OpenAI wrapped the Codex harness as a JSON-RPC over stdio App Server, enabling VS Code, JetBrains, Web, and desktop apps to share a single agent loop. Three core primitives: Item, Turn, and Thread.
Agent memory isn't a plugin — it's part of the harness itself. Pick the right memory type, estimate data volume, then decide on the technology. And finally, figure out whether you actually own that memory.
An open-source Agent Harness framework from HKUDS (HKU Data Science Lab) that implements tool calling, skill loading, memory, permissions, and multi-agent collaboration as complete infrastructure, supporting Anthropic / OpenAI / GitHub Copilot API formats.
The model is the CPU, the harness is the operating system, and the agent is the application. No matter how powerful a model is, without a good harness it's just a demo. Phil Schmid argues that harness is the most critical infrastructure in AI engineering for 2026.