Function allocation_report 

pub fn allocation_report(spec: &RegSpec) -> String

A textual allocation report for the Studio output panel: the physical register assigned to each variable, or — when the block is over-pressure — the spill verdict naming its mutually-interfering clique. This is the “compiler back-end output” view that pairs with the render timeline; the per-variable registers come from the same linear_scan_assignment the animation replays, and the feasibility/clique verdict from the certified allocate result, so the two views agree.