Function observe_token 

pub fn observe_token(s: &str) -> u64

Per-process keyed token for a sensitive string: a SipHash with a random key created once per process. Stable within a run (so the same value correlates across spans) but not precomputable from the input, so exported traces cannot be brute-forced back to the original (e.g. an E.164 phone number). Public so other layers can redact non-Jid identifiers (e.g. a Signal ProtocolAddress name, which embeds a phone number) with the same keyed scheme.