This feature technically already exists in build123d + OCP CAD Viewer (ocp_vscode). You can click a feature in GUI and it will copy the index to clipboard, you can then apply e.g. fillets to it on the code side. See here https://github.com/bernhard-42/vscode-ocp-cad-viewer/blob/ma...

The biggest caveat is that there is currently absolutely zero mitigation for toponaming. This feature is extremely brittle, so I tend not to use it very much -- but I am still glad it exists for those situations when composing a selector is too annoying.