Function transform_request_body 

pub async fn transform_request_body<B>(
    body: B,
    compiled: &CompiledJsonTransform,
    headers: &HeaderMap,
) -> RequestBodyOutcome<B>
where
    B: Body<Data = Bytes> + Send + 'static,
    B::Error: Into<Box<dyn Error + Send + Sync>>,

The REQUEST body transform (DW-028): gate, buffer (capped), parse, apply ops, serialize. Gates in order, cheapest first — no compiled policy (the caller’s None check), then here: non-JSON content type (bodies of other types stream through untouched), an already-encoded body (the transform does not decode), a declared empty body (nothing to transform — bodiless methods pass), and a declared length over the cap (413 without reading a byte). Only then does anything buffer.

Reading the body here preserves every wrapper beneath it: the route’s limit counting guard and the HMAC digest fold still see the ORIGINAL client bytes (the digest binds what the client signed; the transform then shapes what the upstream receives — enforcement and policy are separable by design).