File descriptors climb toward limit

A Go payments-orchestration service slowly climbs toward its 65,536 fd soft limit over ~30 hours and then starts failing outbound calls with 'dial tcp: too many open files', forcing an hourly restart that masked the issue until this week. The open-fd graph rises in a near-perfect straight line that is independent of traffic, it keeps climbing at the same slope even during the overnight trough. lsof shows thousands of sockets in CLOSE_WAIT to one internal dependency, and a heap profile shows a growing number of live http.Transport objects. The only recent change is a refactor two weeks ago that moved HTTP calls into a per-request helper. How do you triage this and stop the bleed?