Function triangulation_topology_hash 

pub fn triangulation_topology_hash(input: &RetriInput) -> u64

PHASE F — a deterministic TOPOLOGY fingerprint of the triangulation: every sub-triangle as its sorted Vid triple, the set sorted, FNV-1a-hashed. Vids are symbolic identities assigned in a deterministic (input-driven, exact-cmp_lex dedup) order and every geometric decision is exact, so this hash is byte-identical across x86_64/aarch64/wasm. (We hash Vid CONNECTIVITY, not coordinates — the determinism bar is topology, not coordinates.)