Function same_host_forward_tier 

fn same_host_forward_tier(current: Option<&str>) -> &str

The delivery_tier a same-host Tier 2a/2b forward carries to the peer instance — SPEC_JEKT_CROSS_CHANNEL_TRUST_2026_09_02.md §D4. See the call site in handle_reactive_inject for the full reasoning; in short: a host-tier (or unlabelled) request becomes channel on the hop, and anything already carrying a network tier keeps it so the peer re-derives that tier’s own verification.