fix(google): tool_choice none with empty tools, response metadata, structured output format

[pawel-twardziak]

Changes

1. tool_choice: "none" with empty tools (converters/tools.ts)

convertToolChoiceToGeminiConfig had a guard if (!hasTools || toolChoice === undefined) return undefined that discarded tool_choice: "none" whenever tools were absent. This meant bindTools([], { tool_choice: 'none' }) silently sent no toolConfig to the API, allowing models like gemini-3-flash-preview to hallucinate function calls.

The fix splits the guard so "none" bypasses the !hasTools check - it is the only mode that is semantically meaningful without tool declarations. All other modes ("auto", "any", etc.) still return undefined when no tools are present.

2. response_metadata.model missing (chat_models/base.ts)

Neither the invoke path nor the streaming path included the model name in response_metadata. Other providers (OpenAI, Anthropic, and now @langchain/google-genai) expose response_metadata.model. The fix adds model: data.modelVersion (invoke) and model: chunk.modelVersion (stream) from the API response.

3. ls_structured_output_format missing (chat_models/base.ts)

withStructuredOutput did not set the ls_structured_output_format config key, so LangSmith could not track which structured output strategy or schema was used. The fix adds ls_structured_output_format: { kwargs: { method }, schema: toJsonSchema(schema) } to both the "jsonSchema" and "functionCalling" paths, matching what @langchain/google-genai already does.

Tests

• New unit test for convertToolChoiceToGeminiConfig("none", false) - verifies NONE config is returned even without tools.
• Updated existing test description to clarify it covers hasTools=false with non-none choices.

Fixes #10432

[changeset-bot]

🦋 Changeset detected

Latest commit: cc9f39d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@langchain/google	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR