## What changed
- Add `PluginCatalog` types for discovery snapshots, warnings, plugin metadata, stable identities, and cloud or executor source locations. Keep MCP server declaration values out of debug output.
- Extend `PluginProvider` with a generic list query, asynchronous catalog listing, and shared error and future types. Provide empty defaults for listing and root resolution so providers can implement their supported operation.
- Add `PluginListQuery` in the MCP extension with thread and turn identifiers and an optional MCP resource client.
GitOrigin-RevId: 0bf2a1713c25d912c41daab788b88729d4871fcf
