## Why
When the remote Sites plugin is installed and its local bundle is available, exposing the bundled copy as well creates duplicate catalog entries and can load the wrong skills.
## What changed
- Persist an account- and backend-scoped exclusion for `sites@openai-bundled` once the remote replacement is installed and loadable.
- Apply the exclusion to plugin catalogs, search, direct reads and installs, runtime loading, hooks, and skill caches while preserving the remote plugin's server-owned enabled state.
- Restore the bundled fallback when the remote plugin is absent or its local files are unavailable, and throttle repeated availability checks for 60 seconds.
## Testing
- Added manager tests for persistence across restarts, account/backend isolation, fallback restoration, concurrent checks, and refresh throttling.
- Added app-server and agent-turn tests confirming that catalog, search, and skill loading prefer remote Sites.
GitOrigin-RevId: bc1154f79d3107910fee9fa27389a0ddb48ce6cf
Jiwon Kim
b6ab99ed87