Previously the queue only drained inside the message.complete event
handler, so anything enqueued while a shell.exec (!sleep, !cmd) or a
failed agent turn was running would stay stuck forever — neither of
those paths emits message.complete. After Ctrl+C an interrupted
session would also orphan the queue because idle() flips busy=false
locally without going through message.complete.
Single source of truth: a useEffect that watches ui.busy. When the
session is settled (sid present, busy false, not editing a queue
item), pull one message and send it. Covers agent turn end,
interrupt, shell.exec completion, error recovery, and the original
startup hydration (first-sid case) all at once.
Dropped the now-redundant dequeue/sendQueued from
createGatewayEventHandler.message.complete and the accompanying
GatewayEventHandlerContext.composer field — the effect handles it.
d32e8d2ace