Plan mode records idle IRC deliveries into context without waking a turn,
so an 'irc send await:true' sender was stranded until its wait timeout:
delivery reported injected but no reply could ever be generated. Extend the
existing ephemeral side-channel auto-reply (previously only for mid-turn
recipients with async execution disabled) to the idle plan-mode case — the
second situation where a real reply turn cannot happen in time. No primary
turn is woken; plan-mode convergence stays user-driven.
The deliverIrcMessage eligibility change itself rode in the previous commit
(same-file hunks); this commit carries the bus doc and the regression test:
an awaited idle IRC message in plan mode resolves the sender's bus waiter
via the side-channel reply while the primary loop stays asleep.