fix: preserve all tool calls in agent streaming (issue #16220)

[fatelei]

Important

1. Make sure you have read our contribution guidelines
2. Ensure there is an associated issue and you have been assigned to it
3. Use the correct syntax to link this PR: Fixes #<issue number>.

Summary

fix #16220

Modified api/core/agent/fc_agent_runner.py to use indexed keys that preserve all duplicate tool calls:

• First call: toolname
• Second call: toolname_1
• Third call: toolname_2
• etc.

This approach:
✅ Preserves all tool calls including duplicates
✅ Maintains backward compatibility (single calls use simple key without index)
✅ Works with JSON serialization/deserialization

Screenshots

Before	After
...	...

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 @fatelei, 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 resolves a critical bug in the agent streaming functionality where duplicate tool calls led to data loss, as only the last call's details were retained. The fix introduces an intelligent indexing system for tool names, ensuring that every instance of a tool call, regardless of duplication, is uniquely identified and its associated data (inputs and observations) is fully preserved throughout the streaming process. This enhancement significantly improves the reliability and completeness of agent execution logs and outputs.

Highlights

• Fix for Duplicate Tool Calls: Addressed issue Agent API Streaming - if a tool gets called twice tool_input and observation are returned for just one call. #16220 where only one tool_input and observation were returned when a tool was called multiple times during agent streaming.
• Indexed Key Mechanism: Implemented a new mechanism to use indexed keys for tool calls. For duplicate tool calls, the first call uses the simple tool name (e.g., toolname), while subsequent calls are indexed (e.g., toolname_1, toolname_2).
• Preservation of All Tool Data: This change ensures that all tool calls, including duplicates, along with their respective inputs (tool_call_inputs) and observations (tool_invoke_meta, observation), are uniquely identified and preserved.
• Backward Compatibility and JSON Serialization: The solution maintains backward compatibility for single tool calls (no index suffix) and ensures that the indexed dictionary can be correctly serialized to and deserialized from JSON.
• New Unit Tests: Added comprehensive unit tests to validate the correct indexing behavior for single, duplicate, triple, and mixed tool calls, as well as the JSON serialization and backward compatibility aspects.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request effectively addresses the issue of preserving duplicate tool calls by introducing indexed keys. The logic is sound and the inclusion of a comprehensive test suite is commendable.

My main feedback revolves around code duplication. The logic for generating these indexed keys is repeated in three places within fc_agent_runner.py and in every test method in the new test file. I've left specific comments suggesting refactoring this logic into helper methods to improve maintainability and adhere to the DRY principle.

Overall, this is a good fix. Addressing the code duplication will make it even better.