[AgentDudu]

What

• README.md (new): what works, quick start (Linux + MinGW + MSVC), limits table (431/413/505 mapping verified against connection.cpp), layout, verification matrix.
• docs/BUILDING.md (new): toolchains, presets, all four gates, Docker/Git-Bash/TSan-ASLR/clang-format gotchas recorded.
• docs/API.md (new): header-exact reference per layer — parser usage loop, ownership rules, threading model (one connection ⇨ one reactor, never shared), error-handling conventions.
• tools/bench-inside.sh: reproducible numbers (Release build, wrk + ab).

Numbers (Ubuntu 24.04 container, gcc 13 -O2, server shares host with clients)

Scenario	1 reactor	4 reactors
1 KiB keep-alive (wrk -t4 -c100)	9,770 req/s · p99 19.8 ms	47,275 req/s · p99 4.3 ms
64 KiB keep-alive	5,683 req/s · 356 MB/s	25,919 req/s · 1.59 GB/s
1 KiB fresh conns (ab -c50)	8,027 req/s	8,443 req/s

Honest gap

Windows numbers were not recorded — no wrk/ab on the Windows box; PLAN.md records the deviation from the original acceptance criterion ("both platforms") rather than faking it.