Function branch_slug 

pub fn branch_slug(branch: &str) -> String

The standardized receipt slug for a branch name — the receipt lives at e2e-attestations/<slug>.json. Lowercased; every character outside [a-z0-9._-] becomes -; runs of - collapse to one; truncated to 80 characters; leading/trailing - and . trimmed; an empty result falls back to branch. Deterministic and git-free, so a script can locate a branch’s receipt; exposed on the CLI as e2e slug.