sessionstart.py

#!/usr/bin/env python3
"""SessionStart hook — inject current branch + working-tree state as session context.

Claude Code treats stdout as `additionalContext` on SessionStart, so this script
prints the current git branch and `git status --short` — giving the agent the
same orientation a human gets from opening the terminal. Runs once per session.

Silent and zero-exit on any failure: a missing git directory or a transient
command error must never block session startup.
"""

from __future__ import annotations

import os
import subprocess
import sys
from pathlib import Path


def project_dir() -> Path:
    env = os.environ.get("CLAUDE_PROJECT_DIR")
    if env:
        return Path(env)
    return Path(__file__).resolve().parent.parent.parent


def git_output(args: list[str], cwd: Path) -> str:
    try:
        return subprocess.check_output(
            ["git", *args],
            cwd=cwd,
            stderr=subprocess.DEVNULL,
            text=True,
            errors="replace",
            timeout=5,
        ).strip()
    except (
        subprocess.CalledProcessError,
        subprocess.TimeoutExpired,
        FileNotFoundError,
    ):
        return ""


def main() -> None:
    base = project_dir()
    branch = git_output(["branch", "--show-current"], base)
    status = git_output(["status", "--short"], base)

    if not branch and not status:
        return

    lines = ["# Repository context (injected by SessionStart hook)"]
    if branch:
        lines.append(f"- Current branch: `{branch}`")
    if status:
        lines.append("")
        lines.append("Working tree (`git status --short`):")
        lines.append("```")
        lines.append(status)
        lines.append("```")
    else:
        lines.append("- Working tree: clean")

    sys.stdout.write("\n".join(lines) + "\n")


if __name__ == "__main__":
    main()