Function nonce_book_key 

pub fn nonce_book_key(vendor: VendorId, nonce: &str) -> String

Build a stable, lower-cased cache key for a (vendor_family, nonce) tuple.

Example

use stygian_charon::token_lifecycle::nonce_book_key;
use stygian_charon::vendor_classifier::VendorId;

let key = nonce_book_key(VendorId::Cloudflare, "NONCE-XYZ");
assert!(key.starts_with("charon:token_nonce:cloudflare:"));