## What changed
- Define `capabilities/discoverV2` request and inventory types and advertise `capabilityDiscoveryV2` in executor metadata.
- Prewarm installed plugin and global skill locations at server startup, with nonfatal scan failures.
- Add sandbox-scoped discovery caching with file watcher invalidation and request-time reloads when watching is unavailable.
- Batch metadata reads through the filesystem sandbox helper and bound discovery responses to 4 MiB and 2,048 capabilities.
- Share plugin identity and installed-version selection in `codex-core-plugin-common`, and fall back to `.app.json` when a plugin does not declare an apps configuration.
The V2 discovery manager is not yet wired into RPC request dispatch.
## Testing
Add coverage for inventory metadata, sandbox cache isolation, watcher invalidation, startup scan failures, response limits, and compatibility with older executor metadata.
GitOrigin-RevId: a223a5bc15fdf251023c0c71f468fd92c3b2d847
