RFC 007 causal-site coverage for the Phase 2 bench (and any downstream
profiling): parse (head parsing attempts in read_head), router (dispatch
matching only — the winning handler and the next fall-through run outside
the guard, so the site measures dispatch, not what it dispatches to;
call() restructured match-then-dispatch for that, semantics preserved
incl. first-path+method-match-wins and the 405 two-pass), pipeline (the
plug chain inside catch_unwind; nested sites like router take over
attribution during their span, so this reads as chain overhead + handler
code outside inner sites), serialize (response head+bytes-body
serialisation; chunked stream framing is not covered — it interleaves
with writes in pump_stream and the bench doesn't stream), and
socket-write (all of write_all, writability parks included: a park
inside a site is exactly what the park-gated resume credit attributes).
progress!("responses") fires once per response fully on the wire, at
both completion points (the common path and the HTTP/1.0 EOF-stream
early return).
Site guards are #[cfg(feature = "smarm-causal")]-gated: the macros are
no-ops featureless, but binding the unit expansion would trip clippy's
let_unit_value. progress! is bare — its featureless expansion is an
empty block, free and lint-clean. Featureless build byte-behavior is
unchanged; both configs clippy-clean, full suite green both ways.