feat: add sketch harness

[zhangxilong-43]

Description

Add a CLI harness for Sketch — generates .sketch design files from JSON design
specifications using sketch-constructor (Node.js). This is the first non-Python
harness in the project, built with Commander.js instead of Click, and Jest instead of
pytest.

The CLI supports:

• sketch-cli build — builds .sketch files from JSON design specs with artboard layout,
  design tokens, and component primitives (rect, text, circle, image, group)
• sketch-cli list-styles — lists available shared styles from design tokens
• Three example specs included: login page, dashboard, card list

Type of Change

• New Software CLI — adds a CLI harness for a new application

---

For New Software CLIs

• .md SOP document exists at /agent-harness/.md
• SKILL.md exists inside the Python package (cli_anything//SKILL.md)
• Unit tests at cli_anything//tests/test_core.py are present and pass
  without backend
  • Note: Node.js harness — tests at sketch/agent-harness/tests/build.test.js, run via
    Jest
• E2E tests at cli_anything//tests/test_full_e2e.py are present
• README.md includes the new software (with link to harness directory)
• registry.json includes an entry for the new software (for the CLI-Hub)
• repl_skin.py in utils/ is an unmodified copy from the plugin
  • N/A: Node.js harness, no repl_skin.py

General Checklist

• Code follows existing patterns and conventions
• --json flag is supported on any new commands
• Commit messages follow the conventional format (feat:, fix:, docs:, test:)
• I have tested my changes locally

Test Results

PASS tests/build.test.js
sketch-cli build
example: login-page
✓ input JSON exists
✓ builds without errors (104 ms)
✓ output file exists
✓ output is a valid ZIP file (PK magic bytes)
✓ ZIP contains required Sketch structure (5 ms)
✓ ZIP contains at least one page JSON (3 ms)
example: dashboard
✓ input JSON exists
✓ builds without errors (77 ms)
✓ output file exists
✓ output is a valid ZIP file (PK magic bytes) (1 ms)
✓ ZIP contains required Sketch structure (3 ms)
✓ ZIP contains at least one page JSON (3 ms)
example: card-list
✓ input JSON exists
✓ builds without errors (79 ms)
✓ output file exists
✓ output is a valid ZIP file (PK magic bytes) (1 ms)
✓ ZIP contains required Sketch structure (3 ms)
✓ ZIP contains at least one page JSON (3 ms)
sketch-cli list-styles
✓ lists styles from default tokens (58 ms)

Test Suites: 1 passed, 1 total
Tests: 19 passed, 19 total
Snapshots: 0 total
Time: 0.458 s

[yuh-yang]

the test results look good to me! putting an approval on my side

[omerarslan0]

Nice work on the tests — the ZIP structure validation is solid.

Two quick questions before I approve:

1. Sketch is macOS-only — do the tests actually invoke Sketch, or just generate the .sketch ZIP format? If it's the latter, this is more of a file format generator than a true Sketch harness.

2. sketch-constructor dependency — the library appears to be largely unmaintained, and Sketch's file format changes frequently. Is there a plan if it breaks with a future Sketch version?

[zhangxilong-43]

Thank you for your question. @omerarslan0

Question 1: Currently, there are many design drafting tools available, but most are commercially operated, and there isn't any open-source design drafting software that can be directly operated using a CLI. To meet the Agent's need to directly draw design drafts, I chose sketch-constructor to create a .sketch format file because its format is publicly available, and the official website also provides sketch-constructor to help with construction (it may not support some advanced features).

Question 2: This tool is temporary, but our need is real. If software that supports a CLI becomes available in the future, I will create it based on that.

[yuh-yang]

I think it makes sense if the CLI supports building realistic and valid .sketch files that Sketch can open. If rendering is not actually needed for the use-cases with Sketch, this'd be enough and complete.

[yuh-yang]

@omerarslan0 bypassing the limitations and merging this first. This may be interesting to a group of people.