fix(desktop): sync model header when switching cached sessions

[Tamaz-sujashvili]

Summary

Fast resume path now applies stored model and refreshes model.options so the picker matches the active session.

Test plan

• Two sessions with different models; switch between them; header model updates without full reload

Fixes #38901

Made with Cursor

[pinguarmy]

I hit this while auditing the Desktop model menu/status UX. Two related details seem important beyond just refreshing the header label:

1. The cached-session path also needs to cache/restore the session runtime fields (model, provider, reasoning effort, service tier/Fast, YOLO). Otherwise switching back to an already-open runtime can repaint the transcript but leave the global model/status stores from the previously viewed chat.
2. session.info should include provider, and reasoning changes should emit a fresh session.info; otherwise the Desktop cache has no authoritative event to keep per-chat controls in sync.

I opened #40163 with a narrow patch for those pieces plus one UI cleanup: inactive model rows no longer show Fast just because a fast-capable sibling exists. Fast is shown only as live state on the active row/status, which avoids making the off Fast toggle look enabled.

This should complement the direction here rather than change the intent of this PR.

[teknium1]

Thanks for the focused Desktop report and patch. This is now covered by a more complete implementation on current main.

Automated hermes-sweeper review verified:

• Merged PR fix(desktop): keep model runtime state per session #43702 (6de3963e37698b0789bdec5a08761bd85ff4502f) superseded the related cached-session runtime-state work discussed in fix(desktop): keep model runtime state per session #40163.
• apps/desktop/src/app/session/hooks/use-session-actions/index.ts:432 restores a warm cached session through syncSessionStateToView(...).
• apps/desktop/src/app/session/hooks/use-session-state-cache.ts:58 restores model, provider, reasoning effort, service tier, Fast, YOLO, and personality from the focused session state.
• apps/desktop/src/app/session/hooks/use-session-state-cache.test.tsx:135 covers switching to a cached session and verifies the model/status stores are restored.

Closing as implemented on main.