feat(build.mcpp): 机制架构落地 —— 指令表收敛、协议契约、host 工具、构建图节点、规则包 (2026.8.5.1) - #356

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4, actions/checkout@v4, actions/upload-artifact@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/