Constant MAX_MESSAGES_PER_RESPONSE 

pub const MAX_MESSAGES_PER_RESPONSE: u32 = 1024;

Maximum payloads in one MessagesResponse, enforced at decode. The byte budget does not bound the count: an empty payload costs one wire byte and no budget, yet is hashed into a leaf, so without this bound one response could carry millions. A consumer fetches the rest under a later request.