fix(core): detect Bedrock Anthropic model IDs

[uuzzrm]

Fixes #2565

AISdkClient infers provider-specific options from the model ID. AWS Bedrock Anthropic IDs use anthropic.<model> or region.anthropic.<model>, so they do not match the existing provider/model format and miss Anthropic's structuredOutputMode: "auto" option.

This change:

• recognizes raw and cross-region Bedrock Anthropic model IDs
• leaves the existing slash-separated and legacy model ID behavior unchanged
• adds regression coverage for both Bedrock ID shapes
• includes a patch changeset for @browserbasehq/stagehand

Verification:

• Prettier check passed
• ESLint passed for the changed TypeScript files
• TypeScript typecheck passed
• ESM and CJS builds passed
• Focused Vitest suite passed (12 tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 225ba80

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

This PR includes changesets to release 3 packages

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

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[uuzzrm]

Local verification is complete: the core build, lint, typecheck, and focused Bedrock regression tests pass. The GitHub Actions runs currently show action_required with no jobs, so they appear to be waiting for maintainer approval for fork workflow runs. I will address any CI feedback once the workflows start.

[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

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

Architecture diagram

sequenceDiagram
    participant Client as AI SDK Client
    participant Infer as inferProviderName()
    participant OptMap as ProviderOptionMap

    Client->>Infer: modelId (e.g. "us.anthropic.claude-sonnet-4-6[1m]")
    Infer->>Infer: const [providerName] = modelId.split("/")

    alt modelId contains "/" (standard provider/model)
        Infer-->>Client: return providerName (e.g. "openai")
    else no "/" present
        alt regex matches /^(?:[a-z0-9-]+\.)?anthropic\./i
            Infer-->>Client: NEW: return "anthropic" (Bedrock style)
        else no match (legacy bare model ID)
            Infer-->>Client: return providerName (original value)
        end
    end

    Client->>OptMap: get provider options for "anthropic"
    OptMap-->>Client: anthropic: { structuredOutputMode: "auto" }

    Note over Client,OptMap: Provider-specific structured output options are now applied for Bedrock Anthropic model IDs.

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