agentClient() built a new agentapi.Client (new bare http.Transport, IdleConnTimeout:0)
per call and discarded it without closing idle conns -> one leaked idle ESTABLISHED
socket per call to the agent :8443, exhausting the ephemeral port range after ~5 days
(EADDRNOTAVAIL). Memoize one shared client via sync.Once; harden Transport
(MaxIdleConns/PerHost + IdleConnTimeout 90s). Agent/firewall untouched.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
