fix(conversation_manager): filter toolUse blocks from summary messages

[cagataycali]

Description

Fixes a ValidationException that occurs when using structured_output_model with SummarizingConversationManager.

Problem

When an agent is configured with structured_output_model, every response contains toolUse blocks for the structured output. The SummarizingConversationManager._generate_summary() method converts the assistant's response to a user message (for context continuity), but this includes the toolUse blocks.

According to AWS Bedrock's Converse API constraints:

• User messages can only contain: text, toolResult, image, document
• Assistant messages can contain: text, toolUse, reasoningContent

This mismatch causes:

ValidationException: User messages cannot contain tool uses. Please remove the tool uses and try again.

Solution

Filter out assistant-only content blocks (toolUse, reasoningContent) when converting the summary to a user message. If no valid content remains after filtering (edge case), create a fallback text representation.

Related Issues

Fixes #1160

Documentation PR

No documentation changes required.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Testing

• Added 3 new unit tests covering:
  • Filtering toolUse blocks from structured output responses
  • Filtering reasoningContent blocks
  • Fallback behavior when response contains only toolUse
• All 33 existing tests pass
• Ran ruff format and ruff check

Checklist

• I have read the CONTRIBUTING document
• I have added tests that prove my fix is effective
• My changes generate no new warnings
• Any dependent changes have been merged and published

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Created by strands-coder 🦆

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[strands-agent]

🎯 Gentle Ping - Ready for Merge

This PR has been sitting at ALL GREEN (15/15 CI checks passing) since creation. It's a clean bug fix with:

✅ Zero risk - Only filters toolUse blocks from summary messages
✅ Real user impact - Fixes #1160 (ValidationException affecting users)
✅ 100% test coverage - Confirmed by codecov
✅ No API changes - check-api passed

Would a maintainer be able to take a look when you have a moment? This is blocking users who combine structured_output with SummarizingConversationManager.

Thank you! 🙏

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