fix(costs): count input images for gemini-3.1-flash-image-preview

[steebchen]

Summary

• Added gemini-3.1-flash-image-preview to the input image counting condition in chat.ts so image costs are correctly calculated for that model
• Updated doc comment in count-input-images.ts to reflect both supported image models

Test plan

• Verify cost calculation includes input images when using gemini-3.1-flash-image-preview
• Verify existing gemini-3-pro-image-preview behavior is unchanged

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Extended image counting functionality to support an additional Gemini model variant in cost calculations.

• Documentation

  • Updated documentation to reflect expanded model support in the image counting feature.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 96b46a49-537e-4373-b4cf-cfde5e94fd02

📥 Commits

Reviewing files that changed from the base of the PR and between 90d7378 and ef62412.

📒 Files selected for processing (2)

• apps/gateway/src/chat/chat.ts
• apps/gateway/src/chat/tools/count-input-images.ts

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Walkthrough

The PR extends the input image counting logic to include an additional Gemini model variant ("gemini-3.1-flash-image-preview") alongside the existing "gemini-3-pro-image-preview". The documentation comment is updated to reflect this broader model support.

Changes

Cohort / File(s)	Summary
Image Counting for Gemini Models apps/gateway/src/chat/chat.ts, apps/gateway/src/chat/tools/count-input-images.ts	Extended input image counting to include "gemini-3.1-flash-image-preview" model variant; updated related documentation comment.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• feat(image): update token calc and pricing #1767: Modifies image handling and pricing for the gemini-3.1-flash-image-preview model variant.
• refactor(chat): extract pure utility functions #1551: Centralizes countInputImages utility function; this PR expands the supported model variants.
• fix(gateway): include image input tokens in accounting #1618: Updates image-input counting logic in chat.ts using parsed model names.

Suggested reviewers

• smakosh

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately describes the main change: adding support for counting input images for the gemini-3.1-flash-image-preview model variant in the costs logic.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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• Commit unit tests in branch add-gemini-3-1-image-model

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[Copilot]

Pull request overview

This PR fixes a bug where input images were not counted (and therefore not billed) when using the gemini-3.1-flash-image-preview model. Previously, the input-image-counting guard in chat.ts only matched gemini-3-pro-image-preview. The fix extends that condition to include the new model, and updates the function's doc comment accordingly.

Changes:

• Extended the requestedModel check in chat.ts to also trigger countInputImages for gemini-3.1-flash-image-preview.
• Updated the JSDoc comment in count-input-images.ts to list both supported models.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
apps/gateway/src/chat/chat.ts	Adds gemini-3.1-flash-image-preview to the input image counting condition
apps/gateway/src/chat/tools/count-input-images.ts	Updates doc comment to reflect both image models that use this function

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[Copilot]

The existing costs.spec.ts tests verify input image counting and cost calculation for gemini-3-pro-image-preview, but there is no equivalent test covering gemini-3.1-flash-image-preview with a non-zero inputImageCount. Given that imageInputPrice is looked up per provider configuration, adding a parallel test case that passes inputImageCount > 0 for gemini-3.1-flash-image-preview would confirm the fix works end-to-end and that the model's provider entry has imageInputPrice configured.