Function pio_dist_geo_apply 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pio_dist_geo_apply(
    net: *const PioDistNetwork,
    layer: *const c_char,
    name_hint: *const c_char,
    errbuf: *mut c_char,
    errlen: usize,
) -> *mut PioDistNetwork

Apply a geographic sidecar (any form pio_geo_parse accepts) onto a NEW distribution network handle; the input handle is unchanged and both are freed with pio_dist_network_free. name_hint (a file name, nullable) picks CSV against JSON as in pio_geo_parse. The returned handle drops the retained source text, so a same-format write re-serializes the placed case. The reader’s notes and an apply summary are appended to the handle’s warnings (pio_dist_warnings). Returns NULL on error.