How to use Google Antigravity CLI inside Claude Code (without leaving your editor)

I work in Claude Code most days. It's where my git, tests, edits, and agent-assisted work happen, and the cost of leaving it for another tool is real, context-switching breaks flow. When Google shipped the Antigravity CLI (agy) a few weeks ago, I wanted access to its capabilities: Gemini 3.1 Pro reasoning, the native Imagen tool, the built-in research and review flows. But I didn't want to abandon Claude Code to get them.