I/O-bound endpoint (/io, Mono.delay(300ms)), concurrency=600, median of 5 trials, 2 vCPU sandbox, Spring Boot 4.1.1 / JDK 25.0.4.1
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webflux (netty) : total=600 success=600 wall=569ms p50=455ms p99=510ms

Mono.delay() never parks a thread -- the event loop schedules a timer callback and
goes back to the selector loop immediately. A single trial at this concurrency swung
50%+ between back-to-back runs on this shared sandbox -- bigger than the gap being
measured -- so the number above is the median of 5 independent trials, not
one shot. Even so it lands in the same range as virtual threads' /io result in
../virtual-threads-benchmark/docs/output/01-io-bound-benchmark.txt (a single trial):
treat any single-run percentage gap between WebFlux and virtual threads here as
noise-level, not a reliable ranking.