@markroth8 feat: add support for Google Antigravity AI assistant

[markroth8]

Summary

This PR adds built-in support for the Google Antigravity AI assistant to the MCP Unity plugin. It introduces automatic MCP configuration logic, a dedicated UI button in the Unity Editor, and updated documentation for a seamless user experience.

Rationale

Google Antigravity is a powerful agentic AI assistant that supports the Model Context Protocol (MCP). By adding native support, we enable Unity developers using Antigravity to connect their IDE to the Unity Editor with a single click, allowing for AI-driven scene inspection, GameObject manipulation, and test execution.

Changes

Core Logic (Editor/Utils/McpUtils.cs)

• Added GetAntigravityConfigPath() to resolve platform-specific config files:
  • Windows: %USERPROFILE%/.gemini/antigravity/mcp_config.json
  • macOS: ~/Library/Application Support/.gemini/antigravity/mcp_config.json
• Added AddToAntigravityConfig() to handle merging the MCP server configuration.

Editor UI (Editor/UnityBridge/McpUnityEditorWindow.cs)

• Added a "Configure Google Antigravity" button in the Server tab.
• Includes success/error dialogs for user feedback.

Documentation

• README.md: Added Google Antigravity to the supported environments and connection instructions.
• AGENTS.md: Included Google Antigravity in the project overview.

Verification Results

Verified the full connection cycle:

1. Configuration: Confirmed the "Configure" button correctly identifies the OS and creates/modifies the configuration file at the standard path using environment-relative variables.
2. Connectivity: Established a successful connection between the Antigravity assistant and the Unity MCP server.
3. Data Flow: Successfully retrieved and inspected the Unity scene hierarchy via the MCP protocol.

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Note: This enhancement follows the existing implementation pattern for Windsurf and Cursor support.

[coderabbitai]

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[markroth8]

Note also that I had to do an npm install and npm run build to get the server to work in Antigravity. I'm assuming this is the same in other IDEs.

[markroth8]

Fixes #88

[CoderGamester]

LGTM
Thank you for this PR @markroth8