Gemma Gem Browser Ai

This teaches Claude to build and extend Gemma Gem, a Chrome extension that runs Google's Gemma 4 model entirely on-device via WebGPU. No cloud calls, no API keys. The skill covers the three-part architecture (offscreen document for inference, service worker for routing, content script for DOM manipulation), adding new tools to the agent loop, and working with the extractable agent module that defines ModelBackend and ToolExecutor interfaces. You'd use this if you want a browser agent that can read pages, click elements, and execute JavaScript without sending data off-device, or if you're prototyping on-device LLM tooling patterns. The built-in tools are practical (screenshot, form filling, JS execution) and the message routing pattern between contexts is clean enough to steal for other extensions.