Constant MAX_CLOSER_NODES 

pub const MAX_CLOSER_NODES: usize = 20;

Wire-level maximum number of NodeIds in a closer_nodes field, equal to the Kademlia bucket size K=20 (ADR 022 §Routing Table). Applies to both FindValueResponse::closer_nodes and FindNodeResponse::closer_nodes. Enforced by the CloserNodes type — at construction (CloserNodes::try_new) and at the wire boundary (its Deserialize).