Private named parameters and experimental primary constructors are the headline language changes in Dart 3.12, but the more interesting story is the AI tooling bundled alongside them. Genkit Dart is an open-source framework for building full-stack AI-powered apps in Dart and Flutter — Google's Genkit ecosystem now has first-class Dart support rather than requiring a Node.js sidecar. The Dart MCP server is the piece worth paying attention to if you're building agentic workflows: it exposes hot reload as a tool that external AI agents can call, meaning a coding assistant can make a change and immediately observe the running UI without leaving its loop. That's a narrower but genuinely useful capability compared to the broader "AI in the IDE" story most vendors are telling right now.