Function prepare_exec 

pub async fn prepare_exec<G, T>(
    guest: &mut G,
    mm: MmId,
    fd_blocking: BTreeSet<RawFd>,
)
where
    G: Guest<Detcore<T>>,
    T: RecordOrReplay,

Notifies the coordinator that guest is about to execve, recording the pre-exec address space mm and any file-descriptor blocking overrides. A backend that handles execve outside Detcore’s syscall handler must call this before the native syscall so the next image reconnects to the existing scheduler identity and logical clock.