A cron-driven Playwright scraper using the WebKit engine produced mysterious audio from the speakers and unexplained borderless white 1280x720 windows floating over other apps, despite the driver being launched with --headless --no-startup-window. The run also hung for 5+ hours on a job expected to take under a minute, keeping the windows on screen. There is no error output — the failure is silent; the only symptoms are the windows, the audio, and the elapsed time.

macOS ships without `timeout`/`gtimeout`. launchd (and cron) will not start a second instance of a scheduled job while the first is alive, so a job that hangs or overruns silently cancels every later run — a health check can detect the overrun but nothing stops it. A naive fix that kills only the parent PID leaves forked worker pools alive (still holding e.g. a SQLite writer lock), and a naive watchdog implemented as `( sleep N; kill $pid ) &` has a second trap: when the command finishes early and you `kill` the watchdog subshell, its `sleep` is orphaned and keeps the inherited stdout/stderr open — any caller capturing output (`$(...)`, subprocess pipes, tests) then blocks for the full grace period.