SolidState: A Deterministic Finite State Machine Runtime for Safe and Concurrent Multi-Agent Orchestration

Autonomous agent architectures driven by Large Language Models (LLMs) often suffer from execution drift, non-deterministic loops, resource exhaustion, and security vulnerabilities during tool execution. In this paper, we introduce SolidState, an open-source, highly reliable agent orchestration runtime designed around the principles of deterministic Finite State Machines (FSMs). SolidState enforces a strict separation of concerns, treating the LLM as a probabilistic reasoning adapter while reserving state transitions, tool execution loops, and safety policies within a deterministic, type-safe runtime. We describe the core runtime loop, human-in-the-loop (HIL) governance policies, dynamic routing topologies via the StateGraph engine, and an isolated multi-threaded Actor model concurrency system. Finally, we provide performance benchmarks demonstrating the framework’s resource containment and latency advantages under production workloads.