Auto-discover AGENT.md and SKILL.md context files

[tyzerrr]

Summary

Automatically discover and include AGENT.md and SKILL.md files from the directory hierarchy as additional context for Claude.

Context

The 99 plugin searches parent directories for AGENT.md files and supports @Skill references to SKILL.md files for injecting domain-specific rules.

Acceptance Criteria

• Walk directory hierarchy to find AGENT.md files
• Parse and index SKILL.md files
• Include discovered context in system prompt