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

Installation and Initial Setup

• Node.js prerequisites and package installation
• Launching the Web UI using npx
• Building and executing from source code

Model Configuration

• Setting the DeepSeek API key
• Selecting and switching between models
• Integrating OpenAI-compatible endpoints

Workspaces and Sessions

• Selecting and switching workspaces
• The session composer and conversation workflow
• File reading, editing, and generation

Executing Coding Tasks

• Summarizing repositories and navigating codebases
• Running commands and delegating tasks
• Maintaining and tracking task plans

Permissions and Sandbox Environment

• Approval workflows and permission policies
• Restricting file and command access
• Local and remote sandbox backends

Built-in Tools and Integrations

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

Subagents and Delegation

• Spawning and forking subagents
• Provider integration for other coding agents
• Distributing work across a session

The Cordis Plugin Model

• Plugins structured as services, events, and effects
• Shared context and lifecycle management
• The absence of a privileged core

Profiles, Bundles, and Configuration

• Profile and bundle layering strategies
• Patching configuration via cordis.patch.yml
• Inspecting the boot sequence and tree structure

Core Subsystems

• The append-only session log
• Assembly of system prompts and tool schemas
• The agent loop and turn processing flow

Events and Extension Points

• Session, agent, and capability-related events
• Waterfall and interceptor event patterns
• Aligning behavior with specific extension points

Plugin Development

• Registering services on context keys
• Adding custom tools and model adapters
• Publishing and discovering plugins

SDK, Headless Mode, and Automation

• Controlling the harness from external processes
• Utilizing the TypeScript and Python SDKs
• Automation via CLI and headless mode