backup_{ts}_")
+    # UUID suffix is 6 hex chars
+    suffix = name[len(f"backup_{ts}_"):]
+    assert len(suffix) == 6, f"Expected 6-char UUID suffix, got: {suffix}"