feat: add safe PR gate

docs/codex_skills/git_pr_workflow.md

@@ -32,6 +32,7 @@ Use for branch setup, syncing from `main`, local commits, staged-file review, pu
 - Before commit: `git status --short`, `git diff --stat`, and `git diff --cached --name-only`.
 - Before push: clean `git status --short` and current branch confirmation.
 - For PRs: include validation commands actually run; do not claim CI status unless checked.
+- For agent-assisted pre-push or pre-PR checks, run `python scripts/safe_pr_gate.py` on the current branch before pushing.
 
 ## Stop conditions
 

scripts/safe_pr_gate.py

@@ -0,0 +1,179 @@
+"""Deterministic local safety gate for agent-assisted PR workflows."""
+
+from __future__ import annotations
+
+import argparse
+import json
+import subprocess
+import sys
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Any
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+if str(REPO_ROOT) not in sys.path:
+    sys.path.insert(0, str(REPO_ROOT))
+
+
+@dataclass(frozen=True, slots=True)
+class GateState:
+    branch: str
+    status_short: tuple[str, ...]
+    changed_paths: tuple[str, ...]
+
+
+@dataclass(frozen=True, slots=True)
+class GateResult:
+    ok: bool
+    branch: str
+    allow_dirty: bool
+    allowed_prefixes: tuple[str, ...]
+    status_short: tuple[str, ...]
+    changed_paths: tuple[str, ...]
+    problems: tuple[str, ...]
+
+    def to_dict(self) -> dict[str, Any]:
+        return {
+            "allowed_prefixes": list(self.allowed_prefixes),
+            "allow_dirty": self.allow_dirty,
+            "branch": self.branch,
+            "changed_paths": list(self.changed_paths),
+            "ok": self.ok,
+            "problems": list(self.problems),
+            "result": "PASS" if self.ok else "FAIL",
+            "status_short": list(self.status_short),
+        }
+
+
+def _run_git(args: list[str]) -> str:
+    try:
+        completed = subprocess.run(
+            ["git", *args],
+            cwd=REPO_ROOT,
+            check=True,
+            capture_output=True,
+            text=True,
+        )
+    except FileNotFoundError as exc:
+        raise RuntimeError(f"git executable not found while running: git {' '.join(args)}") from exc
+    except subprocess.CalledProcessError as exc:
+        raise RuntimeError(
+            f"git command failed with exit code {exc.returncode}: git {' '.join(args)}"
+        ) from exc
+    return completed.stdout
+
+
+def _parse_porcelain_paths(output: str) -> tuple[str, ...]:
+    if not output:
+        return ()
+
+    entries = output.split("\0")
+    paths: list[str] = []
+    index = 0
+    while index < len(entries):
+        entry = entries[index]
+        if not entry:
+            index += 1
+            continue
+        path = entry[3:]
+        status = entry[:2]
+        if status and any(char in {"R", "C"} for char in status):
+            if index + 1 < len(entries) and entries[index + 1]:
+                paths.append(entries[index + 1])
+            index += 2
+            continue
+        paths.append(path)
+        index += 1
+    return tuple(paths)
+
+
+def collect_gate_state() -> GateState:
+    branch = _run_git(["branch", "--show-current"]).strip()
+    status_short_output = _run_git(["status", "--short", "--untracked-files=all"])
+    porcelain_output = _run_git(["status", "--porcelain=v1", "-z"])
+    status_short = tuple(line for line in status_short_output.splitlines() if line)
+    changed_paths = _parse_porcelain_paths(porcelain_output)
+    return GateState(branch=branch, status_short=status_short, changed_paths=changed_paths)
+
+
+def _path_in_prefix(path: str, prefix: str) -> bool:
+    normalized = prefix.rstrip("/")
+    return path == normalized or path.startswith(normalized + "/")
+
+
+def evaluate_gate(
+    state: GateState,
+    *,
+    allow_dirty: bool = False,
+    allowed_prefixes: tuple[str, ...] = (),
+) -> GateResult:
+    problems: list[str] = []
+
+    if state.branch == "main":
+        problems.append("on_main_branch")
+
+    if state.status_short and not allow_dirty:
+        problems.append("dirty_working_tree")
+
+    if allowed_prefixes:
+        disallowed_paths = sorted(
+            path
+            for path in state.changed_paths
+            if not any(_path_in_prefix(path, prefix) for prefix in allowed_prefixes)
+        )
+        if disallowed_paths:
+            problems.append("changed_files_outside_allowed_prefixes")
+            problems.extend(f"outside_prefix:{path}" for path in disallowed_paths)
+
+    return GateResult(
+        ok=not problems,
+        branch=state.branch,
+        allow_dirty=allow_dirty,
+        allowed_prefixes=tuple(sorted(allowed_prefixes)),
+        status_short=state.status_short,
+        changed_paths=state.changed_paths,
+        problems=tuple(problems),
+    )
+
+
+def _parse_args(argv: list[str]) -> argparse.Namespace:
+    parser = argparse.ArgumentParser(description="Run a deterministic local safety gate for PR-ready agent work.")
+    parser.add_argument("--allow-dirty", action="store_true", help="Permit a dirty working tree while still checking allowed prefixes.")
+    parser.add_argument(
+        "--allowed-prefix",
+        action="append",
+        default=[],
+        help="Require changed paths to stay within this repo-relative prefix. May be repeated.",
+    )
+    return parser.parse_args(argv)
+
+
+def _error_response(exc: RuntimeError) -> dict[str, Any]:
+    return {
+        "error": {
+            "message": str(exc),
+            "type": exc.__class__.__name__,
+        },
+        "ok": False,
+        "result": "ERROR",
+    }
+
+
+def main(argv: list[str] | None = None) -> int:
+    args = _parse_args(sys.argv[1:] if argv is None else argv)
+    try:
+        state = collect_gate_state()
+        result = evaluate_gate(
+            state,
+            allow_dirty=args.allow_dirty,
+            allowed_prefixes=tuple(args.allowed_prefix),
+        )
+        sys.stdout.write(json.dumps(result.to_dict(), indent=2, sort_keys=True) + "\n")
+        return 0 if result.ok else 1
+    except RuntimeError as exc:
+        sys.stdout.write(json.dumps(_error_response(exc), indent=2, sort_keys=True) + "\n")
+        return 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())

