Fix: Wrap Gemini function response arrays in object to prevent API error

[bharatvansh]

Description

Fixes an issue where the Gemini API rejects FunctionResponse payloads when the tool response is a JSON Array. The API requires the response field to be a JSON Object (Protobuf Struct).

When a tool returns a list (e.g. from GitHub MCP listing repos), the API throws the following error:

"Invalid JSON payload received... Proto field is not repeating, cannot start list."

Changes

• Modified src/extension/byok/common/geminiMessageConverter.ts to detect if responsePayload is an array and wrap it in an object: { result: [...] }.
• Added regression test in src/extension/byok/common/test/geminiMessageConverter.spec.ts.

Context / References

• Root Cause: The Gemini FunctionResponse expects the response field to be a google.protobuf.Struct (JSON Object), not a ListValue. Sending a top-level array causes a protocol buffer type mismatch.
• Similar reports:
  • Gemini rejects tool JSON schema with array of types (Community discussion on similar Proto error)
  • Firebase Genkit Issue #1393 (Documenting "Proto field is not repeating" error)

Verification

• Added new unit test should wrap array responses in an object which passes.
• Ran existing tests with npx vitest run src/extension/byok/common/test/geminiMessageConverter.spec.ts.

[Copilot]

Pull request overview

This PR fixes a bug where the Gemini API rejects FunctionResponse payloads when tool responses are JSON arrays. The fix wraps array responses in an object to satisfy the Gemini API's requirement that the response field be a JSON Object (Protobuf Struct) rather than a ListValue.

Key changes:

• Modified the type check in geminiMessageConverter.ts to detect arrays and wrap them in { result: [...] } objects
• Added a regression test to verify array responses are properly wrapped

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/extension/byok/common/geminiMessageConverter.ts	Added Array.isArray() check to wrap array responses in an object before sending to Gemini API
src/extension/byok/common/test/geminiMessageConverter.spec.ts	Added test case verifying that array tool responses are wrapped in { result: [...] } format

[Copilot]

While the test for array wrapping is good, the fix also wraps other primitive types (strings, numbers, booleans, null) in an object. Consider adding tests for these cases as well to ensure comprehensive coverage. For example:

• Test with a string primitive: "simple string"
• Test with a number: 42
• Test with a boolean: true
• Test with null: null

This would ensure that all code paths through the wrapping logic are tested.

[Copilot]

Consider adding a comment explaining why arrays (and other primitive types) need to be wrapped in an object. This would help future maintainers understand the Gemini API requirement. For example:

// Wrap non-object values (arrays, primitives, null) in an object because
// Gemini's FunctionResponse expects response to be a google.protobuf.Struct (JSON Object)

This provides context about the API constraint that necessitates this wrapping behavior.

Suggested change

	responsePayload = JSON.parse(textContent);
	responsePayload = JSON.parse(textContent);
	// Wrap non-object values (arrays, primitives, null) in an object because
	// Gemini's FunctionResponse.response must be a google.protobuf.Struct (JSON object)

[bharatvansh]

@vijayupadya Hi, can you please review this?