Hands-on Exercises

Choose one of the following scenarios and design a complete Agent Harness architecture:

Scenario A: Code Review Agent

• Tool set: Git operations, file reading, static analysis, comment posting
• Permission model: Read-only mode + comment writing requires confirmation
• Context strategy: Compress by PR dimension, preserving change summaries
• Hooks: Automatically run lint, type checks, inject results into context

Scenario B: Operations Monitoring Agent

• Tool set: Log queries, metric retrieval, deployment operations, alert management
• Permission model: Queries auto-approved, operations require dual confirmation
• Context strategy: Sliding window + priority retention for anomalous events
• Hooks: Webhook notifications, audit log recording

Scenario C: Documentation Generation Agent

• Tool set: Code analysis, document templates, version comparison, file writing
• Permission model: Automatic mode (trusted write target directory)
• Context strategy: Project-level memory, cross-session style preference persistence
• Hooks: Format checking, link validation

For your chosen scenario, complete the following design:

1. Draw a component relationship diagram (call relationships between dialog loop, tool system, permission pipeline, context management, memory system, and hook system)
2. Define at least three tools with complete buildTool definitions
3. Design the four-stage check logic for the permission pipeline
4. Choose a compression strategy and explain trigger conditions
5. Define at least two hooks and their expected behavior

Extended Exercise: Implementing a Minimal Agent Harness

Based on the six-step roadmap in this chapter, implement a minimal runnable Agent Harness. The suggested implementation order is:

Week 1: Dialog Loop + Tool System

• Implement the core agentLoop function
• Implement the buildTool factory function
• Define 2-3 basic tools (file reading, file listing, command execution)
• Validation: can complete a simple "read file and answer questions" task

Week 2: Permission Pipeline + Context Management

• Implement four-stage permission checks
• Implement a simple snip compression strategy
• Add token counting and budget checks
• Validation: can safely execute operations requiring confirmation; long conversations don't overflow

Week 3: Memory System + Hook System

• Implement simple memory extraction and injection
• Implement the Shell command hook executor
• Add session_start and post_tool_use hooks
• Validation: memory persists across sessions; hooks correctly intercept and modify behavior

Week 4: Testing and Productionization

• Write unit tests for core components
• Add structured logging
• Implement error recovery and circuit breaker
• Use in a real project and collect feedback