fix(provider): handle empty content for bedrock/openai-compatible APIs

[JackFGreen]

Issue for this PR

Closes #16332

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

AWS Bedrock rejects requests with empty text content blocks. This occurred when using custom providers with @ai-sdk/openai-compatible, especially during tool calls that return empty text (e.g., Figma MCP downloading images).

The fix adds filtering for empty content blocks at multiple levels:

• Transforms empty assistant content ("") to null for openai-compatible providers
• Filters out empty text blocks from tool-result content arrays
• Handles edge cases where tool outputs have attachments but no text
• Adds placeholder text when tool output is completely empty

This prevents the "ValidationException: messages: text content blocks must be non-empty" error from Bedrock.

How did you verify your code works?

• Tested with custom provider using @ai-sdk/openai-compatible pointing to AWS Bedrock
• Verified tool calls with empty text outputs work correctly
• Verified tool calls with attachments but no text are handled properly
• Added comprehensive test coverage (500+ lines across 3 test files)
• All existing tests pass

Screenshots / recordings

Not applicable - this is a backend bug fix without UI changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one related PR that may be relevant:

Potential Duplicate:

• fix(provider): skip empty-text filtering for assistant messages in normalizeMessages (fix(provider): skip empty-text filtering for assistant messages in normalizeMessages (#16748) #16750)

  • fix(provider): skip empty-text filtering for assistant messages in normalizeMessages (#16748) #16750

  This PR appears to be directly related as it also deals with empty text filtering for provider messages. It specifically addresses skipping empty-text filtering for assistant messages in normalizeMessages, which relates to the same issue area as PR fix(provider): handle empty content for bedrock/openai-compatible APIs #17396's handling of empty content blocks.

The other results returned were either the current PR itself (#17396) or unrelated PRs about different providers and features.

[rushant001]

same issue,waiting!

[rekram1-node]

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