run_with_label piped output through a while loop, so $! tracked the
formatter PID instead of the actual command. Ctrl-C killed the formatters
but left app/worker/css-watch running as orphans. Switch to process
substitution so $! is the real command PID, and pkill -P children before
killing tracked PIDs.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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