feat(desktop): provide Runtime Host native capabilities

[M4n5ter]

English

Summary

• adapt the existing Desktop Browser and Computer Use MakaTool implementations into self-described, session-affine Client Capability offers;
• validate arguments before admission, forward Host invocation context and cancellation, and preserve Computer Use screenshots as native image content;
• reject identities that were not offered and release provider-owned Computer Use session state during shutdown;
• expose capability replacement and unregistration through the Desktop Runtime Host client boundary.

Runtime Host remains open-world: it does not know Browser or Computer Use names or Desktop implementation details. This slice provides the composable provider but does not activate it in the production or candidate boot path; activation remains part of the final Desktop composition slice.

Validation

• npm --workspace @maka/desktop test — 1665 passed
• npm --workspace @maka/desktop run typecheck
• npm run lint
• npm run format:check
• focused native capability provider tests
• git diff --check

Refs #2010

简体中文

概要

• 将现有 Desktop Browser 与 Computer Use MakaTool 实现适配为自描述、Session-affine 的 Client Capability offer；
• 在 admission 前校验参数，透传 Host invocation context 与取消信号，并将 Computer Use 截图保留为原生图片内容；
• 拒绝未声明的 capability identity，并在 shutdown 时释放 provider 持有的 Computer Use Session 状态；
• 通过 Desktop Runtime Host client 边界暴露 capability replacement 与 unregistration。

Runtime Host 继续保持开放世界设计：它不知道 Browser 或 Computer Use 的名称，也不依赖 Desktop 的具体实现。本 slice 只提供可组合的 provider，不在 production 或 candidate boot path 中提前激活；实际激活仍属于最终的 Desktop composition slice。

验证

• npm --workspace @maka/desktop test — 1665 项通过
• npm --workspace @maka/desktop run typecheck
• npm run lint
• npm run format:check
• native capability provider 聚焦测试
• git diff --check

关联 #2010