Function plg_rt_pred_atom_concat_3 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn plg_rt_pred_atom_concat_3(
    m: *mut Machine,
    env: u64,
) -> i32

Compiled-code entry for atom_concat/3 (nondeterministic in split mode, so — like between/3 — dispatched as a predicate with args in the A registers). env carries the call-site id for error provenance (SPANS.md Layer 3).

Safety

Called from generated code with the live Machine pointer.