DeepSeek Harness: Everything Is a Plugin on the Cordis Kernel
DeepSeek launched DeepSeek Harness right after V4 Pro, built around the idea that everything is a plugin. The core, Cordis, only handles plugin loading, unloading, and dependency management, allowing hot-swapping during agent runs; an 88-page paper describes temporal and spatial composability. UI, tools, skills, storage, and the agent loop are all exposed as plugins, with 100+ first-party plugins and a community plugin marketplace. Setup is a single `npx @deepseek-ai/dsh web` command, and the harness is not locked to DeepSeek models—custom providers, base URLs, protocols, and model lists are supported. The post walks through four modes: Standard, PTC (packing multiple tool round-trips into one run_code), Minimal, and Create, where the agent can inspect its own Cordis environment, build a plugin, and attach it mid-run. Sessions are append-only event logs, making failure traces observable, auditable, and reproducible. It also flags steep price increases for V4 Pro (cache hits up 12x, peak output ¥27) and admits the UX is rough for non-developers. Useful for engineers interested in agent-harness design and composability.