fix(gemini): support structured output with tools on Gemini 3 models

[waleedlatif1]

Summary

• Gemini 3 models support responseJsonSchema alongside tools/function declarations in the same request — Gemini 2 does not
• When an Agent block uses a Gemini 3 model with both tools and a response format, structured output was silently skipped, returning plain text instead of JSON
• Added isGemini3Model() helper and branching logic to use responseJsonSchema (not responseSchema) for Gemini 3 + tools, preserving existing Gemini 2 behavior
• Verified all scenarios against the live Gemini API: Gemini 3 + tools + schema, Gemini 3 no tools, Gemini 2 + tools (400 rejection), Gemini 2 no tools

Type of Change

• Bug fix

Testing

Tested manually against the live Gemini API with comprehensive matrix covering all model/tools/schema combinations.

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Apr 15, 2026 7:12pm

[cursor]

PR Summary

Medium Risk
Changes request/iteration config for Gemini structured outputs and tool loops; incorrect branching could alter response formatting or cause API rejections for some model/tool combinations.

Overview
Fixes structured JSON output when using Gemini 3 models with both tools and responseFormat by sending the schema via responseJsonSchema (while keeping Gemini 2’s behavior of applying responseSchema only when tools are absent or after tool execution).

Adds isGemini3Model() and threads model into the tool-iteration config builder to avoid reapplying/overwriting schema settings when stripping tools for the final response, and updates warnings/logging to distinguish Gemini 2 vs 3 behavior.

^{Reviewed by Cursor Bugbot for commit 8e93c05. Configure here.}

[greptile-apps]

Greptile Summary

This PR fixes structured output being silently skipped when using Gemini 3 models with tools by branching on isGemini3Model() to use responseJsonSchema (which Gemini 3 accepts alongside function declarations) instead of the responseSchema path that only works without tools. The prefix-based isGemini3Model helper is future-proof and already accounts for vertex/ prefixed variants.

Confidence Score: 5/5

Safe to merge — targeted bug fix with correct branching logic and no regressions to Gemini 2 behavior.

All findings are P2 or lower. The implementation correctly uses responseJsonSchema for Gemini 3 + tools, preserves it through the tool execution loop via baseConfig inheritance, and leaves Gemini 2 paths entirely unchanged. No P0/P1 issues found.

No files require special attention.

Important Files Changed

Filename	Overview
apps/sim/providers/utils.ts	Adds isGemini3Model() using a prefix check that handles vertex/ variants; clean and future-proof implementation.
apps/sim/providers/gemini/core.ts	Branches Gemini 3 to use responseJsonSchema alongside tools in initial config and preserves it through buildNextConfig and streaming paths; Gemini 2 behavior unchanged.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Request: responseFormat + tools?] --> B{tools present?}
    B -- No --> C[responseSchema via cleanSchemaForGemini\nresponseMimeType = application/json]
    B -- Yes --> D{isGemini3Model?}
    D -- Yes --> E[responseJsonSchema = raw schema\nresponseMimeType = application/json\ntools kept in config]
    D -- No --> F[Warn: structured output deferred\ntools kept in config]
    E --> G[Tool execution loop]
    F --> G
    G --> H{More tool calls?}
    H -- Yes --> G
    H -- No --> I{isGemini3Model?}
    I -- Yes --> J[Strip tools\nresponseJsonSchema inherited from baseConfig]
    I -- No --> K[Strip tools\nApply responseSchema + responseMimeType]
    J --> L[Final structured response]
    K --> L

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[waleedlatif1]

@greptile

[waleedlatif1]

@cursor review

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^{Reviewed by Cursor Bugbot for commit 8e93c05. Configure here.}