Implements the connection-level serialized frame writer per the plan's
go/no-go gate: tryLock() fast path with an intrusive Vyukov-style MPSC
fallback under contention, ReentrantLock throughout (never synchronized),
and a scan-based write-timeout reaper.
All four gate criteria met and measured: N=1 0 B/op and 42.6 ns overhead
(<=50 ns budget); N=64 65.5% throughput retention (>=60%) and 11.8-14.2 us
p999 (<1 ms); no carrier pinning; stress test 10,000/10,000 green across
1000 iterations x 5 concurrency levels x 2 scheduler configs. Compared
against plain-lock and dedicated-thread designs with real benchmark
numbers, not assertion. Full methodology and results in WRITER.md, DEC-09.
Also fixes a real regression found while resuming this work: the JMH
benchmark broke plain `mvn test` (no -Pjmh) because it lived in
src/test/java, which Surefire's test discovery loads regardless of
whether a class is ultimately selected as a test. Moved to a dedicated
src/jmh/java source root registered only under the jmh profile
(build-helper-maven-plugin), per DEC-17.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Zakaria El OrcheandClaude Sonnet 5
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