feat: allow multipart tool responses to include a metadata field.

[pavelgj]

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[gemini-code-assist]

Summary of Changes

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This pull request enhances the MultipartToolResponse by introducing an optional metadata field. This allows tools to return arbitrary, structured data alongside their primary output and content parts, providing greater flexibility for tool developers to convey additional context or information. The changes ensure consistency across the TypeScript, Go, and JSON schema definitions, and include necessary updates to the JavaScript implementation and comprehensive test coverage.

Highlights

• Metadata Field Introduction: An optional metadata field has been added to the MultipartToolResponse structure across TypeScript, Go, and JSON schema definitions, allowing tools to return arbitrary data.
• Tool Function Signature Update: The defineTool function in JavaScript has been updated to support returning the new metadata field from multipart tool functions.
• Tool Response Resolution: The tool resolution logic has been extended to correctly process and include the metadata field when handling multipart tool responses.
• Comprehensive Test Coverage: New and updated unit tests have been added to validate the functionality of multipart tool responses, specifically verifying the correct handling and propagation of the metadata field.

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Changelog

• genkit-tools/common/src/types/parts.ts
  • Added an optional metadata field to the MultipartToolResponseSchema definition.
• genkit-tools/genkit-schema.json
  • Included a new metadata property, defined as an object with additional properties, within the MultipartToolResponse schema.
• go/ai/gen.go
  • Added an optional Metadata field of type map[string]any to the MultipartToolResponse struct.
• js/ai/src/generate/resolve-tool-requests.ts
  • Modified the resolveToolRequest function to include the metadata field when constructing the ToolResponse.
• js/ai/src/parts.ts
  • Added an optional metadata field to the MultipartToolResponseSchema definition.
• js/ai/src/tool.ts
  • Updated the MultipartToolFn type to allow its return promise to include an optional metadata field.
• js/ai/tests/generate/generate_test.ts
  • Modified existing test cases to include an example metadata field in the expected MultipartToolResponse.
• js/ai/tests/tool_test.ts
  • Added a new test case to verify that a multipart tool can successfully return and process a metadata field.

Activity

• The pull request author has marked the PR title as following conventional commits and confirmed manual testing.

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[gemini-code-assist]

Code Review

This pull request adds a metadata field to multipart tool responses. The changes have been applied to the TypeScript types, the JSON schema, and the Go struct. Tests have been added to verify the new functionality. The implementation is consistent across the codebase, with one minor readability issue in the auto-generated Go code that I've commented on.

[gemini-code-assist]

The new Metadata field is inserted between Content and the comment for Output, which makes the code harder to read. It also lacks a comment explaining its purpose, unlike other fields in the struct.

For better readability and consistency, I suggest moving the Metadata field to the end of the struct and adding a descriptive comment.

I see that this file is auto-generated. If a manual edit is not possible, this might indicate an issue in the jsonschemagen tool that needs to be addressed, as it seems to be misplacing comments when sorting struct fields alphabetically.

	Content  []*Part        "json:\"content,omitempty\""
	// Output contains the structured output data from the tool.
	Output   any            "json:\"output,omitempty\""
	// Metadata contains arbitrary key-value data associated with this response.
	Metadata map[string]any "json:\"metadata,omitempty\""