Add clean closed issue worktrees skill

[haoranyu]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• I have read and followed the Guidance for submissions involving paid services.
• My contribution adds a new instruction, prompt, agent, skill, workflow, or canvas extension file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, agent, skill, workflow, or canvas extension with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.
• I am targeting the main branch for this pull request.

---

Description

Adds clean-closed-issue-worktrees, a safety-first skill for auditing and removing Git worktrees associated with closed GitHub or GitLab issues.

The skill keeps provider access in the agent layer while a deterministic Python script handles local Git inspection, snapshot validation, backup refs, and exact-path removal. Its mandatory scan-confirm-execute protocol refuses dirty, locked, current, main, active-task, and broad-path targets and retains branches by default.

Canonical source and versioned releases: https://github.com/haoranyu/clean-closed-issue-worktrees

Verification

• npm run skill:validate — all 416 skills valid
• npm start — generated docs/README.skills.md
• GitHub Copilot CLI 1.0.82 discovered the skill from .github/skills/clean-closed-issue-worktrees
• Upstream Python suite — 20 tests passing on the submitted payload

---

Type of Contribution

• New instruction file.
• New prompt file.
• New agent file.
• New plugin.
• New skill file.
• New agentic workflow.
• New canvas extension.
• Update to existing instruction, prompt, agent, plugin, skill, workflow, or canvas extension.
• Other (please specify):

---

Additional Notes

The skill and bundled script are MIT licensed. It requires Git and Python 3.9+; GitHub/GitLab state is queried through the agent's available provider route. No paid service or credential access is bundled.

---

By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[github-actions]

🔒 PR Risk Scan Results

Scanned 7 changed file(s).

Severity	Count
🔴 High	0
🟠 Medium	0
ℹ️ Info	1

Severity	Rule	File	Line	Match
ℹ️	skill-script-touched	skills/clean-closed-issue-worktrees/scripts/worktree_cleanup.py	1	skills/clean-closed-issue-worktrees/scripts/worktree_cleanup.py

This is an automated soft-gate report. Findings indicate review targets and do not block merge by themselves.

[github-actions]

🔍 Vally Lint Results

✅ All checks passed

Scope	Checked
Skills	1
Agents	0
Total	1

Severity	Count
❌ Errors	0
⚠️ Warnings	0
ℹ️ Advisories	0

Summary

Level	Finding
ℹ️	✅ clean-closed-issue-worktrees (2/2 checks passed)
ℹ️	✓ [spec-compliance] All 1 skill(s) are spec-compliant.
ℹ️	✓ spec-compliance: All spec checks passed.
ℹ️	✓ [valid-refs] All file references across 1 skill(s) are valid.
ℹ️	✓ valid-refs: All file references resolve to existing files within the skill directory.
ℹ️	1 skill(s) linted, 1 passed

Full linter output

### Linting skills/clean-closed-issue-worktrees
✅ clean-closed-issue-worktrees (2/2 checks passed)
    ✓ [spec-compliance] All 1 skill(s) are spec-compliant.
        ✓ spec-compliance: All spec checks passed.
    ✓ [valid-refs] All file references across 1 skill(s) are valid.
        ✓ valid-refs: All file references resolve to existing files within the skill directory.

1 skill(s) linted, 1 passed