Every caller tears the SSH connection down right after `await
cancelAndWait(scope)`, so resolving on this call's own barrier alone let a
connection-apply teardown overlap the pool stop's still-running afterStop
teardown for the same key. Wait for the composed barrier instead; chain the
barriers (drain promises never reject, so this equals allSettled). The test
now waits a macrotask and asserts that neither the apply nor the new
bootstrap runs before the first teardown completes.
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