## Why
Fetching plugin recommendations while building the first-turn context delays that
context when the recommendation catalog is not already cached.
## What changed
- Start fetching recommendations during session initialization, in parallel with
MCP and plugin setup, and reuse the in-flight request when building context.
- Centralize the feature checks that enable plugin recommendations.
- Prevent an invalidated recommendation request from repopulating the cache after
a newer request has completed.
## Testing
Added coverage for startup feature gating, reuse of the in-flight fetch, legacy
behavior when recommendations are unavailable, and cache invalidation races.
GitOrigin-RevId: 708774b9bfc472c9847973ae8b2774b66e7321e4
8bcac28f93