Cross-chain interoperability has emerged as a critical requirement for blockchain ecosystems, enabling applications to coordinate operations across heterogeneous networks while requiring robust atomicity guarantees to prevent partial failures. Existing cross-chain protocols either impose expensive state rollback costs when transactions abort, or employ bilateral abortion strategies that cascade failures across chains, both degrading system performance under concurrent execution while lacking principled mechanisms for maintaining causal dependencies among related transactions. This paper presents CrossBuffer, a protocol achieving complete atomicity for cross-chain transactions through three synergistic mechanisms that collectively address these limitations. First, revocable state buffering introduces managed queues before on-chain persistence, maintaining cross-chain states as revocable until consensus to achieve atomicity without rollback overhead. Second, unilateral conflict reordering resolves cross-chain conflicts through age-based priority management, transforming bilateral abortion into optimistic single-sided adjustment to ensure system availability under high-conflict scenarios. Third, causal dependency preservation maintains dependency ordering through DAG-based modeling and constraint propagation, preventing descendant transactions from committing before predecessors regardless of conflict-induced reorderings. Implementation on Cosmos blockchain infrastructure and experimental evaluation CrossBuffer’s operational viability, successfully coordinating concurrent conflicts and dependency chains while maintaining bounded abortion rates and resource consumption under varying workload intensities.