fix agent putout the output of workflow-tool twice (#26835)

[Cursx]

Refactor tool response handling to use lists for parts and JSON messages. Ensure proper concatenation and avoid duplication of messages.

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Summary

Previously, there would be repeated output text. Now, regardless of whether the tool's response is in plain text, pure JSON format, or text+JSON format, it can output as expected.

close #26835

I noticed a discussion and code improvement regarding this issue in # 27087. This code may serve as a reference for code improvement.

Screenshots

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[gemini-code-assist]

Summary of Changes

Hello @Cursx, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the internal mechanism responsible for converting tool responses into a single string output. The core objective is to resolve issues with duplicate output and ensure that all types of tool responses, including plain text, pure JSON, or a combination thereof, are correctly and efficiently concatenated. This enhancement aims to improve the reliability and clarity of tool interactions within the system by streamlining message processing.

Highlights

• Improved Tool Response Handling: The _convert_tool_response_to_str function has been refactored to use lists for collecting message parts, enhancing how various tool responses are processed and combined.
• Elimination of Duplicate Output: This change addresses an issue where tool responses could contain repeated output text. It ensures proper and non-redundant concatenation for plain text, pure JSON, and mixed message formats.
• Structured Message Aggregation: Separate lists (parts and json_parts) are now used to intelligently aggregate different message types. A saw_text flag helps determine when to append JSON parts to avoid duplication.
• Efficient String Concatenation: The method now uses "".join(parts) for the final string assembly, which is more performant and readable than repeated string concatenation with the + operator.

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[gemini-code-assist]

Code Review

This pull request refactors the tool response conversion to use a list for building the final string, which is a good performance improvement. However, the logic to handle JSON messages and avoid duplication is too aggressive and could lead to data loss for tools that return both text and JSON. I've suggested a more robust way to handle deduplication that should fix the original issue without introducing this new problem.

[Cursx]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors the tool response handling to prevent duplicate outputs from workflow tools. The change from string concatenation to using lists for message parts is a good improvement for both performance and readability. My review includes a suggestion to remove an unused variable and fix a comment's indentation to further improve code quality.

[Cursx]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors the tool response handling in _convert_tool_response_to_str to fix an issue with duplicate outputs. The approach of separating text and JSON parts and then merging them with deduplication is sound. Using a list of parts and "".join() is also a good performance improvement over repeated string concatenation. My review includes a few suggestions: one to make the deduplication logic more robust by handling duplicates within the JSON parts list, and a couple of minor style improvements to simplify string construction for better readability.

[crazywoola]

Please take a look at those comments, if you think it's not necessary, please resolve those comments.

[Cursx]

/gemini review

[gemini-code-assist]

Code Review

This pull request effectively addresses the issue of duplicate outputs from workflow tools by refactoring the tool response handling. The new implementation correctly separates text and JSON message parts, and then intelligently combines them while avoiding duplicates. Using a list to build the final string is also a good performance improvement. I've included a couple of minor suggestions to further improve code readability by simplifying string concatenations.