The rename test relied on a fixed 300ms setTimeout to fire after the CLI
subprocess had registered its waiter — adequate in isolation but flaky
under full-suite load on Windows (CLI spawn + first HTTP request can
exceed 300ms). Add a tiny public MailboxStore.waiterCount(name) helper
so the test can poll until the waiter is actually registered before
triggering the rename. Also tighten the missing-name assertion from
not-zero to the contract-exact exit code 1.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
