Module layout 

Faithful port of src/render/graph.ts: expand switch edges, classify back edges via DFS, longest-path layering with terminal tail pull-down, virtual pass-through cells, and barycenter ordering. Behavior is pinned against the golden fixtures in fixtures/layout/ — any divergence is a bug in this port, not a stylistic choice.

Structs

GraphEdge

GraphLayout

GraphSegment

Enums

GraphCell

Functions

expand_edges

layout_graph

Build ranks with virtual pass-through cells so every forward edge connects adjacent ranks, then order cells within ranks by neighbor barycenter.