Four registry tests overlapped: sibling independence is a two-line
assertion inside hold-until-stop, and the reject-missing-target case is
the setup half of the empty-scope primary case. Folding them keeps every
invariant covered (hold, no-reconnect-after-stop, sibling isolation,
''-is-a-real-key, baseUrl/token required) with fewer fixtures to keep in
sync. The pool-stop teardown fence is already covered by
pool-stop.test.ts::afterStop and ssh-bootstrap-coordinator.test.ts.
kshitijk4poor
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