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Step-by-step guide to building a real-time research assistant using LangChain's Deep Agents framework, Tavily web search, and CopilotKit. Covers the full stack: a Next.js frontend with live streaming of agent state (todos, files, sources) via AG-UI, and a FastAPI backend hosting a multi-step Deep Agent that plans, delegates to sub-agents, and writes research reports. Key patterns include thread-isolated sub-agents to prevent event stream leakage, CopilotKit middleware for frontend-agent state sync, and a two-panel UI showing the agent's work in real time.