scripts/codex_baseline.py

#!/usr/bin/env python3
"""sessionStart hook: snapshot git tree for codex review threshold gating.

Saves a git tree reference representing the working-tree state at session
start.  The companion stop hook (codex_review.py) diffs against this
baseline to measure how much the session changed, independent of commits.
"""

import subprocess
import sys
from pathlib import Path

project_root = Path(__file__).resolve().parent.parent
state_dir = project_root / ".cursor" / "hooks" / "state"
baseline_path = state_dir / "codex_review_baseline"


def save_baseline() -> None:
    """Record the working-tree state so the review hook can diff against it.

    Uses git add -N to include untracked files in the snapshot, so new
    files created during the session appear in the stop-time diff.
    """
    state_dir.mkdir(parents=True, exist_ok=True)
    subprocess.run(
        ["/usr/bin/git", "add", "-N", "."],
        capture_output=True,
        text=True,
        timeout=10,
        check=False,
        cwd=str(project_root),
    )
    stash = subprocess.run(
        ["/usr/bin/git", "stash", "create"],
        capture_output=True,
        text=True,
        timeout=10,
        check=False,
        cwd=str(project_root),
    )
    sha = stash.stdout.strip()
    if not sha:
        head = subprocess.run(
            ["/usr/bin/git", "rev-parse", "HEAD"],
            capture_output=True,
            text=True,
            timeout=5,
            check=False,
            cwd=str(project_root),
        )
        sha = head.stdout.strip()
    baseline_path.write_text(sha)


def main() -> None:
    """Entry point: read hook input, snapshot baseline, emit empty JSON."""
    sys.stdin.read()
    save_baseline()
    print("{}")


if __name__ == "__main__":
    main()