Werkzeug sets its server socket inheritable unconditionally, so the
os.execv restart carried it into the new process as a zombie listener:
one PID listening on both 5100 (never accepted) and 5101 (the real
server). Mark all fds above stderr close-on-exec before exec'ing so
the old socket dies and the new server rebinds the original port.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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