Distils the things that took a debugging session to learn and cannot be
read off a single file: the two-build-tree workflow, the one-way module
dependency chain, the invariants around the single lwIP stack, and the
traps (asio error categories, self-re-arming io work blocking shutdown,
slice-driven tests being blind to that class of bug).
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
