BreakerBox is an on-chain circuit breaker for oracle feeds. It maintains a state per price feed (e.g. trading allowed or suspended) and supports modular addition of price feeds and breaker logic. In Mento V3, the OracleAdapter reads from BreakerBox when supplying the FPMM pool with a valid rate; if a breaker has tripped, the adapter returns invalid and swaps revert. This protects pools from trading on stale or out-of-bounds oracle data.
For FX pairs, Mento also uses a MarketHoursBreaker. This aligns on-chain trading with reference FX market hours: Chainlink FX feeds typically stop updating on weekends and certain holidays, so Mento can reject FX trading even if the last reported rate is still recent enough by timestamp.
Integrators typically do not call BreakerBox directly; the OracleAdapter uses it. If you need to check trading mode (e.g. for a status UI), use the adapter’s getRate(rateFeedID) and inspect tradingMode, or call getTradingMode(rateFeedID) on the adapter if exposed.
MedianDeltaBreaker
MedianDeltaBreaker is a circuit breaker that trips when the current median oracle rate compared to an exponential moving average over previous median rates exceeds a configured relative threshold.
ValueDeltaBreaker is a circuit breaker that trips when the current median oracle rate compared to a fixed reference rate exceeds a configured relative threshold.
MarketHoursBreaker is a special breaker for FX market-hours gating. Instead of comparing prices, it checks whether the current block timestamp falls inside the configured FX trading window. The current implementation treats the FX market as closed:
from Friday 21:00 UTC until Sunday 23:00 UTC
on Christmas Day (Dec 25) and New Year's Day (Jan 1)
after 22:00 UTC on Dec 24 and Dec 31
When this breaker says the FX market is closed, OracleAdapter.getFXRateIfValid() reverts and FX-priced FPMM swaps revert too. This is especially relevant for GBP/USD, EUR/USD, and similar fiat FX feeds, whose Chainlink rates generally do not update during those closure windows.
