* fix(runtime): charge a steered subagent's usage to the token budget
A task that finishes after a Steer reports through a receipt HumanMessage, so its usage never reached the dispatching AIMessage the token budget reads. Carry the usage over when the receipt is delivered.
* fix(runtime): report deferred usage with no AIMessage to charge
Log the rare case instead of dropping the usage silently, and scan for AIMessages once per delivery.