// Rubber Duck Thursdays - Building from requirements with Agent Mode

In this stream, Chris walks through building a GitHub CLI extension in Go from scratch, taking a spec-driven and test-driven development approach powered by Copilot Agent Mode.

Topics Covered

• GitHub Changelog Review — Model updates in GitHub Models (Mistral, Cohere, Llama), GPT-4.1 as the new default Copilot model, updated rate limits for unauthenticated requests, and the VS Code April release with MCP support and prompt files
• Microsoft Build Preview — A look ahead at sessions and events for the following week
• Building gh-demo from Scratch — Bootstrapping a new Go-based GitHub CLI extension using VS Code’s new workspace creation with Copilot, the Cobra library, and a spec-driven approach starting from a product requirements document
• Test-Driven Development with Copilot — Writing tests first for a hydrate subcommand that reads JSON files to create GitHub issues, discussions, and pull requests, with content type filtering and label collection
• GitHub Actions CI — Creating a build, test, and lint workflow for the new CLI extension
• Custom Instructions — Setting up a copilot-instructions.md file to guide Copilot’s behavior around path handling and project conventions