Estimated Cost not present on traces

[barrettpyke]

Summary

When creating traces with the estimated cost does not appear even if we support the model that's used.

Reproduction

1. Start Opencode with the Braintrust plugin installed (docs).
2. Type /connect to add a Provider e.g. Anthropic.
3. Select a model that Braintrust supports pricing for e.g. Claude Opus 4.1.
4. Enter a prompt e.g. "Tell me a story".
5. Navigate to Braintrust.
6. Open the project that your BRAINTRUST_PROJECT env var is set to.
7. Navigate to Logs.
8. Open the latest Trace that was just added from Opencode.
9. Take note of the metrics associated with it.

Expected:

The Estimated Cost metric should be shown.

Actual:

There is no Estimated Cost.