fix(gemini): set IncludeServerSideToolInvocations when using built-in tools with function calling

[jredl-va]

What type of PR is this?

fix: A bug fix

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• This PR title match the format: <type>(optional scope): <description>
• The description of this PR title is user-oriented and clear enough for others to understand.
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(Optional) More detailed description for this PR(en: English/zh: Chinese).

en:
When built-in tools (GoogleSearch, URLContext, CodeExecution, ComputerUse, FileSearch, GoogleSearchRetrieval, GoogleMaps) are used alongside function calling tools, the Gemini API requires ToolConfig.IncludeServerSideToolInvocations to be set to true. Without this, the API returns INVALID_ARGUMENT: Please enable tool_config.include_server_side_tool_invocations to use Built-in tools with Function calling.

This PR:

1. Bumps google.golang.org/genai from v1.36.0 to v1.52.1 (the IncludeServerSideToolInvocations field was added in v1.51.0)
2. Automatically sets IncludeServerSideToolInvocations = true in the ToolConfig when any built-in tool is present alongside function declarations

(Optional) Which issue(s) this PR fixes:

Fixes #761

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[jredl-va]

cc @meguminnnnnnnnn @N3kox @JonXSnow — tagging for visibility as top contributors to the gemini component.

[jredl-va]

@JonXSnow my apologies for the second direct ping, but I was hoping to get a review from you on this. This allows us to set labels on the vertex api calls for better telemetry.

(please let me know if there is a contributors group / process for these tiny types of maintenance adjustments to conform to the changes in the vertex api)

[tangchaojun-bytedance]

@jredl-va Thanks for the fix. I think this needs two more changes before merge.

1. When include_server_side_tool_invocations is enabled, AUTO mode is not supported. The Gemini docs say it should default to VALIDATED:
   https://ai.google.dev/gemini-api/docs/tool-combination#limitations

Currently WithTools / BindTools can still produce FunctionCallingConfigModeAuto, so built-in tools + function declarations may still generate an invalid config. We should switch AUTO to VALIDATED in this case.

2. This flag is not supported by the Vertex backend. In google.golang.org/genai@v1.52.1, toolConfigToVertex rejects includeServerSideToolInvocations:
   https://github.com/googleapis/go-genai/blob/v1.52.1/models.go#L3968-L3970

So we should return a clear unsupported error for BackendVertexAI instead of setting the flag unconditionally.

Could you also add regression tests for these two cases?

[jredl-va]

@tangchaojun-bytedance thanks for the feedback! Both issues addressed with proper test coverage.

• AUTO → VALIDATED coercion when built-in tools combine with function declarations (handles explicit AUTO, MODE_UNSPECIFIED, and the empty-string default).
• Vertex backend returns a clear up-front error instead of failing in the SDK.