## What changed
- Replace the single `category` and `score` fields in `SecurityRiskScore` with a
deterministic map of category names to scores.
- Validate the full Guardian V2 classifier response before storing it as one
thread extension value and, for non-ephemeral threads, one rollout item.
- Cover serialization and rollout loading with snapshots containing multiple
score categories.
GitOrigin-RevId: 24525de691f96bd34ccfe04acab2f01aca309837