// Rubber Duck Thursdays - Let's build down tech debt

Chris reviews the latest GitHub changelog and explores the major VS Code December release, then continues building custom agents for a game MCP server project.

GitHub Changelog Highlights

• CodeQL 2.23.6 adds Swift 6.2.1 and new C# security queries
• GPT-5.1 Codex Max now in public preview for GitHub Copilot across VS Code, GitHub.com, and GitHub Mobile
• Workflow dispatch inputs limit increased from 10 to 25
• Copilot code generation metrics now available in the enterprise insights dashboard
• Enterprise teams limits increased over 10x — up to 2,500 teams and 5,000 users per team
• Dependabot-based dependency graphs for Go now provide more complete transitive dependency trees
• npm classic tokens revoked — replaced with session-based and CLI token management
• Repository custom properties now support GraphQL management and a URL type with built-in validation
• GitHub MCP server adds tool-specific configuration, lockdown mode for untrusted contributors, and default content sanitization against prompt injection
• GitHub Enterprise Server 3.19 GA with rule set history import/export, SSH/TLS cipher configuration, and OpenTelemetry metrics
• Auto model selection GA in VS Code for all Copilot plans

VS Code December Release — Agent Features

• Agent HQ for managing multiple coding agents — background, cloud, or local — working simultaneously
• Background agents with git worktrees for isolated workspaces, enabling multiple agents to work in parallel without file conflicts
• Custom agents for organizations — share agents at the org level via .github-private repositories
• Sub-agents via run sub agent — delegate tasks to specialized sub-agents with their own context windows to avoid context bloat
• Claude skills support — reuse existing Claude Code skills within VS Code agents
• Session management improvements — integrated sessions view, compact and side-by-side layouts, and persistent local agent sessions

Live Coding — Custom Agents and Background Agents

Chris demonstrates the new VS Code agent features by continuing work on a tic-tac-toe game with an MCP server backend. He creates a testing specialist agent using a TDD workflow, experiments with background agents running in git worktrees, and explores sub-agent delegation for specialized tasks like code quality review.