Protocol for graph lens transforms (focus, zoom, filter, collapse) on Choreo diagrams.

Each diagram module that supports Choreo.View must implement this protocol to define:

• How to rebuild the struct after graph mutation (pruning edge_meta, resolving root, etc.)
• Which nodes are visible at each zoom level
• How virtual edges (created by transitive filtering) are styled

Implementing the protocol

defimpl Choreo.Viewable, for: MyModule do
  def rebuild(diagram, new_graph) do
    # Prune edge_meta, resolve root, return new struct
  end

  def zoom_predicate(_diagram, 0), do: fn data -> data[:node_type] == :root end
  def zoom_predicate(_diagram, 1), do: fn data -> data[:node_type] in [:root, :topic] end
  def zoom_predicate(_diagram, _level), do: fn _data -> true end

  def virtual_edge_meta(_diagram), do: %{edge_type: :virtual}
end