Function pio_geo_apply 

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

Apply a geographic sidecar (any form pio_geo_parse accepts) onto a NEW network handle; the input handle is unchanged and both are freed with pio_network_free. name_hint (a file name, nullable) picks CSV against JSON as in pio_geo_parse. Matched bus points land in Bus.location, matched branch routes in Branch.route. The returned handle drops the retained source text, so a same-format write re-serializes the placed case instead of echoing the original. The reader’s notes and an apply summary (geo apply: N bus point(s), ...) are appended to the handle’s warnings (pio_warnings). Returns NULL on error.