Type Alias VertexId 

pub type VertexId = u32;

The vertex-id type for every graph in this crate.

A u32 addresses just over 4 billion vertices — ample for the discrete / algebraic graph theory this kernel is scoped to. Pinning it to 32 bits (rather than a 64-bit usize) halves the targets array, the largest structure on the CSR traversal hot path, and so doubles its cache density. This is one concrete type, deliberately not generic over the index width.