runProcess() ends the child's stdin with no error handler. A child that
never reads stdin (git check-ignore) can exit and close the pipe before the
write flushes; the unhandled EPIPE then crashes `agent.mjs validate`. This
failed harness/ruview (node 22) on PR #2062 and reproduces 12/12 locally
under CPU load (0/12 after this change). The command's real outcome is
still reported by the 'close' handler; this mirrors the existing handler in
harness/ruview/src/process-runner.js.
Co-Authored-By: claude-flow <ruv@ruv.net>
Claude-Session: https://claude.ai/code/session_015H55jmprfz4oHWXSFbX5rf
