Cannot see all models at /models, only GPT-4.1 available, and CAPIError 400 after model selection

**Description:**
- When accessing /models, I cannot see all available models—only GPT-4.1 is shown.
- Attempting to use other models results in:
CAPIError: 400 The requested model is not supported. (Request ID: 7F9A:4D9FC:86257D:B13592:69C908B5)
- After this error, Copilot’s behavior is not normal.

**Steps to Reproduce:**
1. Go to /models in Copilot.
2. Try to select a different model.
3. Observe the error and limited model list.

**Expected:**
All available models should be listed and selectable.

**Actual:**
Only GPT-4.1 is available, and selecting others causes errors.

Start by reproducing the issue from the /models entry point: check the available model list, select a model other than GPT-4.1, and capture the CAPIError 400 behavior. Done means all available models are listed, selectable, and do not leave Copilot in an abnormal state after selection.

Written by the indexing model from the issue text.