tests/test_safe_pr_gate.py

@@ -0,0 +1,174 @@
+from __future__ import annotations
+
+import json
+import shutil
+import subprocess
+import sys
+import tempfile
+from contextlib import contextmanager
+from pathlib import Path
+
+import pytest
+
+import scripts.safe_pr_gate as safe_pr_gate
+from scripts.safe_pr_gate import GateState, _parse_porcelain_paths, evaluate_gate
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+
+
+def _run_gate(*args: str, cwd: Path | None = None) -> subprocess.CompletedProcess[str]:
+    return subprocess.run(
+        [sys.executable, "scripts/safe_pr_gate.py", *args],
+        check=False,
+        capture_output=True,
+        text=True,
+        cwd=cwd,
+    )
+
+
+@contextmanager
+def _temporary_git_repo(branch: str):
+    with tempfile.TemporaryDirectory() as temp_dir:
+        repo_root = Path(temp_dir)
+        scripts_dir = repo_root / "scripts"
+        scripts_dir.mkdir()
+        shutil.copy2(REPO_ROOT / "scripts" / "safe_pr_gate.py", scripts_dir / "safe_pr_gate.py")
+        subprocess.run(["git", "init"], cwd=repo_root, check=True, capture_output=True, text=True)
+        subprocess.run(["git", "checkout", "-b", branch], cwd=repo_root, check=True, capture_output=True, text=True)
+        yield repo_root
+
+
+def test_evaluate_gate_passes_on_clean_feature_branch_state() -> None:
+    result = evaluate_gate(
+        GateState(branch="feat/safe-pr-gate", status_short=(), changed_paths=()),
+        allowed_prefixes=("scripts/",),
+    )
+
+    assert result.ok is True
+    assert result.problems == ()
+    assert result.to_dict() == {
+        "allowed_prefixes": ["scripts/"],
+        "allow_dirty": False,
+        "branch": "feat/safe-pr-gate",
+        "changed_paths": [],
+        "ok": True,
+        "problems": [],
+        "result": "PASS",
+        "status_short": [],
+    }
+
+
+def test_evaluate_gate_fails_on_main_branch() -> None:
+    result = evaluate_gate(GateState(branch="main", status_short=(), changed_paths=()))
+
+    assert result.ok is False
+    assert result.problems == ("on_main_branch",)
+
+
+def test_evaluate_gate_allows_detached_head_state() -> None:
+    result = evaluate_gate(GateState(branch="", status_short=(), changed_paths=()))
+
+    assert result.ok is True
+    assert result.problems == ()
+
+
+def test_evaluate_gate_fails_on_dirty_tree_without_allow_dirty() -> None:
+    result = evaluate_gate(
+        GateState(branch="feat/safe-pr-gate", status_short=(" M scripts/example.py",), changed_paths=("scripts/example.py",))
+    )
+
+    assert result.ok is False
+    assert result.problems == ("dirty_working_tree",)
+
+
+def test_evaluate_gate_flags_paths_outside_allowed_prefixes() -> None:
+    result = evaluate_gate(
+        GateState(branch="feat/safe-pr-gate", status_short=(" M docs/example.md",), changed_paths=("docs/example.md",)),
+        allow_dirty=True,
+        allowed_prefixes=("scripts/",),
+    )
+
+    assert result.ok is False
+    assert result.problems == ("changed_files_outside_allowed_prefixes", "outside_prefix:docs/example.md")
