Function moq_track_request_dynamic 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn moq_track_request_dynamic(
    request: u32,
    on_group: moq_status_callback,
    user_data: *mut c_void,
) -> i32

Serve fetches of uncached groups on a requested track, before accepting it.

A track requested by a fetch has that group pending from birth. Register the handler here, before moq_track_request_accept, so the request survives the transition; the callback contract is that of moq_publish_track_dynamic.

Returns a non-zero handle on success, or a negative code on failure.

Safety

• on_group must be non-NULL.
• The caller must keep user_data valid until the terminal (<= 0) on_group callback.