Constant HEADER_MAX_LEN 

pub const HEADER_MAX_LEN: usize = _; // 35usize

RNS 1.4.2 Reticulum.HEADER_MAXSIZE. The type-2 (transport-routed) header: flags, hops, transport id, destination, context. Outbound payload budgets reserve this even when emitting type-1, because a relay re-emits the packet with the transport id added.