feat(registry): add Gemini 3.1 Pro to GitHub Copilot provider

[TonyRL]

GitHub announcement: https://github.blog/changelog/2026-02-19-gemini-3-1-pro-is-now-in-public-preview-in-github-copilot/

[gemini-code-assist]

Summary of Changes

Hello @TonyRL, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request expands the capabilities of the GitHub Copilot provider by incorporating the newly announced Gemini 3.1 Pro model. This integration ensures that the system's model registry is up-to-date with the latest offerings, allowing users to leverage the advanced features of Gemini 3.1 Pro through GitHub Copilot.

Highlights

• New Model Integration: Integrated the 'Gemini 3.1 Pro (Preview)' model into the GitHub Copilot provider's registry, making it available for use.

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Changelog

• internal/registry/model_definitions.go
  • Added the Gemini 3.1 Pro (Preview) model definition to the list of GitHub Copilot models.

Activity

• Pull request created by TonyRL.

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[gemini-code-assist]

Code Review

This pull request adds the gemini-3.1-pro-preview model to the GitHub Copilot provider. The change is straightforward, adding a new model definition to internal/registry/model_definitions.go. The implementation is consistent with the existing structure for defining models in the file and appears correct. I have no further feedback.

[Copilot]

Pull request overview

This PR adds support for Google's Gemini 3.1 Pro model to the GitHub Copilot provider registry, following the official GitHub announcement on February 19, 2026 that the model is now available in public preview through GitHub Copilot.

Changes:

• Added gemini-3.1-pro-preview model definition to the GitHub Copilot models registry with appropriate configuration matching other Gemini 3.x models

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