## Why
Reasoning-effort changes should preserve the request baseline while trusted `configuration_update` items carry the selected effort.
## What changed
- Pin request-level reasoning effort for the current model when reasoning-effort overrides are available, including during WebSocket prewarm.
- Re-establish the selected effort after rollback, resume, or a model switch, refreshing the trusted override even when the selection is unchanged.
- Continue using the selected request effort when overrides are unavailable.
## Testing
Add regression coverage for WebSocket prewarm and reconnect, rollback, resume, and model switches. Update transition tests to assert that request-level effort stays pinned while configuration updates change.
GitOrigin-RevId: 89cfee6289543230347b0488d1388190b4da7216
31ccaf40c2