Which Ktor engine minimizes idle resource consumption for a low-traffic server?

For a low-traffic Ktor service, the dominant operational cost is often idle resource consumption: resident memory, parked threads, and event-loop overhead. Ktor offers several server engines—Netty, CIO, Jetty, Tomcat—each with distinct threading and I/O models. Netty relies on event loops and channel pools; CIO is built directly on coroutines and advertises a lighter footprint. The documentation, however, does not state which engine is most cost-effective when concurrency is near zero, nor how CIO's dispatcher scales down under idle conditions.

Given that default configurations vary by engine and JVM version, the choice is not obvious. Should a low-traffic deployment prefer CIO for its coroutine-based model, or does Netty's mature event-loop management lead to lower memory after warm-up? Does CIO actually reduce thread count to near zero when idle, or does it retain a minimum pool? And how do per-engine settings like connection limits and dispatcher sizes interact with these trade-offs?