Skills infrastructure: .claude/skills/, verify:skills, skills:eval #4863

Part of the agentic software factory tracker #4858, Wave 2. Proposed as S2 in docs/agent-guidance-inception.md (PR #4861) §9, from #4859.

Depends on

None beyond #4859. Can run in parallel with the rest of Wave 2.

Scope

• Port from the Inspector's v2/main, with their *.test.mjs files:

  • scripts/verify-skills.mjs
  • scripts/verify-skills-cli.mjs
  • scripts/skill-eval.mjs
  • scripts/lib/skill-manifest.mjs
  • scripts/lib/claude-cli.mjs
  • the helpers these import: scripts/lib/npm-scripts.mjs and scripts/lib/win-shell-args.mjs. Part 4 (TypeScript workspace gate: Prettier, ESLint, root validate, CI #4864) and Part 11 (Add local:gate, pre-push-gate skill #4871) reuse them.

• Add root npm scripts: verify:skills, verify:skills:cli, skills:eval, test:scripts.

• Copy docs/skill-authoring.md (paths only).

• Add the "Maintaining the skills" rules to AGENTS.md:

  • explicit disable-model-invocation, defaulting to false
  • eval cases with ≥ 5 positives plus negatives
  • the listing budget
  • paths only when a skill is useless outside the matched files, with the trade-off stated in the PR
  • quote any # or : in a description

  If Part 2 (AGENTS.md) hasn't merged yet, hand these rules to it instead.

Acceptance criteria

• The ported verifier keeps its "no skills found" failure. Because this issue lands before any skill, it ships an explicit, temporary bootstrap allowance for an empty .claude/skills/, which the first skill-adding PR removes: whichever of Part 6, 7, 10, 11 or 12 lands first.
• It fails on a fixture with malformed frontmatter, or with no disable-model-invocation.
• npm run skills:eval runs against Claude, and against Copilot with AGENT=copilot.
• verify:skills and verify:skills:cli run on every PR in a new root-guards CI job created here (in typescript.yml or a small repo-level workflow; this repo has no main.yml). Part 4 (TypeScript workspace gate: Prettier, ESLint, root validate, CI #4864) extends it.
• The verifier's wiring checks (checkWiring) are ported against this repo's real files. Two links don't exist yet, so each gets an explicit, temporary allowance: root validate reaching verify:format-coverage (removed by Part 4, TypeScript workspace gate: Prettier, ESLint, root validate, CI #4864) and local:gate reaching verify:skills:cli (removed by Part 11, Add local:gate, pre-push-gate skill #4871).

Branch

Targets v2/main. Closes #N won't auto-close an issue on a non-default branch, so close this one by hand on merge and move the card to Done.