Plugin skills load full SKILL.md content at startup, not frontmatter-only

Summary

Claude Code loads the full content of every SKILL.md file at startup, not just the frontmatter. For plugins with many skills, this causes multi-minute cold starts.

Evidence

• Version: v2.1.89 (also reproduced on later versions)
• Plugin: 28 skills, 8,392 lines (~34K tokens total across all SKILL.md files)
• Cold start with skills: 4+ minutes
• Cold start without skills (removed skills/ dir): 3-4 seconds
• All other plugin components are fast: hooks, rules, agents, MCP servers all initialize in <2s

Binary search results

| Skills loaded | Startup time |
|---------------|-------------|
| 0 | 3-4s |
| 3 stubs (~98 lines) | ~5s |
| 5 stubs (~155 lines) | 15-20s |
| 10 stubs (~317 lines) | ~60s |
| 28 stubs (~762 lines) | 4+ min |

Scaling is non-linear per skill count, suggesting per-skill overhead (file discovery, frontmatter parsing, tool schema generation, system prompt injection) rather than pure content size.

Expected behavior

CC should load only the frontmatter (name, description, keywords, allowed-tools) at startup for discovery and routing. The full SKILL.md body should be loaded on invoke — either via lazy loading or the SkillSearch pattern described in #43816.

Workaround

We reduced all 28 skills to 15-line stubs (frontmatter + "Read procedure file" instruction), with full procedure bodies in separate files loaded via Read tool on invoke. This reduced startup context from ~34K to ~3K tokens and brought cold start to acceptable levels.

Related issues

• #43816 — SkillSearch (lazy loading for skills)
• #42906 — Cold cache API calls at startup
• #27721 — Skills registered twice from plugins
• #28660 — Skill catalog re-injected on every tool call

Reproduction

1. Create a plugin with 20+ skills (each SKILL.md ~200-400 lines)
2. claude --plugin-dir ./system
3. Measure time to first prompt response