+
+
+def test_parse_porcelain_paths_handles_rename_status_in_second_position() -> None:
+    assert _parse_porcelain_paths(" R old-name.txt\0new-name.txt\0") == ("new-name.txt",)
+
+
+@pytest.mark.parametrize(
+    ("raised", "expected_message"),
+    [
+        (subprocess.CalledProcessError(1, ["git", "status", "--short"]), "git command failed with exit code 1: git status --short"),
+        (FileNotFoundError(), "git executable not found while running: git status --short"),
+    ],
+)
+def test_run_git_wraps_git_subprocess_failures(monkeypatch: pytest.MonkeyPatch, raised: BaseException, expected_message: str) -> None:
+    def fake_run(*args: object, **kwargs: object) -> subprocess.CompletedProcess[str]:
+        raise raised
+
+    monkeypatch.setattr(safe_pr_gate.subprocess, "run", fake_run)
+
+    with pytest.raises(RuntimeError, match=expected_message):
+        safe_pr_gate._run_git(["status", "--short"])
+
+
+def test_main_reports_deterministic_error_json_on_git_failure(monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]) -> None:
+    monkeypatch.setattr(safe_pr_gate, "collect_gate_state", lambda: (_ for _ in ()).throw(RuntimeError("git command failed with exit code 1: git status --short")))
+
+    exit_code = safe_pr_gate.main([])
+    output = json.loads(capsys.readouterr().out)
+
+    assert exit_code == 1
+    assert output == {
+        "error": {
+            "message": "git command failed with exit code 1: git status --short",
+            "type": "RuntimeError",
+        },
+        "ok": False,
+        "result": "ERROR",
+    }
+
+
+def test_cli_pass_and_fail_outputs_are_deterministic() -> None:
+    with _temporary_git_repo("feat/safe-pr-gate") as repo_root:
+        passing = _run_gate(
+            "--allow-dirty",
+            "--allowed-prefix",
+            "docs/",
+            "--allowed-prefix",
+            "scripts/",
+            "--allowed-prefix",
+            "tests/",
+            cwd=repo_root,
+        )
+        dirty_path = repo_root / "_safe_pr_gate_dirty_test.tmp"
+        dirty_path.write_text("dirty\n", encoding="utf-8")
+        try:
+            failing = _run_gate(
+                "--allow-dirty",
+                "--allowed-prefix",
+                "docs/",
+                "--allowed-prefix",
+                "scripts/",
+                "--allowed-prefix",
+                "tests/",
+                cwd=repo_root,
+            )
+        finally:
+            dirty_path.unlink(missing_ok=True)
+
+    assert passing.returncode == 0
+    assert failing.returncode == 1
+
+    passing_payload = json.loads(passing.stdout)
+    failing_payload = json.loads(failing.stdout)
+
+    assert passing_payload["result"] == "PASS"
+    assert passing_payload["allow_dirty"] is True
+    assert failing_payload["result"] == "FAIL"
+    assert failing_payload["problems"] == [
+        "changed_files_outside_allowed_prefixes",
+        "outside_prefix:_safe_pr_gate_dirty_test.tmp",
+    ]