Implements the Agent Skills specification (https://agentskills.io) for
portable skill packages that give the agent new capabilities.
Changes:
- Add skills module with SKILL.md parser (YAML frontmatter + markdown body)
- Implement skill discovery from ~/.g3/skills/, config extra_paths, and .g3/skills/
- Generate <available_skills> XML for system prompt injection
- Add SkillsConfig to g3-config with enabled flag and extra_paths
- Wire skills discovery into CLI startup
- Add 29 unit tests for parser, discovery, and prompt generation
- Update README with Agent Skills documentation
Skill locations (priority order):
1. ~/.g3/skills/ (global)
2. Config extra_paths
3. .g3/skills/ (workspace, highest priority)
At startup, g3 scans skill directories and injects a summary into the
system prompt. When the agent needs a skill, it reads the full SKILL.md
using the read_file tool.
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