plugins/mattstack: name the three misplaced skills public; dry-run compile in CI

[m4ttheweric]

rt skills compile exited 1 on clean main with three misplaced: notices. The skills were misplaced, and the exit code is correct: this names them in surface.jsonc and adds a CI step so the gap cannot come back.

Why each notice fired

• creating-a-pack and extending-a-pack were added in 0.20.0 (docs: suite settings spec, re-root spec (ruled 2026-08-21) and plan #15), and process-digraphs in 0.25.0 (MAT-383 (L1): rt setup verbs — plan, apply, team, uninstall #32).
• All three live under plugins/mattstack/plugin/skills/, which plugin.json registers as a skill root, so they are slash-menu skills.
• surface.jsonc's public list was never updated for them, so compile's misplaced scan counts each one as registered but not public.

Why fix the files, not the exit code

• Exiting non-zero on a misplaced skill is compile's documented contract (commands/skills.ts: "An errored or misplaced verb is a failed compile").
• The three skills are meant to be public. plugin.json's description names creating-a-pack and extending-a-pack as public doors, and other skills cite process-digraphs by name as a gate skill.
• Moving them to attachments/ (what the notice suggests) would take them off the slash menu.

What changed

• surface.jsonc names all three public
• The plugin-mattstack job adds a skills compile --dry-run step, because CI ran only skills check, which never reports misplaced skills
• plugin.json goes to 0.27.3

Verification

• Before: skills compile --dry-run exits 1 on the old surface.jsonc, with the three notices.
• After: it exits 0. The --json verb rows are identical before and after; only misplaced empties.
• skills check --strict still exits 0.
• The no-plugin-ci-jobs and scripts/ci tests pass (65 of 65).

🤖 Generated with Claude Code

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📥 Commits

Reviewing files that changed from the base of the PR and between 323c49f and 9f0f906.

📒 Files selected for processing (3)

• .github/workflows/checks.yml
• plugins/mattstack/.claude-plugin/plugin.json
• plugins/mattstack/surface.jsonc

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