LOCK(mempool->cs) in ChainImpl::isInMempool(). The method calls CTxMemPool::exists(), which already locks mempool->cs internally. Because the mempool mutex is a RecursiveMutex, double-locking was safe but redundant. Dropping the outer lock matches patterns used elsewhere in ChainImpl (e.g. hasDescendantsInMempool() and GetTransactionAncestry() callers) where mempool read APIs are invoked without an additional lock and rely on the callee’s internal locking. isRBFOptIn() remains unchanged since IsRBFOptIn(tx, pool) explicitly requires the caller to hold pool.cs as indicated by its thread-safety annotation.
