Function pio_scenario_ids 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_scenario_ids(
    dir: *const c_char,
    from: *const c_char,
    out: *mut i64,
    cap: usize,
    errbuf: *mut c_char,
    errlen: usize,
) -> isize

Write the distinct scenario ids (ascending) of the dataset directory dir in the named from format into out, up to cap entries, and return the total count: the cap/count convention of pio_bus_ids. gridfm is the one dataset format today. Returns -1 on error and writes the message into errbuf (unlike the handle extractors, this reads the filesystem and can fail). Built --features gridfm.