Agent Mode & Implementation

⚙️ Setting Up Your Project

copilot-instructions.md

This is your project's AI constitution. Create .github/copilot-instructions.md to set coding standards, architecture constraints, and naming conventions. Applied to every Copilot suggestion.

# Architecture
- Use repository pattern. Never call DbContext directly from controllers.
- All new services must implement an interface and be registered in DI.

# Coding Standards
- C# 12, .NET 8. Use file-scoped namespaces.
- Async methods must have Async suffix.
- No magic strings — use constants or configuration.

# Constraints
- Never modify the migration history.
- All public API endpoints require [Authorize] attribute.

Custom Skills (SKILL.md)

Encode repeatable patterns as reusable agent knowledge. A skill is a SKILL.md file plus optional scripts.

Location	Purpose
`.github/skills/extract-service/SKILL.md`	Step-by-step service extraction pattern
`.github/skills/add-endpoint/SKILL.md`	API endpoint scaffolding with tests
`.github/skills/migrate-db/SKILL.md`	Safe database migration workflow

MCP Servers

Connect Copilot to external data. Configure in .vscode/mcp.json.

Connection	What It Provides
PostgreSQL / SQL Server	Query schemas and data directly in context
Jira / Azure DevOps	Pull ticket details and requirements
Confluence / Wiki	Access documentation and architecture decisions
Custom internal APIs	Domain-specific data and operations

🚀 Using Agent Mode

Agent Mode vs Coding Agent

Feature	Agent Mode (VS Code)	Coding Agent (GitHub.com)
Where	VS Code, local	GitHub.com, cloud
Trigger	Chat panel, Ctrl+I	Assign issue to @copilot
Scope	Multi-file, runs terminal	Full repo, creates branch + PR
Supervision	You watch in real-time	Asynchronous, review the PR
Best for	Complex tasks you want to steer	Well-defined issues, autonomous work

Effective Agent Mode Prompts

1. Refactoring:

Extract the add-to-cart logic from ShoppingCartController
into a CartService. Update all callers and add unit tests.
Don't change existing behaviour.

2. Feature implementation:

Add Redis caching to the ProductService.GetById method.
Use IDistributedCache. Cache for 5 minutes.
Include cache invalidation when product is updated.

3. Multi-file scaffolding:

Create a new NotificationService following the repository
pattern in this project. Include: interface, implementation,
DI registration, unit tests. Follow the same structure as
OrderService.

The Feedback Loop

Agent mode's real power is its feedback loop. It runs terminal commands (build, test, lint), reads the output, and self-corrects. Make sure your project has: a working build command, runnable tests, and a linter. The better your harness, the better the agent performs.