Function acquireLock

design/src/daemon-state.ts:194–220

(lockPath: string)

 * once; if reclaim also fails the caller waits and retries via state re-read.
 */
export function acquireLock(lockPath: string): (() => void) | null {
  try {
    fs.mkdirSync(path.dirname(lockPath), { recursive: true });
    // 'wx' = create exclusive, fail if exists. Atomic check-and-create.
    const fd = fs.openSync(lockPath, "wx");
    fs.writeSync(fd, `${process.pid}\n`);
    fs.closeSync(fd);
    return () => {
      try {
        fs.unlinkSync(lockPath);
      } catch {
        // already gone
      }
    };
  } catch {
    // Held — check if holder is alive
    try {
      const holderPid = parseInt(fs.readFileSync(lockPath, "utf-8").trim(), 10);
      if (holderPid && isProcessAlive(holderPid)) return null;
      // Stale, reclaim
      fs.unlinkSync(lockPath);
      return acquireLock(lockPath);
    } catch {
      return null;
    }
  }
}