BlockGuard: A PureChain Safety Framework for Agent Validation in Mission-Critical Systems

Large Language Model agents show increasing potential for mission-critical edge environments, including autonomous drones, smart grid controllers, and industrial automation systems. However, the non-deterministic nature of LLMs poses significant safety risks when deployed in physical systems where erroneous decisions can lead to catastrophic failures. We present BlockGuard, a blockchain-anchored safety framework that binds agent actions to immutable, verifiable safety policies. The system employs a fast-path local validator for real-time deterministic enforcement, while PureChain smart contracts operate in a slow-path role to provide post-decision immutability, auditability, and policy provenance. PureChain does not sit on the real-time control loop; instead, it provides authoritative evidence, dispute resolution, and compliance guarantees without impacting control latency. Through simulation-based validation across 150 industrial control scenarios, BlockGuard blocked 100% of unsafe actions with a mean validation latency of 25.9 ms and 32.6 ms (with twin). Twin anchoring improved latency stability, bounding worst-case checks to ≤ 101 ms versus 272 ms spikes in baseline; explainability recall and audit completeness were both 1.0.