In DeepSeek Harness, you extend capabilities not by editing source, but by mounting plugins alongside other plugins. This page covers the basics of Cordis plugins and where common capabilities should attach.

Cordis plugin basics

Cordis is the framework underneath dsh: plugins contribute services, typed events, and reversible side effects to a shared context.

• Loading & unloading: the Cordis meta-framework handles only plugin loading, unloading, and dependencies
• Services: plugins offer capabilities to other plugins through services
• Events: plugins observe or intercept in-flight work through typed events
• Reversible side effects: every registration is a side effect, undone when its plugin unloads — so there's no privileged kernel to patch

Where new behavior belongs

New behavior attaches to documented extension points. Common goals and their mechanisms:

Goal	Mechanism
Add a model provider	Register its adapter on ctx.llm
Add a model-facing capability	Register on ctx.tools; its schema joins prompt assembly
Give a session a different capability set	Assemble an agent preset
Add shell execution	Register a ctx.shell backend
Add persistent terminal execution	Register a ctx.terminals backend
Add a user command	Register on ctx.commands
Add background work	Register on ctx.jobs; job_* tools collect or stop
Add filesystem access or policy	Register a ctx.fs provider, or listen to fs/* events
Constrain launched processes	Use a ctx.sandbox backend
Intercept requests, tools, or turns	Use the relevant agent/* or tools/* events
Add model-visible context	Call agent.inject()
Add UI or editor integration	Drive ctx.agents and render from session/event
Add persistent session state	Extend SessionEventMap; render and replay from the log

Events are the extension points

Choosing the right event domain is the first decision in most changes:

• Session events: persistent facts appended to the log and broadcast via session/event — use when a fact must survive reload
• Agent events (agent/*): carry the active Agent — inbox, steps, state, requests, validation, resumption — use to observe or intercept in-flight work
• Capability events: attach policy and adapters to a seam (fs/*, tools/*, telemetry/*) without import cycles

Publish your plugin

• Declare the profile and bundle in package.json via the dsh field: dsh.profile lists a profile's bundles, dsh.bundle points to a bundle's patch file
• Add the dsh-plugin topic to your repository for discoverability
• Share and discuss via GitHub Discussions

Want to get hands-on?

The official repo offers an extension cookbook with step-by-step guides (adding a package, a tool, an LLM adapter, a chat node), plus the Cordis tutorial.