Set a timed allowance budget for an operator (e.g. OperatorHub). The account grants the operator a notional USD spending budget, enabling the backend to execute orders on the account's behalf without per-order signatures. Required for TPSL (Take Profit / Stop Loss) orders.

Prerequisites:

1. GET /v1/system/config — get operator_hub address (the operator to approve)
2. GET /v1/auth/eip712-domain — get EIP-712 domain for signing
3. GET /v1/nonce-state/{account} — get nonce_anchor and current_bitmap_index

Account signs PermitSingle (EIP-712):

PermitSingle(address account, address operator, uint96 budget, uint32 allowanceExpiry, uint48 nonceAnchor, uint8 nonceBitmap)

Struct hash: keccak256(abi.encode(PERMIT_SINGLE, account, operator, budget, allowanceExpiry, nonceAnchor, nonceBitmap))

Uses the EIP-712 domain from GET /v1/auth/eip712-domain.

Constraints:

• budget must be > 0 (notional USD in WAD, 18 decimals, uint96)
• allowanceExpiry must be in the future (unix timestamp in seconds)
• Cannot overwrite an active (non-expired) allowance — call lockdownAllowance(operator) on the Authorization contract first, or wait for expiry
• All submitted fields must exactly match the signed EIP-712 values

Budget management:

• Each executed order consumes size × price (notional) from the budget
• Query remaining budget: call getAllowance(account, operator) on the Authorization contract
• Emergency revoke: call lockdownAllowance(operator) directly on the Authorization contract (msg.sender = account)