Add Dev Proxy Agent Skill

[garrytrinder]

Summary

Add an Agent Skill to the extension to provide Dev Proxy knowledge to AI agents.

Background

Agent Skills (https://agentskills.io/) are an open standard for giving agents procedural knowledge. They're supported by Claude, OpenAI Codex, Gemini CLI, and others.

A Dev Proxy Skill would:

• Trigger when developers work on API mocking, error testing, rate limiting, etc.
• Provide best practices dynamically via HTTP fetch
• Guide agents to search Dev Proxy documentation
• Enable version checking for schema compatibility

Blocked By

• VS Code Extension API contribution point for Skills (not yet available)

Work Done

• Draft dev-proxy/SKILL.md created in skill branch
• Description covers 10 key developer scenarios
• Instructions reference HTTP endpoints for dynamic content

Next Steps

1. Monitor VS Code API for Skills extension point
2. Implement contribution when API is available
3. Consider impact on @devproxy/mcp server (may become redundant)