Skills SDK should replace custom build scripts for skill vendoring

[krisrowe]

Problem

claude-coding has a custom ./build script that vendors skills from echoskill into plugin/skills/. This works but is bespoke — every plugin that consumes marketplace skills needs its own build script with the same clone-and-copy logic. Meanwhile, echoskill already has a marketplace JSON model (#23) and Vercel's npx skills ecosystem (#16) has proven that skill installation is a solved problem with established patterns.

The build script should be replaced by a proper skills SDK and CLI (echoskill/eskill) that can:

1. Install skills from a remote marketplace (git URL with marketplace JSON)
2. Install skills from a local marketplace path (for development/testing)
3. Support in-marketplace references to skills in other repos/paths — similar to how claude-plugins marketplace.json uses git-subdir sources pointing to arbitrary repos
4. Maintain compatibility with Gemini CLI's gemini skills commands to the extent currently supported (install to ~/.gemini/skills/)
5. Support --target <dir> for plugin builds (install skills into plugin/skills/ rather than the user-global directory)

What this replaces

In claude-coding, the ./build script currently:

• Reads build.cfg for marketplace URLs and skill paths
• Clones marketplace repos into temp dirs
• Copies SKILL.md files into plugin/skills/
• Skips native skills (source of truth in ./skills/ at repo root)

This logic belongs in a reusable tool, not a per-repo script.

Marketplace linking model

A marketplace should be able to reference skills hosted anywhere, not just in its own repo:

{
  "skills": [
    {
      "name": "sociable-unit-tests",
      "source": {
        "url": "https://github.com/echo-skill/echoskill.git",
        "path": "coding/sociable-unit-tests"
      }
    },
    {
      "name": "safe-commit",
      "source": {
        "url": "https://github.com/echomodel/claude-coding.git",
        "path": "skills/safe-commit"
      }
    }
  ]
}

This mirrors the claude-plugins marketplace.json pattern — many-to-many between marketplaces and skill repos. A marketplace is curation, not hosting.

Gemini CLI's gemini skills commands would not need to support in-marketplace linking — it would continue to install from its native sources. The echoskill CLI handles the marketplace indirection and writes to the same target directories.

Standards and compatibility research needed

Before building, fully explore:

1. npx skills (Vercel) — How does it handle multi-source installation? Does it support marketplace-like registries, or is it purely npm-based? How does it resolve skill names to repos? Unverified claim: npx skills add <owner/repo> registers and installs skills from a specific GitHub repository. Verify this syntax and semantics. See Research: vercel-labs/skills ecosystem overlap with echoskill #16 for prior research.
2. OpenSkills CLI — Unverified claim: npx openskills install <your-org/your-repo> adds skills from any public or private Git repository. Research what OpenSkills actually is, its maturity level, maintenance status, and whether it's a credible authority or an early/abandoned project. Do not treat it as established until verified.
3. agentskills.io standard — Does it define anything about skill distribution, installation, or marketplace semantics? Or is it purely a format spec?
4. Gemini CLI skill commands — Current gemini skills install/list syntax and capabilities. What source types does it support? Can it install from arbitrary git URLs?
5. Claude Code plugin marketplace — How marketplace.json sources work (git-subdir, url, github). Patterns to adopt or diverge from.
6. Skill dependency resolution — If skill A references skill B (see Skill reference syntax: convention for delineating skill dependencies in SKILL.md #25), should the install tool resolve and install dependencies? Or is that out of scope for v1?

Acceptance criteria

• eskill install <name> --from <marketplace> installs a skill from a registered marketplace
• eskill install <name> --from <local-path> installs from a local marketplace directory
• Marketplace JSON supports references to skills in external repos
• eskill install <name> --target <dir> installs to a specific directory (for plugin builds)
• Gemini CLI compatibility: skills installed to ~/.gemini/skills/ work with gemini skills list
• Claude Code compatibility: skills installed to plugin dirs work when plugin is loaded
• claude-coding's ./build script can be replaced by eskill install --from build.cfg --target plugin/skills/ or equivalent

Related

• echoskill CLI: skill marketplace management tool (eskill) #23 — echoskill CLI design (eskill)
• Research: vercel-labs/skills ecosystem overlap with echoskill #16 — Vercel skills ecosystem research
• Skill reference syntax: convention for delineating skill dependencies in SKILL.md #25 — Skill reference syntax and dependencies
• Repo restructure: source/plugin split, claude-coder agent, agent marketplace echomodel/claude-coding#8 — Repo restructure (currently uses custom build script)