Function graph_to_codegraph 

pub fn graph_to_codegraph(graph: &Graph) -> CodeGraph

Reconstruct a CodeGraph from graph.yml code-layer nodes and edges.

This is the reverse of codegraph_to_graph_nodes(). Used by legacy CLI commands (schema, code-search, code-trace, etc.) that still operate on CodeGraph APIs. Reads only code-layer nodes (source == "extract") and code-layer edges.