Reports how much pipeline spend allowance the caller has left on this
compute node, without starting a run. Intended for rendering a usage
meter and for disabling submission with a real reason before a user
configures a run.

Returns the same numbers the run-creation gate enforces, from the same
resolver and usage read, so the displayed allowance cannot drift from
the applied one.

enforced: false means the node has no spend policy configured — the
normal state for a customer-owned node, whose owner pays their own AWS
bill. Every allowance reads unlimited and no meter should be shown.

allowed is advisory, not a reservation: a run's cost is only known
once it finishes, so another run completing or starting between this
call and a submission can change the answer.