A plugin with both a root manifest and a host manifest

[QuentinBisson]

Many plugins will ship plugin.json next to .claude-plugin/plugin.json (or .codex-plugin/) to serve Agent Plugins hosts and a host's native format from one directory. The spec doesn't say what a host does when it finds both. Hosts already differ: Codex 0.164 checks its own manifest path first, while kagent prefers the root one. Should the spec say that the root manifest describes the portable part, and a host may also load its own native part from the same directory?