Model selection resets to GPT 5.4 when creating a new thread #1276

Summary

When a user selects a non-default model (e.g. Claude Opus 4.6) and then creates a new thread — either in the same project or a different one — the model resets to GPT 5.4 instead of preserving the selection.

Steps to Reproduce

1. Open the app (web or desktop)
2. Select Claude Opus 4.6 (or any non-default model)
3. Send a message to create a thread
4. Click the "New Thread" button (pencil icon) on the same project in the sidebar
5. Observe the model picker — it shows GPT 5.4 instead of Claude Opus 4.6

Expected Behavior

The new thread should inherit the user's last selected model (Claude Opus 4.6).