By CDP's design, DevTool is a separated client like the one wrapped by Inspector, and each client maintains its own Command Line API like $0, so we must inject some code in browser's DevTool to get it. That's why this extension is needed.
Can be replaced by eval in devtool page? not sure compatibility and limitation. https://github.com/ChromeDevTools/chrome-devtools-mcp/commit/796aed72b7126ed4332888ffbc06d6cb678265ef