Constant MAX_SANE_USD_RATE 

pub const MAX_SANE_USD_RATE: f64 = 1_000_000.0; // 1.0E+6f64

Upper bound for any configured or discovered USD cost rate.

For model tokens this is $1 per token, orders of magnitude above current provider prices. Keeping the bound in the config cost module gives config, runtime recording, and live-provider normalization one policy source.