fix[evals] remove braintrust api key requirement (#2145)

[miguelg719]

why

Evals should be able to run without the braintrust dependency

what changed

• Added hasBraintrustApiKey() and made tracedSpan() a passthrough when no key.
• AISdkClientWrapped falls back to the plain ai SDK when braintrust wrapping isn’t available; introduced a WrappedAI type and lazy load keyed on BRAINTRUST_API_KEY.

test plan

• Added tests for key-present/absent paths and updated core-runner test to set a dummy key; fixes for test stability and build.

---

Summary by cubic

Make Braintrust optional for evals. Evals run without BRAINTRUST_API_KEY and skip sending logs; behavior is unchanged when a key is set.

• Bug Fixes
  • Added hasBraintrustApiKey() and made tracedSpan() a passthrough when no key.
  • Runner now passes noSendLogs: true to Eval and skips flush() without a key; sends logs and flushes when present.
  • AISdkClientWrapped falls back to the plain ai SDK when braintrust wrapping isn’t available; introduced a WrappedAI type and lazy load keyed on BRAINTRUST_API_KEY.
  • Added tests for key-present/absent paths and updated core-runner test to set a dummy key; fixes for test stability and build.

^{Written for commit 482e49b. Summary will update on new commits. Review in cubic}

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[cubic-dev-ai]

No issues found across 6 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

Architecture diagram

sequenceDiagram
    participant Runner as RunEvals
    participant Braintrust as Braintrust Module
    participant AISDK as AISdkClientWrapped
    participant Env as Environment

    Note over Runner,Env: Braintrust API key governs two independent paths

    Runner->>Braintrust: hasBraintrustApiKey()
    Braintrust->>Env: Read BRAINTRUST_API_KEY
    Env-->>Braintrust: Key present or absent
    Braintrust-->>Runner: boolean

    alt Key present (sendLogs = true)
        Runner->>Braintrust: loadBraintrust()
        Braintrust-->>Runner: { Eval, flush }
        Runner->>Runner: Eval(..., { noSendLogs: false })
        Runner->>Braintrust: flush()
        Braintrust-->>Runner: Logs sent

        AISDK->>Braintrust: loadWrappedAISDK()
        Braintrust->>Braintrust: import("braintrust").wrapAISDK(ai)
        Braintrust-->>AISDK: wrapped AI SDK

    else Key absent (sendLogs = false)
        Runner->>Braintrust: loadBraintrust()
        Braintrust-->>Runner: { Eval, flush }
        Runner->>Runner: Eval(..., { noSendLogs: true })
        Note over Runner: flush() skipped entirely

        AISDK->>Braintrust: loadWrappedAISDK()
        Braintrust->>Braintrust: Return plain ai SDK as WrappedAI
        Braintrust-->>AISDK: unwrapped AI SDK

        Braintrust->>Braintrust: tracedSpan() calls fn() directly
        Braintrust-->>Runner: No Braintrust tracing
    end

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