## Why
The model picker can open from a cached startup catalog that no longer reflects the models available to the current account.
## What changed
- Fetch the current model list asynchronously whenever the picker opens, while showing cached choices immediately.
- Refresh an open model picker in place, preserving its highlighted model, dismissal behavior, and reasoning submenu.
- Apply accepted catalog updates to model-dependent UI, service-tier controls, and new-thread defaults. Ignore stale, failed, empty, unchanged, or account-invalidated responses.
## Testing
- Added coverage for catalog refreshes, stale and unusable responses, popup state preservation, empty choices, service tiers, and new-thread defaults.
GitOrigin-RevId: 45abe1d309ff7f90701fffe29c6544ca4157f836
Benjamin Carlsson
5fc7840cf6