Live-verified all three cluster_open_listener code paths not exercised by
the 3-node soak: no --peers binds hardcoded default 9990; a single
self-referencing --peers entry binds its custom port instead; --peers
given but local name absent still refuses to start with -EINVAL, unchanged.
Independently reproduced by the reviewer. This closes the actual
regression risk this spec's design was built around.
Review also found (bug-1457, logged, not fixed here) that pre-spec
single-node startup was already broken with -EINVAL before this spec
began, due to an unrelated myapp_run listener-open/config-load ordering
issue -- task 2.1's rewrite incidentally repaired it. research.md updated
to record this against the spec's original preservation premise.