Function compose_rust_host_init 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn compose_rust_host_init(
    handshake: *const u8,
    len: u32,
    out: *mut MutationBatch,
) -> i32

Initializes the UI-thread Host from the handshake and returns the initial batch.

Safety

handshake must address len readable bytes and out must be writable.