<p>Sharding enhances blockchain scalability and throughput but poses significant challenges for cross-shard transactions, often limiting parallel execution and degrading real-time performance. This paper presents a sharded blockchain system that employs account-based partitioning, co-locating frequently interacting accounts within the same shard to reduce cross-shard overhead. To further improve cross-shard transaction processing, we introduce an enhanced three-phase commit protocol that extends the traditional two-phase commit by integrating global hash signatures and a dual-pipeline mechanism. In this design, transaction hashes are aggregated into a global hash, while validator signatures collectively form an availability certificate. The commit phase is refined into two sub-stages, enabling two transaction batches to be processed concurrently within a single round of computation and communication. Furthermore, a cross-shard commit protocol leveraging aggregated signatures is incorporated to minimize communication overhead. These improvements align closely with high-performance distributed systems, where reducing synchronization costs and achieving scalable parallel execution are essential for supercomputing-grade applications. Extensive evaluations on a dataset of one million real Ethereum transactions, performed using the BlockEmulator simulation framework, demonstrate the effectiveness of our approach. Compared to conventional hash-based partitioning schemes (Monoxide), the proposed system reduces the cross-shard transaction ratio by approximately 40% and lowers transaction confirmation latency by up to 80%.</p>