Function idle_should_wait 

pub fn idle_should_wait(children_running: bool, queue_len: usize) -> bool

Returns true when the agent idle loop should park on queue.notified() instead of immediately nagging with a user message.

Invariant: exactly one waiter on queue.notified() exists in agent mode. The caller must drop any registry lock before awaiting the future.

Conditions to wait:

• At least one child subagent is still running, or
• The event queue already has items (drain them first on loop-top).