bug: generated SKILL.md descriptions with colons are invalid YAML

[kesslerio]

What happened

Codex/OpenAI skill loading skips several gstack skills because generated SKILL.md frontmatter contains inline plain YAML scalars with unescaped colons.

Example generated frontmatter:

---
name: setup-gbrain
preamble-tier: 2
version: 1.0.0
description: Set up gbrain for this coding agent: install the CLI, initialize a local PGLite or Supabase brain, register MCP, capture per-remote trust policy. (gstack)
triggers:
  - setup gbrain
---

A strict YAML parser treats the second colon (agent: install) as a mapping separator and fails with:

invalid YAML: mapping values are not allowed in this context

Affected examples

Observed in exported gstack skills:

• setup-gbrain/SKILL.md
• guard/SKILL.md
• design-html/SKILL.md
• design-shotgun/SKILL.md
• design-review/SKILL.md
• ship/SKILL.md
• design-consultation/SKILL.md
• plan-tune/SKILL.md

Expected

Generated SKILL.md frontmatter should parse as YAML in strict loaders.

Suggested fix

Quote one-line generated description: values or emit block scalars consistently. The generator should also parse every generated frontmatter block in tests, not just check that name: and description: strings exist.

Locally, this shape fixed the issue:

• Quote inline description: values with JSON.stringify(...)
• In gen-skill-docs.ts, normalize inline descriptions before writing generated content
• In gen-skill-docs.test.ts, parse generated frontmatter with Bun.YAML.parse(...)

Verification

Local validation after patching exported skills:

checked 545 SKILL.md files, bad=0

Also no remaining unquoted inline descriptions with colons were found by:

rg -n '^description: [^|"'"'].*:' /path/to/exported/gstack --glob 'SKILL.md'