Second review of PR #45, non-blocking: two behaviours were right by hand
and held by no test.
- a listener on 3099 that closes at once, then one that accepts and stalls:
the port rule is "anything but connection refused", not "an HTTP answer"
- a server that stays alive and never listens: the wait ends on its
deadline, with a message and exit 1
Also moves the port check above the "Fixtures" comment it had split from
its mkdir lines, and counts four protections in CLAUDE.md, not three.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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