I/O-bound endpoint (/io, Mono.delay(300ms)), concurrency=600, 2 vCPU sandbox, Spring Boot 4.1.1 / JDK 25.0.4.1
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webflux (netty) : total=600 success=600 wall=852ms p50=591ms p99=738ms

Mono.delay() never parks a thread -- the event loop schedules a timer callback and
goes back to the selector loop immediately. Wall time for 600 concurrent requests
stays close to a single 300ms round, same shape as virtual threads' /io result in
../virtual-threads-benchmark/docs/output/01-io-bound-benchmark.txt.