Blend V2 callback. Called after Blend transfers amount of token
(USDC) to this contract. We execute both swap legs, transfer enough
USDC back to caller (the user) so Blend's subsequent Repay request
has tokens to pull, and keep any profit sent alongside.
fn exec_op(
env: soroban_sdk::Env,
caller: soroban_sdk::Address,
token: soroban_sdk::Address,
amount: i128,
_fee: i128,
)Entry point. Off-chain executor builds a tx that invokes this once.
Args chosen so the off-chain executor sizes the trade against the
current signal, and passes the Aquarius pool hash it already knows
from scripts/stellar-executor/probe-aquarius-swap.ts.
amount is the USDC notional we flash-borrow from Blend. min_profit
is the floor: if Sushi returns fewer USDC than amount + min_profit,
the tx reverts and only fees are paid.
fn execute_arb(env: soroban_sdk::Env, user: soroban_sdk::Address, params: ArbParams)