* fix: advisory + exit(1) when port 53 is already in use (#45)
Detect AddrInUse on bind, print a human-readable diagnostic explaining
systemd-resolved / Dnscache as the likely cause and offer two concrete
fixes (sudo numa install, or bind_addr on a non-privileged port), then
exit(1) instead of surfacing a raw OS error.
Adds tests/docker/smoke-port53.sh: end-to-end Docker test that
pre-binds port 53 with a Python UDP socket and asserts the advisory +
exit code.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
* refactor: collapse port53 advisory to single flat path
The per-platform cause sentences were cosmetic — they didn't change
the user's actions (install, or bind_addr on a non-privileged port),
but they introduced duplicated "another process..." strings, a
dead-from-CI branch (is_systemd_resolved_active() == true is never
reached by any test), and a pub visibility bump on
is_systemd_resolved_active for a single caller.
Replace with one flat format! whose cause line mentions both
systemd-resolved and the Windows DNS Client inline. The existing
smoke test now exercises 100% of the function.
is_systemd_resolved_active reverts to private.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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