[Bug]: That model is already built in error when custom model collides with known slag

[S4AR-inc]

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

packages/contracts or packages/shared

Steps to reproduce

1. Run litellm proxy(or any other proxy/model runner with custom naming) and configure a model with the name "opus"
2. Configure Claude code to the litellm url
3. Try adding "opus" as a model in t3 code

Expected behavior

You could add "opus", could be with a warning

Actual behavior

You get "That model is already built in." error

Impact

Blocks work completely

Version or commit

0.0.28

Environment

Window 10 connected to linux with claude code connected to litellm

Logs or stack traces

Screenshots, recordings, or supporting files

No response

Workaround

Finding and removing the offending slag in MODEL_SLUG_ALIASES_BY_PROVIDER in the transpiled js