Payload for a Diagram node.
Diagram
Mapping from SVG anchor id (k_* data attribute on an SVG element) to the node id whose live state should be overlaid on that element.
k_*
Optional free-form description shown in the editor's info pane.
Last known error message for this node, or empty string when healthy.
Display name shown on the project chip and in the editor.
Filename of the SVG inside the server's diagram directory.