Add level edge definition to plane depth sequencing paper

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/colored_graphs.py

@@ -53,8 +53,8 @@ def plot_colored_graph_to_data_uri(g: Graph, coloring: VertexColoring) -> str:
     return f"data:image/png;base64,{base64.b64encode(png_bytes).decode()}"
 
 
-def canonize_and_save_graph(g: Graph) -> Graph:
-    """Canonize g, save to data/graphs/<graph_id>/graph.sobj, and return the canonical graph."""
+def canonize_and_save_graph(g: Graph) -> tuple[Graph, Path]:
+    """Canonize g, save to data/graphs/<graph_id>/graph.sobj, and return the canonical graph and its folder."""
     canonical = cast(Graph, g.canonical_label())
     graph_id = base64.urlsafe_b64encode(canonical.graph6_string().encode()).decode()
     out_dir = DIR / "data" / "graphs" / graph_id
@@ -63,7 +63,7 @@ def canonize_and_save_graph(g: Graph) -> Graph:
     canonical.is_planar(set_embedding=True, set_pos=True)
     canonical.plot().save(out_dir / 'graph.png')
     save(canonical, str(out_dir / 'graph'))
-    return canonical
+    return canonical, out_dir
 
 
 def save_colored_graph(g: Graph, coloring: VertexColoring) -> tuple[Graph, VertexColoring, ColoredGraphId]: