fix[evals] remove braintrust api key requirement

[chromiebot]

why

what changed

test plan

---

Summary by cubic

Make Braintrust optional for evals. Evals run without a BRAINTRUST_API_KEY and skip sending logs, removing prior errors/warnings; 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 uses the plain ai SDK unless braintrust can wrap it (key present), avoiding “Please specify an api key” and flush warnings.
  • Added tests covering both key-present and key-absent paths.

^{Written for commit 0a850a0. Summary will update on new commits. Review in cubic}

[changeset-bot]

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Latest commit: 0a850a0

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[github-actions]

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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 Evals Runner
    participant Braintrust as Braintrust Module
    participant AIWrapped as AISdkClientWrapped
    participant AISDK as AI SDK
    participant BraintrustAPI as Braintrust API

    Note over Runner,BraintrustAPI: Runtime flow based on BRAINTRUST_API_KEY env var

    alt BRAINTRUST_API_KEY is set
        Runner->>Braintrust: hasBraintrustApiKey() → true
        Braintrust-->>Runner: true
        
        Runner->>Braintrust: loadBraintrust()
        Braintrust-->>Runner: Eval, flush
        
        Runner->>Runner: sendLogs = true
        Runner->>Runner: noSendLogs not set
        
        Runner->>AIWrapped: loadWrappedAISDK()
        AIWrapped->>Braintrust: import("braintrust")
        AIWrapped->>Braintrust: wrapAISDK(ai)
        Braintrust-->>AIWrapped: wrapped AI instance
        AIWrapped-->>Runner: wrapped AI
        
        Runner->>Braintrust: Eval(..., { noSendLogs: false })
        Braintrust->>BraintrustAPI: Send logs
        BraintrustAPI-->>Braintrust: Ack
        
        Runner->>Braintrust: flush()
        Braintrust->>BraintrustAPI: Flush pending logs
        BraintrustAPI-->>Braintrust: Complete
    else BRAINTRUST_API_KEY is not set
        Runner->>Braintrust: hasBraintrustApiKey() → false
        Braintrust-->>Runner: false
        
        Runner->>Runner: sendLogs = false
        Runner->>Runner: noSendLogs = true
        
        Runner->>AIWrapped: loadWrappedAISDK()
        alt Key absent
            AIWrapped->>AIWrapped: Return ai SDK directly (passthrough)
            AIWrapped-->>Runner: plain AI SDK
        end
        
        Runner->>Braintrust: Eval(..., { noSendLogs: true })
        Note over Runner,Braintrust: No logs sent to Braintrust
        Braintrust-->>Runner: Result
        
        Note over Runner: flush() is NOT called
        
        alt tracedSpan called
            Runner->>Braintrust: tracedSpan(fn, options)
            alt No API key
                Braintrust->>Braintrust: Call fn() directly (passthrough)
                Braintrust-->>Runner: Result from fn
            end
        end
    end

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_{Re-trigger cubic}