Coding Agent

What This Demonstrates

The Copilot Coding Agent implements features, applies cross-cutting changes, and fixes bugs — generating code that follows existing project conventions.

Prerequisites

• VS Code with Copilot Chat open
• Repository loaded with services running (docker-compose up -d)

Prompts

Prompt A — Small Implementation

Implement health/readiness endpoints for `services/payment-service` and add
unit tests for them, following existing code style and API response format.

Why this works

Copilot identifies the Express router pattern, the success/data/error/meta response format, and the test setup used in other services — then applies the same conventions to new endpoints.

What to look for:

• /health and /ready endpoints following the project’s response format
• Unit tests matching existing test structure and assertion style
• Proper TypeScript types from @octo-eshop/types

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Prompt B — Cross-Cutting Change

Add standardized request ID propagation middleware to all backend services and
ensure logs include the request ID. Make minimal, consistent changes only.

Why this works

Cross-cutting changes require understanding all services simultaneously. Copilot applies the same middleware pattern across user-service, product-service, cart-service, order-service, and payment-service.

What to look for:

• Consistent middleware implementation across all services
• Request ID in log output
• Minimal diff — no unnecessary refactoring

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Prompt C — Bugfix Scenario

Find and fix one realistic input-validation gap in `services/order-service`
checkout flow. Add/adjust tests to prove the fix.

Why this works

Copilot audits the checkout flow for missing validation (e.g., negative quantities, empty carts, invalid payment references) and produces a targeted fix with tests.

What to look for:

• Identified validation gap with explanation
• Surgical fix (not a rewrite)
• Tests that cover both the happy path and the edge case

Follow-Up Prompts

• “Now add integration tests for the health endpoints using supertest.”
• “Show me the diff summary of all changes made.”
• “Are there similar validation gaps in cart-service?”