Function strip_hop_by_hop 

pub fn strip_hop_by_hop(
    headers: &mut HeaderMap,
    keep_upgrade: bool,
    preserve_te: bool,
) -> Vec<String>

Header names always treated as hop-by-hop per RFC 7230 section 6.1 (plus the de-facto Proxy-Connection), and any name listed in ANY Connection header (RFC 7230 allows multiple; only get_all sees them all). TE is dropped — EXCEPT for a gRPC request (DW-039), whose spec-mandated TE: trailers rides through so conformant gRPC servers see the client’s dialect (h2 carries trailers natively; the header is the courtesy contract). Upgrade (and its Connection token) survives only when the request is being tunneled.

Returns the Connection token list collected before stripping (original case, deduplicated, order preserved) so the tunneling caller can rebuild a Connection header with the surviving tokens. The owned list is materialized only when keep_upgrade is set — the one caller that consumes it is the upgrade-tunneling path; everyone else gets an empty Vec (PERF: no per-request String allocations for the ubiquitous Connection: keep-alive).

(Public so the DW-024 micro-benchmark can exercise it directly; it is not part of the stable public surface.)