/skill-builder — Scaffold or absorb a new SKILL.md

Materializes a new skill against the unified template at references/skill-template.md (extracted from anthropics/financial-services). Runs skill-auditor on the new skill as a self-check before declaring success.

⚠️ Critical Constraints

• Template is canonical. All four modes produce SKILL.md files conforming to references/skill-template.md. Do not invent ad-hoc structures. Why: skill-auditor validates against this template; drift creates auditor false-fails.
• Self-audit is mandatory. After every successful build, the build script invokes /skill-auditor against the new skill directory. A FAIL verdict aborts the build. Why: PR-002 (external validation gate) — the builder must not declare its own work complete.
• Codex parity is day-1, not later. from-scratch, from-template, and absorb-external modes must produce both skills/<name>/SKILL.md AND skills-codex/<name>/SKILL.md + skills-codex/<name>/prompt.md. Why: finding 2026-05-03-codex-skill-shape-is-dual-file — codex SKILL.md uses slim frontmatter (no skill_api_version); prompt.md is mandatory; audit-codex-parity.sh is a content scanner that won't catch frontmatter drift.
• 250-line ceiling on new SKILL.md. Use references/ for overflow. Why: finding f-2026-05-01-025 — every Skill() invocation reloads 5-15KB; multi-lifecycle sessions compound to 150-200KB+ pure scaffolding.

Modes