Architectural Patterns for Multi-Agent Systems: Conditional Routing, State Persistence, and Human-in-the-Loop Orchestration

Abstract: The transition from monolithic language model prompts to multi-agent architectures represents a fundamental paradigm shift in autonomous software engineering. As artificial intelligence applications shift toward production environments, systems must execute deterministic business logic, maintain state across asynchronous boundaries, and integrate human oversight without corrupting execution flows. This paper evaluates two fundamental agentic design patterns: Intent-Based Conditional Routing and Event-Driven Human-in-the-Loop (HITL) Orchestration. Utilizing execution traces, state persistence schemas, and graph-based workflow engines, we demonstrate how structured agent topologies resolve the latency, security, and reliability limitations of unconstrained LLM execution. Key Topics & Technologies: Architectural Frameworks: Agentic Engineering, Directed Acyclic Graphs (DAGs), and state machines. Development Tools: Google Agent Development Kit (ADK) framework and external FastAPI management UIs. System Capabilities: Intent classification, deterministic fallback routing, and asynchronous event ingestion via pub/sub messaging. State Management: Asynchronous state pausing (RequestInput) and persistent Human-in-the-Loop (HITL) checkpoints.