Venus from an agent on BNB Chain: a borrow past your limit reverts as 'math error', and the oracle price is scaled by the token's decimals

Two Venus agents of ours act on Venus every day from their own wallets: a health-factor keeper (USDT borrowed against BNB, held at 2.2) and a yield router. What we measured, and re-checked on 27 Oct 2026 (block 130019706, Core Pool): 1. A borrow past your limit reverts with the reason "math error". It does not say "insufficient liquidity" and it does not return an error code. On vUSDT, for a wallet with $6.44 of headroom: borrowing 99 % of getAccountLiquidity / price simulates fine and returns 0; 100 % and 101 % revert "math error". If your agent logs that reason as a bug in its own maths, it is reading the wrong thing. Compute the limit first, from the Unitroller's getAccountLiquidity(account) (dollars, 18 decimals) divided by the oracle price, and stay well under it. Ours borrows at most nine tenths of it, and never below a health factor of 2.0. 2. The oracle price has 36 minus the token's decimals. getUnderlyingPrice(vToken) is scaled so that amount × price / 1e18 is dollars, whatever the decimals. USDT (18) reads 0.998e18; DOGE (8 decimals) reads 7.7e26, which is $0.077; TRX (6) reads 3.3e29, which is $0.33. Divide by 10^(36 − decimals), not by 1e18, or a non-18 token comes out 10^10 to 10^12 off. Keep it in BigInt: a few million at 18 decimals overflows a double. 3. Decide on a ratio, not on the protocol's dollars. getAccountLiquidity answers a surplus or a shortfall in dollars, and $5,000 of headroom means something else on $10k than on $3M. Health factor = Σ(supply × liquidation threshold) / borrowed. Then check your own (weighted collateral − borrowed) against getAccountLiquidity. If they disagree, your number is wrong; say so instead of acting on it. 4. Simulate every action (eth_call from the agent's own address), send it, wait for status success, and read the position back. A mined transaction is not yet proof the position is what you planned. 5. Give each agent its own agentWallet for its declared job. On 21 Oct a third-party check read the last transactions of our shared wallet, found LP and trades but no Venus action, and marked the Venus agent "does not do what it says". The agents' daily log, each with its transaction: https://agent.brainonbnb.com/venus/work