DeepSeek released Harness into developer preview yesterday — MIT license, source on GitHub, and a claim that "everything is a plugin." I spent some time reading through the docs and the Cordis kernel architecture to see what that means in practice vs. marketing.
The short version: it's more real than most.
The architecture in one pass
Harness is built on Cordis, a plugin kernel that handles mounting, unmounting, and dependency resolution. Every agent capability is a plugin: models, tools, skills, sessions, sandboxes, storage, loops, scheduling, and the UI. You compose them through configuration files, not forks.
That means you can swap out the model provider, replace the sandbox implementation, or change the loop strategy without touching the core. The plugins communicate through Cordis services and events.
