feat: add Cocos Creator 3.8 engine support (4 agents + engine reference docs)

[realUC]

Summary

Adds Cocos Creator 3.8 as a fully-supported engine alongside Godot 4, Unity, and Unreal Engine 5. The new engine set follows the existing tiered specialist pattern (1 lead + 3 sub-specialists) and is wired into the same routing, setup, and testing infrastructure.

This brings the engine specialist table from three to four major engines, with Cocos Creator's strengths (mini-game platforms, TypeScript-first component model, lightweight web/mobile build) available to projects that need them.

Motivation

Cocos Creator is widely used for mini-games (WeChat / ByteDance / Alipay / Baidu / Honor) and lightweight cross-platform titles — a segment not well served by the existing Godot/Unity/Unreal sets. Because the LLM knowledge cutoff predates Cocos Creator 3.8.x (Spine 4.2 support, Box2D JSB native binding, restored node.x/node.y accessors), version-pinned reference docs are included so agents give correct, non-deprecated guidance rather than hallucinating pre-3.0 APIs (e.g. cc.loader, cc.Class).

What's Added

1. Engine Specialist Agents (4 new)

All four include the required Collaboration Protocol section (ask → options → decision → draft → approval) and documented domain boundaries.

Agent	Role
cocos-specialist	Lead — engine routing, project structure, multi-platform build config
cocos-ts-specialist	TypeScript components, @ccclass/@property decorators, assetManager async loading, event bus
cocos-shader-specialist	Effect files (CCEffect / CCProgram), built-in uniforms, Custom Render Pipeline
cocos-ui-specialist	UITransform, Layout, Widget, Canvas, multi-resolution adaptation, mini-game UI constraints

2. Engine Reference Documentation (11 new)

Pinned to Cocos Creator 3.8.6, under docs/engine-reference/cocos/:

• VERSION.md — version pin + knowledge-gap baseline
• breaking-changes.md — 3.x migration notes
• deprecated-apis.md — deprecated APIs + replacements (cc.loader → assetManager, cc.Class → ES classes, etc.)
• current-best-practices.md — modern project structure, component pattern, async loading, object pooling, multi-platform config
• modules/ — animation, audio, input, navigation, networking, physics, rendering, ui

The rendering.md doc codifies the rule that built-in uniforms (cc_matViewProj, cc_matWorld, cc_matWorldIT, cc_cameraPos, cc_time, cc_screenSize, …) are engine-injected and must NOT be redeclared in Effect files — redeclaration causes black screen / compile errors. The shader specialist agent and its test spec are aligned to enforce this.

3. Testing Specs (4 new)

Under CCGS Skill Testing Framework/agents/engine/cocos/, mirroring the existing engine test structure. Each has 5 behavioral cases covering correctness, anti-patterns, and critical errors. Registered in catalog.yaml with last_updated bumped.

4. Framework Wiring (modified)

• .claude/skills/setup-engine/SKILL.md — Cocos Creator added to engine options, with honest tradeoffs, Technology Stack template, naming conventions, file-extension routing, and knowledge-gap baseline block.
• CLAUDE.md — Cocos Creator 3.8 + TypeScript added to Technology Stack choices.
• README.md — Cocos Creator row added to the Engine Specialists table; "all three major engines" → "all four major engines".
• CCGS Skill Testing Framework/README.md — cocos/ directory added to folder structure.
• CCGS Skill Testing Framework/skills/utility/setup-engine.md — Case 3b added for Cocos mini-game platform config.

Files Changed

26 files, +2826 / −14.

Area	Files
Agents (new)	cocos-specialist, cocos-ts-specialist, cocos-shader-specialist, cocos-ui-specialist
Engine reference (new)	11 docs under docs/engine-reference/cocos/
Test specs (new)	4 under CCGS Skill Testing Framework/agents/engine/cocos/
Framework (modified)	setup-engine/SKILL.md, CLAUDE.md, README.md, catalog.yaml, testing README, testing setup-engine.md

Testing

Verified end-to-end in a Claude Code session:

1. Agent structure — all 4 agent files contain the required Collaboration Protocol section and respect domain boundaries (no cross-domain file modification without delegation).
2. Routing — /setup-engine correctly presents Cocos Creator as a fourth option and routes .ts / .effect / .scene files to the right sub-specialist.
3. Reference docs — catalog.yaml validates; all 4 Cocos test specs resolve to existing files.
4. Bug fix verification — the shader specialist's example Effect file and its test spec were checked for the built-in uniform redeclaration issue. Example code uses cc_matViewProj / cc_matWorld directly without redeclaring them, and the test spec treats redeclaration as a critical error (Case 3). The two are consistent.

I did not run the hook suite against Cocos-specific paths since the change adds agent/reference files (no new hooks); existing hooks continue to pass on the modified framework files.

CONTRIBUTING.md Compliance

• Agents include a Collaboration Protocol section
• Agents don't modify files outside their documented domain without explicit delegation
• Reference index updated (catalog.yaml last_updated bumped; README Engine Specialists table updated; CLAUDE.md Technology Stack updated)
• No new skills/skills-flat-md; existing setup-engine skill extended in place
• Conventional Commit message (feat:)
• Platform-neutral — docs/agents only, no shell/grep changes

Notes / Caveats

• Cocos Creator is optional — projects not using it incur no overhead; the agents are only loaded when routed to.
• The reference docs are intentionally version-pinned to 3.8.6. If the maintainer prefers a different pin (e.g. 3.8.x latest), the VERSION.md baseline is the single place to adjust.
• I kept the change additive and avoided touching unrelated engine sets or the studio hierarchy. If a different naming/layout convention is preferred (e.g. cocoscreator- prefix vs cocos-), happy to rename.

Thanks for considering this — happy to address any review feedback.