Cross-OS platform documentation that does not belong to a single backend's source
tree. The per-backend implementation notes still live next to the code
(`src/platform/<os>/status.md`); this directory holds the **cross-cutting** view.
任何「某平台可用 / 已验证」的结论,按它在哪个宿主上被证实来归类,**不得混用**:
1. 2.3.4.5.