Which affordance initiated the create.
Graph-space position the node will be placed at (correct under any zoom/pan).
Prompt the user for the new node's data payload via a modal — a declarative
form (PromptDataOptions.fields) or custom HTML (render + getValues).
Resolves to the collected object, or null if the user cancelled. Feed it
straight into the decision — e.g. return { accept: true, data: values }.
Context passed to InterractionCallbacks.onBeforeNodeCreate.