spotState has the Spot Clearinghouse State
response shape, including signed total/hold fields, real debt, and pUSD trading capacity.
A funding/pricing failure emits an error frame instead of numeric balances with invented credit.
Discard expired capacity and recover with HTTP. Active tracked accounts refresh on account events
and on a bounded three-second schedule for pool-wide changes. Subscriptions do not enroll arbitrary
accounts into background monitoring.
Use the same subscription with method: "unsubscribe" to stop receiving updates.