This is an early-stage architecture blueprint for building a modern agentic harness from the ground up in 2026. It is not a product spec and not a vendor pitch. It is a practical plan for how to structure the runtime, state model, context system, tool layer, subagent orchestration, approvals, protocols, and observability so the harness stays useful as models, tools, and deployment surfaces evolve.
This blueprint synthesizes the uploaded source material with current official documentation from Anthropic, LangChain/LangGraph, Moonshot Kimi CLI, MCP, ACP, and A2A. Where the sources conflict, the plan below favors patterns that appear repeatedly across multiple production systems or formal protocols. [U1][U2][U3][U4][U5][E1][E7][E15][E18][E24][E26]