Support Antigravity CLI as an alternative provider for Copilot and Copilot CLI features

### **Feature summary**

Add support for Antigravity CLI to serve as an alternative AI provider for Copilot-style completions and CLI commands.

### **What problem are you trying to solve?**

Users are locked into the default Copilot backend for code generation and terminal commands. Developers who prefer Google’s advanced agentic ecosystem, or want to utilize different context window sizes and cloud-native execution limits, cannot use their preferred tooling within the app's AI workflows.

### **Proposed solution**

Allow users to swap the core AI engine by integrating Antigravity CLI as a drop-in replacement backend. The app should map standard Copilot inline assistance and CLI execution flags to the Antigravity CLI binary using standard Google Cloud or Google AI Studio credentials.

### **Workflow impact**

This gives developers full flexibility to choose their underlying AI model. Switching to Antigravity CLI unblocks massive context capabilities and seamless terminal-driven automation, keeping agentic workflows fast, accurate, and cost-effective.

### **Installation context**

Local user configuration settings and workspace execution layers.

### **Additional context**

Integrating this tool allows the app to leverage native cloud-driven terminal context for highly tailored repository behavior.
👉 Project Reference: [https://antigravity.google/product/antigravity-cli](https://antigravity.google/product/antigravity-cli)