Function run_token 

pub fn run_token(scope: &str) -> String

A run idempotency token, unique per attempt. Same rule as create_token.

Cheaper to get wrong than the image case — a replayed run returns the original MicroVM rather than wedging anything — but the failure is worse to read: a caller who asked for a second VM gets the first one’s id back, and two callers then drive the same guest.