feat: Add Claude Opus 4.8 CUA support

[Kylejeong2]

Summary

• Add anthropic/claude-opus-4-8 to the CUA model whitelist.
• Route bare claude-opus-4-8 model names to the Anthropic CUA client.
• Treat Claude Opus 4.8 as a Claude 4.6+ adaptive-thinking CUA model and document it in the supported CUA model lists.

Validation

• pnpm --filter @browserbasehq/stagehand run typecheck
• pnpm run test:core -- packages/core/dist/esm/tests/unit/public-api/llm-and-agents.test.js packages/core/dist/esm/tests/unit/anthropic-cua-adaptive-thinking.test.js

Note: the focused test command passed 38 tests, then the test wrapper printed a non-fatal CTRF conversion warning from glob/minimatch under Node 22.

[changeset-bot]

🦋 Changeset detected

Latest commit: 790abd7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 4 packages

Name	Type
@browserbasehq/stagehand	Patch
@browserbasehq/browse-cli	Patch
@browserbasehq/stagehand-evals	Patch
@browserbasehq/stagehand-server-v3	Patch

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Project	Status	Preview	Updated (UTC)
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[cubic-dev-ai]

No issues found across 8 files

Confidence score: 5/5

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

Architecture diagram

sequenceDiagram
    participant Dev as Developer
    participant Config as Stagehand Config
    participant Agent as AgentProvider
    participant Client as AnthropicCUAClient
    participant API as Anthropic API
    
    Note over Dev,API: CUA Model Registration & Execution Flow
    
    Dev->>Config: Configure agent with "claude-opus-4-8"
    Config->>Agent: Lookup model in modelToAgentProviderMap
    Agent->>Agent: CHANGED: Match "claude-opus-4-8" -> "anthropic"
    Agent-->>Config: Return Anthropic provider
    
    Config->>Client: Instantiate with model "claude-opus-4-8"
    Client->>Client: Determine model capabilities
    
    alt Adaptive thinking model (4.6+)
        Note over Client: "claude-opus-4-8" treated as 4.6+ model
        Client->>Client: Enable thinking.type: 'adaptive'
        Client->>Client: Set output_config with effort level
    else Standard model
        Client->>Client: Use default behavior
    end
    
    Client->>API: Send request with model identifier
    API-->>Client: Return computer use response
    
    Config-->>Dev: Provide agent instance
    
    Note over Dev,API: Model Configuration & Documentation
    
    Dev->>Config: Query AVAILABLE_CUA_MODELS
    Config-->>Dev: Include "anthropic/claude-opus-4-8"
    
    Dev->>Config: Query supported models
    Config-->>Dev: List including Opus 4.8 entries

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