lastIndexUsed is the highest HD index at which any handler discovered a
contract (-1 if nothing was found). handlerErrors collects per-handler
discoverAt failures — non-empty means the gap window may have closed
early and the caller should surface this (the scan itself still resolved).
Outcome of a IContractManager.scanContracts run.
lastIndexUsedis the highest HD index at which any handler discovered a contract (-1if nothing was found).handlerErrorscollects per-handlerdiscoverAtfailures — non-empty means the gap window may have closed early and the caller should surface this (the scan itself still resolved).