fix(bedrock): Empty responses when enabling Bedrock citations for Anthropic models

[lewwolfe]

Background

When using Anthropic models through AWS Bedrock with citations enabled (via providerOptions.bedrock.citations.enabled), the SDK returns empty responses. This is because Bedrock changes its response format when citations are enabled - instead of returning TextBlock objects, it returns CitationsContentBlock objects. The current implementation only handles TextBlock types, causing the text content within citation blocks to be ignored.

Enabling citations significantly improves Anthropic models' ability to work with PDF documents and other source materials in Bedrock, making this an important feature for RAG applications.

Summary

• Added support for parsing CitationsContentBlock in Bedrock responses
• Updated the response stream handler to extract text content from citation blocks
• Ensured backward compatibility with existing TextBlock responses

Manual Verification

1. Created a test setup with AWS Bedrock using an Anthropic Claude model
2. Configured the provider with citations enabled:

   providerOptions: {
     bedrock: {
       citations: { enabled: true },
     },
   }

3. Sent a request with PDF documents attached
4. Verified that:
   • Responses now contain the expected text content (previously empty)
   • Citations metadata is preserved in the response structure
   • Standard requests without citations continue to work as before
   • No errors occur when processing citation blocks

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Related Issues

Fixes #9823

[gr2m]

Thanks for submitting another great PR to the anthropic provider!

Could you please update tests and add or update an example (in examples/ai-core/generate-text) to cover the new functionality?

[lewwolfe]

@gr2m Tests and documentation is now added, went ahead and fixed the streaming version too and refactored to align with the anthropic provider

[lewwolfe]

@gr2m just in case you missed it, this is ready for review and merging