Function lumen_signal_array_len 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn lumen_signal_array_len(
    name: *const c_char,
    out_len: *mut usize,
) -> LumenStatus

Report the row count of an array signal (ABI 0.3).

Writes the number of rows the embedder last pushed through lumen_signal_set_array (0 after a clear) into *out_len. Returns LumenStatus::ErrBadArg when name / out_len is null, name is non-UTF-8, or the array signal has never been set through the FFI.