GitHub Copilot Agent Skills: The Cross-Tool Standard Arrives

GitHub Copilot Agent Skills in .github/skills/ are now an open standard working across Copilot VS Code, CLI, and Coding Agent. Skills use three-stage progressive disclosure (Discovery -> Instructions -> Resources) to scale to hundreds without context window exhaustion. The Coding Agent automatically references skills during Issue-to-PR execution, enabling autonomous PR creation following your team's procedures. Write a SKILL.md with YAML frontmatter and procedural markdown — the agent loads it on-demand when a topic matches. Cross-tool compatible with ~/.agents/skills/ for personal skills.