Exact financial + token math. POST {op:…}: compound (growth with per-period contributions), amortize (payment, total interest, schedule), npv, irr (deterministic bisection) — and token_units: exact decimal↔base-unit conversion via BigInt for any token decimals (ETH 18, USDC 6), the 18-decimal math that float64 silently corrupts. Iterative series computed exactly, never guessed.