DeepSeek Harness: Building and Extending AI Coding Agents Training Course

Introduction to DeepSeek Harness

• Overview of DeepSeek Harness and its role in the ecosystem
• The "everything is a plugin" design principle
• Web UI, CLI, and headless operational modes

Setup and Initial Execution

• Node.js prerequisites and package installation
• Starting the Web UI using npx
• Compiling and running from source code

Model Setup

• Configuring the DeepSeek API key
• Selecting and swapping between models
• Integrating OpenAI-compatible endpoints

Workspaces and Session Management

• Selecting and changing active workspaces
• Utilizing the session composer and managing conversation flow
• Reading, modifying, and generating files

Executing Coding Tasks

• Summarizing repositories and navigating codebases
• Executing commands and delegating specific tasks
• Maintaining and updating task plans

Permissions and Sandbox Environments

• Managing approval and permission policies
• Restricting file and command access
• Implementing local and remote sandbox backends

Native Tools and Integrations

• Filesystem, terminal, and shell utilities
• Support for the Model Context Protocol
• Integration with the Language Server Protocol

Subagents and Task Delegation

• Creating and forking subagents
• Product providers for alternative coding agents
• Distributing work across a single session

The Cordis Plugin Model

• Defining plugins as services, events, and effects
• Understanding shared context and lifecycle management
• Rationale for the absence of a privileged core

Profiles, Bundles, and Configuration

• Managing profiles and bundle layering
• Modifying configuration via cordis.patch.yml
• Reviewing the booted configuration tree

Core System Components

• The append-only session logging mechanism
• Assembly of system prompts and tool schemas
• Managing the agent loop and turn processing

Events and Extension Points

• Handling session, agent, and capability events
• Working with waterfall and interceptor events
• Aligning behaviour with specific extension points

Plugin Development

• Registering services using context keys
• Implementing new tools and model adapters
• Releasing and locating plugins

SDK, Headless Operation, and Automation

• Controlling the harness from external processes
• Utilising the TypeScript and Python SDKs
• Automating workflows via CLI and headless mode