work_checkpoint.py

#!/usr/bin/env python3
"""PostToolUse hook that logs Write/Edit operations to .claude/checkpoint.md.

Reads a JSON payload from stdin describing the completed tool call,
and appends a one-line summary for Write and Edit operations so that
the record survives context compression.
"""

import json
import os
import sys
from datetime import datetime, timezone


TRACKED_TOOLS = {"Write", "Edit"}


def _summary(tool_name: str, tool_input: dict) -> str:
    """Return a one-line human-readable summary of the tool call."""
    file_path = tool_input.get("file_path", "<unknown>")
    basename = os.path.basename(file_path)

    if tool_name == "Write":
        return f"Write: created/overwrote {basename} ({file_path})"

    if tool_name == "Edit":
        old = tool_input.get("old_string", "")
        new = tool_input.get("new_string", "")
        replace_all = tool_input.get("replace_all", False)
        verb = "replaced all" if replace_all else "replaced"
        old_preview = (old[:40] + "...") if len(old) > 40 else old
        old_preview = old_preview.replace("\n", "\\n")
        return f"Edit: {basename} – {verb} `{old_preview}` ({file_path})"

    return f"{tool_name}: {file_path}"


def main() -> None:
    try:
        payload = json.load(sys.stdin)
    except (json.JSONDecodeError, EOFError):
        return

    tool_name = payload.get("tool_name", "")
    if tool_name not in TRACKED_TOOLS:
        return

    tool_input = payload.get("tool_input", {})
    line = _summary(tool_name, tool_input)

    timestamp = datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
    entry = f"- [{timestamp}] {line}\n"

    checkpoint_dir = os.path.join(os.getcwd(), ".claude")
    checkpoint_file = os.path.join(checkpoint_dir, "checkpoint.md")

    os.makedirs(checkpoint_dir, exist_ok=True)

    needs_header = not os.path.exists(checkpoint_file)
    with open(checkpoint_file, "a") as f:
        if needs_header:
            f.write("# Work Checkpoint Log\n\n")
        f.write(entry)


if __name__ == "__main__":
    main()