Function: concurrencyMiddleware()
concurrencyMiddleware(
options):Middleware
Pace this process's requests: at most max in flight, started no closer together than
minIntervalMs.
Calling this twice with the same settings returns the SAME gate — that is the point. The budget belongs to the process, so short-lived clients all draw on one counter.
Distinct settings get distinct budgets, so a process mixing max: 4 and max: 6 can have
ten requests open. Pick one configuration per process unless you mean otherwise.