Type Alias NemoRelayNativeAsyncNextStreamCb 

pub type NemoRelayNativeAsyncNextStreamCb = unsafe extern "C" fn(user_data: *mut c_void, chunk_json: *const NemoRelayNativeString, error: *const NemoRelayNativeString, done: bool) -> bool;

Receives one downstream stream item. chunk_json is non-null for a chunk, error is non-null for failure or consumer cancellation, and done marks clean completion. Unless the callback itself returns false, the host invokes one terminal callback so the plugin can reclaim user_data. Return false to cancel downstream production after the current callback; in that case, reclaim user_data before returning because no later callback is made.