feat: rewrite build-skills.ts as copy-only from the pinned boxel-skills tag

[lukemelia]

Linear: CS-11543

boxel-skills is markdown-first now (skills/<name>/SKILL.md + references/ + scripts/ directories, commands/<name>.md slash-command files), so the plugin build no longer transforms Skill card JSON into SKILL.md files. Per Spec §7, build-skills.ts reduces to copying skills/ and commands/ from the pinned tag into plugin/, byte-for-byte.

This PR ships only the machinery (4 files). The ~234-file content cutover is intentionally not committed here: the on-main publish workflow runs pnpm build:skills after merge and commits the regenerated plugin/ itself, as it does for every regen. The content is byte-copies of the already-reviewed boxel-skills v0.0.28 tag.

What stays, per the ticket:

• Pinned-tag model — bumped from v0.0.22 to v0.0.28, the current tag with the merged workspaces content and the boxel.commands → boxel.tools rename. BOXEL_SKILLS_REPO=/path still overrides for local iteration.
• Manifest-based stale sweep — scripts/.boxel-skills-manifest.json records copied skills and commands; entries that drop out of the source get deleted from plugin/. CLI-authored skills (file-ops, realm-sync, …) are never in the manifest, so the sweep can't touch them. The old manifest shape (no commands key) still loads, which is what lets the first post-merge run sweep the four retired generated dirs (boxel-development, dev-*).

What's gone: the SkillSet/SkillPlusMarkdown emission plan, DESCRIPTION_OVERRIDES, and EXCLUDED_IDS — descriptions are authored in each SKILL.md's frontmatter, and the new content is written for this consumer (the previously host-only boxel-environment material now drives Boxel via npx boxel).

New surfaces after the post-merge regen:

• plugin/commands/ ships the 17 upstream commands as /boxel-cli:<name> slash commands.
• plugin/README.md's auto-generated block gains skill and command tables, read from frontmatter (minimal single-line reader — the copied files are the contract; the table is a convenience). The README is the only file the script still prettier-formats.
• The publish workflow's auto-commit stages plugin/commands, plugin/README.md, and the manifest alongside plugin/skills.
• .prettierignore covers plugin/skills/ and plugin/commands/: lint-staged routes staged markdown through prettier, which rewrites the verbatim copies away from upstream bytes (its markdown parser even mangles underscore emphasis like error_doc). Verified eslint . and tsc are unaffected by the copied content (including the patterns' example.gts files, which this package's eslint config doesn't lint).

Verified: copies are byte-identical to the tag (diff -r; the only extras under plugin/skills/ are the nine CLI-authored skills), a second pnpm build:skills run is a no-op, 13 unit tests cover manifest back-compat / stale-sweep math / the frontmatter reader, and the full boxel-cli unit suite passes (348).

Version bump is left to the release automation (feat: + plugin surface → minor).

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR rewrites packages/boxel-cli/scripts/build-skills.ts to stop generating/translating skill content and instead verbatim-copy skills/ and commands/ from a pinned cardstack/boxel-skills git tag into packages/boxel-cli/plugin/, while keeping a manifest-based stale sweep and regenerating the plugin README tables from frontmatter.

Changes:

• Replace the previous JSON-card → markdown emission pipeline with a copy-only pipeline from boxel-skills@v0.0.28, including stale-entry sweeping for both plugin/skills/ and plugin/commands/.
• Update unit tests to cover the new manifest shape/back-compat and the minimal frontmatter parser used for README table generation.
• Ensure repo formatting tooling doesn’t rewrite the copied markdown, and ensure the publish workflow stages the new generated surfaces.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
packages/boxel-cli/scripts/build-skills.ts	Replaces “emit” logic with copy-only skills/ + commands/, updates manifest shape, and updates README regeneration from frontmatter.
packages/boxel-cli/tests/scripts/build-skills.test.ts	Drops emission-plan tests; adds coverage for new manifest parsing/back-compat and frontmatter parsing.
.prettierignore	Ignores copied plugin markdown to avoid prettier drifting verbatim upstream bytes.
.github/workflows/boxel-cli-publish.yml	Adds plugin/commands, plugin/README.md, and the manifest to the staged regen commit set.

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