poll_lan_discovery's comment said Noise XX, but LAN-discovered peers dial over
UDP through initiate_connection, which uses Noise IK (IK at FMP). compute_mesh_size's
header comment still described the obsolete sum-of-disjoint-subtrees estimate;
the function OR-unions every connected peer's inbound filter plus self and
estimates cardinality once (matching the body comment). Comment-only, no
behavior change.